Crux 5 | The Equation of Gravel Speed

Gravel racing has changed. What used to feel like an endurance event has become a full-speed race, with stronger athletes, higher speeds, sharper tactics, and bigger consequences for every equipment choice.

Crux has always been loved for its light weight, lively ride, and pure race feel. But as gravel racing got faster, Specialized had to answer a harder question: how do you make Crux faster without losing what riders already love about it?

In this episode, guest host Ben Edwards sits down with Leo Cadena, Doug Russell, and Alex Jerome just north of Barcelona to go inside the creation of Crux 5. They discuss the evolution of gravel racing, the shift from cyclocross roots to a dedicated gravel race platform, and the engineering work behind making a bike that is not simply light or aero, but faster against the only metric that matters: time to finish.

They get into Specialized’s equation of speed, Formula 1 style simulation, moving-leg mannequin wind tunnel testing, race-course telemetry, tire rolling resistance, 55 mm tire clearance, the new Terra cockpit, Terra wheels, and the challenge of preserving the Crux ride feel while building a faster bike for modern gravel racing.

This episode covers:

• How gravel evolved from an event into a race
  
  
• Why Crux 5 was built as a dedicated gravel race bike
  
  
• The equation of speed and why time to finish matters most
  
  
• How Specialized balances aero, weight, rolling resistance, and ride quality
  
  
• Why bike-only aero testing does not tell the full story
  
  
• How moving-leg mannequins make wind tunnel testing more realistic
  
  
• How race telemetry from Unbound and other courses shapes product decisions
  
  
• Why tire choice and tire clearance can decide a race
  
  
• The role of 50 mm and 55 mm tires in modern gravel performance
  
  
• How Crux 5 became 15.2 watts faster than Crux 4
  
  
• Why the new Terra cockpit matters for comfort, control, and aero efficiency
  
  
• How Crux 5 keeps the light, lively ride that made Crux so loved
  
  
• What simulated Unbound time savings reveal about real race performance
  
  
• Why the future of gravel race bikes is about systems, not isolated numbers
  
  

Guests:
Leo Cadena, Doug Russell, Alex Jerome

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Transcript

SPEAKER_03 0:00

The clock doesn't know how arrow you are. It doesn't know how light you are. All it knows is how quickly you get to the finish line. So for us as a company, that's the only metric we want to design towards in terms of just those performance targets.

SPEAKER_01 0:13

I'm Ben Edwards and welcome to the specialized podcast. I'm filling in for Ben Capron because you may have noticed we're not in our normal studio today. We're actually it's a very special edition of the podcast. We are here just north of Barcelona on the coast of Brava, and we're about to launch Crux 5. It's a bike the team's been working on for years, and I have three of the key members of that team with me right now. I have Leo Bardina, the aerodynamicist behind the bike, and everything we do at specialized. I have Doug Russell, the lead engineer for Crux 5, and we have the leader of the road and gravel team, Alex Jerome, with us. Welcome guys. Thank you for having us, guys. Great to be here. Yeah, it's gonna be fun. It's gonna become we're gonna we're gonna dig into this bike that I know you guys have been working on for a long, long time. But before we do that, I actually want to just take a step back and look at gravel racing. How has gravel racing really evolved over the last five, six years? And what were you all thinking about when it came time to make a new crux? When it came time to say, crux four, see you later. It's time for crux five. What were you thinking about as you saw gravel racing over the last few years and how it evolved?

SPEAKER_00 1:14

I'll I can speak to that a little bit. I mean, the biggest evolution we've seen in gravel racing is just speeds are going up, the riders are going faster, courses are as rough as ever, and we really saw an opportunity for building a bike that was better suited for the higher speed intensity of gravel racing today compared to five years ago. I mean, if you look at unbound, for example, five years ago the average speed of the race was around 31 kilometers an hour, and last year's race was around 37, close to 38 kilometers an hour. So speeds are just going up and up, and there's a lot of opportunity to make a bike that was more aerodynamically efficient to rib be better suited for those high speeds, and that could fill the other needs of a gravel racer that they're the things they're looking for today in their bikes.

SPEAKER_01 2:00

Yeah, that's wild, actually. Think about that increase in speed, right? And I know I think you know, specialized is probably we've played our part in in making gravel racing faster. We kind of you know reset the table this year with an all-new specialized factory team on the off-road side of things, with with Mads coming over on the team, Keegan, obviously the big signing on the team. Uh, we know Matt Beers how strong he is on the women's side, Sophia's still leading the charge there. We have G as well with her, and then obviously Annika on that side. So we have a little bit of a super team we kind of put together. You know, I think some people think maybe we ruined Gravit a little bit with that super team, but is that something you guys saw? The Alex, the professionalization of gravel and the athletes coming to Gravel now.

SPEAKER_02 2:40

Yeah, I mean, even going back to Doug's comment, I would say five years ago, obviously there were some people racing Unbound. It's been raced for a while. But I think uh even five years ago or earlier, probably more of an event versus a race. And even just over the course of the last five years now, I mean, we are just seeing people, like a huge number of people actually racing that event. Um, and you see a lot of high caliber racers and riders coming over from Europe, obviously in the US as well. And especially with Lifetime Grand Prix, just the level of the racing year over year has gotten faster and faster and faster, and the level of athletes is just continues to rise. So, yeah, to your point, this year we have a pretty stacked team. Um, we also have Matt on the team as well. I mean, it's just uh the roster is is pretty pretty stacked right now.

SPEAKER_01 3:24

Yeah, yeah, I know, phenomenal squad for sure. And I will say five years ago, that was uh Ian Boswell in first and Lawrence Tendam in second. So a couple ex-world tour pros there, pretty pretty strong, pretty strong guys as well. But yeah, amazing when you think about you have two World Tour guys doing 31k an hour, and now it's what almost eight kilometers an hour faster.

SPEAKER_02 3:44

I mean, same with the women, like the front end of that race, there's like a huge group of extremely fast women that raced the entire lifetime Grand Prix. And um, yeah, it's it's impressive.

SPEAKER_01 3:53

So that was really it, right? You sort of looked at it and said, this is really professionalized, it's really turned into a race and I mean in many ways, a you know, a bit of a road race, the way you see the tactics playing out now.

SPEAKER_02 4:05

And uh not to go farther backwards, but if we're talking about the crux specifically, obviously for us, yes, it is our gravel race platform now, but that has been more of a cycle cross bike for us in the past. And uh, as we see, let's say, some of those events declining slightly, especially in the US, and the gravel scene just continuing to grow year over year, that is definitely the direction that the team has taken, taking the platform.

SPEAKER_01 4:27

Yeah. So that's a good segue then. Let's talk about Crux 4, right? Because that is the bike, you know, for most part, when it came to the fast gravel. If it was rough gravel or even a rough unbound, our teams were picking diverge. But when it came to that really fast performance tip of the spear, smoother race, hillier race, they were always choosing Crux 4. And I think it's sort of a bike pretty universally loved, you know, it seems it's been really well reviewed, a bunch of riders really passionate about Crux 4. What made Crux 4 so special?

SPEAKER_02 4:56

What made Crux 4 so special, Doug?

SPEAKER_00 4:57

I mean, I think the thing that really shines with that bike is how light it is. It's insanely light, and I believe one of the lightest gravel bikes on the market. And that made it climb hills wonderfully. Its ride characteristics and descending and handling characteristics were also just top-notch. It was just a really fun bike to ride and it was lively, and it just you felt like a almost like a superhero when you're on that bike because it's just so light. It dances around up the hills, and it just had a really good ride characteristic that I think everyone appreciated.

SPEAKER_01 5:29

So I mean, obviously, one of the key things it didn't have, you know, was kind of inspired by Athos, right? Round tubes.

SPEAKER_02 5:34

Not exactly arrow.

SPEAKER_01 5:35

Not a lot of arrow going on there, and of course, we have Leo sitting with us, so that maybe telegraph a little bit about Crux 5 and some of the direction we took on Crux 5. But I want to talk about that specifically. So you have this bike that really is a loved platform that has that incredible ride quality, super lightweight, a lot of really big fans, and now you're gonna change this bike, right? You have to try and make this bike faster, you have to make this bike what that modern gravel racer needs. How do you decide what to do? Is it just, oh, we should make an arrow and throw more arrow at it? You know, how do you know what it's actually gonna make the bike faster?

SPEAKER_02 6:08

I think one of the key priorities for us was retaining the pieces that people love. So the compliance, the ride quality, handling characteristics, that was obviously one piece that we did not want to lose any, even if we were trying to add some arrow perspective there. And then also just the weight perspective as well. That is something we wanted to obviously had a budget to increase the air of the platform, but wanted to retain a super lightweight chassis and just a lightweight overall package, which Doug and the team has certainly delivered.

SPEAKER_01 6:37

So talk about that though. You just mentioned something that maybe people aren't familiar with. They said you have a budget to make the it more arrow, which means you decided that you could actually add a little bit of weight to the frame to trade off for arrow. How do you determine how much weight you can add to get the arrow gain? And know you've made the bike faster, you haven't hampered it with extra weight it didn't need, and maybe the arrow isn't, you know, they're going 38k an hour pretty fast, they're not doing 50k an hour like we see on the world tour. How do you make those decisions?

SPEAKER_00 7:05

I think Leo can speak to that really well.

SPEAKER_02 7:08

I would say one more thing though, and and not to correct you, because yes, you're right, the average speed is 38 kph, but I would even say we're making a bike to go faster than that because average over the race is 38, but those moments when the race is actually like key race defining moments, they're going faster than that. Like, especially at Unbound, if it's like if there is an attack, it's definitely over 38 kph. Super good. Like they have slower, they have faster, and then the average.

SPEAKER_01 7:34

You're targeting really those moments that really matter. Yeah, they defined it. Not when you're sitting in the group, maybe as that 38k average, you know. Yeah, got it.

SPEAKER_03 7:43

I mean, we chat a lot, right, about the increasing professionalism and speed of gravel racing. So I think it's important to put the crux in the same perspective as a tarmac, right? Both of these chassis were optimizing to be the fastest possible chassis for the courses they're raced on. So that's the exact approach that we transferred from our years of developing tarmacs into the crux. So we're looking at the equation of speed, we're taking the trade-off of weight to arrow for every bike we develop and seeing where the sweet spot is for the races it does. So with crux, what you see on gravel, right, is rolling resistance coefficients are a lot higher than on the road, right? Way bumpier surfaces, way bigger tires, um, just gnarlier terrain. So weight actually plays quite a bit bigger of a role. And then with those lower average speed, arrow plays a little bit less of a role. So on a chassis like a crux, we actually have to be a lot more conscientious of our weight gain for aero benefit than we do on a chassis like the tarmac. But they both are getting that level of scientific, almost maniac level detail to attention, right? Yeah to fine-tune them for their specific courses for how they're raced.

SPEAKER_01 8:50

So you talked, let's back up a little bit because you mentioned equation of speed.

SPEAKER_03 8:53

Yeah.

SPEAKER_01 8:53

Right, which is something I've heard you guys all talk about quite a bit. And I want to make sure I understand it and our listeners understand this idea of equation of speed. So, equation of speed, the the result of that is something you guys say is time to finish. Yeah. Right? Can you talk a little bit about time to finish and chasing that metric of just trying to lower the time to finish through right through like pretty advanced simulation?

SPEAKER_03 9:13

Yeah, so I think this is how most advanced sports, especially motor sports, approach their designs, right? F1, you're not gonna set an arbitrary weight target, an arbitrary arrow target, an arbitrary horse target, horsepower target. You're gonna try and develop the chassis that gets you around the track the fastest, right? That's all that matters. That's the same methodology we apply to our bikes. We're not gonna say this needs to weigh exactly 6.2 kg, or this has to weigh exactly 7.1 kg, or this is the arrow target for this chassis. Our goal for this bike is to be the fastest where it's raced. That is our only goal. And the equation of speed is how we take in all of those possible inputs, right? What's your tire clearance? What tires can you run? That affects the rolling resistance a lot, right? What's your weight of the chassis? What's the arrow of the chassis? And we look at every single trade-off of maybe you add some arrow, but that costs you weight, right? Are you fast or are you slower? So it's not an arbitrary add 20 grams to make it more arrow. It's where is the sweet spot for this bike for how it's raced?

SPEAKER_02 10:14

I think I would just add, like Tilia's point is we're trying to make a fast bike. We're not trying to make the most arrow bike or let's say the lightest bike. We just want the combination of all of that together to have the fastest platform for our athletes.

SPEAKER_01 10:26

Yeah. It's funny, I know we call our wind tunnel mortgage the wind tunnel, but you don't win races in there, right? That's one piece of a an important piece, but one piece of the recipe.

SPEAKER_02 10:35

As Marcel would say, the clock doesn't know how arrow you are.

SPEAKER_01 10:38

Yeah, I imagine you guys almost like, I think of like those record producers, you know, when you got this giant board with all these dials, and they're, you know, they're tweaking all the dials until they get it just right.

SPEAKER_00 10:46

That's actually pretty accurate to how we started the Crux 5 project. We had uh to kind of go back to the premise of how do we decide what to do for Crux 5 coming off of Crux 4, we knew we wanted to make the bike faster across a race course. So we targeted some specific races that we wanted to optimize around, uh, some of the most critical ones being like unbound, UCI, gravel worlds, uh and a few others, and we ran them through the simulation and of the equation of speed to see how each of those metrics of weight, aerodynamics, and rolling resistance impact that overall time to finish. And we used that to understand where is the sweet spot balancing weight to arrow to rolling resistance, and that helped us set our targets on the beginning of the Crux 5 project to say, okay, if we wanted to get more arrow at this much weight penalty, is that faster or slower? Yeah. Well, if we had a little less arrow and more weight savings, would that be faster or slower? And we did kind of like you were alluding to all the different dials of like, well, if we change the variables this way or that way, what will get us the combination that is the fastest overall time to finish? And that's what helped drive a lot of the targets from the very front end of the Crux 5 project when we kicked it off to say, well, if we can be X amount more arrow, even if we have to gain Y amount more weight, that we will be a faster bike overall.

SPEAKER_01 12:02

So this equation of speed, it's a literal equation. You have the the rider inputs, their mass, their CDA, the rope, you know, their power numbers, you have the the course itself, right? The elevation gain, the descending, the surface roughness, wind conditions. Yeah, and and then you've got the bike.

SPEAKER_03 12:20

Yeah.

SPEAKER_01 12:20

The mass of the bike, the rolling resistance, the mechanical efficiency, all those things, right? And it makes this actual equation. And just so I'm clear, that like the result of that equation is time to finish.

SPEAKER_03 12:29

Correct, yeah.

SPEAKER_01 12:30

Exactly.

SPEAKER_03 12:30

So this is take a one-to-one for motorsports, right? Our engineer who developed this tool came from F1. This is how every flagship level motorsports approaches their design decisions, and there's no reason why cycling shouldn't approach it the same way. And just like Doug said, right, from Marcel, the clock doesn't know how arrow you are, it doesn't know how light you are. All it knows is how quickly you get to the finish line. So for us as a company, that's the only metric we want to design towards in terms of just those performance targets.

SPEAKER_01 12:57

That's very cool. But I think so you have this equation, right? And I'm sure there's plenty of magic that happens within this equation. Um, but we're probably not gonna give our secrets away. It's like the formula for Coke, right? Like you can see the ingredients on the can, yeah. And then you can taste it and go, oh, that tastes pretty good, but they're not gonna tell you the formula.

SPEAKER_03 13:16

No, of course not. That's where the magic happens. Getting accurate numbers to put in there, right, is the hardest part.

SPEAKER_01 13:20

That's what I'm saying. I was gonna say, yeah, garbage in, garbage out. So yeah, let's that that's actually a great segue. Let's talk about that. I think there's two things that um it feels like you guys are really advancing on, and one is that idea of the moving leg mannequin.

SPEAKER_03 13:32

Yeah.

SPEAKER_01 13:32

And the other one is the telemetry, the race day telemetry. So maybe we'll start with a moving leg mannequin.

SPEAKER_03 13:38

Yeah, so moving leg mannequins for us are really important, right? You see a lot of bike testing where it's bike only, or a lot where it's legs only, or a lot where it's a human on a bike. Right? A human on the bike is the most realistic. That's how we all ride our bikes, right? We sit on the bike and we pedal it. The hard part with that is humans aren't robotic, right? They're not repeatable. You'll see error bars sometimes that are twice or three times the drag delta between two different chassis. So that data is useless. It's meaningless, right? You can't draw any conclusions from it. And then you go all the way to the other extreme with just the bike. That is so incredibly unrealistic that we almost don't care. It's really precise, it's really repeatable, it gives you these beautiful charts, but it's meaningless because your bike doesn't ride itself without a person on it. So that's where that design question of how do I balance that robotic precision, that robotic repeatability to get really accurate, usable data with data that's still realistic and meaningful to human riders. That's where our mannequin systems come in. We're on now our sixth generation of mannequin systems. You know, we've gone through a lot of iterations of this. We figured out what works, what doesn't work, what needs improvement, and it's a constantly evolving thing for us because we need to be on the pinnacle of both resolution and realism to make bikes that are designed for a real rider properly, right?

SPEAKER_02 14:53

And repeatability compared to a human on a bike.

SPEAKER_01 14:56

Yeah, yeah, for sure. It's interesting, you see, like, you know, the mannequin, you think, oh, that's like state of the art. And to realize you guys are on your sixth iteration of the mannequin. How long have we had a mannequin in a wind tunnel? Since we've had the wind tunnel. Really?

SPEAKER_02 15:09

Yeah. We also have different styles of mannequins. Maybe you want to speak to that. But I mean, we have mannequins like let's say uh mimicking the position that you might be just in like a world or Peloton. We have mannequins that we do a lot of our development now in terms of like breakaway position, especially if we talked about like building the bike for kind of key defining moments within a race. That's super critical.

SPEAKER_03 15:28

Yeah. We have multiple TT mannequins for different riders. We have the upright road, the arrow road, we have male, female, we have pedaling, we have non-pedaling, and all of these different mannequins are used for different things, right? Like we would never use a non-pedaling mannequin to develop a bike, but it can work great if you're just developing a helmet. So different tools for different and ultimately, right?

SPEAKER_01 15:50

It's because the the rider influences the airflow around the bike so much that bike alone is basically irrelevant.

SPEAKER_03 15:56

Yes, and we have some really clear data that we're gonna share with people, right, on roval wheels, where it's I think one of the most beautiful charts that explains this in a very simple way we've put together. If you take a traditional aero wheel set that's deeper in the back, shallower in the front, and then you compare it to our wheel set, which flips the script deeper in the front, shallower in the back, right? We get the same exact drag as them when tested bike only. But the second you put that pedaling mannequin on the bike, we're way faster than them. I don't know about you, but I care how my wheel performs when I'm riding the bike more than when the bike's by itself.

SPEAKER_01 16:29

And that's because having a deeper rear, you're in that turbulent air from the rider. And so any perceived gain that you may have had when you tested it without a rider is lost.

SPEAKER_03 16:38

Yeah, it's very marginal. So that's our design language across all of our bikes now, right? Is we really invest a lot of our arrow where it matters. You can make every tube super deep and it will give you a more arrow chassis, but you're spending a lot of weight for almost no gain on the back of the bike. So when we look at the equation of speed, right, that's a very clear takeaway is you don't want to just throw hundreds of grams of mass at this chassis. You want to be very methodical in where you add weight to get the best payoff.

SPEAKER_01 17:05

Yeah, which is why you optimize like the wheels are a great example. Yeah. The deeper front, spend a lot of time optimizing that because that's where you're hitting the clean air, that's where the arrow is.

SPEAKER_03 17:13

The speed sniffers, the wheels, the deep forks, all of that stuff. We see huge benefits on. Similarly, the seat posts, right? A seat post is still the leading edge of a bike, even though it's pretty far back.

SPEAKER_01 17:23

So the other thing we touched on too, when to get back to that idea of you need to have this hyper-accurate data, right, to really trust what's coming out at the end and the time to finish the results of that equation of speed. And you touched on it a little bit, you know, talking about the tires. Telemetry. What are we doing to get the telemetry so you really understand surface roughness on these gravel races?

SPEAKER_03 17:45

Yeah, so we had one of our engineers, um, Chris Sells, travel with the gravel team and instrument their bikes, and he's basically getting vibration profiles from different courses. We then have our treadmill systems where we can replicate those in a lab environment. By replicating the same roughness profiles in a lab environment, we're able to very precisely now test different tire sizes and different tire models for rolling efficiency in those levels of vibration. And that's the data that we can then feed into the equation of speed, because like you said, garbage in, garbage out, right? If we just do open road testing with uncontrolled wind conditions, uncontrolled line choices, we're not going to have that level of precision that we need to match the precision that the wind tunnel offers. So we need every single data source going into that equation of speed to be to that highest level of precision. Because if one of them is off, that could determine the balance to be completely different than where it actually should be.

SPEAKER_00 18:43

I think that telemetry uh data collection is actually really interesting because we are going out and collecting the actual profile of the races that we care about, and so like we unbound is one of the ones that we really focused on optimizing our Crux 5 for, and so we truly measured like what does the ground surface vibration what does that look like? And we mapped it with vibration data by putting accelerometers and sensors on bikes that were ridden across these terrains, and to collect the rolling resistance data, we essentially replicated that exact surface roughness profile on a treadmill in a lab environment to be able to collect rolling resistance data on surfaces that are representative of exactly where these bikes are being used. So it's not just a smooth treadmill that's being rolled along, it's like an actual roughness profile that's got bumps all along it of different frequencies and different heights that actually represents the true terrain the bike's being used on. So we can measure that rolling resistance data to the accuracy of exactly the surfaces that it's being used on, and that is a huge gain that we've started doing in the last few years.

SPEAKER_02 19:49

Just helps with decision making. I mean, we have that from Unbound Traca in a ton of the lifetime Grand Prix courses, but once we have that, we can get an understanding of like what tire we should be using for those courses, then we can develop the chassis and the wheel around that tire. So I think with Crux, obviously our fastest setup is based around the tire that our athletes are using basically 90-95% of the time, which is a 50 mil tracer. So it's not only the fastest tire for us from a rolling resistance perspective on those courses, it's also the fastest tire for us from an aero perspective with the wheel chassis tire combo.

SPEAKER_00 20:24

And we know that because we have measured all of our different gravel tires of all the different sizes of between pathfinders and tracers and 40, 45, 50, all the sizes we offer, and basically measured them in the lab against each other and in the wind tunnel to know with the equation of speed, essentially, like you choose one of these tires, and this is exactly going to be the effect, both from a rolling resistance perspective, a weight, and an aerodynamic perspective on how it'll influence your time to finish.

SPEAKER_03 20:49

It's really a stark effect, right? That's something that we talk about with Crux. If you can't run the right tire for your race course, the race is over before it started. In these time to finish simulations, we looked at what is the impact of having a minimal tire clearance gravel bike. And you really are at a multiple minute disadvantage over unbound. We looked at only clearing a 45 C max versus a 50 and a 55. You can't compete almost if your bike doesn't have enough tire clearance to get those good rolling results, even though there is an arrow penalty. The rolling far outweighs it on those courses.

SPEAKER_01 21:23

Yeah, I think that's something that'll surprise people that rolling resistance. One, the size of the tire isn't impacted that much, and then it has an outsized influence even beyond arrow.

SPEAKER_03 21:33

Yeah. And it's very course dependent too, though. That's the thing. That's why we have data from so many courses. You're not going to see our athletes on 50 tracers for every course they race. Obviously, smoother gravel, smaller tires. Yeah. But we have to be able to give our athletes the opportunity to choose the right tire for each course that they race.

SPEAKER_02 21:50

I think the fun part there, though, is like once we have all that data, that's when you can like get into your time to finish and actually like look at a rider profile from an event and actually. Understand what the impact is.

SPEAKER_01 22:01

Let's let's put time to finish aside for a second. And I think we talked about what you all saw happening in gravel. And we talked about Crux 4 and how you felt it needed to, you know, needed to shift into more of this pure race-focused bike for these faster races and these stronger athletes and the team that we ended up building. So what did you actually make? You have these toys, you got telemetry, you got this wind tunnel, you got a you know moving leg mannequins, you got a treadmill. Alex, why don't you take that? So what did you make?

SPEAKER_02 22:30

What did we make? We made uh we made a fast bike. Yeah. It's uh the new Crux Doug and team, I think we're what, 15.2 watts faster than Crux 4. So uh, I mean, granted, Crux 4 is like a round tube style bike, so we expected to see huge results, but that's huge results for us from an aero perspective. It's 55 mil tire clearance. So our athletes take plenty of rides or races where they're they're using, let's say, a 2.2 air track or a 55mm style tire. Um, yeah, so they have whatever clearance they want plus mud clearance. And I think from a weight perspective, you guys nailed it as well. You ended up, what, 789 for a size 56 frame?

SPEAKER_00 23:09

Yeah, so the frame gained pretty minimal weight for a huge still sub-800 grams. Yeah. With 55 millimeter tire clearance. Exactly. So we both increased the tire clearance, increased the max chain ring clearance, yeah. Uh, and yeah, it gained a lot of aerodynamic performance for a very small weight penalty.

SPEAKER_01 23:27

So you you've dialed this equation of speed, right? And you've got, okay, you know, we we think we need to be 15.2 watts faster. Uh, but you can't gain any weight. And by the way, uh, it has to have the same stiffness that Crux 4 had. It has to, you know, at the bottom bracket, the same compliance, the same responsiveness at the bars, because everyone loves the ride feel. Like, when you get that brief from Alex and the team, are you like, you guys are crazy? Like, how are we gonna do this?

SPEAKER_00 23:51

It was definitely a tough one. I mean, it made us really look deep at all the choices that we made throughout the frame, the fork, the cockpit, every the wheels, everything really was scrutinized. It was a tough bill to fill, but uh I'm I think we nailed it basically.

SPEAKER_01 24:07

Sub 800 grams is is wild still for a gravel frame, any gravel frame, but a gravel frame that's this fast and this arrow. What were there any like specific call-outs, any moments that you were like, how do I do this? I don't have enough material.

SPEAKER_00 24:23

Yeah, well we we did some fun prototyping early on in the concept phase to sort of understand how achievable those targets were. Uh, we having this platform like a tarmac where we've already developed another frame that is exceptionally light for the aerodynamic performance of being a leader in that space, we took some of the learnings from that and did some iterative concept bikes that evolved the Crux 4 into essentially a concept version of the chassis we have today. So we sort of split in different tubes one by one to understand the impact of the aerodynamic performance of each section of the frame. So, for example, I took a Crux 4 frame and put in a tarmac seat tube and seat post to see, right, we just changed this one tube on the bike, how much aero performance can we gain? And we can also quantify exactly how much weight delta that would have from the current Crux 4 frame and round seat post. And we thought, okay, we can gain this much performance at virtually no weight. Now let's take the front end and the fork. And if we change these to have more deep arrow tube cross-section, what's the weight impact and what's the arrow impact? And we started to understand the how much of those knobs had an effect on both weight and aerodynamics in the concept phase to realize that we could or could not achieve the targets that we set out to do.

SPEAKER_01 25:35

I think that's another toy we have to add to your arsenal. You have the carbon lab, right? Because you're doing you're doing this in Morgan Hill, you're doing it in the carbon lab, you're walking it across the street, putting it in the wind tunnel.

SPEAKER_00 25:44

Yeah, we're talking about like a two or three-day turnaround of, oh, we want to test this iteration of changing out whole entire tube cross-sections in the frame on a full composite carbon fiber bike. We can splice it and dice it and bond it in, overwrap it, walk it to the wind tunnel the next day, put it in, get the data, and then take it out on the road and ride it the day after that. Actually, like that seat tube frame I rode myself for several months because it was just a fully structurally carbon fiber manufactured.

SPEAKER_01 26:12

When a rider walks into the bike shop and sees Crux 5 for the first time, you know, what are the arrow updates they're gonna see? Kind of just walk us through the you know, bike kind of front to back. You know, what are they gonna see and how it stands apart from Crux 4?

SPEAKER_03 26:26

Yeah, so starting at the front, working our way back, right? First thing you'll see is a speed sniffer. I think that's iconic of specialized. You might notice it looks a little less extreme than on a tarmac. That's on purpose, right? We just chatted about how weight matters more relatively speaking on a gravel bike than a road race bike. So we have to keep these aerial features a little more toned down relative to the tarmac family of products if we want to be optimal here. Similar story on the fork, um moving back. Everything just kind of mirrors what we did on the tarmac. It works really well. The seat post is actually a shared part. Same exact seat post on the tarmac, it's super compliant, super comfortable, super aero, super light. That's everything we need on this style of bike as well. And then one of the most unique features you'll see are the new uh Terra Aero wheels, right? The truncated airfoils. This is letting us get best in class aero performance with a relatively shallow wheel that keeps the weights super low. These two things were designed as a system together. These wheels were designed for this frame, this frame was designed around these wheels. They were optimized as a family. Same story on the cockpit. A lot of work went into shaping the tops of that cockpit to balance comfort, compliance, and aerodynamics. So there wasn't, I think, a single place on this bike that we didn't look at aero trade-offs.

SPEAKER_00 27:43

It's a new cockpit. Yeah, that's something uh actually one of the other cool features of the bike from the front is an all-new Terra one-piece carbon cockpit designed to be a lightweight cockpit for gravel bikes specifically. So it's got shorter drops compared to the Alpinist or Rapide cockpit, mirroring the Terra handlebar that we've had in the past. And it is uh built in a lot of compliance because off-road riding is really rough, and having a handlebar that breaks away some of that impact is really, really nice.

SPEAKER_02 28:13

I think that's a key point. Again, like going back to like working with our athletes to create product that works for them. About the compliance on the cockpit, like we get about 70 to 80 percent more compliance at the drops, which is where a lot of those individuals, like Sophia, if she is, you know, she ends up being solo a lot in those long races. So if she's sitting in a pretty arrow position in the drops, she just wants to be as comfortable as possible. So we have even more compliance built into kind of the drops just to be in that nice position and just be comfortable and kind of motoring along. Whereas like a rape cockpit is way stiffer in the drops because a lot of times when our world tour athletes are in that, it's like pretty hefty sprint going on or something. Yeah, yeah. Yeah.

SPEAKER_03 28:53

I think that's a really interesting area where it's kind of crazy how much work and RD went into that one part of the bike, right? So the shaping of the top of that cockpit had a lot of iterations to balance the arrow performance with the comfort. Right on the road bike, the repeat, we know that the tops aren't really a position that are used, so it's really just arrow optimized. But on Terra, we had to balance those two factors. Another thing you'll notice is these are backswept while repeat is forward swept. That back sweep means that we're actually modifying the rider's body position to also be more arrow efficient. So if you just hold your hands up right like this, your elbows come out. If you rotate them back like this with a flared cockpit, all of a sudden those elbows are tucked. We know from our gravel pros that they can spend a lot of time in those positions over these long races. You're not gonna have your hands on the bars in the same spot the whole race. So we want to make sure no matter how they ride the bike, they're as arrow as possible. So there was a whole RD study just for that in the wind tunnel.

SPEAKER_02 29:48

I honestly think the cockpit's one of the coolest parts on the bike. Uh, to your point, it's like the biggest portion of aerodynamic drag is the rider. Yeah. So just like putting them in a faster position is gonna have even a bit, you know, just as much of an impact as like the rest of the bike as well, if not more. Yeah. Um, so those are crucial small tweaks that just make a huge difference, especially over like an unbound race that's whatever, nine to ten hours for riders.

SPEAKER_01 30:13

Yeah. And that's a a really good overview of the the arrow side of things and how deep you all went there. So, but you still came up with a sub-800 gram frame, right? Because you didn't want to lose that. Let's talk a little bit about how you got to an 800 gram frame and it looks quite different than Crux 4, it looks very different than Athos, which are the other super light bikes you've made in the past. What did it learn from those bikes?

SPEAKER_00 30:36

Well, there's a lot about balancing the tube cross-sections to gain aerodynamic performance while maintaining the structural efficiency of those areas of the frame. So a traditional super truncated airfoil might have really sharp corners and trailing edges, and that is not very well suited to transferring load throughout the frame. So, one of the things we learned with Athos and the flow state design is essentially shaping all of these transition zones specifically, but every tube cross-section in a way that helps carry the load through the frame and balance where that load is being shared and transferred across the cross-section. So finding tube shapes that were both aerodynamically optimized but also structurally optimized at the same time was the main approach for where the frame got the shape that it has.

SPEAKER_01 31:19

And so by sharing loads between tubes and through tube joints, you you're eliminating extra material, eliminating different layers?

SPEAKER_00 31:27

Exactly. So if each tube is more efficient at carrying load, you don't need as much reinforcing plies just to over-strengthen the zones that are being stressed unnecessarily excessively. So if the FEA shows you a hot spot, you're not just throwing more carbon at it, you're saying maybe that shape's not right. Right, exactly. There's a lot of balancing of that on the early design phase of like where are the high stress zones and how do we minimize those high stress zones with tube design and not just with the carbon fiber layup.

SPEAKER_02 31:53

But also refining the layup, making sure you know plies are pulling double duty from, let's say, a stiffness perspective and a structural perspective. Yeah.

SPEAKER_00 32:00

It's a hand-in-hand balance of both the carbon fiber layup and the 3D shape of all the sections of the frame.

SPEAKER_01 32:06

So I think one of the things that actually impressed me the most about this bike, and Doug and I just got back from about a three-hour gravel ride, which is pretty incredible. This stuff out here, the riding out here is absolutely insane, is how smooth the bike still feels. And you look at it and you see that arrow seat post, you see the arrow seat tube, you see shapes that you think of you know as an aero bike, which traditionally, you know, haven't been the smoothest riding bikes in the world. Uh, tarmac's done an incredible job of bringing that kind of you know compliance into an aero frame. Um, how did you get the same level of compliance out of a crux 5, which looks arrow, versus a crux 4 with those simple round tubes?

SPEAKER_00 32:43

Yeah, there's a few ways we did that actually. So, I mean the teracockpit, which we already spoke about, introduces a whole lot of extra comfort on the front end of the bike. Uh, and the shaping of the tops, as Leo mentioned, is a big part of that. And uh so that gained a ton of the front. The rear, the we knew a aero seat post was going to lose a little bit of compliance compared to a round traditionally, but the frame itself was able to gain a lot of compliance to balance that out as a system. So the ways we did that with the frame were a couple of things. The drop seat stays on the Crux 5 compared to the Crux 4 helped introduce a lot of frame compliance at the rear end, so like comfort at the saddle. And there's a bit less exposed seat tube, or the seat tube length overall on the Crux 5 frame is a little shorter, allowing for more exposed seat post. And the seat post exposed length has a lot to do with the flex you get at the saddle, too. So while the shape of the seat post is a little less compliant compared to a round, the fact that there is more of it exposed allows it to flex more inherently. And so the combination of the frame getting more flex and the seat post having more exposed length to also flex gave us an overall system that matches the compliance at the rear of the crux 4.

SPEAKER_02 33:50

So we just shifted. Crux 4 relied more on seat post, less on frame, and now we rely more on frame, less on seat post. Yeah.

SPEAKER_01 33:57

I I do think honestly, that's something that you know those those dedicated Crux 4 riders are gonna love to hear. And I and I think once they get on the bike, gonna love the feel because the ride quality of that crux 4 is really something special, and I think really the primary reason that so many riders fell in love with that bike. So it's it's really cool to hear that even though you were making something that was, you know, really about time to finish and then as fast as you could, you didn't forget about the compliance, about that ride feel that Crux is just so loved for.

SPEAKER_02 34:25

Yeah, as we said, that's probably was our number one priority was not to lose that. And especially going back to just the use case again. I mean, you're talking about a 10-hour event on gravel. You want the bike to be as comfortable as possible.

SPEAKER_00 34:37

Absolutely. And the other benefit with the Crux 5 is that you can now fit the larger tire than ever. So having a larger tire can also introduce a bit more comfort on the chassis front and rear. So by giving you the option to run up to a 55 millimeter tire to gain a little extra comfort there as well, if you want it, that's now an option where it wasn't in the past.

SPEAKER_01 34:55

Yeah, nice. So the last thing I want to touch on when we think about the bike itself specifically is the geometry. You know, what um what changed, if anything, and why did it change?

SPEAKER_00 35:05

Yeah, absolutely. So Alex kind of alluded to it before, but historically the Crux has been more of a cyclocross-focused frame, and the geometry was more kind of dialed in for cyclocross with a higher BB, steeper head tube angle, kind of designed for those short, fast, twisty cyclocross style races. Since we really wanted to shift Crux 5 and do a gravel race focused platform, there were a few main things that we adjusted in the geometry to accomplish that. The head tube angle got about a half a degree slacker on all the frame sizes to give a bit more wheelbase length and a little more stability on the type of fast, flowy, sweeping long gravel descents that you see. And we also lowered the bottom bracket on the crux 5 by roughly by exactly six millimeters on all the frame sizes to get you a little bit more stability by lowering your center of gravity. And also knowing that the Crux riders of the Crux 5 and gravel racing generally runs a bigger tire than a 33mm. You don't need the really high BB to account for the fact that you're running undersized tires in the cyclocross race. You can lower the BB and run bigger tires and have either a roughly equivalent center of mass on the bike or just generally sit lower if you were already running big tires on your Crux 4. So are we comfortable telling riders now that this is a gravel race bike? It's a gravel race bike. That was the number one brief for Crux 5 was it is a dedicated gravel race bike. How do we make it the fastest gravel race bike? Yeah, and that was the objective. Yeah, yeah.

SPEAKER_02 36:31

Longer, slacker, lower, steeper had or a steeper seat tube angle as well.

SPEAKER_00 36:34

That is another thing we've seen with both road and gravel racing positions evolving over the years, is that a lot of riders are drifting to a more forward position. So we did increase the uh steepness of the seat tube angle by a half a degree as well to facilitate that more modern position that a lot of riders are taking.

SPEAKER_01 36:50

And I guess that gave you a little bit of room as well to keep the package fairly tight, but keep that 55mm tire clearance in the back.

SPEAKER_00 36:56

Yeah, I mean, tire clearance to the back of the seat tube is definitely one of those design parameters that we're always balancing and a slightly steeper seat tube angle. It definitely helped us accomplish a bit of that too. I think the biggest challenge around the tire clearance is usually the chain stay bottom bracket area between the chain rings that we wanted to fit up to a 52-tooth for the Crux 5 and a 55mm tire. Everything gets really tight in that zone. That's certainly the place that took a lot of design attention to get us to that tire clearance, but the steeper seat tubing will help too.

SPEAKER_01 37:25

Nice. Alright, so that's a pretty good deep dive into what you all made. So, I mean, to go back a little bit, you had the equation of speed, you went and tweaked your dials and said, you know, the bike needs to still be a complete at 7.1 and full arrow spec. You want to be 15 watts faster, and you know, between the the chassis and the the bars and the wheels, you got there. Um you wanted that same same ride quality you had with Crux 4, and you somehow managed to deliver on this insane brief that you were handed. So when you put that in the equation of speed, you know, you have all the numbers from our top athletes. You know, we got this great gravel team, and so we have access to the numbers of the best riders in the world, you know. And I know you ran these numbers, right? On if they were on a crux 4 versus a crux 5 at 2025 unbound.

SPEAKER_03 38:10

What happened? It's a lot faster. Uh seven to ten minutes, depending on the rider. Yeah. Um, we saw the biggest time savings with Sophia. She is the smallest rider, sees a bigger impact from changing the arrow of the bike, but she also rides solo a lot more than most of the men. So for her, having a more arrowed chassis makes a lot more of a difference. Um, and then for most of the male riders, it was kind of in that seven and a half minute range. Yeah. We looked at Ian and Mads. Ian and Mads and Sophia, yeah, were the three main ones we looked at.

SPEAKER_01 38:37

So Ian, Mads, and Sophia 20. So kind of a trick question because I actually have the exact numbers here. I wanted to see how close you'd get. So what I have here, and you can tell me if I'm wrong or not, Boswell would have been seven minutes and 40 seconds faster on Crux 5 versus Crux 4. Same exact power numbers. So you're just talking about equipment efficiency. Right? Just equipment efficiency. Same effort from him, 7 minutes and 40 seconds faster. Mads, 7 minutes and 45 seconds faster. And then Sophia, yeah, to your point, 9.58, almost 10 minutes faster. Yeah. Which is which is wild. And then so I did a little bit of math too. And if you subtracted those from their times, Oswald would have gone from eighth to third. Mads would have gone from fourth to first. And Sophia would have gone from third to second with those kind of time savings. And of course, these are simulations, but you know, to your point, hyperaccurate. This is what Formula One's been doing, this is what America's Cup Sailing has been doing. Um, so I would imagine the athletes are pretty excited to finally get to race. Pretty excited to race this bike at uh Unbound, which is where it'll be unveiled, right?

SPEAKER_03 39:44

Yeah. And we've already had really good feedback, right, on parts of the system that were launched early, the wheels they've been racing for a while, the cockpit they've been racing. And I think Alex can speak more to it, but from everything I heard talking with the riders, we've had extremely positive feedback.

SPEAKER_02 39:59

Yeah, for sure. They also have now been on the complete bike for some time and have spent a ton of time on it. So yeah, unfortunately, now that they're on the bike, it's hard to keep them off of it.

SPEAKER_01 40:08

Yeah. I heard I heard Mads got spotted uh at a car wash. Pressure washing his car. Pressure washing his bike, and of course it made it up on Instagram. Yeah, yeah.

SPEAKER_02 40:15

So I think they're quite excited to get on the new platform.

SPEAKER_01 40:18

So I know they're excited. So for you, you all, you know, you worked on this bike for years, you know. Um, how's it gonna feel, you know, when tomorrow we're inviting a bunch of media from around the world to come and ride bikes with us and you're gonna tell them this correct story, you know?

SPEAKER_00 40:34

It's always such a treat to see the bike finally out in the wild for the first time after staring at it for so long on the computer screen and in the lab and in the wind tunnel. It's almost like sending your little child off to college or something, like you've raised them the best you can, but let's see how they do in the real world on their own. And it's always super rewarding to see the athletes actually using it and liking it and preferably winning on it. Like it's just it's really rewarding.

SPEAKER_01 41:00

Nice. And and so, yeah, you all gonna be tuning into Unbound? Absolutely.

SPEAKER_02 41:04

It's really fun to see it on some of the bigger riders in the race, and uh, I would say the biggest race in the world for gravel right now.

SPEAKER_01 41:11

So nice. So, so Alex, you as the you know, as the leader of this team that you know created this incredible product, you know, tell me a little bit about the effort with the team and you know, and and the team that has been assembled to to create these bikes. It's super impressive.

SPEAKER_02 41:24

I mean, we have three of us here. We have a pretty large team and uh a global team, and there's way more people involved in a project like this than just you know a hand like an engineer or two and an aero engineer. Um, I mean, we yeah, there's so many people involved, so it's not just us that will be excited to see it in Unbound. There's, I would say, the entire company, but especially our entire team and road and gravel organization will be quite excited to see the bikes unveiled. So we've all been working towards it for quite a while, so it'll be good.

SPEAKER_01 41:55

Awesome. Well, thank you guys for taking us through that that deep dive and the you know what was in your heads to make this bike and then the equation of speed and time to finish. And and it was very cool to hear from the actual creators of the bike how it all went down from behind the scenes. So appreciate it. And for for all of you on the podcast, uh, this is dropping obviously right when the bike launches. So you can go to your local dealer and you can find the Crux 5. You can get a demo, you can go and admire the handiwork of this crew and you know, and hopefully pick one up for yourself for your next ride. And then don't forget to tune in to Unbound as the specialized off-road squad tackles the biggest gravel race in the world on the all-new Crux 5. Thanks for listening.