Interview: Trek's Travis Brown On Experimenting With 32" & 36" Wheels

A reader put the question to us a few weeks back, if a larger wheel size was coming, and if 29 was better than 27.5, would a bigger size be even better? I did some digging, and learned that Travis Brown at Trek is testing larger-than-29-inch wheels as we speak. Of course we reached out for more info, and Travis was kind enough to let us peek behind the curtain.

You can listen to the interview with Travis in this week's Pinkbike Podcast, as well as our commentary on what it could mean for the industry. But we figured this deserved its own transcription as well, for the people who don't want to listen to an hour of banter.




If you followed cross country racing in the '90s and the 2000s, you've probably heard of Travis Brown. He was a regular on the World Cup circuit, before turning his attention to product development with Trek in the mid-2000s. These days he's the field test manager, running an entire crew of riders who are working on products that we're going to see in the future.

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Mike Levy: Travis, how's it going today?

Travis Brown: It's going well. Nice to see you Mike. Nice to see you Brian.

Mike Levy: A little birdie tells me that you've been riding some interesting and larger wheel sizes lately.

Brian Park: Can you confirm or deny?

Travis Brown: Yeah, I don't know what bird got out of the cage, but we have been messing around with some unusual wheel sizes. It has always been interesting from the 26, 29 comparison and mixed wheel platforms in 27.5, those kinds of things influence the character of a bike so much. So yeah, we're still messing with that.

Brian Park: You were at the forefront of pushing some mixed wheel size stuff at Trek quite a long time ago. You did that 69 bike, how many years ago?

Travis Brown: That was probably about 15 years ago, 14 years ago, we started doing that.

Brian Park: So, it might be that the things that we're talking about now are still 15 years away?

Travis Brown: It could be, hopefully, if we discover something that has a performance advantage, we don't have to let it languish that long for the right landscape. But there are a lot of factors.

Brian Park: I've heard people love new standards in the bike industry. They've been clamoring for this. [sarcasm]

Travis Brown: Yeah. Well, we're kind of all enduring 26 to 29, back to 27 and back to 29 and I think there's a little bit of sour taste in consumer's mouths when they look back across that whole spectrum, and fair enough.

Mike Levy: And you were also in the thick of it in the development of 29er as well too, weren't you?

Travis Brown: When I moved into the R&D department, we still had the Trek brand and the Fisher brand independently. The Fisher brand was our 29 inch wheel platform brand and we honestly struggled with that wheel platform under that brand for nearly 10 years before the rest of the biking world decided, "Yeah, that's probably pretty good for some applications. We should try it."

Ironically for the Fisher brand and as it got absorbed into Trek as like the Gary Fisher line in Trek, was right around the time where it didn't seem like the European market was going to ever adopt the 29 inch wheel. And then almost overnight, there were a couple German mags that did some field tests and said, "Hey, this works really good." And the next year 29 inch wheel bikes in Europe were huge. So, I don't know how you predict that kind of thing.

Mike Levy: I'm just going to come out and ask Travis, what wheel sizes have you been testing?

Travis Brown: Well, we've done a little experiment. We've continued to experiment with mixed wheel platforms, not with the idea that we're going to go to production with it, but because it gives us a really good understanding of the independent roles of the front and the rear wheel. We've been also messing with diameters larger than 29 to see if there's efficacy and where that space might land and what the advantages and what the liability are.

Brian Park: Come on now. How much larger? What are the inches?

Travis Brown: Well there are 32 inch tires and there are 36 inch tires. The quality compared to what enthusiasts are accustomed to of those tires is pretty low, so that kind of influences the impressions, but you can ride those platforms and learn a lot about what the potential might be for larger wheel sizes.

Brian Park: Can you tell us a bit about the mules that you're testing?

Travis Brown: Yeah. I can tell you a little bit about them. I mean, they're as simple as it gets, it kind of goes back to the '80s and '90s, they're rigid hardtails. That way you don't have to cross the hurdle of suspension, the size and packaging when you don't have suspension travel, is much easier with this, be it, what would be considered an extreme wheel size, which is a 36 inch wheel mountain bike. So, we're doing our testing on, on rigid mules and comparing those to rigid 29 inch wheel bikes.

Mike Levy: And have you guys had tires and rims made for this?

Travis Brown: We have used what exists from a tire standpoint and we do custom frames and forks and aluminum extrusions are really easy to roll into whatever diameter... [for the rim]

We haven't done custom tires. Doing a custom tire in 29, for an R&D project is pretty easy because all the vendors have tooling to create that size - just cutting a mold and applying it to the existing build drums and the ovens is not that big of a challenge. There are very few tire manufacturers that have tooling to produce tires larger than 29 inch. Those vendors are a little more economy based tire manufacturers so the quality isn't quite what we're accustomed to.

Brian Park: So, with sh*tty tires and rigid mountain bikes, how do you extrapolate your results? How do you compare that to existing bikes and what those advantages might be?

Travis Brown: I mean, that's kind of the big question at this point and trying to evaluate larger wheel sizes, but what we do is we just put the same sh*tty tires on the 29 inch wheel mule. So, we kind of eliminate that variable.

I haven't been able to find identical tread patterns, but you find the same case in construction. So, it's a two ply, low thread count wire bead tire and then you just do a little math between those and try to find a weight that's the right comparison. The tires that we're riding right now, say on a 36 inch mule, it's a 1700 gram tire in a 2.25 width so there's a lot of weight penalty in there that just has to do with the construction quality.

Brian Park: So it's a 1700 gram tire that wouldn't need to be a 1700 gram tire. We were used to heavy 1400 gram tires for downhill and enduro applications, but this is narrower.

Travis Brown: If you scale that back, the comparable 29 inch wheel that we're testing is in the 1200 to 1300 gram range for a 2.25 trail tire. We all know that that should really be an 800 or 900 gram tire for the best quality of what we're accustomed to. So, that's kind of a big filter that you try to work through in your comparisons.

Brian Park: So what's the verdict? What is different on the trail?

Travis Brown: Well, I mean, the reason to experiment with both 32 and 36 is that, that's what exists. The reason to try 36 is when we prototype stuff and we're field testing, whether it's suspension tune or tire inserts or geometry, we try to put some pretty broad bookends in that performance comparison to start with, so that people can really clearly feel what the differences are and if they're preferable. Then we start moving those bookends in with smaller and smaller differences to find the point where either the test group and the riders can't tell a difference or they don't care. I would take this one or this one. And yeah, that's a point where you can't really refine the evolution anymore.

Mike Levy: Can you describe to me how that 36 feels?

Travis Brown: Sure. Well, first it's pretty heavy for a rigid hardtail. That mule I think is about 32 pounds. So, the characteristics by comparison to 29 that we find with these larger diameters, and you could guess this from comparing 26 and 29, but the negative characteristics are that it's heavier. Even if you didn't have that tire quality challenge, the wheels are less stiff because the spokes are longer and that the hoop is bigger. There's a little more inertia to the wheel.

Brian Park: So, it's harder to accelerate?

Travis Brown: It's a little harder to accelerate, but that inertia has a positive side too. It's easier to carry speed through rough terrain than with a smaller wheel because of the characteristic of the contact patch being longer, you're engaging more knobs. So, both climbing and braking traction are better and cornering traction is better.

When you're in a type of terrain where you can take advantage of those positive characteristics, they might outweigh the negative characteristics.

Mike Levy: Have you been doing time testing, back to back, on these 32s and 36ers versus like a 29 or even a 27.5? And what's the result?

Travis Brown: Yeah, what we learned with the 26 to 29 comparison is that timed laps are really important. There's something about the larger wheel, that extra weight and the inertia of the larger diameter that almost always feel slower and more stable and as riders frequently we perceive that as being slower.

We found this with 26 and 29, you could ride equal 26 and 29 inch bikes on the same course, if you didn't time it, you'd swear the 26 inch wheel bike was faster on almost all off road conditions. If it was a closed loop climbing and descending and you put a clock on it, the 29 inch wheel was almost always faster. That instability that you get from a smaller wheel, stiffer wheel, we perceive that as going faster because we're closer to the limit of control, but that window moves with the wheel size, so...

Mike Levy: Yeah. So, all things being equal, Travis, which bike are you faster on? Are you faster on a 29er? Or are you faster 36er?

Travis Brown: Well, to the degree that we've been able to do comparisons on like different terrains, there are definitely some terrains and trails that you're faster on the larger wheel size - the rougher stuff. If there's stuff that has like high speed sweeping flat turns, your corner speed is higher [with the larger wheel]. If there's stuff where you're braking really hard and like dumping your momentum and then you directly have to accelerate again, those circumstances are faster on a smaller wheel. So, I think that the most accurate way is to just find the characteristics that a 26 might be faster than a 29. It's the same for something larger than a 29.

Brian Park: When I think back to the days of 26 versus 29, one of the scariest things for people was cornering with a bigger wheel. Then on top of that, we had reaches growing, exponentially, and wheelbase used to be a really scary number for manufacturers, thinking "Oh my God, this is going to be so cumbersome." That fear has kind of gone away, but I could see that being a concern, when you go with that drastically up to 32 or even to 36. So how does it corner?

Travis Brown: I mean, I had that a similar concern for backcountry, switchbacks, tight switchbacks and I think what I've learned from this experiment is that appropriate front, rear weight bias for cornering, whether that's uphill or downhill, is really crucial. And tire grip is really crucial. So, say on the 36 mule, the chain stays are really long, even though the front center's really long so your front wheel bias weight is higher than on most bikes. That makes up for a lot of the extra length and actually it corners switchbacks really well.

There aren't that many switchbacks that are so tight that the length of the bike, whether that wheel base is a 1000 or 1200, you're not going to get around there.

Mike Levy: What are we looking at here for head angles and offsets on these bike? I assume they're all custom and pretty out there.

Travis Brown: Yeah. Well, we're talking about a 36 inch wheel that is pretty gargantuan. And with this wheel, we've done some similar things that we did when we were 26, 29 comparison and we've used offset to standardize head angle and trail figure. So, the offset on this mule is huge. It's around 90 millimeters.

Mike Levy: Oh boy.

Travis Brown: And that's to get a trail figure that's comparable to a 29 inch wheel bike with a 69 degree head angle.

Mike Levy: How does that huge offset feel at lower speeds? Those half mile an hour corners.

Travis Brown: That cornering like flop that you might get at lower speeds has way more to do with the trail figure than it does the offset. That is something that we learned in this. You would think that big offset would make it really fall in, but it feels really close to the 29 inch with a standard offset.

Brian Park: I imagined that we'd get an exaggerated at like a 65 degree head angle though.

Travis Brown: Well, we haven't tested that. The geometry and shape of the fork already, to get to 90 millimeters of offset already kind of looks a little bit like a chopper. It's definitely worth experimentation to find where those limits are. That's part of the exercise is pushing the bookend out beyond what you think is practical and then proving yourself right or wrong.

Brian Park: So, let's switch gears from the nuts and bolts of it because it sounds like there are some advantages and some clear disadvantages from a more, maybe not commercial, but from a more practical standpoint, like what do you think the future of wheel sizes is in mountain biking? Do you think it's inevitable that we're going to have a bigger wheel size either, either or both?

Travis Brown: Well, I mean, you see in the boutique builder space, there's some enthusiasm for 36ers or 32 inch wheel bikes and that's an opportunity for those small custom builders. And that cycle just continues with the small builders and the big manufacturers. I'm sure if we're interested in looking into if there might be a potential advantage, that we're not the only ones. So, how that field science comes back and then how it overlays the opportunities in the marketplace, which sometimes those circles overlay right on top of each other but more often there's a pretty small part of that Venn diagram where there's a community space. Fortunately for the guys in R&D, we don't have to worry about the trends and the marketing and the taste and the fashion as much. Our responsibility is to just build a performance profile. It does this better, it does this not as well.

Mike Levy: So, everybody that's out there right now, that's already getting angry about this. There is no 2022 Fuel EX with giant wheels. This is experimenting. You guys are figuring things out and just for experiment's sake, it sounds like.

Travis Brown: Yeah, and it's valuable to our existing wheel platforms. It's valuable to the decisions that we make with 26, 27,5 and 29. Having that extra data point and what happens when you change wheel diameter informs everything that you do with wheel diameter.

Brian Park: So, if we're in make believe land. You said you're 6'1"-ish. And if you were building, let's say your perfect cross country hardtail today, what wheel size would it have? With good tires and good components.

Travis Brown: If I had one fully custom ticket to spend, with what I know now and what I've experienced, I would spend it on a 36 inch wheel race bike.

Mike Levy: That says a lot.

Brian Park: We've talked about the limitations in terms of testing, but if there are some advantages there, like it sounds there are, would it be for everyone? Levy's tired of hearing me beat this drum, but...

Mike Levy: Not his again.

Brian Park: Do you think that wheel size is tied to rider size in intended use or would a 36 inch wheel or a 32 inch wheel just be the magic bullet for everybody?

Travis Brown: Well, it's definitely tied to rider size, but it's tied to a handful of other things too. So, what characteristic does the rider want, is a big part of it. I think through this exercise, we speculated that maybe my size rider might be the lower limit to utilize the wheel size. I think it's lower than that. I think with all of the tricks that we learned on making a really small 29ers and all the geometry exercises that we've done with long travel 29ers, if somebody wanted that 36 inch wheel characteristic or the efficiency for a given terrain, you could probably make a medium bike.

I think you could make a 32 inch wheel XC bike for someone that's 5'1", with a lot of geometry acrobatics, but...Short travel, like probably not a 100mm fork.

Brian Park: What would happen if we were talking about trail bikes?

Travis Brown: Depending on the amount of travel, it looks like there's potential for a larger wheel size, but I had to speculate a lot because we haven't tested full suspension bikes. I would say 100 to 120 millimeters of travel. There probably could be some adaptation for larger than 29, but larger than that, you just can't package it.

Like you said, I can confidently say we don't have a pipeline production project, but I speak for, I think everyone in my R&D group, is that the projects that are pure R&D exercises are always the most fun because there's the most unknowns. And there's the least tethers as far as, will it be successful as a production bike. So, you have a lot of freedom to try stuff.

Mike Levy: That opens the doors for you to do some crazy sh*t. That's got to be fun. Like that first ride on that thing, you must have been like, what the hell is going to happen?

Travis Brown: Yeah. Well, I had ridden other people's [36er] bikes over the years, some small manufacturers and I remember the first 36er I rode was actually at the Sea Otter. I just wanted to have the impression, like, what does it feel like? We were in this space of plus tires and fat bikes so, I kind of had a lot of benchmarks for differences from a regular bike and what it felt like. My first thought was that it feels way less different from a normal bike than a fat bike does. So, maybe you could actually make a competitive bike or maybe there are some performance advantages in this.

Brian Park: I've got your marketing slogan. You can have this one for free: "36ers, it's less stupid than a fat bike."

Travis Brown: You're not wrong. Yeah, well, they might look more stupid though. The conventional eye for a bike when we've adapted and calibrated towards fat bikes now, but when I ride this bike...

Brian Park: Well hey, thanks a ton for sitting down with us. I'm very curious to see where things go. Obviously, the industry and commercial perspective of these things is going to play a factor. I'm sure somebody is going to be reading the comments below...

Travis Brown: Yeah. People are definitely going to be messing with this for a while and depending on what happens with tires, I see that as kind of the biggest restriction on really feeling into what the potential is of larger diameters than 29. I would bet that when one of the quality tire manufacturers or someone commissions a prototype of a really high quality tire, our understanding of what the potential is will experience another breakthrough. And that'll be fun. We don't know until we have all the apples to apples comparisons.

Mike Levy: Yeah. Well, thanks for indulging our questions and we definitely are going to be hitting you again on this topic because we'll want to hear where it goes.

Travis Brown: Thanks guys. Thanks for indulging me on one of the fun R&D projects.

Posted In:
Interviews Reviews and Tech Trek Brian Park Mike Levy Travis Brown