From the Archives, originally posted January 1st, 2015.
Happy New Year!
Travis Brown interview on everything fat and where Trek and Bontrager fall into that world.
I met Travis while living in Boulder, Colorado over 15 years ago. I was starting to ride for the grassroots Ionic-Nema MTB racing team (a baggy shorts pro team!) in my attempt to become a winning pro racer. That did not happen. He was well established with Trek but i’ll never forget his generosity and how he helped the up-and-comer racers in any way he could. He continued to succeed in what was an incredible racing career winning 2 National titles, representing the US at the 2000 Sydney Olympics, and winning the inaugural (and a couple of other) World Singlespeed Championships, among many other things along the way. Since retiring from racing he has been heavily involved in trail advocacy, trail building, and working for Trek as their Product Developer/Field Test Manager. This position fits Travis so perfectly. I remember getting coffee and going on training rides with him all the while talking-shop endlessly on what works and doesn’t in the world of cycling components, geometry, cold weather clothing, trails, whatever. What cycling-related inventions we could come up with and how we always wanted to build our own frames and components. We had both signed up for a UBI framebuilding class in 2004 but I had to bail last minute because of getting a new job that wouldn’t let me have 2 weeks off right at the start (go figure). Had he gone I’ve no doubt he’d be fabricating his own frames, bars, and parts to test all his theories. Nobody I know has more interest in the details of what makes a bike ride well and why, from tread pattern to geometry and how they all interplay. So when Trek came out with the Farley fatbike frameset, Hodag 4″ TLR fatbike tire, Jackalope TLR fatbike rim, and TLR Chupacabra 29+ tire, I got very interested in hearing from Travis’ own mouth how these products came to be and what is in the future for Trek in the fatbike world.
Tell me about the testing you’ve done, and are doing, related to fatbike and 29+ tire and rim development with Trek/Bontrager?
We test our product against what we consider best in class competitor product and we have an iterative progression of prototypes that lead to the production item. Compounds, casing design, knob layout etc are all part of process. For example with the Chupacabra competitor testing was pretty simple. The Knard/Rabbit hole was the only competitor product at the beginning of that project. We identify a performance profile of that wheel system and define the positive and negative characteristics we want to address in our own product. We then start building and testing prototypes to prove out the theories.
How does rim width play into the picture? How do the same tires ride when on a 60/80/100mm wide rim?
This is a great question and one that we are still not at an end conclusion yet. One thing that is clear is that the tire/rim section ratio that is the rim width compared to the tire is growing considerably from the norm. Rim technology is progressing quickly and is becoming a more and more efficient method to simply add volume to a wheel system than in the past. Performance at lower air pressures is also positively effected by additional rim width. There are limits to the benefit based on the tire profile and design. There is a point that mounting a tire on a wider and wider rim section outpaces the initial design profile of the tire and performance suffers. There is also a point that the outside diameter of the tire stops growing and starts shrinking as a rim gets very wide.
Rim width to tire ratio is a hot topic and a quickly moving target. I think the optimal ratio also differs with the riding surface, for example on snow with a 4″ tire I like a rim about 90mm but prefer a rim about 70 mm for riding on dirt. There are lots of factors in that specific example with that specific tire but the fact that rims are getting wider for a given tire is a clear trend and one that is improving tire performance. We did one test with cyclocross tires to try to get some bookends on where the breaking point was in improving performance. We rode rims between 21mm and 35 mm on standard 33mm cyclocross tires. The 35 mm rim was in there to ensure that we had something way off the reservation but it turned out that with some tires that rim was the best performer in a few characteristics. My tastes are definitely trending toward wider rims. Tire design is prime to catch up to the rim options that we have now. For very soft snow you are usually better off with the widest rim you can get regardless of the weight. What effect does rim width have on the same tire pressures? Wider rims clearly allow more integrity to the tire casing. This is most relevant at low psi. For example a 2.3″ width tire may have good performance for a given rider weight on a 25mm rim at 31 psi but on a 35 mm rim that same level of casing integrity my be lowered to 29 psi. and so there will be an improvement in tire compliance and traction performance on the wider rim. This does not however improve the resistance to pinch cuts on rim outs. Rim and casing design come in to address that. Growing rim width section also adds volume to positive effect, but to a point. After that the OD of the tire starts to shrink. In many cases a rim 10-20 mm wider than what we thought of as normal in the past is still within that range of adding net positive characteristics.
What is TPI and what effect does it have on ride quality, flat resistance, weight, etc.?
TPI refers the Threads Per Inch in a tire casing. It is generally considered as one layer of casing material meaning thinner and therefore usually lighter and more flexible threads to weave into the casing. But sometimes tire manufacturers count two layers of threads in order to get a higher count. Higher TPI usually means lighter, more supple and less durable but the material and manufacturing process has as much to do with the tires performance as the thread count. Manufacturers can also add additional layers of various materials at high stress parts of the casing. It isn’t that complex but there are more components to the tire than you would think. What have been the results of speed testing on up and downhills with the various tire sizes? 29/27.5/26? How do these times compare with a 29+ and 4″ fat bike? For rough conditions weight penalties can quickly be overcome by rolling efficiency advantages. In those rough conditions over all wheel diameter, and minimum reliable inflation pressure define how efficiently a wheel system rolls over terrain. There are a lot of variables to account for in each terrain type but if you want to race over very rough terrain or very soft terrain, a five pound weight penalty for a wheel system that can be run at 8 psi rather than 25 psi can easily be faster.
What do the tests look like? Timed laps? How many individuals? All other variables kept constant?
We try to eliminate as many variables in a field test as is reasonable. Same rider, same course, same bike with only one equipment change per lap. We try to conduct tests as scientifically as is possible. If the testers have it in them we also try to repeat the same set up in a test battery to identify ‘drift’ due to fatigue, familiarity with loop, changing loop conditions, changing ambient conditions, etc. We often overlay time, HR and sometimes power with riders impressions of a products performance over a test lap. We do find that the best testers have a sensitivity that accounts for more variables than all of the science and technology at our disposal. Those sensitive riders who can sense and then communicate what a bike is or is not doing to the engineer are rare though.
What do you think are some frame designs that Fatbikes could benefit from and why?
There is a lot going on with fat bikes right now to catalyze alternative drive trains like Pinion and Rolloff. We might be at the limit with a 120mm BB shell when you weigh in bio mechanics for most riders. One could still go wider (if a tire existed) with those alternative drive trains. Fatbike suspension – your thoughts on it in general and specifically the benefits or costs on snow vs. dirt riding. Suspension for off road riding is a benefit to fat bikes. A 3.8 or 4.8 inch tire is still not suspension in terms of where that technology is in mountain bikes. The big tire adds a lot in terms of stability and traction but very little in terms of suspension the way we design it currently. Obviously, it is more advantageous in some terrain than in others. For summer riding it is almost always a positive if your trails are rough. There isn’t need for suspension on machine groomed snow but that does not encompass all kinds of winter riding either. Air sprung, oil damped suspension also has some unique challenges to performance in low temps but those challenges are fairly easily addressed.
Discuss the weight, contact patch, cornering and other potential trade offs you get when riding a 29+ or fatbike. What are the costs and benefits when on each type of bike?
The maximum contact patch is uniquely defined buy the minimum reliable tire inflation pressure of the total vehicle. That system includes the wheel design, bike, rider weight and rider style. In low traction, soft or rough terrains that lowest threshold is not just the most comfortable but also the fastest set up. Casings folding under cornering forces and pinch flatting indicate being below that threshold for the given system. Everything is a mixed bag when comparing wheel volume sections or diameter based on the given terrain challenge. We still don’t have all of the products to define the book ends of performance in this regard right now. For instance there are some conditions that a 4.7 inch tire is faster than a much lighter 3.7 inch tire accounting for the weight penalty and wider necessary frame/drive train. But is that width the limit where the liabilities outweigh the benefits for all terrain types? I don’t think we know that yet and there are still unanswered questions on how diameter effects those capabilities as well. I like to distill measuring equipment weight differences to % of vehicle weight (bike + rider) and I think that is a more accurate method and perspective on determining if a particular technology is of benefit. It also accounts for different rider weights. A 200lb rider can obviously accept a much greater weight penalty for additional performance than a 100lb rider. The smaller rider by comparison can get away with lighter tire casings and rim sections. We rarely end up producing end products for a specific rider weight but the exercise in the prototype stage does a lot to inform our overall understanding of performance. Bontrager is going tubeless out of the gates. How did that arise and what are the challenges and benefits to going tubeless on fat bikes? Tubeless is firmly established as a favored and in most cases superior wheel system set up for mountain bikes. There are some unique design challenges in reliable low psi tubeless systems but we also see a progression of perception of the ‘fat bike’ to more of just a unique capability mountain bike. It made sense to put effort into solving the factory tubeless challenge for fat bikes early.
Will there be a 4.8″ Hodag?
I don’t see a 4.8 Hodag in the near future.
What about a 29+ Trek complete bike?
It is hard for us to forecast a bike category that is so new and only has one major player in it.That being said the test mules that we built in order to do the development of the Chupacabra tire are some of the most coveted prototypes.
What about a Bontrager 29+ tubeless wheelset?
The Chupacabra is a TLR tire now and will work well on existing rims down to about 35mm in width.
What is your favorite goto bike for snow?
My only choice is the Farley and it works as both a winter and 4 season bike but for winter only riding I ride one with a rigid fork both for a bit lower BB and the weight reduction.
For rocky dirt riding?
Around Durango Fuel EX 29 is my favorite bike.
I have spent a lot of time riding the Farley and Chupacabra in desert terrain. The uncompacted rock and dirt and roughness there rewards larger and lower psi tires a lot but you also need really refined suspension so my go to bike is a Remedy 29.
All-rounder desert island bike choice?
Desert island bike? I would probably avoid the maintenance of suspension and so I would want a tire that is wider and larger diameter than anything that exists yet.
What’s next for Trek and Bontrager in this niche?
That is hard to say with as quickly as the market taste is changing right now with regard to tire volume and diameter. Enduro bikes are also evolving. As far as categories that really are niche segments I think Trek is pretty happy with letting custom builders own those. To me a fat cargo bike is a niche and something I would like for bike packing/town utility work probably not something in the near future for Trek.