Q&A with Bike Fit Expert Zack Allison

Photo credit: Hot Route Media

|Zack Allison is the owner and operator of Bike Sports, a bike fitting studio in Fort Collins, Colorado, as well as a cycling community-building program, which he runs with his wife, Whitney.  Zack and Whitney are also professional road and gravel racers, promoters of the FOCO Fondo gravel cycling event, and pillars of the cycling community along Colorado’s Front Range.

Zack sat down with us to delve into the connection between professional riding and bike fitting expertise.

How has your experience as a professional cyclist influenced your approach to bike fitting? 

In cycling, tech has always been a big part of the sport. As a professional bike racer, it’s important to stay up to date on these developments in order to keep pace, but trying new things like tires, wheels, frames, and bars in races also allows me to better fit people on their bike, no matter what their goals are. The better the understanding I can have of what’s available, the better I can apply that knowledge to a person getting a bike fit at whatever level of racing or riding they are doing. 

What are the three most common mistakes you see cyclists make when it comes to bike fit? 

The most common mistakes have changed in recent years. It used to be that the most common mistake I saw was people slamming their stem, or otherwise fitting a bike along aesthetic lines, as opposed to for comfort or power. Today, with relevant bike fit information and bike fitting apps readily available online, and most bikes being somewhat aero optimized, people are realizing that comfort creates more power, and therefore more speed. The most common mistakes I see now are more minute, such as saddle choice, setback, and tilt. These are not really mistakes by the client per se; finding the right saddle and getting the tilt right to account for pelvic rotation and fit is always tricky, and there are no apps or tools that dial that in well. 

How does a proper bike fit contribute to both performance and injury prevention? 

Performance and injury prevention are the primary goals of every bike fit, coming way before aero optimization and aesthetics in my practice. In general, if you’re more comfortable, you can make more power for longer. Only after we get you comfortable and producing more power do we look for tweaks that can enhance aero optimization without detracting from comfort or performance. In rare cases, like in a fit on a pursuit bike for the track or a short time trial, we toe the line between aero optimization and comfort more, simply because those events are so short. 

With bike companies using so many different sizing philosophies, is there a single benchmark that a layperson can rely on to determine the best bike size from a specific manufacturer? Should they focus on top tube length, seat tube length, or even the old standby, standover height? 

This is super relevant; nearly every newer rider that gets a new bike is terrified of buying the wrong size. Fortunately, I’ve found that the fit apps on most manufacturer’s websites are quite accurate and will get you the right size 99% of the time. If you’re between sizes, it’s ideal to find a dealer that has your size and try something out. Otherwise, look for the stack and reach measurements to help you make your decision: sizing down would make you a little lower and longer in the reach, while sizing up would situate you a bit higher. You can also back-calculate what size stem you’d need if you sized up or down. If the “reach” measurement between sizes is 30mm (3 cm) different, you’d need a 3cm longer stem on the smaller bike, and potentially some added stack underneath it. Conversely, on the larger bike, you’d need a 3cm shorter stem to have your bars in the same spot. In plenty of cases, the math can decide what’s best for you: for instance, if you’re already on a 120mm stem, sizing down and adding 3cm in reach would require a 150mm stem, which isn’t feasible. 

What are the key elements you focus on during a bike fit session? 

My process is a result of mixing protocols from Guru and Retul, and I think of a great bike fit as one that strikes a balance between each body angle and touch point on the bike. Shoes and cleats, saddle height and setback, bar reach, hood angle and pitch: every one of these factors is in conversation with each other, and it’s my job to move it around to find that balance of comfort and performance. 

Speaking of cleat position, can you touch a bit on your philosophy there?

My approach to cleat position starts with looking at a rider's stance. I have clients do some squats and other movements to determine if there's a significant hip rotation, shift, or varus/valgus foot position. These hip rotations and shifts are usually from hip imbalances caused by repetitive movements like driving an automatic car for a long time with your right hip forward and engaged. If the squat stance is super wide or super narrow, I'll start the cleats to match, check the knee alignment on the bike, and adjust the medial/lateral cleat position as necessary. If the rider is really varus or valgus, we can use a shim to correct that. If the rider presents with a bad hip imbalance, rotation, or tilt on the bike that pushes them out of my pay grade, I refer them to a PT to diagnose the cause of the imbalance, but continue the fit process. 

In setting up the fore and aft, I run most cleats nearly all the way back in a mid-foot position. If you think about the foot as a lever, a mid-foot position shortens the lever arm so the power made from your bigger movers, like quads, glutes, and hamstrings, can more efficiently be transferred to the pedals, while also requiring less stabilization from the Achilles and calf muscles.  

Lastly, some hip imbalances can present as leg length discrepancies. On our motion capture software, this looks like one knee angle being different than the other. Unless there was an injury or trauma to the hip, leg, or back, it's rare to see an anatomical leg length difference and visual knee angle difference from the hip imbalance alone. In my practice, I don’t shim the cleat for that imbalance: instead, I'll push the rider to a PT to diagnose the hip asymmetry and fit the rider with a middle ground knee angle.

What technology or tools do you find most valuable in your bike fitting practice? 

One of the biggest technological breakthroughs in fitting is motion video capture. Even 10 years ago, fitters were still using goniometers (angle measuring tools) and having riders pause during their pedal stroke. Crazy inaccurate. Now, whether using Retul or another video bike fit app, we’re able to measure knee, hip, torso, and elbow angles in real-time. That data shows us what someone is doing in their pedal stroke at varying intensities, which allows us to better refine the overall fit. 

Are there any “old school” philosophies that still hold a place in today’s modern fit studio experience? 

Honestly, not really; I’d say everything from cleat positions to seat tube angles and amounts of setback have changed. The oldest school thing I do is in looking for the right saddle. There’s not really a tech to apply to that process: it still just involves asking a female if she has soft tissue discomfort, or a guy whether he gets a stop light boner or not (I really do this: it indicates blood flow issues or numbness.)

Speaking of old school philosophies, what’s your take on the current shift in pro cycling toward much shorter crank lengths? 

Oh man, people have debated crank lengths since the dawn of time, and I love it. There’s been some great research on this out in the last few years. Power, comfort, and efficiency went up as crank length went down; until something like 150mm cranks, which no one produces for road or gravel, power goes up and oxygen demand goes down. There is obviously a point at which your height matters. If you’re 6’6”, for instance, you may hit your best efficiency at 170mm cranks. If you’re 5’1”, you’re better off even shorter than 165mm, though again, manufacturers aren’t producing many of those. Beyond shorter cranks having better performance, the hip angle being impinged is a huge driver of performance and comfort. 

How often should a cyclist get a professional bike fit? Is it a “one and done” situation that carries over to the other bikes in one’s quiver, or does it need to be evaluated with every new bike purchase or even the “leveling-up” of a rider’s abilities? 

On a modern drop bar bike, we can usually get your fit dialed with one session and make minor adjustments down the line if you get a new bike or saddle and have trouble matching measurements. For juniors that are still growing, it just depends on how much growth is left, but usually doing a tune-up every six months to a year is advisable.

Have you ever observed a gain in sustained power output in a cyclist after making an adjustment(s), and if so, what were the particulars of that adjustment? 

This happens all the time, especially if someone is running a very low saddle height and they aren’t getting everything out of their glutes and hamstrings. The bigger saddle height might feel weird at first, but getting more out of your glute stroke means you’re making more power. That’s not true across the board, though; don’t just raise your saddle thinking you’ll get faster, but in general, when someone’s fit is off, proper adjustments gain speed and power in a significant way. 

Finally, what advice do you have for riders who might be considering a bike fit but aren’t sure if they really need one or not? 

I think we have the cycling world convinced of the benefits of having a bike fit. Even if you think you’re close, it’s worth getting your fit looked over. More often, the debate about not getting a fit is a financial one. A good fitter has multiple certifications, and in my case a degree in kinesiology. It’s a specialty service, and it’s not cheap. If you’re strapped financially, give your fitter a call and let them know what’s going on; there’s usually a deal that can be worked out.