Bike Fit 101: The Basics

It’s a brand new year, and at TriRig, we think 2024 is already looking like a great time for the sport of triathlon. To ring in the new year, we’re starting a new series of videos which will cover all aspects of technology in the sport.

So we thought we should start at the very beginning. What is the most fundamental, most important, most foundational aspect of triathlon technology? Some of you might be ahead of me. It’s bike fit. That core concept is the foundation for every ride, and every piece of technology we put on a tri bike. And even if you think you have a firm grasp on the subject, you might just learn something new today.

Now, bike fit is a vast concept, wildly misunderstood, and definitely not something we could cover adequately in a single video. So for our purposes today, we’re just going to take a surface-level dive at the fundamentals: what tri bike fit is, what it means, and how we measure it.

1. So, first off - What is Tri Bike Fit?

This may seem like a silly question. But essentially, bike fit is your relationship to your bike, at a few key points. The pedals, the saddle, and the aerobars. And where those points lie in space determines the physiology of your pedal stroke, the strains you are putting on your body, your ability to produce power, your exposure to the wind, and more. If you’ve poked your head around a fit studio, you may have seen some basic diagrams showing bicycles in profile, and measurements at a few key areas. That’s what bike fit is. It’s the blueprint for how YOU set up YOUR bike.

2. So then, what does it mean to “get a bike fit”?

This is the one where I might break from traditional norms just a little bit. Over the past 20 years or so, our sport has developed really fantastic protocols and tools to help athletes learn how to set up their bicycles for best results. In our sport, everything is a balance of three things: your comfort, your ability to produce power, and your aerodynamic profile. Depending on your fitter’s skill level, the equipment available to them, and your own budget, you may end up skimping or ignoring those last two priorities. But every fitter worth their salt should be able to make you comfortable on the bike, which should at least help you produce power to some extent. And when I say comfortable, I mean both in the ordinary sense of not feeling pain, and also in the sense that you aren’t going to get injured.

Fitters these days have access to an amazing array of tools, from dynamic motorized fit bikes, to 3D measurement tools that track your pedal stroke in real time. These tools, in the hands of a competent fitter, can help determine the best way to set you up on the bike. For professionals, these are often combined with wind tunnel testing to determine whether changes to hand position, or equipment swaps like a different aero helmet, can yield savings in aero drag.

BUT, the critical piece that I feel like most people don’t understand, and which I think belongs here in this very foundational video about bike fit, is that bike fit is not, and should not EVER be considered a fixed set of coordinates for all time and for all purposes. Dan Empfield, founder of Slowtwitch and a godfather of triathlon bike fit, has been fond of saying that “bike fit is immutable.” And there’s a sense in which that’s true. When you know your current best fit, you should ONLY be riding a bike which can be set up with that fit. No new technology, no amazing sale, no lusting after the latest pro gear should ever cause you to abandon your fit in exchange for a piece of gear.

So in that sense, I’d prefer the phrase “bike fit is primary.” But “immutable” by definition, means “unchangeable.” And that’s simply not ideal for any athlete, whether you’re a first-timer in our sport, or a multiple-time world champion. EVERY athlete, every single one, will need and benefit from changes to their fit over time. This may be for one of any number of reasons. Fitness improving (or deteriorating), injuries coming and going, gut coming and going, changes in our own flexibility, improvements in our understanding of bike fit and its relationship to aerodynamics, the list goes on forever.

So the piece I want you to take away from this, is that bike fit is about how you relate to the bike, but like every relationship, it should evolve over time. Don’t be afraid to change your position on the bike as you learn, and grow, and make sure you have equipment that can accommodate that. That’s the philosophy behind TriRig’s Alpha One and Sigma One, to be the simplest and most versatile fit solutions on the market to help you better achieve the optimal fit for where you are right now, but ALSO where you might be in the months and years to come.

That brings us to part three.

3. How do we measure bike fit?

Now here I’m talking about fit systems, not the tools themselves. And this one is a pretty big can of worms, as there are measurements for your bike, but ALSO for the rider, you the human being and what happens to you as you’re pedaling the bike. For now I’m going to just focus on the bike measurements.

No matter your fit system, our primary measurements concern the bike as viewed in profile, using a coordinate system with the bottom bracket as the origin, the zero coordinate.

Then, we discuss things in terms of stack (a vertical measurement) and reach (a horizontal measurement). We measure a few critical coordinates from this system – for frames, we define their stack and reach to the top/center of the bottom bracket. This is the point from which we can add additional cockpit components; spacers, stem, handlebar, and finally cups. Each of those components add their own stack and reach. Ultimately, what we want to do is achieve a total stack and reach to your arm cups, because this is your initial contact point at the handlebars. 

So, let’s say you’ve gone to a bike fitter, and they’ve told you that you need a pad stack of 620mm and a pad reach of 510mm to the center of your pad. But if you look at bike frame measurements, they only measure to the headset, which isn’t the measurement your fitter just gave you. For example, the size Medium TriRig Omni measures 525mm of stack, 425mm of reach. So we need 85mm of reach and 120mm of stack

Okay, so how do you achieve that? The primitive way of doing this was to either measure your actual physical bike, then change things until you get there by trial and error, or otherwise to try to calculate the best way to get there using a series of individual component measurements, trigonometry to get the stem’s contribution, etc. It was all a bit of a nightmare. And in fact, a surprising number of companies STILL leave you out in the cold in this way. Just … measure it yourself, and good luck.

Fortunately, there are better ways to go. These days, ANY aerobar worth its salt, whether it’s part of a complete bike system or sold independently, should include a fit chart or guide to help you determine exactly how to set it up. That’s how we designed the Alpha One, with a dynamic web-based interface that will spit out a fit chart for you no matter what frame you’re using. No one should EVER have to calculate a cosine or an inverse tangent just to set up their bicycle.

Okay, so that’s going to be all for today’s very brief look at tri bike fit. In future videos we will explore other dimensions of this critical topic, like the relationship between your cups and your shifters, pad tilt and its effects, stance width, how wide your elbows go and what effects that can have on your overall comfort and ability to generate power, there are literally an infinite number of ways to approach the subject of bike fit.

But there’s one more thing I want to mention. For 2024, one of our New Year's Resolutions here at TriRig is that we are going to be working harder to reach out to you, the triathlon community, through videos like this one. We've got a lot of great content in the works, but we'd also like to hear from you. What is it you’d like to know more about from an equipment perspective? What is it you’d love us to help you learn?

So please, leave a comment on YouTube letting us know your thoughts, give this video a like if it’s the kind of thing you want to see more of, and of course to see all the products we make, head to the TriRig Store.