The Bike Fit Mistakes I See Most Often — And the Assumptions Behind Them

I see a fair number of riders at RedEye who have already had a bike fit. Quite a few have had several.

Some arrive with relatively straightforward problems. Others have spent years chasing discomfort through different saddles, stems, handlebars, insoles, cleat positions, physical therapy, and repeated changes to their position. By the time they get to me, there's often an impressive collection of measurements, screenshots, recommendations, and explanations for why they sit on a bicycle the way they do.

What surprises me isn't that previous fits sometimes haven't worked. Bike fitting is difficult, human beings are complicated, and I've certainly made decisions over the past 20-plus years that I would approach differently today. If anything, experience should make us a little less certain, not more.

What interests me is the pattern behind many of the unsuccessful fits I see. The problem often isn't that someone made an unreasonable adjustment. It's that the adjustment appears to have been made because that's what bike fitters have been taught to do.

Cleats belong beneath the metatarsal heads. Saddle height should produce a particular knee angle. A flatter back is healthier for the spine. Moving the saddle forward opens the hips.

Each statement sounds plausible. Each contains enough biomechanical truth to survive for decades. And each becomes problematic when it's turned into a prescription rather than a hypothesis.

That's the distinction I think bike fitting needs to get better at making.

Mistake #1: Putting the Cleat Under the Metatarsal Heads Because That's Where Cleats Go

I've spent a lot of time recently writing about fore-aft cleat position because it's a wonderful example of how convention can become accepted as biomechanics.

Traditional bike fitting generally establishes cleat position by identifying the first and fifth metatarsophalangeal joints and positioning the pedal spindle relative to those landmarks. There are variations between fitting schools, but the underlying assumption is remarkably consistent: find the ball of the foot and use it to determine where the cleat belongs.

My question is increasingly simple: why?

Once a foot is placed inside a sufficiently rigid cycling shoe, movement through the metatarsophalangeal joints is dramatically constrained. The shoe and foot effectively become a lever between the pedal and the ankle. Yet we're still using the location of joints whose mechanical role has been intentionally diminished to determine the length of that lever.

Consider five riders with the same total foot length but different proportions between their metatarsals and phalanges. An MPJ-based fitting system potentially gives those riders five different pedal-to-ankle relationships. Before accepting that result, I think we should at least be able to explain why those differences are desirable.

This isn't an argument that anatomical landmarks are useless. It's an argument that a repeatable measurement isn't necessarily a meaningful one. If we're going to use the metatarsal heads to determine cleat position, we should have a biomechanical reason for doing it beyond "that's where cleats go."

Mistake #2: Setting Saddle Height From Knee Angle

Knee angle is useful information. I have measured it. I have documented it. I look at it all the time, but I don't prescribe it.

That distinction matters.

A measured knee angle is the product of far more than saddle height. Pelvic orientation, ankle strategy, crank length, foot mechanics, where the rider actually sits on the saddle, and even the effort they're producing can all influence the number that eventually appears on a screen. More important than any of that, muscle recruitment strategies of the leg, and neurological signaling to higher processing centers will ultimately determine the optimal amount of knee flexion at maximal extension.

Two riders can therefore arrive at exactly the same knee angle through remarkably different movement strategies. One may be quiet and stable through the pelvis while transferring force effectively through the pedal. The other may be reaching through one hip, plantarflexing excessively at the ankle, shifting across the saddle, or rotating the pelvis simply to accommodate the position. The measurement can look identical while the riders look nothing alike.

This is where normative ranges become particularly seductive. Give a fitter a target angle and suddenly saddle height appears to become an equation: move the saddle until the rider enters the acceptable range and declare the problem solved.

But what happens as the saddle moves? Or a new saddle is introduced?

Does the pelvis become more stable or less stable? Does ankle plantarflexion increase to preserve knee extension? Does one hip begin reaching at the bottom of the pedal stroke? Does the rider begin shifting on the saddle? Does muscular recruitment become more balanced, or does the rider simply find another strategy for achieving the prescribed number? Is the leg capable of controlling it’s own flexion/extension velocity?

Those questions are far more interesting to me than whether someone's knee measures 35 degrees.

Knee angle is something I use to describe a position. It isn't something I use to create one.

Mistake #3: Making the Back Flat Because a Flat Back Is "Better"

This one comes up surprisingly often as an artifact of “breathing with the diaphragm”. And recently quite common here in Golden, Colorado, as there’s an allied health professional that’s gotten into bike fitting - so of course, protecting the lumbar spine... Ugh.

A rider has a rounded back on the bicycle, so someone decides the back needs to become flatter. Sometimes that recommendation is accompanied by the suggestion that a flatter spine is healthier, stronger, more aerodynamic, or simply what a cyclist is supposed to look like.

The problem is that a position doesn't become healthy because it photographs well from the side.

Cycling inherently places the body into flexion. That's part of the bargain we've made in exchange for riding a machine that is remarkably efficient at moving through the world. The question isn't whether flexion exists; it's where that flexion comes from, how it's distributed, whether the rider has the capacity to tolerate it, and what compensations are required to maintain it for several hours.

One rider may create a relatively flat-looking torso through available hip motion, appropriate pelvic orientation, and good thoracic contribution. Another may create almost exactly the same silhouette by forcing pelvic rotation, increasing lumbar stress, restricting their ability to breathe, or extending the cervical spine simply so they can see where they're going.

Those are not the same positions simply because a camera says the angles look similar.

Nor is a naturally rounded lumbo-thoracic posture necessarily something that needs to be "fixed." Human spines vary. So do pelvises, femurs, hip morphology, mobility, training history, age, and the accumulated consequences of everything we've done to our bodies before arriving at a bike fit.

I'm much more interested in whether the rider can support their position comfortably and sustainably than whether their spine resembles the picture in a fitting textbook.

Soon I’ll finish a complex article on the coordination of the musculature of the trunk, and how unique it is compared to our upright demands. And why it’s important for cyclists to understand the fact that a strong and protected “core” is one that’s strong in flexion. Yeah, that’s right.

Mistake #4: Moving the Saddle Forward to "Open the Hips"

This may be my favorite because the explanation sounds so wonderfully mechanical.

The rider's hip is "closed," so move the saddle forward to open it. Except the rider isn't a compass.

Yes, moving the saddle forward can alter the relationship between the torso and femur, depending on what happens to saddle height, pelvic orientation, handlebar position, crank length, and the rider's actual posture afterward. But describing saddle fore-aft primarily as a way of manipulating hip angle ignores nearly everything else that happens when we move the rider relative to the bottom bracket.

Saddle fore-aft changes balance.

It changes how the rider's center of mass is distributed around the bicycle. It changes the mechanical relationship between the hip, knee, and crank. It can influence muscular recruitment and the amount of support demanded from the upper body. It can change how much weight ends up in the hands, how the rider interacts with the saddle, and ultimately how the bicycle handles beneath them.

That's an enormous collection of consequences for an adjustment supposedly made to "open the hips."

And there's another problem: if hip angle is genuinely the limitation we're trying to address, we have other variables available. Crank length changes minimum hip angle without necessarily relocating the rider's entire center of mass. Handlebar position influences torso orientation. Pelvic position changes the relationship between the femur and pelvis. Sometimes the rider doesn't need the bicycle changed at all—they need greater usable hip motion.

The correct intervention depends on why the hip is constrained in the first place.

Saddle fore-aft is one of the most consequential balance adjustments available to a fitter. Using it primarily as a way to manipulate a single joint angle ignores most of what moving the saddle actually does.

The Mistake Behind the Mistakes

The four examples above aren't really four different mistakes. They're manifestations of the same one. Reductionism.

None of these interventions is inherently wrong. Sometimes I move a saddle forward. Sometimes a rider ends up with a knee angle comfortably inside a commonly cited range. Sometimes the metatarsal heads provide useful information, and sometimes changing spinal posture is exactly what a rider needs.

The mistake is deciding what should happen before observing what actually happens.

Bike fitting becomes much easier when every rider is supposed to fit within a set of accepted rules. Find the landmarks. Measure the angles. Put the dots inside the green boxes. Unfortunately, human beings have shown remarkably little interest in cooperating with that idea.

The human body is constantly negotiating. Change the position of the foot and something can change at the hip. Change saddle height and the ankle may respond. Move the rider forward and the hands may suddenly carry more load. Change crank length and a movement limitation that appeared to originate at the hip may disappear altogether. A fitter can't understand those relationships by looking at any one measurement in isolation.

After more than twenty years of doing this, I've become less interested in whether a rider matches a fitting convention and much more interested in why they move the way they do. Measurements can describe that movement. Technology can document it. Research can help us understand it (being generous). But none of those things absolves the fitter of having to observe the rider, experiment, and ultimately make a judgment.

That's the part of bike fitting I don't think we'll ever successfully reduce to a number.