Bike Fit Case Study - Mismatched Crank Length
New - A quick introduction to bi-monthly bike fitting case studies, starting with this recent mismatched equipment case
A few weeks ago, I asked on Instagram if people would be interested in seeing real bike fitting case studies. The overwhelming answer by 100% of those who responded was yes. I am going ahead with bike fit case studies, but I still want to post the same poll here too, because I am curious…
I have done more bike fits than I can count over the last 20 years, from recreational cyclists to Olympians, and everything in between across road, gravel, tri, TT, MTB, bikepacking, track... At this point, I have seen it all.
The plan - Real cases, outcomes, follow-ups and learning. The unusual problems, but also the common ones... Some cases will be complex, others simple and straight forward - We can learn something from either one! The format is simple. Two tiers, every other Tuesday, right here on Substack:
Case summaries, outcome, general learning points (free)
A deep dive into the complete assessment, data, a breakdown of how I assess complex fitting problems, why I choose specific interventions and the outcome (paid subscribers)
The Mismatched Crank Length
This is a relatively recent case, from mid November. In all the years I’ve been doing bike fits, it was only the third time I have seen mismatched crank length.
The first time was shortly after I left my bike shop job and went out on my own, in 2008 I think? Someone I knew (but never fitted) sold their bike because of chronic hip issues that just wouldn’t go away, and were aggravated by the bike. The women who purchased the bike from him came in for a bike fit. While looking at her hip alignment, knee extension and fore-aft position, it was obvious something was off… I couldn’t see anything off the bike that would be a red flag, so I checked the equipment. She had 170 and 172.5 cranks, not only explaining what I was seeing on the bike, but also the previous owners hip issues.
The second time was in 2010/2011. It was 170 and 172.5 cranks again. This time, I didn’t catch that myself, but I heard the story and have seen the aftermath while working with this athlete to undo the damage. This high level triathlete (highest level of draft legal racing) has seen several bike fitters in various cities and countries, have had hip x-rays done, etc, yet she was always working through injuries. The mismatched SRM cranks went unnoticed until they were taken off her bike by a mechanic to be sent for calibration. It took months of small changes at a time to undo the effects this had on her body… I continued working with her until Rio 2016.
All these years later, I was hoping I would never encounter another case of mismatched cranks again, but here we are. This time, 170 (right) and 175 (left).
About the rider + Case summary
27 year old male who started riding about 1.5 years ago, so relatively new to the sport. His focus is triathlon events up to the 70.3 distance, and he put aerobars on his road bike a few months before coming in to see me.
He had a few minor (resolved) injuries from a crash and some mild hip and back tightness, but generally injury free and nothing that would be a red flag. Other than minor external rotation through the right hip, everything was pretty even off the bike left and right.
He had a bike fit elsewhere the previous year, where the fitter installed a 3mm leg length lift under the R cleat, and moved that cleat so it was ~3-5mm back compared with the L.
The bike - Trek Domane AL, size 52. It is important to note that it is a size too small for this rider.
The saddle was very low, the position too short and the handlebars too high. The rider felt like he was too cramped and the saddle didn’t feel great in the aerobars.
What we did
Saddle raised by ~20mm
Saddle changed from the stock road saddle to a triathlon saddle
Handlebars lowered by ~50mm
Aero bar pads and extensions adjusted
Handlebars rotated up slightly
Shifters repositioned so they are neutral and balanced left and right
Both cleats all the way back, all the way inward, neutral rotation
Right cleat lift reduced from 3mm to 1.5mm temporarily, to be taken out once the cranks have been swapped
Crank length to be changed so it is 170 on both sides asap
Outcome + Learning points
The position is appropriate for the athletes goals (triathlon), regardless of the bike he rides - While the bike is a road bike, it’s intended use is only triathlon, which gave me a bit more freedom with the positioning, as opposed to trying to balance the position for both road and triathlon.
Caution is needed when introducing something like a leg length lift or other forms of compensation when there is no apparent injury (especially chronic) or imbalance.
If there is a noticeable imbalance on the bike, explore further before adding something that might be a ‘band aid solution’ and could lead to compensation and potentially injuries.
Check your equipment when you purchase a bike, used or new! This bike was purchased new from a local shop and it has been back at that shop for a few tune ups since. This should have been noticed by the shop, the bike mechanic and the previous bike fitter at some point.
Do you want to know why I chose a certain action and what the outcome was? Are you interested in why I was not concerned about the bike size? What about that lift? Interested in the before and after footage? Do you have questions about this case?
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