The difference 3mm can make (hint: a lot)

You know how sometimes you can understand something intellectually, but not really FEEL it until you experience it directly? Kinda like when gas is $3/gallon and it costs $40 to fill up your car, but when gas goes to $4/gal, you know the tankfull is going to cost more, but when it costs $50…… you go, WOW, that’s expensive. Well, I had one of those recognitions the other day in the fit room!

I was fitting one of my athlete’s on his new Trek Madone 9 (a beautiful bike, BTW). Both physical assessment and the Retul knee extension measurements (the primary metric for determining saddle height) showed that he likely had a leg length difference. The difference was small enough that I wasn’t convinced that we NEEDED to install a cleat shim (to help balance him out).  I explained the situation to him, and we agreed there was no downside to trying a shim. So, I installed one 3mm shim under his left cleat (as his right leg was longer) and re-measured him using the Retul. Prior to the shim, his R/L knee angle difference was 3 degrees . After the shim, his R/L knee angle difference was gone……a 3mm shim balanced him out completely…..and he felt more balanced and stable on the bike.

For a variety of reasons, I personally very recently switched from Keywin pedals (obscure but very good New Zealand brand) to Speedplay pedals. Speedplay pedals are a bike fitter’s friend, as they offer easy adjustability on every dimension that matters to achieving a proper fit at the critical foot-pedal interface. I started out with the stock 53mm spindles (the “axle” that connects the pedal body with the crankset) and went out on a 20 mile ride. Within about 4 miles, my left knee started to hurt and continued to hurt for the remainder of the ride and into that evening. Based on past experience with my body, I knew this likely meant that I needed to install longer spindles (Speedplay offers 5 total spindle lengths, 3 of which are longer than stock). I decided to try the 56mm spindles. After an easy install, I went out on a ride with several of my athletes. I was prepared to cut the ride short if I got a recurrence of knee pain….but I was delighted that after 55 pretty fast and hilly miles, my knees felt fine! Again, a (seemingly tiny) 3mm difference made the difference between pain and comfort.

The longer I do bike fitting, the more I see that for most people, small changes can add up to big differences in comfort and injury prevention. If you are uncomfortable on your bike, I strongly encourage you to seek the help of a bike fitter to get you set up properly. Sometimes it’s the small changes, even just 3mm worth, that can make a big difference!