How do I know which crank length to use on my road bike?
I’m 6’1, ride a Tarmac. I’m comfortable riding most of the day in an aggressive/drop position, cadence usually starts ~100 but when I fatigue it drops to high 80s /low 90s
I’ve been riding the Tarmac for about a year and feel really good on it - it has 175 cranks. Before I bought this bike I always road 172.5 (on TT and Road).
A friend gave me his 170s to try - they are on my bike, hip angle opened up ~1degree at the top of pedal stroke (also lifted seat a smidge), but the shorter crank is also noticeable when I pedal. Not sure if that matters or is a placebo
How do I assess which one is better for my fit? Just keep riding it and measure power in a week or two when I get used to them?
I’d be willing to bet that if someone gave you (or me) a 10mm shorter crank to try and didn’t tell you what length it was, you wouldn’t be able to tell the difference when riding unless you were riding some place where your gearing was limited.
With that said, if you can get your hip angle and reach correct for you, then ride whatever crank you can successfully push over the top of the pedal stroke.
Thanks. I thought I noticed difference on my first two rides, but perhaps just placebo like you said. Racing on it tomorrow, so will have real effort / power to compare
What’s the right hip angle when you’re in the drops on road bike?
This is just me and I have really short legs: I need to be under 100 degrees to feel powerful and closer to 85-80 degrees for max power.
If I remember correctly, torso to femur angle can be as tight as 40 degrees on the top of the stroke but then my legs then hit my ribs and I can’t get any lower.
According to my PM I can still push over the top when doing that but it’s uncomfortable banging my ribs.
My shoulder > hip > knee angle (@top of pedal stroke) is the one that I referenced originally and it opened up from 48 to 49 degrees. I had good room before, now have plenty of room before hitting my ribs
My hip > knee > foot angle (not sure what to call ) actually increased from ~79 to ~83 with the shorter cranks and slightly higher saddle
The change seems to have brought me right into your sweet spot
Just not sure on road bike what angles / variables I’m trying to optimize towards … as much as I am w a TT
On a road bike, crank arm length isn’t that important. If 172.5mm is on sale, buy that. At your height, 175mm wouldn’t be a bad choice either.
This is where I come out. On my tri bike, I went from a 172.5 to 165 and could feel a difference, particularly at the top of the pedal stroke. Subtle difference and I don’t know whether it resulted in any performance gain, but it felt better.
On my road bike, I swapped my crankset from a 172.5 to 165 only because I wanted better climbing gearing, so I picked the shorter crank to match my tri bike. Plus, because I use power pedals (Assiomas), I no longer have to switch the crank arm length setting when I move the pedals between bikes. But from a cycling standpoint, I really don’t feel any difference.
Now if I was using a road bike with aero bars and expected to spend a lot of time on those bars, I would probably switch to shorter cranks for the same reasons it can be beneficial for a TT bike.
I recently went from 170 to 160 on my tri bike. If I didn’t do the work myself I wouldn’t have noticed the difference except my knees didn’t come up as far, but that is really subtle.
I don’t know anyone who has regretted going to a shorter crank. Either they like it better or notice no difference. Again, just my personal anecdotal experience. You could give it a try if you’re okay with the $ to buy a new crankset.
As a practical matter, a short crank will require raising your seat height, which might put you in a slightly more aggressive aero position? Not sure if that’s actually a benefit but worth considering.
) actually increased from ~79 to ~83 with the shorter cranks and slightly higher saddle