I think most tri/TT fitters are onboard with short cranks now. However, it seems that roadie world isn’t completely sold, or seem tot hunk that switching from 175mm to 170mm constitutes a switch to short cranks.
I’m happily riding 165mm cranks on my TT bike. I’m going to be replacing cranks on my road and gravel bikes (currently at 170mm), any reason to not switch to 165mm for road and gravel?
I think most tri/TT fitters are onboard with short cranks now. However, it seems that roadie world isn’t completely sold, or seem tot hunk that switching from 175mm to 170mm constitutes a switch to short cranks.
This is one of these personal things and you’ll get a range of responses.
For me I had ALWAYS ridden on 175’s - simply because on every bike I have ever owned in my life all 58cm or size Large bikes came specced with 175 cranks. I only ride road bikes now and don’t race triathlons any more and I few years ago I started to really suffer with back issues (long story), I was also finding difficulty getting the right fit on my bike that I had been riding for a while, and while never being the best sprinter, I was really finding getting on top of big up-shifts to bigger gears, challenging.
I had a Dura Ace 170 crank set sitting around the home shop that had come off one of my wife’s bikes - and I thought what the heck - just swap it in and see how it goes. I did and I could feel a difference almost right away. Just that minor opening of the hip angle at the top of the pedal stroke (Which is one of the key things you do when you go shorter), seemed to be better for my back and, staying on top of the gear “easier”.
Numerous studies have proven that there is NO loss of power riding in a range of crank arm lengths. So do it for fit and comfort if it makes sense for you.
I do for the cross bike down to 170 for a mm or two in case of pedal strikes in races.
Road bike is also 170 but just to stay consistent. TT bike is 165.
I went to 165mm on my tri bike and then also on my gravel bike. I dig it on both.
As a very early adopter of short cranks personally (155’s in 2010) and professionally (been shortening cranks via dynamic fits since 2008), I think the question comes into focus better when we consider what we are trying to do for the rider, as opposed to simply considering what type of bike the rider is on.
When bike fitters really lean in to this question, what most of us find is the fit bike answers it for us. We don’t have to decide, choose, or guestimmate what crank length would be best. For me anyway, I take riders through a dynamic process, and when the pedaling appears or is reported as compromised or suffering, hip angle, and therefor crank length, is on the table. So crank length changes in a dynamic bike fit are done almost the same way as seat height changes: Quickly, and in response to what the fitter sees and the rider reports.
A rider comes to see me for two bikes fits, road and tri. They are 5’7" so not terribly short but firmly in the range of riders who are generally largely overcranked on stock tri bikes. So we set saddle height, reach, and as we play with drop, the rider reaches the “cry uncle” stage when we are at 80mm of drop and stock crank length. BOOM! That’s the spot. NOW change the crank fast!! Get them back on, same position, same power… do that 3-5 times and riders really sharpen their awareness of what crank length changes do for their pedal stroke. This way we can incorporate crank length changes the same way we do everything else. Dynamically! We don’t have to dictate, extrapolate or mathematicsize. (Slowman - did you get that email?)
I do the exact same process for the road fit. While less often do I observe or hear reports of compromised pedal stroke, so I shorten crank less frequently in road fits and sometimes not at all. I pay attention to the same things and ask the same questions. Around 5’7" or 5’8" or so seems to be the ‘break point’, where taller riders end up not shortening, but most shorter riders prefer something shorter than stock even on their road bikes.
Done this way thousands of times, the picture becomes clear, as most tri riders are self selecting cranks from 10-20mm shorter than what would be stock for them, while road bike riders are choosing stock lengths to maybe 5-10mm shorter.
I’ll close it with this. When in doubt go shorter. There is really very little downside to going shorter. If you want simple numbers, take 15mm of crank length off what most tri bikes would come to you with, and 5mm off the average crank length on a road bike that you would buy.