Short cranks
Asking others experience in switching to shorter cranks. I've ridden 172.5 s for ever. I'm not sure if I have any problems, per se, but wondering what I might gain going to something like 165s. My inseam is 32 in. I would like to buy a cheap set to try. Since I'm running SRM for power, switching crank lengths will be expensive so I want to be sure it's worth it. Thanks for the advice!
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Seems to work for a lot of us for a few reasons.
One is allowed me to get more aero. Seat up. And you end up with less severe hip angles.
Favors the higher cadence as the lever arm is shorter.
I have gone down to 170 mm. Not super short in general but pretty short considering I am 6-6. I might have gone shorter but my current quarq/sram not allowing this.
I went from 172.5 to 167.5 at the start of this year. The main benefit I was looking for? Allowing a deeper drop (one more 5mm spacer) at the front end by reducing how high my knees come up at the top of a pedal stroke. To keep the same hip angle, this means the saddle needs to come forward a bit, as well as the saddle coming up 1 cm (which is a lot).
There may also be issues related to increased ability to breath, easier pedal stroke, etc, none of which I really notice. I can't say that my time or power was materially affected.
Definitely find some to try out before you buy. I imagine your local LBS has a set they can throw on for you to try?
As others have said, here's the logic on why a shorter crank does a couple of things that are helpful:
When the crank is straight down, the crank being shorter means the bottom pedal is a little higher and the top pedal is a little lower. The bottom pedal being a little higher means that your seat actually gets raised by the same amount as the difference in length between your old crank and your new crank to keep your leg angle the same. Keeping the bars at the same height means that you will have more "drop" in your position essentially getting your front end lower relative to your back end which is a more aero position. The problem with a ton of drop is that your knees might hit into your chest while pedaling, but you get a double bonus here because your seat is a bit higher and your top foot is also a bit lower creating 2x as much space before your knee hits your chest. Also because your top foot is a little lower, this opens up your hip angle allowing you to generate slightly higher power. The shorter cranks also allow you to pedal at a higher cadence easier because the circumference is shorter with the shorter cranks.
So summary, more open hip angle and more aero position and higher cadence potential for faster bike split.
I don't notice any increased (or decreased) power or speed, because I haven't gone back to the longer ones to test it. But given my aggressive position, my knee barely bumps my belly while breathing and going hard. That extra half a centimeter is actually important to me.
Is that worth the expense of swapping out an already expensive SRM just to test that, hard to tell. But I can say that I personally will NOT go back to longer cranks on a tri bike (on a road bike it's less relevant IMHO).
Kurt,
I've only changed cranks becuase of a new bike purchase so never gone shorter or longer.
My first and only thought was the hip angle and opening it up at the same drop or perhaps lowering your position as Al mentioned.
See a local fitter or send in a video to Todd at ttbikefit. Todd would give you feed back on your current hip angle, and perhaps the need to open it up. It maybe that you don't need the shorter cranks but given the costs I'd check with a fitter first.
Maybe there is someone local that could loan you a set of shorter cranks to take to a fitter?
Gordon
Each person who switches gets to decide how much of the extra room they use to open up their hip angle and how much they use it to get more aero. I did a little bit of both. :-)