Advice needed: Track Crank Length
 

I did a search did not find what I was looking.
Any suggestions/info on choosing crank length? I am about to purchase Sugino 75's and they come in 2 lengths, 165mm and 170mm. I know the shorter the better for avoiding pedal strike but I am more concerned with choosing right length for efficiency. Any input would be appreciated.

How tall are you?

Don't listen to onetwentyeight...1/8" is no stronger than...wait wrong thread ;)

alright man, you keep this up its gonna come to fisticuffs... :D

I am 6 foot.

i should have asked this the first time, but are you using a track frame or is this a conversion bike?

A real track frame.

If youre gonna ride on the street, i think 165 would be your best bet, though you could get away with 170. On a track frame the bb is higher up than on a road frame. If you are riding it on the track, go for 170 for sure, your legs will be happy. I am 5 foot 11 and I ride 165 on a track frame on the street and its nice and I feel I will never have to worry about pedal strike. I do take corners rather conservatively though. Comfortwise though I think i would be happier on a 170 just for the ability to have more length to deliver power, 165 feels very... compact?

anyone is welcome to correct me if they think im full of ****, I do not pretend to be an expert, i just am full of opinions ;)

Thanks for the insight. This bike is my commuter so it will be on the street most days so maybe the shorter will be better. I have ridden both 170's and 165's on a different frame and it was just a matter of adjusting the seatpost height to find my fit. I have yet to venture out to the local velodrome because of sheer intimidation but maybe one day...which has brought on this deliberation about which length I will purchase.

businesscycles.com has sugino 175s that are 167.5

wlennon,

bs aside, your optimum crank length is a compromise between pragmatic issues and your femur length. Think about how your leg works. Your whole leg length more or less sets how high your saddle goes, but your calf is just along for the ride. The actual difference in height from top of stroke to bottom is determined almost entirely by your femurs. As your femur lengthens, your knee will describe a bigger circle with each pedal revolution. You'd like to have your pedals roughly follow suit -- so if your femur is longer, generally you'd go for a longer crankarm.

That's just for starters. Then look at how you ankle. A good and supple track rider will point his/her toe down at the bottom of the pedal stroke and then pull upwards on the back stroke, with the toe still pointing down. Watch Chris Hoy start a kilo or most top sprinters on the backstroke and their toes will be pointed almost straight down while they're pulling up on the pedal. This has the effect of increasing your leg length overall, but it also takes up part of your pedaling circle.

Then come pragmatic issues: Longer crankarms need more leg velocity to achieve the same pedal RPM, which makes them more sluggish when you need a snappy acceleration or when your legs are tired. But longer crankarms give you a bit more leverage if you have to push a big gear. Then there's the matter of what you might ride on other bikes -- most riders' knees don't handle changing crank arm lengths all the time. Plus, consider your pedal height, how far forward or back on the pedals your feet are located, and simple issues like pedal clearance on a steep track or tricky roads. If you have to ride around a lot of curbs, you may just want a high bottom bracket and short cranks. Getting track cranks in 165 mm is pretty much a safe bet -- you don't hurt your knees easily with cranks that are too short, but the same isn't true if they are too long, and you can always sell 165's easier than any other size. Sugino's come in 2.5 mm increments from 162.5 to 175 (Shimano's go from 165 to 180), but at a track you'll find 165, 167.5 and 170 cranks almost exclusively. Definitely don't worry about the long cranks you find on the road or mountain.

listen to 11.4... hes on to something. there are sacrifices you have to make when you ride on the street, what may be the most efficient on the track, is not the most pracitcal when you're dodging traffic. I designed my bike really conservatively to allow myself to be nimble and precise, not to be a speed bomber. im attracted to fixed gear because of the higher level of control, not the speed. I think the 167.5 would be a good compromise and if i could have found the cranks i ride in that length I think thats what I would have gone for.

Possibly a stupid question...
We're talking a difference of 5mm here, is that really noticable?

yea... i used to ride a 170 and i feel a difference now that I run 165. It's not major but it's deffinately noticable.

This thread has jogged my memory to my second track bike I owned that was running 49 16 with 170mm crank arms. I always felt sluggish on it. My bike prior to that was running 48 16 with 165's and I was content with that. Keeping in mind that one extra tooth made my gear heavier. I am thinking the 165's are going to be it. I might go up one tooth again this time and ride 49 16 though.

I went from 170mm to 165mm on one of my bikes, and I liked the feel of the ride better but there were too many other variables that changed (BCD pattern, nice chainring) for me to pinpoint it to arm length.

When I switched from 170 sugino's to 165 bmx cranks on my road FG coversion, I noticed it big time.

It takes more torque to spin the shorter cranks, but once I adjusted, it became second nature. =)

Wait, do longer arms required more or less torque.
We now have conflicting experiences.

Now I am more curious...how does BCD pattern factor in? (no hijack intended)

I was just saying that along with switching from 170mm to 165mm, I went from 130BCD to 110BCD and a cheap chainring to a nice Salsa one, so I can't exactly pinpoint what made the ride so much nicer.

More tourque to get started (shorter lever) but less RPMs for the same speed. I think.

And yeah, you can tell the difference. Not as much as you would with a different gearing, but it's there. You can tell when you move your saddle or stem 5mm, can't you?

I've ridden/raced 172.5's on a conversion for years and never scraped a pedal. My IRO will be built up with 170 Sugino 75's, eggbeater pedals and I don't anticipate any problems. If you're using the 75's with an appropriate bb and pedals that aren't outrageously wide you'll never have any problems because the q is so low.

If you really want to feel the difference, next time you're at the local co-op switch one crank to a different size. On a smooth stretch, it is easy to tell and will quickly get really annoying.
(I run a 170 on the left and a 175 on the drive side because those are the only two cranks that fit on the spindle without bottoming out onto the face of the BB. My co-op only has used JIS cranks and I've got an ISO BB. It seems absurd no one wants to donate their NOS Record Pista cranks. Jeez.)

I'm pretty sure I'm runnin 175's on my conversion and haven't had pedal strike issues yet....that doesn't mean I'm not scared of it, and I definitely don't do anything overly crazy. When I build up my next bike I might just make the conversion into a single speed to really do away with any pedal strike worries.

When I stripped the pedal threads on my Bianchi, I had a 175 on one side, and a 165 on the other for about a month before switching to 171s. It was weird. I think it also led to the original unsealed BB getting pitted on one side...