Q: Crank length

[Chris]

Ok I am going to get some compacts the only decision to make now is crank length. I currently ride 175s. This is what came with my bike (new and old). I assume this is an OK length. I am about 183cm and have a inseam of about 87cm so 175 seem about right.

Based on what I have read I think I should go with 175mm right? Any contrary views?

[Driver]

yep sounds right.

[Jez]

175mm is the longest you can get ( I believe) I am around the same height and wouldn't consider anything smaller. This again might be up to personal choice again however..……

[Hoops]

Does it make a big difference? I run 172.5's and am 174cm. I know no other way.

[SSSimon]

Personally I'd go shorter - I'd say 172.5's which will allow you to spin up faster and ride at a higher cadence. 175mm crank length is really more of an TT crank length - i.e. where spinning and sprinting are not required.

MTBs started the move to 175mm cranks as in MTB racing you need to absolute grunt power to get the bike up steep inclines and over obstacles. As with a lot of MTB component design, the 175mm crank length has spilt over into road usage where the advantages of long cranks are often outweighed by other factors - like spinning, sprinting, cornering clearance, repetitive use injury (as with road riding there is a lot more continuous pedaling than in MTB riding).

If you are running the OB BB set up I'd recommend going to 172.5mm cranks for your road riding, and re-fit your 175's just for TTs.

Of course there are always exceptions to the rule - the great Miguel Indurain rode 180mm cranks - if you look around you can find 177.5 and 180mm cranks - but I'd leave this area to the cyclists with a lot of scientific support.

[Startrek]

170cm i run 170mm cranks

[SSSimon]

Very traditional! I'm 184cm and I also use 170mm cranks on the track bike, road fixie and crit bike. The track sprint bike is 165, while the RR bike is 172.5 and the TT bike is 175mm as is the MTB.
Nothing like being broadminded I say!
Crank length is not really based on height though. Generally the guideline is 20% of your inseam measurement - this is a guideline - what and how you will be using the cranks also comes into the equation.

[milto]

I am around the 183cm mark and I don't know my inseam. I tend to be quite sensitive to changes in crank length. I had 175's on the Mtb and touring bike but really dislike them both. 172.5 seems to be really good for me. I have now changed the MTB and feel lots better on it.

I think there is a bit of a trap to think that longer is better.

[Bean]

I think the easiest decision would be to stick with your current crank length Chris. The feel should be similar and would require no other adjustments.

[SSSimon]

No Bean's been! Shorter IS the go - move to 172.5 AND raise your seat height 2.5mm to compensate. Remember this rule - longer is wronger (usually).

[Bean]

Well you heard the Prez Chris... get the 172.5's!

[Chris]

172.5's it will be.

[anla]

im 185cm do you think that the 172.5's would be a better option for me aswell? all the new bikes im looking at have 175's - are bike stores cool to swap them or do you have buy the other 1's seperate?

[SueP]

Some people don't notice the difference at all, others (like Milto said - and I'm one to) are quite sensitive to a change in cranklength. I'm a little on the short side and ride 165's for everything.

Best bet would be to have a quick ride (with some high speed corners, a sprint effort and a climb) on a similar size bike with the shorter (or longer) cranks and see if you notice the difference. If you do, then it will be immediately apparent whats best for you, if not, then I reckon Simon is on the right track and go the slightly shorter option.

[Chris]

My very old bike have 172.5mm cranks. I can tell the difference between the two but I am happy with either so I will go the 172.5.

Anla depending on the bike shop they will either charge you the change over cost or do it for free. Ultegra 6700 cranks can be got for under $300 on the net if you want.

[Hoops]

If all you giants are getting 172.5's it makes me think i should go for a smaller option as well.

[Chris]

If all you giants are getting 172.5's it makes me think i should go for a smaller option as well.

I am not a giant, but I can understand that it may feel that way if you are a midget.