Crank arm length
 

I am 6'3" and ride a 175mm crank. Would I see any benefit to going to a 180mm or longer crank? Would it be possible to generate more power or speed with longer crank arms?

There was just a response in a thread that talked about the advantages of a SHORTER crank arm. The thought was that the legs do less work to get the crank around. I believe the website that was referenced was something like Bikesmith. Made for an interesting read.

I'm a wee bit taller than you. I have a 165 on the fixie, a 175 on my custom road bike and have ridden 180.

The shorter arm on the fixie allows for cornering (because it's fixed, you have to keep pedaling) and allows you to get the spin muscles going. The longer crank arm allows for more torque and a bigger range of movement.

Zinn's opinion on it: http://zinncycles.com/Zinn/index.php...sked-questions

Whatever justification there might be for moving to shorter cranks that isn't one of them. If you maintain your speed/power your legs do the same amount of work. They might have to use less force but the amount of work is not related to crank length.

Changing your crank length can alter the cadence you normally use and can have a beneficial effect for getting into a more aero position but it won't provide any extra power.

Scientific study: http://www.plan2peak.com/files/32_ar...gTechnique.pdf

"and I don't wanna talk to a scientist
ya'll mother****ers lyin' and gettin' me pissed"

I ride 180mm cranks and I dont think I'm going anywhere faster. These do feel more natural for my knee flexion and feel nice for constant, but slower, cadence. With 175s spinning up and going 100+rpm feels a lot easier, these go on my "go fast" bike. It's all preference and adjusting a bike for its intended purpose.

You might hate 180 cranks though. I know people that claim they make their knees hurt.

Good stuff. This guy sums up the key points of Martin's paper, and there's a lot of discussion underneath: http://myworldfromabicycle.blogspot....-you-just.html

I'll try to keep this short: :p

I was a bit obsessed about this a few years ago, and I still have over 15 sets of cranks, ranging from 165 to 177.5. I'm 6ft with long legs, and I persisted with 180s for probably a bit over a year (I think in 2003/2004). I loved them at first, and thought I had a 'secret weapon' but then they started to annoy me after about 6 months, because I felt like I couldn't "get on top" of the pedal on the start of the downstroke, especially on longer rides on flat roads. I kept wanting to get off the saddle to compensate for this feeling.

I'm not a sprinter, so cadence never bothered me with long cranks.

I eventually started experimenting back on my 175s, and 172.5s, and found that I felt no slower with these shorter lengths. I also found I could get more much aero (lower upper body) on the shorter cranks, because my thighs weren't hitting my stomach (there's a whole 'thing' going on in the tri world at the moment with John Cobb getting everyone super-aero on 165s, coz they can get way low).

I continued switching between the different lengths for a couple of months, then, after having one particurlarly awesome ride on 175s :p (and after some persistent medial knee pain), I ditched the 180s. This meant that I needed some more shorter 7800 Dura-Ace cranks, and my local second hand store did a good price on 2 pairs of 172.5s, so I settled for that length. I probably would've been just as happy with 170s or 175s. So, now I ride around mostly on 172.5s, and sometimes on 170s, and i don't feel any slower. I've had a bit of a knee injury lately, so I sometimes roll around on 165s, which reduces the flexion at the top of the stroke.

One thing I did really like with 180s was that I felt as though I had more power when stomping off the saddle when riding over short hills, and bridging gaps, etc, (darting out of corners) in criteriums. So, I did sometimes miss the 180s for this, especially in hard criteriums on wind-effected courses, so I went and got a couple of pairs of 177.5s. I sometimes race on these, and occasionally take them to the local hilly group smash-fest.

Anyway, having said all that, you might like 180s -- a lot of taller guys do -- so I figure they're worth a try. As the article in my previous post says, the issue is more complicated that just "leverage vs cadence, with some positional things thrown in".

Also, there are some logistical issue when using longer cranks, especially if you have big feet and ride with your toes out/heels in. Some dudes have problems with their heels hitting the stays, and even (rarely, maybe) the rear derailleur. Long cranks also (obviously) reduce pedal ground clearance when cornering. And, depending on your bike, your toe might hit the front tyre. :thumb:

Great post. Thanks this helps. Cornering isn't an issue for me. I can stop pedaling for a second and make a quick right or left but I think I will stick with my 175mm crank. I thought that it would help me generate more power that there are trade offs.

Here's another good little article, which briefly mentions the conundrum of power vs torque when using longer cranks.
http://www.arniebakercycling.com/pub...m%20Length.pdf

A little late to the party but basically longer cranks give you more leverage but force your feet to make bigger circles. It's the whole lever thing again - you have a longer lever but that means you need to move the "push end" farther to do the same work. You trade leverage for rpms. I've ridden 167.5, 170, 175 cranks. With 170s I would routinely do 110-120 rpm; with 175s it's more like 90-95 rpms.

http://sprinterdellacasa.blogspot.co...th-take-3.html

I choose to ride with 175s for a very specific reason - they allow me to get up short power climbs easier than when I'm on longer cranks. As a side benefit my sprint seems to be the same or a bit better on the longer cranks.

I find that for me longer cranks work well. Although I spin I have high peak force/power. I prefer to get over short hills quickly - on long hills I learned that crankarm length doesn't do anything for me. Shorter, longer, I still suffer.

I have two very good friends (one was my best man, the other a groomsman) who are about your height. Both swear by 180s. Both used to race for many years, both are now "less competitive".

I'd see if you can get some used 180s, maybe off someone that decided that the 180s weren't for them. I happened to buy the least expensive 175s I could find but 180s are a bit more unusual. There may be other ways of getting one - BMX or mountain bike cranks. The length is the key, and remember to adjust your saddle height. Your cadence drops with longer cranks also.

Thanks, this helps a lot.