Realtion Between Crankarm Length and Cadence

Hi,

I'm 170cm (67") and my inseam length is 78cm (31"). I usually train at high cadences. Does a 175mm 53/39 fit me? Or is it so long that it can overload my knees?

thnx

 

This might help - http://www.myra-simon.com/bike/cranks.html

Or do a search on the web. Tons of articles.

Good luck!

 

This is tough to answer. Strictly speaking you will be making a slightly bigger circle so it may be a little slower.

That doesn't really mess it up though. Wrong seat position absolutely can kill the benefits of a longer crank.

One thing you should understand that is if you are properly positioned on a longer crank it will move your center of gravity slightly forward. Your seat should also be higher (but forward too) to reduce too much bending at the knee joint (opens hip angle).

Before people start arguing with me. Look at how guys with 28" inseams ride 170mm cranks. Yeah that's right 76 degree seat tube and long tope tube. Of course they can get away with this becasue their bike is built for it. (center of gravity is adjusted into the frame: short chainstays/slack headtube angle etc)

 

Hi Aron, I am 170cm and same leg length. I trained on 170 cranks and when I recently bought my new trekking bike had difficilty getting comfortable. Only when I measured the cranks, 175mm, I found the problem. Changed the crankset to 170, seat forward a little more, 76 deg, and up came the cadence, all smiles now.

 

175 does sound kinda long for you. That's 22.4% of your inseam, which is longer than the Zinn measurement (21.4%), which tends to put people on long cranks.


All the formulas on these sites put people on longer than "traditional" cranks, but I'm sure none of them will put you on 175s

http://www.cranklength.info/
http://www.zinncycles.com/cranks.aspx
http://www.nettally.com/palmk/crankset.html
http://www.billbostoncycles.com/crank_length.htm

http://www.bsn.com/Cycling/cranks.html

 

I'm almost 73 inches and I ride 172.5mm cranks. Much more comfortable than the 175mm I had on my previous bike. I climb much better now.

 

I've been using 175mm cranks (because it came with the bike I bought). Tried a 170 and felt a world of difference!

 

I'm the same size as you, and when I ride anything with a cranklength less than 175mm I feel like I'm trying to run with my ankles shackled together. I have no trouble spinning a cadence well above 100 RPM without bouncing, and I have no knee trouble either. But that's just me.

There is endless debate about proper cranklength. Despite the "theories" you'll unfortunately have to experiment for a while to find your ideal because it is clearly not a simple function of your static measurements. It has to do with the dynamics of your body while pedaling which is a function of not only the length of your limbs but the way the muscles are attached to them. This is as unique as your gait. You don't have to worry too much about it though because you can adapt to whatever size (within reason) and not lose much power.

 

over the years i have gravitated from 170 to 172.5 to 175 on the road after havin the mtb experience with 175 and developing a fairly smooth high cadence spin and all condition degree of competence from mashin' to spinnin'.

i am now considering 177.5...

 

175 is to the long side for your inseam but you really never know until you try. If you lower your saddle by the change in crank length like a lot of people do (I don't) the real limiter will be that your thighs and abdomen become too cramped at the top of the stroke.

A 175 crank requires about a 3% larger circle than a 170 so it's possible your cadence would be 3% lower at your maximum cadence. However the highest cadence you can reach is probably more related to the number of revolutions and the inability to properly sequence the muscle activity above a certain cadence rather than the distance involved, at least within the small range of available crank lengths.

 

Thanks everyone for the answers.

I was used to 170mm cranks and high cadences but sometimes I felt that it was too short that I can rev much too fast (BTW that was a MTB).

I bought the 175mm, put it on my sloping geometry road bike and guess what?? I feel really comfortable. I don't really feel any difference at all. My saddle is at 67cm, which is just 1cm below my standart. I'm planning to raise it anyway...

Again, thanks.