crank length

[madscot13]

I'm looking at new cranks this week. Currently I have 170, but I'm 5'2" with a 26" stand over height so my cranks should be much smaller. I'm a bit surprised as I've never really hit knee problems that couldn't be adjusted with shoes and a seat height raising.

Just wondering what some others have and their height.

[LBTC]

I'm 5'1.5" with a 28" inseam and I run 165 cranks on all of my bikes. I had 170s on my old road bike, but I hated them. Okay, well the whole bike didn't fit me, but I'm very very happy with my 165s!

Hugs and butterflies,
~T~

[Crankin]

I'm 5' 1" and I have 165 cranks. I tried 170s when I got the bike I have now, and I hated them! I felt like I had to make a huge extra effort to pedal. The shop owner thought it would "unleash my power" but I quickly told him to get over that notion.
I had 165s on my other 2 road bikes, too.

[OakLeaf]

I'm 5'3" - not exactly sure of my inseam, but petite pants are usually a tad short for me while misses (except very low rise) are unwearably long/tall.

I run 165s. I tend toward patellofemoral dysfunction anyhow, and back in the day I had a couple of nasty exacerbations brought on by 170mm cranks (although I learned to stretch my knees before every ride, and that helped a lot). When I built up my race bike I put on 165s, and wow, what a difference both in comfort and in the ability to spin at high cadence.

A couple of years ago when I first returned to road biking I demo'ed a bike with 167.5mm cranks. Although I only got about 150 miles on that bike and didn't get to tweak the fit in any depth (and it was the first time I'd been on a road bike in 12 years), those cranks still seemed too long for me. At any rate I felt I needed to set the seat height too high, to compensate. I didn't even realize they were 167.5s until much later when I started bike shopping and spec'ed out the one I'd demo'ed.

Can you test ride a bike with shorter cranks, just to see?

[VeloVT]

It's amazing how you can really feel a few mm difference. I'm 5'6", 31.5" inseam. I have a bike with 170s and a bike with 172.5s, and I can tell the difference. I prefer the 172.5's because I get better leverage -- it's noticeable all of the time but particularly on hills. I suppose it's a tad easier to spin faster on the shorter cranks, but the 172.5's allow me to spin as fast as I need to (normal cadence on 172.5's is around 90-100; when I get really tired at the end of a windy ride, I might ride in lower gears and spin between 100-110).

When bike shopping I often feel lucky (perhaps even grateful) that I'm very average sized (that is, I'm not petite). I am on the small end of the range where it's reasonably easy to find components to fit (and it drives me nuts how few models of bars come in 38cm, and that my size XS, WSD bike came stock with 40s), but I think it's still much easier for me than for many smaller women.

[HillSlugger]

I don't feel any real difference between 170's and 172.5's on my two road bikes but I had to switch out the 175's from my commuter bike as I was getting knee pain.

[madscot13]

sometimes I'm just surprised at the difference 2.5 mm will make

[KatyLady]

At 5'4", I have a 30" inseam and wear petite slacks. But because I have long femurs (not uncommon for women) I ride a 170 crank very comfortably.

[sgtiger]

5' 1 3/4" w/26" standover, the builders for my custom Rodriguez reccomended 170m cranks for me. Besides taking the standard standover measurement, the LBS guys took another measurement with me kneeling to get my femur-to-tibia ratio. Turns out my femurs are way longer than my tibia. Who knew? I think shoe size went into consideration too. My knees are definitely happier now than when I had 165m cranks. Just so you know my current bike's geometry is way different than the bike I had with the 165m cranks on them, so that may make a difference too.

[OakLeaf]

Good point. Short femurs here.

[madscot13]

how can you tell with the ratio of femur: tibia which crank you need? I've never heard about that and would like to hear more

[LBTC]

how can you tell with the ratio of femur: tibia which crank you need? I've never heard about that and would like to hear more

me too! not only that, how can you tell what the ratio is? What is way longer?

H&B
~T~

[sgtiger]

I don't know what the calculations are exactly. The following pic is from the LBS's site:



More here:
http://rodcycle.com/articles/fitting_example.html

The black tubing(Rodriguez on side) is fully adjustable. They used it take different height measurements. First, of course, was overall height. Then one just between my collarbones(like 3rd pic down), although that has nothing to do with the crank length. Stand-over where I was asked to place the tubing as high as I could get it: to the point where it was a bit uncomfortable, but my feet are still flat on the floor. The last kneeling: knees against the wooden part that juts up from base, again the tubing placed as high as it would go. They just subtract the kneeling measurement from the stand-over height to get the difference.

BTW, kneeling like this(pose 1), not with buttocks sitting on feet(Um....actually my buttocks don't sit on my feet. Heels come only to the bottom of my bum!):



Besides anatomy, your bike's geometry also plays into crank length:
-Seat tube angle: it can affect the distance from bottom bracket to saddle
-Angle of seat post: some have a bend that put the saddle farther back from BB than staight seat post
-??? I'm sure there's more, but I have no clue.

I also read somewhere(Bicycling maybe?) that pedaling style can affect one persons peference for a certain crank length vs. another person given that their measurements and bike specs are similar. Longer crack=more leverage(Whoops! I guess my mind is still on bums. Should be crank BTW). So the person who likes to spin at a higher RPM tends to prefer shorter cranks than someone who mashes.

But please don't just take my word for it, 'cause I'm still learning and I have MUCH to learn. Hehe!

Where's our PT(A) and bike fitting gurus when we need them? Knot? Wahine? Velogirl?

[KnottedYet]

I don't know nothin'.

There are some pretty wild equations you can use to figure out crank length. Don't know where they went, but if I find 'em I'll post 'em.

Honestly, that's too much math for me.

I have 170's on one bike and 175's on the other. I like my 175 a lot. I'm a masher with long femurs.

I guess you just start with what you've got, list out any problems you have with them (do they hurt your knees, can you get a good KOPS, do you feel like you are struggling against them, and so on) and then change out from there.

Before going after crank length, though, I'd get a really good bike fit. Make sure it isn't an issue of saddle placement or reach or cleats affecting your leggies.

[RoadRaven]

Hmmm... interesting reading...

My first bike had 175 cranks.
Then I got a smaller frame/bike (Giant) and it had 170 cranks. That is the bike I raced on.

Then we bought another race bike for me - also with 170 cranks on - and a women specific frame (EMC2) and turned my Giant into a time trial specific bike.

I have just reverted to 175 cranks on my time trial bike (Giant) to hopefully help my speed...

I have enjoyed reading this. Thank you for starting it.