Beverly

I bought a new bike late last year (Trek WSD) and have only been able to put 500 miles on it. I love it but was having a slight problem with soreness around the knees after 30+ miles. I also felt like I wasn't getting good leverage when I stood to climb. Tweaks in cleat position and seat position made slight improvements but never completly eliminated the problem. While doing some research on the subject I kept finding reference to the crank length could cause the problems I was experiencing. If I use the common formula of inseam x 5.48 I get 172.6.

The crank size on the new bike is 170mm and all the old bikes have 175's. I called the bike shop and they said to bring the bike in and they would put a 175 on it for me to try for a couple weeks. If this doesn't solve the problem they suggested going through another fit session. I just picked the bike up tonight and it's 8F here so I won't be taking it outdoors for a spin. I'll be putting it on the trainer later but wanted to know if anyone else has any experience with changing crank length and what differences they felt.

Skipper

I found the information at this site to be pretty interesting.

https://www.nettally.com/palmk/Crankset.html

Blackberry

This from Sheldon Brown: https://www.sheldonbrown.com/cranks.html

bobkat

Don't know much about upright bikes but on my recumbent I went down from 175's to 152's! Now peddling is absolutely comfortable and the bit of knee pain is totally gone.
I agree with Sheldon and many others who maintain that cranks on most bikes are supplied too long. Now it's winter up here in ND and I've been peddling every day on a recumbent trainer, and now have knee pain again. This morning I thought I'd check crank length - sure enough - 175's supplied by the factory on my bent trainer. Trouble is I can't change them on the trainer.

bobkat

Check out Mark Stonich at bikesmith designs. He echos Sheldon and has more thoughts, too. He shortened my cranks and turned biking into pure heaven for me! Maybe shorter cranks aren't for everybody but its something to consider.

https://www.bikesmithdesign.com/index.htm

Richard Cranium

There is nothing about the using of a shorter crank arm that would cause knee problems. Go ahead and switch back to 175s, but whatever is responsible for your knee problems will not be solved by lengthening the arms, and effectively enlarging your spin circle. (and joint stress)

Good luck.

cyclintom

Wow! You have an inseam of 37"? What are you - 6'6"?

Beverly

After looking at the information on those websites I feel more convinced switching from 170 to 175 might just solve my problem. One site suggested you could increase the formulated crank length if you were a woman, had larger than average feet for your size or prefer a larger gear rather than spinning. I happen to fit all three of these categories. I'm a woman, wear a size 8-8.5 shoe and would much rather push the larger gears than sit and spin. I guess this comes from riding a bike that was wayyyyyyyyyy too large for me when I first started riding. When I was six my dad bought me a 26" women's fully loaded Schwinn and I rode that thing until I was 16 and discovered cars. I don't think I was able to sit on the seat and pedal for a couple years Sure wish I had kept that bike.

Beverly

31.5 x 5.48 = 172.62

Maybe you hit the wrong keys on the calculator

deraltekluge

The numbers given work out to an inseam of 31.5"

Shorter crank means you gotta push harder on the pedal to get the same torque. Longer crank requires less force at the pedal, but at the expense of making your joints work through larger angles. So, which is going to hurt your knees more?

BlazingPedals

This past spring, I installed a nice Thorn triple, in 155mm. My knees really liked the smaller circles, but I found I couldn't go as fast, nor could I climb hills as well. I even had to walk a 7% grade! So now I'm back using 170s. I may put the 155s on another bent and give them another try next season, but not on my fast bike!

Louis

I'm a short guy, 5'7" on a good day. I've always rode 170mm cranks. Also, I'm somewhat of a natural spinner (spinner not sinner ).

When I bought my Lemond (53cm) I noticed it came equipped with 175mm crankset. Decided I would give it a try rather than ask them to swap it out. I've ridden it a few thousand miles including a cross state ride with no problems of any kind. However, I can tell it screws up my spin a little and just doesn't feel right. When I ride any of my other bikes with 170's the smooth spin returns.

Recently I picked up a 170mm replacement, just havn't gotten around to changing it yet.

I still cannot understand why Lemond would spec a longish crank on a 53cm bike.

Tom Bombadil

I'd love to try 160 or 165mm at some time. Didn't run the calculator today, but I believe it works out to 155 or so for me. My bike has the standard 175 and I'm sure that impacts my enjoyment of riding it.

Beverly

I wasn't real clear when I said I had soreness around the knees. It's not pain but a feeling of tightness in the muscles around the knee area. I always felt better when I got off and stretched the legs for a few minutes. I've never experienced this problem on the old bike which had 175's.

Blackberry

So, do we share the same fate, Louis? I don't have to avoid temptation any more. These days it's avoiding me.

Louis

Notice I spoke in the present tense. In days gone by it would be a lie. Getting old is a good thing.

Dchiefransom

Just put on some crank arm shorteners and spin away. They also bring your feet out a bit like pedal extenders.

https://www.hostelshoppe.com/cgi-bin/...ory=1033761548

Tom Bombadil

Interesting design, but rather drastic in their effect. The smallest change is to shorten the crank by 24mm! With a 175mm crank arm, they would yield the following options:

151mm
134mm
116mm
99mm

Dchiefransom

I'd say from the picture that that is about the smallest change they can make and still have a strong crank. They are designed for tandems, so that different stokers can ride in the back.
Most recumbent riders that have shortened their cranks are saying they went to 155-150mm.

Tom Bombadil

I should have noted that if you start with 170mm cranks, as many recumbents come with, you'd have to subtract another 5mm from my numbers. The description states that the obvious targeted audience is to modify tandems to fit children. Or people with knee/leg problems.

I think it's a solution that addresses the need for unusually short cranks, where new crank arms at such short lengths are difficult to find.

cyclezen

ANy change from the circles you;ve pedaled on the prior bike will have an effect. Given that you haven't given much info I would still expect that your 'position' is different enough to make the muscles work differently and thereby complain some. Given that, I don;t think going to 175 will change how your knee area will feel, riding your new steed. Match the position more closely to the old nag and you'll be more likely to accommodate the muscles and joints. Our body does develop a 'memory' for things of repetition, which is part of the 'training' effect we feel. Change it, and we often 'fall apart'.
truly, not knowing much about you, I'll add that the closer your position to the BB (as in leg length, which at 31.5 is well on the shorter side of avg) and the greater circle you demand of the legs (as with longer cranks) the more range you demand of the legs. Longer cranks can be fool's gold. With a greater circle you;re legs work less efficiently thru more of the pedal revolution. This is poorly compensated by a hair's longer crankarm leverage.
The reason you feel more 'effective' with a longer crank at slower rpms IS because its the only thing that works within that 'box'.
But then cycling is what we want it to be, hope it all works out for you...

Big Paulie

I measure out exactly the same as Beverly... 8.5 shoe size, 31.5" inseam.

I started out on 175's for about 3 years, then realized that I was feeling uncomfortable in terms of my seat height...it felt either too high or too low, but it never felt right. I dropped down to 172.5, and all of sudden everything felt right. Then, after a few years, I got a set of 170s, and I'm peddling in even rounder strokes and nothing hurts.

But, since Beverly has had success in the past with 175's, at least go back to them for a try.

Carusoswi

I am 5'8" - 31" inseam. I use 185 mm cranks - I believe those are the longest cranks available. I turn a typically slower cadence than what is considered normal around these parts, but, I feel as though I'm in good shape for my age and can (and do) ride for miles with no discomfort of any kind.

I guess it's what works for you. I cannot say that shorter cranks we less comfortable - they just felt much less natural to me. I don't recall ever experiencing pain on a bike except when I purchased my newest steed, and the LBS had the nose of the saddle adjusted too high. After two days I thought I was going to die. A slight nose dive straightened everything out.

Love my 185mm cranks.

Caruso

cyclintom

Bev, with an inseam like yours a 170 should work fine. A 172.5 might feel a little long. A 175 feels like swinging a Big Wheel to me and I'm 6'4".

Here's something to think about - the ratio difference between going from a 39-17 to a 39-18 is about 5%. The ratio difference going from 170 to 175 cranks is 3%. So changing the gear down one is more leverage change than putting those super long (compared to your inseam) cranks on a bike.

Garfield Cat

I think if you seek out a professional bike fitter, telling her that you have an injury, the first thing she would do is to observe your walking and then your pedalling. This is a much missed processing when going in for a bike fitting at a local bike shop.