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Shorter crank length as you age?

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Shorter crank length as you age?

Old 08-01-10, 09:16 AM
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Shorter crank length as you age?

I'm curious about crank length for older riders (I'm 56 with one knee surgery under my belt and anticipate another one in the next few years). I read Kriby Palm's pages on crank length but didn't see any discussion of crank length and rider's age. My concern is that as you age and your knees get more creaky longer cranks will be harder on your knees as you try to produce power at the beginning of the power stroke, when your knees are in their maximally flexed position. A shorter crank will not flex your knees as much.

That's my thought/concern anyway. Opinions and advice gratefully appreciated...

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Old 08-01-10, 09:48 AM
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I don't know but it's an interesting subject.

I recently was forced to switch over to riding recumbents. Recumbent riders frequently use somewhat shorter cranks than is common on a conventional bike. I've been advised that the 175 mm cranks that I have on my single recumbent bike right now may be hurting my knees. One rider even posted a favorable report after modifying a crank to 130 mm!

I'm wondering how much difference 5 mm can make. I'm probably going to rework my drive train this winter. I'd like to reduce the angular motion of my legs - not because of stress on my knees but because my knees bump the recumbent handlebar. If I were making the decision today I'd probably get 170 mm cranks but a lot of recumbent riders use 165 mm cranks so I might go with that.
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Old 08-01-10, 10:02 AM
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I'll be 68 in September; I've noticed my saddle height has needed to come down slightly in the last few years. You may be on to something.
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Old 08-01-10, 05:58 PM
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If you knee motion or the efficient portion of it is compromised with age, then shorter cranks make sense. I would change to proportionately lower gears to compensate for the lost leverage. Having said that, I really don't notice any difference between the 165mm cranks on my Peugeot and the 170s on my other bikes.
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Old 08-02-10, 09:40 AM
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While my studies involved athletes in their teens and twenties, I was taught that a person at any age can improve strength and flexibility, and that proper biomechanics should always be used. While I am not an expert in bicycling, I would say to try and stay using proper technique as long as you can. If due to physical limitations that are age related, then you may need to adjust, but in general, I believe, you would want to keep things as normal as possible. You may need a new bike fit as you may have changed with age. Due to my age and injuries, I've lost over an inch in height, my weight has also gone up due to injuries, so I'm shorter and fatter than I used to be, so this changes how I can do things. Since my back is also shot, I've had to modify the things I can and can't do, so I would think that an increase in age alone wouldn't require a change in crank arm length, but you should get a good fit in relation to your new limitations.
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Old 08-02-10, 10:29 AM
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Hmmm, I think shall refrain about making comments about shorter crank lengths on older riders. That looks like TMI.
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Old 08-02-10, 04:35 PM
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Originally Posted by Pat View Post
Hmmm, I think shall refrain about making comments about shorter crank lengths on older riders. That looks like TMI.
Don't touch this one with a ...... pole.
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Old 08-02-10, 11:24 PM
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I'm 65.5 (today), and I'm still using the same 175s i've ridden for 40 years, mostly because it never occurred to me that i should change them. Still feels OK, though. I have had to lower my seat maybe a centimeter, and I just found out at the doctor last week that i'm 6'3" now, not 6'4". He said most men older than 50 are shorter than they think they are, because they haven't really been measured since college or military service.
The last bike I sold had 170mm cranks, and they felt tiny, like I was going in little bitty circles. But that was six or eight years ago, so who knows?
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Old 08-02-10, 11:54 PM
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I can't tell any real difference in 175 or 172.5. Bikes are ridden frequently and interchangably.

I've read some Leonard Zinn articles and have always wanted to try 180s.

59 years and 6'1". No knee issues.
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Old 08-03-10, 01:20 AM
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I'd have thought shorter cranks would be harder to turn.... why would a longer lever be harder to turn at the beginning of the power stroke... doesn't make sense. Sorry.
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Old 08-03-10, 04:43 AM
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Skip, Age probably is important primarily as a lifetime of disuse, misuse, wear and tear can rear an ugly head. Aside from some type of physical issue we're pretty adaptable to a range of crankarm lengths. A shorter crankarm is desireable if there is a joint issue with range of motion. Aside from that, a longer crankarm will require less rider effort for a given torque output because of it's mechanical advantage over a shorter crankarm.

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Old 08-03-10, 05:55 AM
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I had a brief experiment with 155mm short cranks. I found that I couldn't spin enough faster to make up for the lost leverage, and it felt like I was pushing harder all the time. I also lost hill-climbing ability, of which I have little enough in the first place. So now I'm back to using 170s.
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Old 08-03-10, 06:48 AM
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Originally Posted by maddmaxx View Post
Don't touch this one with a ...... pole.
With over 50 years of usage, one has to expect some wear.
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Old 08-04-10, 06:20 PM
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Am 77 years old; have bicycled 300,000+ miles. Still using 170mm cranks.
Pedaling 100+ miles a week.
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Old 08-04-10, 08:30 PM
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I have bio pace on my Trek 1400 and 86 Bianchi as well. Both with 172.5 mm cranks IIRC. No knee problems. When they started to hurt i found the my seat post had slipped down some what. After putting back higher I put a piece of tape as a marker so i can tell if starts to slip again. So far so good.
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Old 08-05-10, 12:30 AM
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Just to add to the database: I am 59, 6'1", 175 lbs, with 34" inseam. I use 175s on the tandem, but most of my riding is on a fixie using 165s. I really don't notice much difference, but it should definitely be easier to spin the shorter cranks, and in fact I can hit over 60 kmh spinning down an 8% grade. For a given crank rpm (angular velocity), your foot speed is slower the shorter the cranks (linear velocity). When I go up hills on the fixie, I forget all about the crank length. I went up Hurricane Ridge near Port Angeles, WA, last Saturday on 44x16 fixed with the 165s (5200' in 17 miles), no problem, but I've been riding (much of it on the track) for the past 38 years. When I'm on the longer cranks, I've also got gears, which a physics teacher long ago told me was an impedance-matching device.

Bottom line: The gears make a bigger difference than the crank length. If you're on a fixie, then you might be concerned with crank length. On a geared bike, I don't think it makes any difference what crank length you use, but you will probably get a psychological boost going up hills if you have a longer crank, although 5 or 10mm of extra crank length (3 to 6% longer) won't really make a bigger gear any more comfortable or any faster.
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Old 08-05-10, 08:53 AM
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I've been struggling with what to do about crank lengths on my bikes lately. My alum. Raleigh has 172.5's and my steel Miyata has 165's. Side by side, the seat, bars, etc. line up very close. Of course they ride a little different, the geometry is a bit more aggressive on the Raleigh, but my knees hurt after riding the Raleigh, even on a shorter ride of 10- 20 miles. I've ridden 40 mile rides the last 3 weekends in a row on the Miyata, no knee pain. I know all other things are not the same, but I'm looking hard for some more 165's right now.Oh, I'm 5'8" now according to the Dr., though I've been 5'9" for years. Darn cheap yardsticks don't measure like they used to!
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Old 08-05-10, 12:26 PM
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I also have one bike with 170mm and another with 175mm...I can't tell the difference. But it's the subtle things that add up many times. I'd like to hear more on this subject.
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Old 08-05-10, 02:32 PM
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With knee pain developing on my LWB recumbent, I went from the stock 175's down to 152's with appropriate gearing down of the front chain rings.
The knee pain went right away, and I'm as fast (or maybe as slow) as I always was and climb seems unchanged.
I think the shorter cranks make your knees flex and extend less, and while shorter cranks DO result in decreased leverage, with appropriate gearing you won't notice any difference in speed or hill climbing, etc. Unless you are Lance Armstrong or some young jpck or speedster.
I doubt 5 or even 10 mm change would be noticed at all.
When you think of it, we all require different size frames, handlebars, seat heights, so why do we all accept 170 to 175 one size fits all cranks. But most of it is trial and error anyway - if it feels good, do it. What works well for one guy might make the next guy's knees hurt.
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Old 08-05-10, 07:28 PM
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I'm 62 and 5'9" with short legs... about 30 inseam. I have no orthopedic issues. I have recently ridden the same exact bike with both 172.5 and 170 cranks ... and I CAN tell the difference. I can ride the 172.5s okay, but prefer the 170s because the longer cranks seem to require a greater bending (more acute angle) of the legs and lower back, especially when riding in the drops. I can also spin the 170s more easily though I am no great fast spinner to begin with.

IMO matching the crank length to one's own body geometry comes first, but the limitations of age and infirmity could come in to play to cause a move to a shorter crank. I can't think of a reason why age would dictate a longer crank but perhaps there is one.
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Old 08-05-10, 07:59 PM
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I have a similar build and experience to billydonn.

As a youngster I always had 175 or 172.5 cranks and thats just what they were. Heck, I really didn't care much (and still don't waste a lot of sleep on it) about a couple of millimeters one way or the other anywhere on my bike. I was young, dumn and flexible. Heck, I rode a frame that was too big (way too big) for 25 years.

I bought a SS bike a few years ago for the flatland I was moving into at the time and found my pedal stroke was really nice with this bike. I liked the efficiency and the power I could put through it. Turns out it has 170 cranks. Huh!

Had to replace a frame I loved (my second "good" one but a much better fit than the first) and rode easily 25,000 miles on it and with as nearly an exact duplicate as I could find. Including 172.5 cranks.

What I found was this: Comparing the bikes in the flats (where they were "equal") I liked the shorter cranks better. Better spin. Huh!

So I've replaced the stock 172.5s for 170 and it's good. But I keep thinking the leverage with the longer cranks will be better in the long steeps for me. I like to stand on my pedals going up. So I've got them in reserve. Maybe in the fall I'll get a chance to compare...
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Old 08-05-10, 08:30 PM
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Going from 170's to 160's made a big difference to my knees. Changed the angle of the knee bend enough to get some relief. No knee problems? D
don't change crank length. bk
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Old 08-05-10, 10:28 PM
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I guess one point no one has mentioned is whether or not they moved the saddle up or down when they swapped cranks. I firmly believe that the saddle needs to be set in relation to the pedal at its lowest point. To set my seat height, I have always used the classic technique:
1. set crank to be in line with the seat tube
2. sit on bike in riding shorts and stocking feet
3. there should be a slight break in the knee with the heel on the low pedal
4. when the saddle is at the correct height, you should just be able to spin the cranks backwards with your heels on the pedals, rocking only slightly

My saddle height using this technique has been corroborated by more sophisticated methods of determining proper saddle height. But the point of my post is this: when I am using 170mm cranks, my saddle is set so that it is 79.0 cm from the middle of the bottom bracket. With 165mm cranks, it goes up to 79.5 cm; with 175's, the saddle goes down to 78.5. Everything is in relation to the pedal at its lowest position. If you keep the saddle at the same height, I think you can wreck your knees with the wrong crank length.

L.
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Old 08-06-10, 06:32 AM
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Yes. I forgot to mention it but I did change saddle height in my A/B testing.
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Old 08-07-10, 12:01 PM
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though i don't ride a recumbent on one of my bikes i recently purchased a felt, i put a compact crank 170- 50/34 and a 11/25 cass.
i have always used 172.5 cranks and 11-23 cass. it is a hell of a lot easier on your joints and for me it helped produce a nicer spin more fluid lie more of a smooth pedal stroke What i personally noticed with the 172.5 cranks there was a lope type affect coming from the dead-spot to the top, with the 170 crank it is far more fluid and constant
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