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Are Your Cranks Too Long?

Old 11-10-07, 12:33 AM
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Are Your Cranks Too Long?

I decided to "service" my BB's on my 2 bikes, since my "main ride" was getting "gritty" feeling.
It turned out both spindles were the same size and I thought- Why not try the 170MM arms from my "back up" bike on my good bike and put the 175's on the back up. (I didn't have a crank puller before)
The difference is AMAZING!
I'm running the SAME cogs in back, but using the 38T ring instead of my former 46. That's about 21% higher cadence to do the same speed! I think I'm also cruising about 0.5 MPH faster, but it's hard to tell for sure with the wind/cold etc. (edit: after today-did a 9 mile ride- I'm pretty confident I'm doing at LEAST 0.5 MPH faster- maybe closer to 1 MPH!!!!)
Before, I had to keep focused to try to keep my cadence at 65 or it would drop right down to 60 or less. My feet would come off the pedals at around 68 RPM. Now when "madly spinning", my feet still feel "stuck" to the pedals. My cadence is still relatively slow, but at least it's greatly improved. STAMINA has improved as much!
I went on a 15+ mile ride last Sat. I wouldn't have attempted 10 miles on one trip before! (10-12 miles spread over 4-5 separate "errands" per day, with rest breaks in between, was my limit) And, NO PAIN/stiffness!

My conclusion is-
With the longer cranks, I was exceeding the range of motion in my old arthritic/bad knees and was wasting energy on the "down stroke" by having to help "lift" the other leg "over the top".
I'll be curious if another 5MM shorter helps out much more. I certainly don't expect another 20%, but even 5% more would be great. (I ordered a cheap set of 165MM cranks)
My old 175 MM cranks were the stock Specialized from an 86 rock Hopper (26-36-46)
The "new" ones are the cheapest looking Bio Pace that I've ever seen. One piece arm with integrated, riveted rings (28-38-48) off my 91? TREK 820. However, as they say, it works. I don't know if the Bio Pace part helps???
BTW, I'm kind of a "short legged" 6 footer. Maybe a 31" inseam on dress pants? 30" on my Levi's.
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Old 11-10-07, 12:51 AM
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I have 170mm on both of my primary bikes. 175's are too long for me, on every stroke it feels like I'm trying to step up over an obstacle.

I'd love to try 165's, sure wish it wasn't so difficult to try different lengths.
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Old 11-10-07, 12:53 AM
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My 53cm LeMond came with 175mm crank arms, all my other bikes have 170mm, which is what I'm used to. I rode it for over a year trying to get comfortable with the extra 5mm but it never felt quite right. I picked up a good used exact replacement in 170mm on eBay and switched 'em out. Big difference. I'm still kicking myself for not doing it sooner.
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Old 11-10-07, 02:58 AM
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Same here...

I'm 5'10", with pretty long legs for my height, and 175's drove me nuts. I could never get the saddle the right height, and was never able to really spin. 170's rock!

Last edited by Big Paulie; 11-10-07 at 11:49 AM.
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Old 11-10-07, 03:23 AM
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I have short legs and love my 167.5 cranks. They are a bit hard to find.
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Old 11-10-07, 03:55 AM
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I stayed with 175's for years because it was the "thing to do" for my size bike. Year before last I went to 170 because of an availability issue and with the exception of "bogged down and mashing" hill climbs my performance and comfort improved.
It is expensive to outfit you bike this way (especially if you don't like it) but well worth the inevitable test rides.
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Old 11-10-07, 09:43 AM
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I had been having trouble with my knees and occasionally with my right hip for the last two years. It had gotten to the point that I was avoiding riding. After reading a post in the forums (recumbent I think) about using shorter cranks and spinning more I decided to give it a try. I went from 170mm to 140mm because that is what I had. No more knee or hip pain. Not even so much as uncomfortable. I'm never going back. I may not be fast but at least I can hang in there.
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Old 11-10-07, 10:09 AM
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I went from 175 to 170, spinning too high, no power. So I'm at 172.5, which works perfect for me!
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Old 11-10-07, 10:34 AM
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I'm 6:1 with a 32" inseam and Went from 170 to 175's on my Touring/Commute bike. Almost ruined my knee's. Went back to 170's. Less knee pain.

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Old 11-10-07, 10:37 AM
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How does one easily find their crank length?
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Old 11-10-07, 10:49 AM
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crank length= (1.25 x inseam in cm) + 65
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Old 11-10-07, 11:04 AM
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Originally Posted by rvdv
crank length= (1.25 x inseam in cm) + 65

Thanks, but I was interested in finding the length of the current crank on my bike, not the length I should have. Is it stamped somewhere on the crank, or does one have to measure it?
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Old 11-10-07, 11:17 AM
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I ride a varierty of Bikes with cranks from 165 to 175. For some reason I do not not find that 3/8" affects the feel of the bikes in any way.
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Old 11-10-07, 11:21 AM
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Denver -

Most cranks are stamped with length in mm on the inside of crank arm. If not, measure from center of pedal axle to center of bottom bracket spindle .
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Old 11-10-07, 12:27 PM
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I had the opposite problem with the 170 cranks that came on the Madone. I rode it 500 miles and couldn't get used to the cranks. I had 175 cranks installed and love them. I guess it's all related to what we're accustomed to riding.
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Old 11-10-07, 02:09 PM
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Originally Posted by Beverly
I had the opposite problem with the 170 cranks that came on the Madone. I rode it 500 miles and couldn't get used to the cranks. I had 175 cranks installed and love them. I guess it's all related to what we're accustomed to riding.
Beverly, aren't you more of a "casual" rider where you like to "enjoy the view" and speed ISN'T the issue? I can see where with trail type riding (slower speeds), the longer cranks might work better for you. The longer arms give a little better "torque" for accelerating from a stop or "crawl".
I stick to mostly flat pavement and ride a bike because I don't have a car. I pretty much want the fastest speed that I can comfortably maintain. I'm NOT fast, so going from 10 MPH to 11 MPH is a 10% increase! The shorter cranks HAVE helped my speed slightly, but they have REALLY helped my endurance. At this early time, it appears I can ride about 60-70% further with the same level of fatigue. On my shorter errands (1-2 miles), I can "crank it up" an extra 2-3 MPH. That doesn't help much when you speed up to a stop light, but maybe I'll catch a few when they are still green Actually, there is one "timed" light I can now catch with a little "burst"! If only it was on my "usual" route
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Old 11-10-07, 04:26 PM
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I'm running three length cranks. 165's on my touring bike. 172.5s on the full carbon road bike, and 175s on my 853 steel and carbon raod bike. the 175s are by far the easiest for me to ride. I notice no difference in ability to spin all three in the 90 to 95 rpm range. I like the 175s the best when standing while climbing. Personally, I find the difference not worth worrying about. Meaning that if there were a bike with any of the three length crankarms on it, and I liked the bike, I'd be comfortable with purchasing it. If given a choice, I'd go with the 175s.
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Old 11-10-07, 04:32 PM
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Originally Posted by DnvrFox
Thanks, but I was interested in finding the length of the current crank on my bike, not the length I should have. Is it stamped somewhere on the crank, or does one have to measure it?
Denver, it's often stamped on the back of the crank arm, but you can measure it with a ruler if your good at eyeballing where the centers are. Measure from the center of the BB axis to the center of the pedal axis, that should be the number. Common values are 165 thru 175 in increments of 2.5 mm. It might be easier to see if you pull off one of the pedals.

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Old 11-10-07, 04:50 PM
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Man, you guys are confusing me. I have been all set to replace by triple with a compact double with 175 cranks, but now I'm not so sure. I'm 6'0" with a 35" inseam, and I've always understood that longer cranks are appropriate for longer legs. Maybe I should think about something shorter.
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Old 11-10-07, 05:29 PM
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Originally Posted by kerlenbach@cfl.
Man, you guys are confusing me. I have been all set to replace by triple with a compact double with 175 cranks, but now I'm not so sure. I'm 6'0" with a 35" inseam, and I've always understood that longer cranks are appropriate for longer legs. Maybe I should think about something shorter.
Welcome to the club. With those long legs I suspect 175 may be your best bet.
I don't know what you have, but you could keep an eye on ebay for some used cranks in a size you want to try. Nashbar often has great prices on leftover cranks.
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Old 11-10-07, 05:45 PM
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Originally Posted by Louis
Denver -

Most cranks are stamped with length in mm on the inside of crank arm. If not, measure from center of pedal axle to center of bottom bracket spindle .
OK - mine on the Lemond are 175 mm.

Wouldn't changing the cranks to a smaller crank effectively change your gearing ratios, considering the crank to be a lever, and the pivot point a fulcrum??

I see no need to change mine.

Last edited by DnvrFox; 11-10-07 at 06:55 PM.
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Old 11-10-07, 06:11 PM
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Originally Posted by Bill Kapaun
Beverly, aren't you more of a "casual" rider where you like to "enjoy the view" and speed ISN'T the issue? I can see where with trail type riding (slower speeds), the longer cranks might work better for you. The longer arms give a little better "torque" for accelerating from a stop or "crawl".
I stick to mostly flat pavement and ride a bike because I don't have a car. I pretty much want the fastest speed that I can comfortably maintain. I'm NOT fast, so going from 10 MPH to 11 MPH is a 10% increase! The shorter cranks HAVE helped my speed slightly, but they have REALLY helped my endurance. At this early time, it appears I can ride about 60-70% further with the same level of fatigue. On my shorter errands (1-2 miles), I can "crank it up" an extra 2-3 MPH. That doesn't help much when you speed up to a stop light, but maybe I'll catch a few when they are still green Actually, there is one "timed" light I can now catch with a little "burst"! If only it was on my "usual" route
Eighty percent of my riding is on the road and my average speed is in the 13-15 mph range. The problem with the shorter crank was when standing to climb. I felt like I was on a kids tricycle trying to turn the shorter cranks. I was also experiencing slight hip and knee pain. I took the old Trek road bike out for rides (it has 175mm cranks) and I didn't have the problems. After 500 miles with the shorter crank I was really beginning to think purchasing the new bike had been a big mistake. After talking to the LBS they suggested trying a 175 crank and it made a world of difference for me. According to many of the measurement systems I should be able to use a shorter crank but it just doesn't feel comfortable for me.

I'm not a tall person but I have longer legs than most women my height (5' 3"). My sister and I are the same height....she has a 29" inseam and I have 31" inseam. I still think the biggest factor was I was used to 175 cranks. Every bike I've ever owned had them. I also prefer to push the gears instead of spin.
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Old 11-10-07, 06:23 PM
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Yes, I believe the effect is that with shorter cranks you always are riding effectively in a lower gear. You can compensate of course by upshifting, but you always have a smaller circle to pedal. If you keep your seat-to-bottom-pedal range the same, your knee angle at the top is eased up.

The key thing with crank length is that a .23" difference is doubled to .46" when you look at the full circle.

What is confusing is that usually the longer lever = more leverage = better.

???

I've been riding 175's and having knee trouble, which nothing seems to fix. I'm probably going to soon try 170. In fact I recently had a rental bike with 165's and that worked out better for me than my current bike.

My beef with crank length is that so few manufacturers list the info on websites. (Kudos to Jamis as one of the only exceptions).
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Old 11-10-07, 06:57 PM
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Anyone make adjustable cranks?
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Old 11-10-07, 06:59 PM
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172.5 on the single, 175 on the tandem. I do not seem to notice any difference.
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