A longer crank is effectively a lower gear. You get more torque for same force, while you have to move your feet a greater distance. But the difference between 170 and 175 is less than 0.2 inch. That's a pretty slight difference...can you really tell just by riding, without measuring? The difference in gearing is equivalent to the difference between a 35 tooth and a 34 tooth chain ring.

on another thread about a Chorus BB, someone asked for a picture of my crank. I thought, that's odd for this site.

Yes, but it isn't so much the "gearing" effect, but the height and depth of the pedalling circle.

Exactly. On 175's it feels like my knees are about to hit my chin.

These allow you to try different lengths, but they move your feet out to a wider angle. On my recumbent I'd like to eventually try out some 165mm cranks. The different position on the recumbent means shorter cranks are easier on the knees.

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

I have had bikes like this and and always with the 175 cranks. In hindsight- those bikes have always been the ones with longer top tubes. Since changing to compact frames- I have not had the problem. Only thing I can put it down to is the more upright position that is possible on a compact.

The "effective distance" is twice the actual crank length difference.
The shorter crank means you raise the seat up by that amount to set the proper height for the "down" crank. Since the "up" crank is also that much shorter, the seat is now twice as much higher over the "up" crank.

For MY knees, the difference was amazing for the reasons I suspect as in my original post. My knees were simply beyond the limits of "free" movement and basically "binding" at the top of the stroke!
You do lose "torque", but you go to a lower gear and SPIN to make up the difference. I'm maybe spinning around 75 RPM, which is still considered "slow", but it was a large % increase for me. My STAMINA is so much better, I've already ridden more miles this month than last! (It has to something to do with lactic acid build up in the legs? as I understand it)

I posted this in the +50 forum for a reason. There is most likely, more people with bad knees here! If I thought my "revelation" would have applied to ANY of the other forums, I would have posted it there!

I'm not claiming shorter cranks are the solution for everybody! I just know they have helped me to a degree I would not have imagined. If someone told me they would make that much of a difference to me, I would probably told them they were full of it!

I'm convinced enough, that I ordered 165's! I totally expect that there is a point of "diminishing returns", but I'm going to take the next step toward shorter cranks. With my monetary situation, this IS a major investment. Hopefully I won't be disappointed.
One problem, is I'll be changing more than one thing at a time. I'll have to go back to my original 26-36-46 rings, from the Bio Pace 28-38-48 I'm using now. I do have a 28-38-48 "round" ring set in the "junk pile" off an Xmart bike I'd forgotten about. I could also try that, but I'm not sure how much I want to "cheapen" my bike!:) Maybe they'll end up on my "back up" bike and I can sell my nicer 175's and recoup a bit of my outlay?

175mm cranks are on almost every bike I've owned as an adult. My old Fuji came with 170mm. I don't notice any difference between them. Both lengths seem to work just fine for me.

I concur. See Sheldon Brown's related discussion of "gain ratios."
http://www.sheldonbrown.com/gain.html

According to the formula, I should be riding 167s. I put 165s on the UO-8 to reduce toe-to-tire overlap, and I have 170s or 171s on all of my other bikes. For folks who have always wondered why older Sugino cranks came in a 171mm length, note that 6-3/4", a traditional British crank length, works out to about 171.4mm.

Changing from 170'a to 160's on my LWB recumbent really helped out the pain situation in my right knee. I was amazed at the difference 10mm made. bk

If your knees don't BEND far enough with the longer cranks, you can definitely spin a lot faster with the shorter arms! More than enough to make up the difference, as in my situation!!!!!

It's the other way around, Sportsman. To compensate for shorter cranks you should adjust the front triple gear accordingly, and gear them down a bit.
Shorter cranks are much easier on the knees, provided you gear your triple ring down accordingly. Or you can leave it alone if you don't like to spin a bit faster but you'll lose pwer on the hills without gearing down much more than the usual. In any case it is much easier on the knees. My knee pain on my left knee went away immediately after I went fro 175's all the way down to 153's! Although I wouldn't recommend taking a big jump like that for upright bikes. Worked extremely well on my bent though. I'd never go back to loger crank arms. Even the few times I ride an upright with stock 172 or 175's I can feel my knee grating after a mile or so.
I think someone makes adjustable cranks. I've seen them in a catalogue somewhere, I think maybe Hostel Shoppe (a bent bike shop) But putting on shorter cranks is only half the changes you have to make to the overall bike. You'd have to gear down on hills a lot as you lose torque (remember physics 101) going to the shorter ones, but because your knee isn't being wrenched so far with every pedal stroke it is much easier on them. Your cadence will increase a bit but your knees will really thank you!
I got my shorter cranks from a guy named Mark Stonich at Bikesmith.com. He has a very informative web site and loves to talk on the phone.

Oh swell, a forum of old guys and gals having a cranky old conversation ... and I'm joining in. Sheez.

I would wager that the shorter the rider is ... the more noticeable the difference when riding two crankarms that are different in size by 5mm. My pubic bone height is under 76 cm, and perhaps the difference I feel between 165mm and 170mm would be more than the difference that would be felt by someone who is over six feet tall. It would appear that the angle of the short rider's knee would be more influenced by difference in crankarm lengths ... than would be the angle of the tall rider's knee.

My 1995 Trek came with 170mm crankarms. When my Saluki was built, it came with 165mm, and this was an easier spin for me than the 170mm on the Trek. In about two weeks, my Saluki/Serotta/Trek bikes will all have 165mm crankarms.

According to the on-line crank arm calculators, I should be using around a 155. I currently have 170 on both my upright and bent. The 170 seems okay on the upright, but too long on the bent, where I have a difficult time keeping a smooth motion going - either the downstroke feels too far away or the upstroke is too close, depending upon where I have the seat.

(I make this observation every time we discuss this subject .... which I think has been about 4 times in 2007)

I do find this to be an interesting subject, that bike shops never mention when I talk about being fit properly on a bike. I've been trying to find a bike with 165s on it for several months now and haven't been successful.

I ran some 155mm cranks last summer. A lot of recumbent riders swear by short cranks. My knees loved them but I couldn't climb hills. I may put them back on next spring, but I'll gear them down more this time. They upped my cadence by almost 10 rpm.

I'm 5'8" - my old setup had a long gear of 63/11, and I turned that through 185 mm cranks. I had to be careful in sharp turns not to snag the pavement, but I loved that setup. My small ring was only a 52 or 54 (can't remember which), so the bike was definitely setup up for cruising, not climbing. OTOH, standing out of the saddle on those cranks was quite comfortable.

Watching motorists' reactions as I casually pedaled downhill at 40+ mph was always a stitch.

My current setup is Dura-Ace, long gear is a more modest 56/11, cranks are the longest that Dura-Ace offers (don't have the bike here to check, and I don't remember, but, I know they aren't 185 mm).

Which setup do I prefer - it's hard to say. I enjoyed both bikes. The new one is definitely easier to ride over long distances - it's much lighter (CF) road bike than the previous AL Cyclocross with discs, so I don't know if the comfort is the result of a lighter bike, shorter cranks, mental newness factor, or what.

When the Cyclocross was new, I almost took it back because the gearing was just not to my liking - comparatively short long gear until I had my LBS do some major re-gearing.

Can't do a comparison, because bike #1 was destroyed in a crash.

. . . but I enjoyed bike #1, enjoying Bike #2 . . . and this topic is always of interest to me.

Caruso

+1
Most ride with 170-175 mm cranks -- that is less than 1/4" in difference. Not noticeable to me.

The total difference between the top of the stroke vs the bottom of the stroke varies by nearly 8/10ths of an inch between 165mm and 175mm cranks. For some, that is going to be a significant difference.

The first time I noticed it was when I took a test ride on a bike and found it quite uncomfortable to pedal. I took note of the crank length and then compared it to my bike (which up to that time, I had never made note of it). I found that mine was 170 and the other bike was 175. Since then I've paid attention to this and have never felt comfortable on a 175. Of course, since I have short legs and should be using a 155 or 160, it goes that I would notice once it got too long.

I have smaller cranks on my new bike, a WSD Madone. I have to say, I like them. And I'm pretty tall -- 5'7" with a 33 inseam. It helps my cadence and takes some strain off my neck and shoulders. Seems like I'm not having to push as hard on the pedals.

Check this out: http://www.nettally.com/palmk/crankset.html

Although that link tends to confirm my choice of shorter cranks, it still doesn't address the issue of someone with bad knees. There's just more factors involved than a one size fits all formula!

Physical condition- General health/fitness AND "defective" joints.
Age- One would expect that a younger rider could spin faster than someone 40-50 years older.

As I stated, for ME, the shorter cranks have increased my speed slightly, but have increased my ENDURANCE significantly. OTOH, on my "short errands", where I don't have to "save myself for the long ride", I can ride noticeably faster. I can sweat and gasp after I get home!:)

Several of my girlfriends have complained about my crank being too long...oh, wait...never mind, wrong forum. :D

5mm makes a big difference on recumbents where the leg length is locked in. On a regular bike, the body can compensate for slight differences by moving back and forth on the saddle which a recumbent rider can't do. I run 165s on my bents and can tell quite a bit of difference if I put on 170s, mainly because I'm shorter than average (5'7"). With 170s, my knees come back too far causing an over-contraction and I get sore thighs. FWIW, I've got a line on a set of 155 mm carbon cranks and might give them a try.

It seems we all have such different experiences with crank lengths. I have a Madone WSD and changed the 170 cranks to 175 as I felt like I was constantly spinning out on the shorter cranks. I tried them for 500 miles and was happy when I made the switch.

I would think you'd have the opposite effect?
With the 175's, 65 RPM was all I could maintain and it took a conscious effort. 68 RPM and my feet were coming off the pedals.
With the 170's, I'm aware that I'm spinning faster, but I don't feel like I'm "spinning out". I kind of expect to increase my cadence somewhat, through "repetition".
I messed up my back though, so I'll be off the bike for a few more days. The 165's should be in the shop tomorrow. I guess they'll be there a few more days!

Good article..

http://www.velonews.com/tech/rev/crank.html

Shorter crank arms = more fun & endurance
 

"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."

...I agree that short cranks give you more endurance. My speed on flat roads averages 14 mph, but seniors like me can keep it up "forever".

I'm 5'9" with a 35" inseam and I find 175mm cranks much more comfortable than anything shorter. I would like to try longer cranks, but they are hard to find.