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172.5 or 175 crank arms??(19 posts)

172.5 or 175 crank arms??neo
Apr 16, 2003 12:34 PM
I am looking at upgrading my crankset on my roadbike and wondering if I should increase the arm length to 175 from the current 172.5. I am 5'11" with a 32 inch inseam. I know the 175 will give more leverage and I am not really a "spinner" so would my climbing be easier or will my endurance suffer with any changes???? I know tall guys run 175 and I dont quite qualify for that, but would I notice???

re: 172.5 or 175 crank arms??ClydeTri
Apr 16, 2003 12:56 PM
2.5mm is approx 1/10th of an inch...from all I have read, you could have one of each on your crankset, and you couldnt tell it unless you knew it, ....175 is the most common ...
try it...sievers11
Apr 16, 2003 1:06 PM
it makes a big difference...if you ride alot. you may not notice if you put on 20-30 miles a week. I put on 150+ a week and I can tell 5mm extra in my spin in a second.

172.5 is the most common on road bikes from 55-58cm frames.
175 is most common on MTB bikes. 175 is common on road bikes only if they are 59+ cm frames.

For specific sizing a nice little chart...make sure you measure your inseam very accuratly in bike shorts.

When in doubt, go small to be safe or better yet try both.
try it...ClydeTri
Apr 16, 2003 1:09 PM
I read an article by Leonard Zinn a few years ago, the author of the bicycle mainenance books...anyway, the article was on this issue..he tried all different lengths for the article and..some times afterwards he discovered he had left ones of different lengths on and he hadnt noticed..and his a very knowledeable high mileage kind of cyclist I guess...was taking that from that..will try to find a link to that article..but, may have been in a magazine...
Apr 16, 2003 1:13 PM
You don't know Lennard, do you? He is not a very high mileage kind of cyclist. He's a writer. And he tests so much equipment that he doesn't really have a bike that's a perfect set-up, because it's always changing. Lennard is very good at some things, but he is very much the type of guy who would have different length crankarms and not notice it.
It's noticable,TJeanloz
Apr 16, 2003 1:10 PM
The effects of different crank lengths are definitely noticable -- we did a double-blind test at the shop once to demonstrate it. It's a Princess-and-the-Pea type feeling when you change, something doesn't feel quite right, but it isn't obvious what it is.

172.5 is also by far the most common length on road bikes -- some bigger bikes come with 175s.

The additional leverage is noticable in climbing, and adversely noticable when sprinting. A lot of people who switch to longer cranks rave about their climbing improvements, but wonder why they've "lost" their sprint.
re: 172.5 or 175 crank arms??sievers11
Apr 16, 2003 12:56 PM
It will be your knees that suffer not your endurance. I wouldn't do it, but I spin pretty good 90-110. You will be increasing the diameter of your peddle stroke by 5 with this upgrade, this will also increase the angle of you knee at the top of your stroke.

Unless you are compeating, I wouldn't mess with the 175. If your body can handle the change then go for it, My best suggestion would be to try someone elses bike with a 175, before I made a big purchase. Or look on ebay for a cheap 175 crank give it a try...then decide if you want to shell out the $ for the carbon record crank.
re: 172.5 or 175 crank arms??Jon Billheimer
Apr 16, 2003 1:35 PM
Last year I went from 170 to 172.5mm cranks when I upgraded my Ultegra drive train to D/A. I'm 5'11". I noticed the difference for about a week then seemed to adjust, FWIW.
subjective opinion from similar size person...BenR
Apr 17, 2003 1:28 PM
First of all, I'd like to mention that 2.5 (5 mm total) makes more difference than you'd think.

I tried 175 cranks for 4 months before switching back to 172.5's (same bike, crank model, and pedals) after continous and increasing amounts of pain deep in my knee joints. I noticed a definite improvement in climbing and low cadence/high torque attacks but my top speed sprint was a bit slower, even after weeks of practicing spinning with the longer cranks. Spinning at a proper cadence always took more conscious effort despite plenty of time to get used to it.

I switched back to the shorter cranks and the pain went away very quickly, despite steadily increasing mileage. I liked the climbing and time trialing advantage of the longer cranks but the 172.5's were a better all-around size since. It's personal though, so you should really try it on your own. Give it 2 or 3 weeks - it took about 5 consecutive days of riding for me to develop symptoms, but don't keep trying for months like I did hoping your body will "adapt" and destroying your knees in the process. Thankfully, I was young and had a large mileage base so recovered quickly. If you can't find a pair to borrow and are looking at guessing and making a major purchase, I'd say stick with what works unless you want to put them on a strict TT or climbing bike. The grass only seems greener on the other side.
My legs must be thoroughly confused...KEN2
Apr 16, 2003 1:41 PM
because I run 175s on the mtn. bike, 172.5 on road, and 170 on the fixie!
Dunno, but I went from 170 -> 175 (MTB) and it was instant pain.Eug
Apr 16, 2003 1:55 PM
I tried 175 mm cranks on my MTB because of the increased leverage - extreme uphills, logs, etc.

Within the first couple of rides, I had lots of knee pain.

After much adjustment (seat height, seat fore/aft, stem height/angle, cleats) I just gave up and went back to 170 mm. Pain never did go away 100%, but even after my first couple rides on 170 mm with only coarse adjustments, the pain was way less than before.

It did make my spinning much worse too.

P.S. 5'7" 30.5-31" inseam. 16.5" C-T MTB. nmEug
Apr 16, 2003 1:57 PM
I'd err on the short side ...Humma Hah
Apr 16, 2003 1:58 PM
I made the mistake of jumping from 170 to 175 mm while simultaneously raising my seat and attempting a tough century, and wound up with a knee injury. If you're comfortable with 172.5, why mess with it?

We discussed this here a couple of years back, and found some links with studies on the subject. Basically, there were no clear advantages to going longer, and some riders in one study surprised everyone by being more efficient with cranks traditional wisdom said were "too short".

Trackies often run 160 mm for track clearance.

I've switched between 170, 160, and 175 mm on the same bike, and the transition from 160 to 175 was striking: the long cranks felt really inefficient, which I believe was because I was using more energy bending my leg more, squishing soft tissue excessively. Going from 175 to 160, on the other hand, felt very good.
I'm tempted to go 167.5 or 165. Does 167.5 exist?Eug
Apr 16, 2003 2:11 PM
I'm riding a 54 cm C-T Trek (which is probably too big).

I'm 5'7" with a 30.5-31" inseam. Because of knee problems I'm tempted to go with a 167.5 crank, or possibly even 165.

I have not been able to find 167.5 though. Do they exist?
Don't think I've ever seen one ...Humma Hah
Apr 16, 2003 2:37 PM
... seen a lot of 165's. I had to hunt like heck for the cruiser's 1-piece 160's in a good quality BMX grade.
I have 167.5's on my fixed gear bike,TJeanloz
Apr 16, 2003 2:41 PM
I'm not sure who made them, maybe Topline? Maybe Sugino? I'm not even sure where my track bike is...
Check out Peter White's site @coonass
Apr 16, 2003 5:13 PM carries the 165.5mm crankarms......super nice guy and knowledgable...
Bon chance!
Do you see any difference with 2.5mm ???PeterRider
Apr 16, 2003 2:09 PM
Just switched from 172.5mm to 170 because I've read that it would be better for my knees. I don't see any difference.

OK, if somebody tells me 5 or 10 mm make a difference I'll believe it, but 2.5mm... I think it's a joke.

No answer to this questionKerry
Apr 16, 2003 3:35 PM
It is generally the case that longer cranks make it harder to spin, and high cadence is the best way to minimize knee problems. That said, an extra 5 mm in crank length may only take away 3-5 rpm of spin, so it is not a large effect. Every increment of crank length is about 2-3 rpm. Spinning is more physiologically efficient, all else equal.

You will find no high quality data to support any particular crank length as being better than any other. This is true whether or not you correct for leg length, femur length, etc. What little research has been done on crank length suggests that people adapt to different crank lengths and there is no optimum or formula related to body proportion. On the other hand, you will find lots of anecdotal or low quality data to support all kinds of conclusions, and more theories than you can shake a stick at. A rider's response to changes in crank length is 1) highly individual, 2) dependent on riding style and the event (TT, climbing, crits, track racing, etc.), and 3) most important, highly adaptive. This is why it is so hard to study the effect of crank length.

The short answer is: if it feels better and measures faster, do it. If it doesn't feel better but measures faster, maybe you should do it and hope to adapt. And even if it doesn't measure faster, you may adapt and get faster. Simple, eh? NOTE: measures faster means repeat timed distances on different days in different weather, not just "faster on my nightly ride" which can be masked by the effects of weather, fatigue, and the placebo effect of riding on "faster" equipment.