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I realise this could be thought of as cheeky/plain wrong to post this here..but I figuered the ones that would be best able to help in this situation would be hanging around this forum!!

So here goes....
Ive been training and racing for about 4-5 years now and its been a roller coaster of trying to find my optimal position (like lots of people I guess),

anyway one thing that has stayed constant in all of that time is my crank length 172.5. Now Ive decided to go over to compact cranks (no....nobody try to talk me out of that I have my reasons :cool: , namely 5000m climbing in one day race on a gruelling tour stage).

But over those years Ive heard alot about changing crank length in larger steps ie, 5-7.5mm like form a 170-175 or 177.5 but not so much about the 2.5mil difference of changing from one to another. I want to change over from 172.5 to 175's as its worth an extra 5watts (everything else being equal) and more leverage on these long steep mountainous climbs I have in mind.

Ok so its a bigger deal changing from say a 170-177.5........but

Bearing in mind that Im finally close to 'dilaing in' my position on the bike right now close to optimum :) , should I try and make a change to a 2.5mm longer cranks?? considering a 5 watt increase and slight decrease in cadence is usefull to me???


any thoughts??

cheers.
 

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Resident Curmudgeon
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I don't think you'll notice much difference. I like 175's, because I'm tall. I have 170's on my commuter bike, (too cheap to buy new cranks for it), and I can tell the difference. I have also tried 177.5 cranks. I found they were too long. They just didn't feel right to me. I felt the circle my feet / legs felt had to turn was too big.
 

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What the Hell is going on
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177.5 vs 175

I just put on a set of 177.5 cranks after riding 175's for over 20 years and I have to say that I noticed a difference. I'm 6'2" with a 36" inseam (using the LeMond method of measuring) and 230lbs. I can motor on the flats at least 1 mile an hour faster than normal. I can muscle my way up short steep climbs better and I can stay with the practice crit group much longer. I usually get dropped on the beginning of the 3rd lap but today I was able to hang on until the 5th lap (had to drop out 'cause I was in a hurry to get to the ride after work that I forgot to bring, and drink, water and I started to cramp). Anyway, I like the 177.5 so much I'm thinking of toying with the idea of 180's!!!
 

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gastarbeiter
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i've just made the switch from 170s to 172.5s. After several weeks and around 800-900 kms i can say that i haven't noticed any difference.
 

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Cannot bench own weight
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I switched from 172.5 to 175.0, and i'd almost swear the reason I had trouble with my left knee last year was because of it. Almost like my knees were flexing and stretching more than they should. I lowered the seat but I still can't get over that feeling. Seems crazy though, as 2.5 mm really doesn't look to be a big difference.

I'm 5'11", no idea on the inseam.
 

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Einstruzende said:
I switched from 172.5 to 175.0, and i'd almost swear the reason I had trouble with my left knee last year was because of it.
Same here. But then I've gone back and forth between my MTB (175) and roadie (172.5) for years without trouble.

My take is that a change in crank length is a semi-significant change in position. I've now relegated those sorts of changes to the fall/off season. Doing them during the peak/race season, when I'm trying to extract every last watt is when I get into trouble. Even seemingly insignificant changes can put that last 1.5% of stress on a joint to the point that it says "whoa, dude, too much."
 

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Old, slow, and fat.
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shawndoggy said:
Same here. But then I've gone back and forth between my MTB (175) and roadie (172.5) for years without trouble.

My take is that a change in crank length is a semi-significant change in position. I've now relegated those sorts of changes to the fall/off season. Doing them during the peak/race season, when I'm trying to extract every last watt is when I get into trouble. Even seemingly insignificant changes can put that last 1.5% of stress on a joint to the point that it says "whoa, dude, too much."
BTDT...

I was switching back and forth from my track bike with 165mm arms and the road bike with 170mm arms and the mtn bike with 172.5 arms. Yes, there's a difference.

I think my 'sweet spot' is somewhere around 167.5, but I haven't actually found a pair to ride.

M
 
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