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Discussion Starter · #1 ·
I'm currently putting together a bike for touring and for a few Duathalons. It is a med Giant TCR Aero 1 with Centaur Groupo. My Question is what size of crank will I go with. My current ride is a 1989 Concorde with Campy that has a 170 crank. I also have a second bike, a Gardin with Shimano 105. This has a 172.5 crank, and I tend to like the feel of that. Does a riders size, weight or type of riding have any bearing on crank length, or is it all just preference. I am 5'10", 185lbs and have an inseam of 83cm (32in). Any advice would be appreciated.
 

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Preference

Some of the decision to go with a specific crank length is personal preference. There are formulas out there that suggest a starting point for a crank arm length, but these figures should be viewed as a starting point and not an "etched in stone" answer. If the 172.5's feel good to you, then go with them. I have an 83.44cm inseam and have used 172.5's on all my roadbikes...that I can remember anyway. My rain bike (frankensteined mtn bike) has 175's on it and my knees do not like riding that bike more than a few days in a row.
 

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I can't tell the difference.

Aside from having to change the seat height, it makes no difference to me. After a few minutes it just feels like riding. I have 170's on my fixie to cut down on toe overlap and 175's on my other 2 bikes. No problems with either. If I had a significantly longer leg, as some people do, I'd try one of each.
 

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Stick with what works..

I have a 34.50 cycling inseam and use 175 cranks. I was fitted for 172.5 but I insisted on 175's as I did not want to make a change. You might not be able to tell the difference between 172.5 and 175's (I could). I would stick with what works for you. I do a lot of climbing and the 175's might be better for leverage-I dunno, I just like them...they say knees don't like changes...
 

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oneputts said:
I'm currently putting together a bike for touring and for a few Duathalons. It is a med Giant TCR Aero 1 with Centaur Groupo. My Question is what size of crank will I go with. My current ride is a 1989 Concorde with Campy that has a 170 crank. I also have a second bike, a Gardin with Shimano 105. This has a 172.5 crank, and I tend to like the feel of that. Does a riders size, weight or type of riding have any bearing on crank length, or is it all just preference. I am 5'10", 185lbs and have an inseam of 83cm (32in). Any advice would be appreciated.
The 172.5's more than the 170's. The 170's are easier to spin but i "think" a bit tougher for staying opn top of a big gear or push up climbs. With the 172.5's i get more torque/leverage which i'd ratherhave verses the ability to spin easier.
 

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how much should i trust what feels right?

i have a cycling inseam of ~85cm/33.5" and my two road frames are a 57 and 58. most charts say i should use 172.5 which always felt fine on my dry weather bike.

this winter i have been riding my hill/rain bike which has 175s (triple) and it has felt great. most of my rides are short and steep - my morning loop is 8 miles with 1100 feet of climbing and max pitch of 19%- but i have done a few 40 - 60 milers which still felt pretty good. now when i hop back on my 172.5s, they feel short and constrained. especially when i am climbing out of the saddle.

i am tempted to put 175s on my dry bike but my concern is that i don't have great knees from years of skiing and i wonder if i would know if the 175s were causing a problem.
 

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I am 5'11" with a 32" inseam (short legged). I have two bikes, one with a 175, the other with 170. Both cause no problems. I find the 170 easier to spin with. I do my climbing rides with the 175, but that is because it is a triple, not because of the longer crank arms.

If you have no problems with the 172.5 why would you want to change? If it ain't broke, don't fix it!
 

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MikeBiker said:
I am 5'11" with a 32" inseam (short legged). I have two bikes, one with a 175, the other with 170. Both cause no problems. I find the 170 easier to spin with. I do my climbing rides with the 175, but that is because it is a triple, not because of the longer crank arms.

If you have no problems with the 172.5 why would you want to change? If it ain't broke, don't fix it!
sorry, i forgot to add that i am going to try a compact 50/34 crank and i need to decide if i get 172.5s or the 175s. as i said above i have grown to like the feel of the 175s, but want to make sure i am not going to set myself up for knee damage with the 175s.
 

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Discussion Starter · #10 ·
lostrancosrd said:
sorry, i forgot to add that i am going to try a compact 50/34 crank and i need to decide if i get 172.5s or the 175s. as i said above i have grown to like the feel of the 175s, but want to make sure i am not going to set myself up for knee damage with the 175s.

where are you located?? I am assuming a mountainous area....does the 175 provide more leverage for inclines?? also why the compact crank? (just curious)
Paul
 

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oneputts said:
where are you located?? I am assuming a mountainous area....does the 175 provide more leverage for inclines?? also why the compact crank? (just curious)
Paul
i live in northern california (near stanford) but i live ON TOP of a big steep hill. i also have got more into hill riding this winter on the bike with the triple. with the longer cranks, i have found myself pushing bigger gears - especialy out of the saddle - but i also like having the low gears (30-21and 30-23) to take a rest and sit back down when i need it. it does seem to me that i can climb out of the saddle longer with the long cranks. i am not sure why, but it amost seems like i can maintain better/slower cadence and not get tired as fast when i use the longer cranks (it is probably just my bad technique ;) ).

to get similar range to my triple, i thought i might change my 53/39 to a compact crank (like FSAs) with a 50/34. thus my need to decide if i can go to the 175s all the time.
 

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Several people, in the reply threads to your query, are stating their inseam and cranklength. I've read that crank length should be determined by the 'exseam'. The measure from the tip of the femur to the floor when standing straight and tall. To me, crank length relative to the 'exseam' makes more intuitive sense as the femur head is the pivot point. The inseam goes to the crotch. An important measure for saddle height ... but perhaps not functionally relative as the exseam.

I've also read, in several places, that a good guideline is to use 18% of your 'exseam' for the cranklength.

When using that formula I should be using about a 168.5 crank. I ride with 172.5 and it seems just fine - though I've never tried anything else.

Just something else to chew on regarding cranklength.
 

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I read that one some South African site I think - the guy who sells those adjustable carbon cranks. Came up with basically the same number of around 175.2mm. There might be slight variance but I think it's safe to claim someone with longer inseam would normally also have a longer exseam. In the end it's still very much about feel however and according to some the taller ones amongst us are all riding on cranks that could be 5-10mm longer than generally recommended.
 

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not your bad technique

What you feel fits the conventional wisdom that footspeed is closely related to metabolic cost. I found this in a article by Lennard Zinn in Velonews.

Here is the link
http://www.ncbi.nlm.nih.gov

and the quote

Jim Martin concluded that pedaling cadence "does not significantly contribute to metabolic cost." Instead, foot speed, which you can maintain with any length of crank, was found to be one of "the main determinants of metabolic cost during submaximal cycling." High cadences are unrealistic with super-long cranks, just as low cadences make it hard to get anywhere with super-short cranks, but you can always still attain the same foot speed with any length crank as, say, the foot speed associated with riding a 170mm crank at 90rpm.

So with the longer crank you get more leverage on the climbs and a slower cadence overall if you maintain the same foot speed.

So the choice is your's, more leverage on the climbs with longer cranks or a higher cadence and easier spin on the flats with the shorter ones.

Good luck,
JC
 

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Last year was my first year riding a road bike.....

I'm 5' 8", and my road bike has 170's. I put about 1000 miles on the bike in 4 months, while still being an avid mt biker. I purchased a Surly Cross Check over the winter. Mainly to use for some touring this year. I have 3 rides on it so far. 20 miles first ride. 25 miles this past Saturday, and 35 miles on Sunday. This morning (Tuesday) I noticed a bit of pain in my right knee. After reading this post, I went to check the crank arm length on the Surly to find out they are 175's. Could this be the cause? Are 175's definitely too long for me being only 5' 8" with a 31" inseam?
Only having ridden one bike, with one length crank arm, I don't have much to go on.
 
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