Mountain Bike Reviews Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
917 Posts
Discussion Starter #1
I posted this over in the single speed forum but not much feedback so I thought maybe it might work better here:

I currently ride 175mm length cranks on my single speed 29er and 172.5mm om my road bike with a 87.9 cm or 35" cycling inseam. I do like to spin. Is there any real advantage for more power for climbs going to 180mm cranks? I really struggle or just can't make some climbs but my gearing is perfect for the flat and going down.

Let the rock throwing begin!
 

·
Registered
Joined
·
54 Posts
Well, as far as gain ratios are concerned, changing crank length or changing gearing gives you the same results. There is nothing you can do to gearing on a singlespeed to make it easier uphill without making it slower on the flats. You would need magic for that. Or maybe I'm totally missing something here?
 

·
Bike to have fun.
Joined
·
153 Posts
wes m. said:
There is nothing you can do to gearing on a singlespeed to make it easier uphill without making it slower on the flats. You would need magic for that. Or maybe I'm totally missing something here?
Put some of that on your chainring or rear cog, not both!
<img src= "https://memphis-bbq.com/catalog/images/magic_dust.jpg" >
 

·
Jacob 34:19
Joined
·
508 Posts
For a given gear ratio and wheel size, a longer crank will give you more leverage (longer lever, right). However, that will come at a theoretical cost of making it more difficult to spin and more pedal strikes.

That said, I run 180's with a shorter (34.25") inseam on both my single speed and geared MTB's. They just feel "right" to me. Some would say you should be on even longer cranks.

In the end, lighter wheels made a bigger difference in climbing than longer crank arms.
 

·
Always Learning
Joined
·
9,607 Posts
Juanmoretime said:
I posted this over in the single speed forum but not much feedback so I thought maybe it might work better here:

I currently ride 175mm length cranks on my single speed 29er and 172.5mm om my road bike with a 87.9 cm or 35" cycling inseam. I do like to spin. Is there any real advantage for more power for climbs going to 180mm cranks? I really struggle or just can't make some climbs but my gearing is perfect for the flat and going down.

Let the rock throwing begin!
No need for any rock throwing. With a 35" inseam, you might indeed benefit from a little extra leverage of a 180mm crank arm. Shimano, Middleburn, Mr. Whirly, TA, Truvativ, etc... all have gotcha covered. Or comb eBay for 180mm arms from the older Race Face Turbines and Next LP if external BB's are not your thing.

BB
 

·
808+909 = Party Good Time
Joined
·
2,072 Posts
Juanmoretime said:
I posted this over in the single speed forum but not much feedback so I thought maybe it might work better here:

I currently ride 175mm length cranks on my single speed 29er and 172.5mm om my road bike with a 87.9 cm or 35" cycling inseam. I do like to spin. Is there any real advantage for more power for climbs going to 180mm cranks? I really struggle or just can't make some climbs but my gearing is perfect for the flat and going down.

Let the rock throwing begin!
1. I'm confused, you said you 'like to spin' yet you are geared to be ok on flats and downhills... sounds like you don't like to spin

2. An extra 5mm in crank arm will never make up for an extra 5 weeks of muscle building
 

·
Frt Range, CO
Joined
·
2,576 Posts
Crank length choice is very particular to the individual. Inseam length is a very rough indicator, things like ratio of upper/lower leg ratio/ ratio of fast/twitch/slow twitch muscles, age (longer cranks as you age) all factor in.

Since it's too hard to figure all this out on paper, best thing to do is try 'em and see how it goes. Don't fall for the idea that proper crank length is like your shirt size, all you need is a tape measure to fit it right....

Back in the day story about crank length:
When I was younger in my roadie USCF days (late 70s), they tried to get me to use 172.5mm on the road, I died every time. Don't know why, don't really care. I always like shorter cranks, used 170mm on the track too, but I wasn't a sprinter. Now that I'm almost 48 years old, 175mm feel good on the road or trail. If I was a real roadie again, I'd start with 172.5mm and try 175mm on the road. I still run my 175mm 85-100 rpm, I'm a spinner.
 

·
Harmonius Wrench
Joined
·
8,254 Posts
pursuiter said:
Crank length choice is very particular to the individual. Inseam length is a very rough indicator, things like ratio of upper/lower leg ratio/ ratio of fast/twitch/slow twitch muscles, age (longer cranks as you age) all factor in.

Since it's too hard to figure all this out on paper, best thing to do is try 'em and see how it goes. Don't fall for the idea that proper crank length is like your shirt size, all you need is a tape measure to fit it right....

Back in the day story about crank length:
When I was younger in my roadie USCF days (late 70s), they tried to get me to use 172.5mm on the road, I died every time. Don't know why, don't really care. I always like shorter cranks, used 170mm on the track too, but I wasn't a sprinter. Now that I'm almost 48 years old, 175mm feel good on the road or trail. If I was a real roadie again, I'd start with 172.5mm and try 175mm on the road. I still run my 175mm 85-100 rpm, I'm a spinner.
I'd tend to be in agreement with this opinion.

I will say that at almost 48 years young I have "discovered" 170mm cranks for my 29"er single speeds and I do not think I'll be going back. For the record, I ran 34 X 20 for most of the summer and fall. I have increased that to 34 X 18 and will try to stick that out for '09. Hopefully I'll get strong enough to drop that one more tooth to 34 X 17 by the end of the year. All with 170mm cranks.
 

·
Registered
Joined
·
117 Posts
pursuiter said:
Crank length choice is very particular to the individual. Inseam length is a very rough indicator, things like ratio of upper/lower leg ratio/ ratio of fast/twitch/slow twitch muscles, age (longer cranks as you age) all factor in.
Where are these sources? Any links for folks on the forum to use, as a resource or guide?
 

·
Frt Range, CO
Joined
·
2,576 Posts
ShoMyOFace said:
Where are these sources? Any links for folks on the forum to use, as a resource or guide?
I learned this from Eddy B and Tim Murphy when I was at the Olympic Training Center in Co Springs. Never seen it in a book or properly documented anywhere. Most good roadies understand this. Here on MTBR, loudest person wins, that's why the tape measure method dominates here....

If you think about what I've written, it make sense. If runners went with the tape measure, stride length would be set by leg length or maybe shoe size, we all know it isn't the case. Application is important, good climbers always seem to have longer cranks relative to dimension, good sprinters always have shorter cranks relative to dimension.
 

·
Out spokin'
In cog? Neato!
Joined
·
11,538 Posts
Personally I read what you wrote and I agree. I'm an advocate of long cranks but only to the degree that the individual rider likes them. A rider might have a 37" inseam but prefer 165mm cranks -- so be it. Riding bikes should come down to what works best for the individual, and "what works best" is a subjective and personal thing.

That said, there's a lot of assumptions and misinformation out there about crank length and I always hate to see anyone make a decision based on someone else's uninformed, untested conjecture.

--Sparty

(Late edit: In case it sounded like it, my last sentence was not aimed at you or anybody else in particular -- I was speaking in general terms based on the comments I've read on multiple forums over the years.)


pursuiter said:
I learned this from Eddy B and Tim Murphy when I was at the Olympic Training Center in Co Springs. Never seen it in a book or properly documented anywhere. Most good roadies understand this. Here on MTBR, loudest person wins, that's why the tape measure method dominates here....

If you think about what I've written, it make sense. If runners went with the tape measure, stride length would be set by leg length or maybe shoe size, we all know it isn't the case. Application is important, good climbers always seem to have longer cranks relative to dimension, good sprinters always have shorter cranks relative to dimension.
 
1 - 12 of 12 Posts
Top