170 vs 175mm chainsets

What bike and bike bits should you buy?
BuckMulligan
Posts: 655
Joined: Sat Mar 12, 2011 20:18 pm

170 vs 175mm chainsets

Postby BuckMulligan » Wed Oct 10, 2012 10:29 am

I'm thinking about upgrading my groupset and in my research have started paying attention to all of the small, specific details that in the past I've completely overlooked!

The one bothering me the most though is crank length. Having just downsized frames from a 54 to a 52 cm I was astounded at how much difference those 2 cms make! On the smaller frame I'm much more comfortable, more balanced and can put a lot more power down than I ever could on the larger frame. Would I notice a similar effect exploring different crank lengths? Currently I've got 175mm cranks (came as standard) which seems odd since I'm at the smaller end of the frame size spectrum but running the largest (standard) crank arm length. When I upgrade, should I make sure I go shorter (170 or even 165), am I likely to notice the difference and how much difference does 2.5mm on a crank arm really make?!

User avatar
maddog 2
Posts: 7824
Joined: Thu Jun 03, 2004 14:47 pm

Re: 170 vs 175mm chainsets

Postby maddog 2 » Wed Oct 10, 2012 11:46 am

sounds like you need 170 (or even lower)

there are guides based on leg length, in particular femur length, which you can use. Also be prepared for some trial and error, to find a comfortable length. A shorter length encourages you to spin and use a higher cadence. Longer makes more power. I tend to run slightly shorter on the roadie than the MTB, for this reason.
Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer

User avatar
mfin
Posts: 5080
Joined: Wed Jul 11, 2007 21:46 pm

Re: 170 vs 175mm chainsets

Postby mfin » Wed Oct 10, 2012 11:59 am

Id say 170. From 175 at your size you might well notice a difference. Most average size bikes come with 172.5mm, so you're the wrong side of the 172.5

Your legs per rotation will travel 1099.5mm on 175s and 1068mm on 170s, but more importantly, your legs will come up 5mm less and down 5mm less.

You could go smaller than 170s of course, but look up as much info as you can... 170s are available in pretty much every crankset you can buy as well.
.

User avatar
fivethirtyonepm
Posts: 153
Joined: Sun May 22, 2011 14:13 pm

Re: 170 vs 175mm chainsets

Postby fivethirtyonepm » Wed Oct 10, 2012 14:18 pm

if you're less than 5'7" then 170mm is worth a look, if you are 5'7" through to 6'2" then 172.5mm should be fine... if you are stupidly tall or have powerhouse legs, then 175mm works well.

if you are tiny, then 165mm cranks are the order of the day (as featured on my 5'0" better half's bike)

User avatar
amaferanga
Posts: 6595
Joined: Sun Apr 18, 2004 16:44 pm

Re: 170 vs 175mm chainsets

Postby amaferanga » Wed Oct 10, 2012 14:48 pm

I'm 5'8" and have ridden 170mm, 172.5mm and 175mm cranks. I didn't notice any difference, nor did it have any noticeable effect on my power output.
More problems but still living....

User avatar
drlodge
Posts: 3646
Joined: Thu Jul 26, 2012 08:29 am

Re: 170 vs 175mm chainsets

Postby drlodge » Wed Oct 10, 2012 15:55 pm

I'm 5'9" and just moved from 170 to 172.5mm chainset. I would say there is little difference, certainly I don't feel any different generally or after a long ride. May be I feel I can put a little more power down going up hill, but that could be placebo affect. If I were in your position, I'd go with 172.5mm as it just gives you a little more leverage than 170.
WyndyMilla Massive Attack | Rourke 953 | Condor Italia 531 Pro | Boardman CX Pro | DT Swiss RR440 Tubeless Wheels
Find me on Strava

User avatar
markos1963
Posts: 3729
Joined: Mon Jan 21, 2008 20:42 pm

Re: 170 vs 175mm chainsets

Postby markos1963 » Wed Oct 10, 2012 17:10 pm

fivethirtyonepm wrote:if you're less than 5'7" then 170mm is worth a look, if you are 5'7" through to 6'2" then 172.5mm should be fine... if you are stupidly tall or have powerhouse legs, then 175mm works well.

if you are tiny, then 165mm cranks are the order of the day (as featured on my 5'0" better half's bike)


Power has nothing to do with the length of crank, the longer the crank the less force is needed to turn it. The riders femur length is the deciding factor.

For the OP, a proper bike fit might be beneficial before deciding on what to buy.

BuckMulligan
Posts: 655
Joined: Sat Mar 12, 2011 20:18 pm

Re: 170 vs 175mm chainsets

Postby BuckMulligan » Wed Oct 10, 2012 18:32 pm

Thanks for the replies! Having done a bit of research online it does seem to be one of those topics that there's a wealth of opinions on. I'm about 5'7" (not sure about inside leg measurement, but I don't think I'm too abnormally proportioned!) so I suppose I might notice a difference if I shift down in size. I'm not expecting a massive difference, but I do tend to favour longer rides (80-120 miles) so I'm hoping any marginal gains will have an noticeable effect over those sort of distances.

I certainly would like a professional bike fitting session, because I'm constantly fiddling with my saddle position. Maybe I should try measuring my inside leg and femurs and see what the internet says I should be doing! At least I've got my current 175 to directly compare it to when I do upgrade.

cougie
Posts: 19028
Joined: Wed Apr 21, 2004 22:34 pm

Re: 170 vs 175mm chainsets

Postby cougie » Wed Oct 10, 2012 22:30 pm

I've used all sorts of lengths. Can't say I've noticed any difference.

User avatar
Thelonegroover
Posts: 1030
Joined: Thu Aug 13, 2009 11:04 am

Re: 170 vs 175mm chainsets

Postby Thelonegroover » Thu Oct 11, 2012 06:51 am

markos1963 wrote:
fivethirtyonepm wrote:if you're less than 5'7" then 170mm is worth a look, if you are 5'7" through to 6'2" then 172.5mm should be fine... if you are stupidly tall or have powerhouse legs, then 175mm works well.

if you are tiny, then 165mm cranks are the order of the day (as featured on my 5'0" better half's bike)


Power has nothing to do with the length of crank, the longer the crank the less force is needed to turn it. The riders femur length is the deciding factor.

I think you are correct in saying power it’s self has nothing to do with crank length, but the longer the crank, the smaller the force on the peddle for the same forward motion. But as there is larger diameter and greater leg movement the total work output from the rider may not change much.

For the OP, a proper bike fit might be beneficial before deciding on what to buy.
Genesis Core 30 green - the naughties
Giant Trance X2 - the teens
Genesis High Latitude 2x10 - the future (Until 650b came along!)

User avatar
mcp73
Posts: 92
Joined: Tue Jun 07, 2011 12:26 pm

Re: 170 vs 175mm chainsets

Postby mcp73 » Thu Oct 11, 2012 08:01 am

amaferanga wrote:I'm 5'8" and have ridden 170mm, 172.5mm and 175mm cranks. I didn't notice any difference, nor did it have any noticeable effect on my power output.



I'm 5'9" and can say exactly the same thing. I've got 170, 172.5 and 175 cranks and I don't notice any discernible difference.

User avatar
jonomc4
Posts: 848
Joined: Wed Feb 29, 2012 15:51 pm

Re: 170 vs 175mm chainsets

Postby jonomc4 » Thu Oct 11, 2012 09:45 am

I'm 5'11 with 32 inch inside leg - I went from 175 to 172.5 and I noticed the difference quite a bite - mostly on hills.

User avatar
amaferanga
Posts: 6595
Joined: Sun Apr 18, 2004 16:44 pm

Re: 170 vs 175mm chainsets

Postby amaferanga » Thu Oct 11, 2012 10:04 am

jonomc4 wrote:I'm 5'11 with 32 inch inside leg - I went from 175 to 172.5 and I noticed the difference quite a bite - mostly on hills.


What did you notice exactly? A quantifiable difference in speed up the hill due to an increase or a reduction in power output? Or a feeling that something's different, but that it actually made no difference to your riding? Did you adjust saddle height when you changed crank length?
More problems but still living....

User avatar
Thelonegroover
Posts: 1030
Joined: Thu Aug 13, 2009 11:04 am

Re: 170 vs 175mm chainsets

Postby Thelonegroover » Fri Oct 12, 2012 06:37 am

I've never changed my chain set or crank length, but I can well appreciate, when going up a fill, it may well feel easier with longer cranks. Laws of physics/mechanics prove this. However, the same laws also show it will be slower.
Genesis Core 30 green - the naughties
Giant Trance X2 - the teens
Genesis High Latitude 2x10 - the future (Until 650b came along!)

User avatar
drlodge
Posts: 3646
Joined: Thu Jul 26, 2012 08:29 am

Re: 170 vs 175mm chainsets

Postby drlodge » Fri Oct 12, 2012 09:31 am

Having a longer crank arm length is a bit like using a lower gear. You have a a greater mechanical advantage, so need less force through the leg, but the leg has to move further.

I like to think of extremes to help understand the effect...think what would happen if your crank was 1" long, you'd struggle to move it since the force required would be much much larger - you'd end up having to use lower gears and a higher cadence.
WyndyMilla Massive Attack | Rourke 953 | Condor Italia 531 Pro | Boardman CX Pro | DT Swiss RR440 Tubeless Wheels
Find me on Strava

User avatar
jonomc4
Posts: 848
Joined: Wed Feb 29, 2012 15:51 pm

Re: 170 vs 175mm chainsets

Postby jonomc4 » Fri Oct 12, 2012 11:02 am

amaferanga wrote:
jonomc4 wrote:I'm 5'11 with 32 inch inside leg - I went from 175 to 172.5 and I noticed the difference quite a bite - mostly on hills.


What did you notice exactly? A quantifiable difference in speed up the hill due to an increase or a reduction in power output? Or a feeling that something's different, but that it actually made no difference to your riding? Did you adjust saddle height when you changed crank length?


Yes I did change my saddle height - for me the difference I felt was a more even pedal stroke - I have no idea on power I would imagine it was the same (or as near as damn it) - it was just more comfortable to spin the pedals.


Return to “Road Buying Advice”

Who is online

Users browsing this forum: ayjaycee, Cliveyp, COYS, Dork Knight, Google [Bot], nickmac and 5 guests