2.5mm - Will I notice a difference?

by jasonm945   January 29, 2014  

I am 5'11" and currently run a 172.5mm crank set. So my question is would I notice a difference if I replaced it with a 175mm.

I have 175 on my MTB and don't see that as different, so would it just take a few rides to settle in?

Thanks in advance.

Jay

22 user comments

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I run 170 + 172.5 cranks on different bikes and don't really notice a difference, obviously the saddle is slight;y higher relative to the handlebars so does depend whether you are at the extremes of your bike's position. There are some schools of thought that think that a smaller crank size is more efficient. Worth a search on google. Personally I wouldn't spend the money changing the crank size. Think how small 2.5 mm are, although it makes a significant difference on circumference, i wouldn't worry about it terms of leverage as some people discuss.

posted by tommygarland [16 posts]
29th January 2014 - 23:28

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I feel a big difference between my 175mm and 180mm cranks (BMX). Not sure if this helps as its twice the difference you are talking about.

I've used 165mm and 170mm on the road and can feel the difference although its certainly not enough to throw me off my stride. 155mm felt odd.

I think that there's probably a comforatable maximum length depending on your build and leg length and anything up to this length will feel OK even if its not the most efficient. For fixed gear bikes shorter cranks help to avoid pedal stike too.

posted by Matt eaton [0 posts]
29th January 2014 - 23:38

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I'm not just changing for the size, I have knackered the thread in one of my pedal arms by not tightening the pedal in and riding 15 miles till it fell out!

I have seen an excellent deal on a SRAM force chain set but can only get it in 175mm, hence the question.

I believe I'll notice it for a ride or two and then forget about it but wanted to check if this is correct or not.

posted by jasonm945 [17 posts]
29th January 2014 - 23:45

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You'll probably not notice, I have both - that said I *think* I prefer 172.5 to 175 on my road bikes but it may be psychological. 85cm inside leg for what it's worth.

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posted by joemmo [693 posts]
30th January 2014 - 1:14

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I doubt you will notice, I have 170 on my track bike and occasionally use a 165. My road and MTB have 175, and my wife's bike has 172.5 and the only time a feel any difference is if I dont drop my seat a little on the track bike

posted by jason.timothy.jones [252 posts]
30th January 2014 - 10:51

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I knackered my 175 mm cranks on the penultimate day of a trip to Spain. So I could ride on the last day I managed to borrow some 172.5 mm ones off our host. I noticed 2 differences.

First, if I was riding hard then my quads seemed to be working in a slightly different area of the muscle so I was getting pain further up my legs than usual. Not a big deal and I'm sure you'll quickly adjust.

Second was on steep sections (>15%) I felt like I had less leverage (to be expected) and had to work harder at a lower cadence. So the opposite going the other way I guess.

Probably worth mentioning, if you do make the change, don't forger to adjust your saddle height slightly as the change in crank length will change the distance from the bottom of the pedal stroke to the saddle.

posted by pirnie [163 posts]
30th January 2014 - 10:57

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pirnie wrote:
Second was on steep sections (>15%) I felt like I had less leverage (to be expected) and had to work harder at a lower cadence. So the opposite going the other way I guess.

I went from 175 to 172.5, and I am "sure" that hills are now harder . . . could all be in the mind though . . .

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posted by manoirdelourde [26 posts]
30th January 2014 - 12:08

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You wont be able to get your knee down so much during those 100mph Crit races. Other than that...you'll probably not notice after the first minute.

arrieredupeleton

posted by arrieredupeleton [519 posts]
30th January 2014 - 12:41

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Isn't crank length supposed to be related to shin length?

Boardman CX Team '14 | Cannondale CAAD8 '12 (written off, SMIDSY) | Scott Sportster '08

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posted by Gizmo_ [642 posts]
30th January 2014 - 13:17

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Why not just get the thread in the crank arm repaired..? or ebay it (LH ones should be easy and cheap to obtain if that's the side in question).

posted by ficklewhippet [26 posts]
30th January 2014 - 13:57

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jasonm945 wrote:
I'm not just changing for the size, I have knackered the thread in one of my pedal arms by not tightening the pedal in and riding 15 miles till it fell out!

I have seen an excellent deal on a SRAM force chain set but can only get it in 175mm, hence the question.

I believe I'll notice it for a ride or two and then forget about it but wanted to check if this is correct or not.

I did that. Got it re-threaded and its been fine for 2000+ miles. If that doesn't work they can drill it out put and put a new screw in thread that gets bonded. The pedal screws in as normal

posted by dunnoh [143 posts]
30th January 2014 - 13:58

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2.5mm about the same as a pair of thick winter socks!

posted by lookmanohands [78 posts]
30th January 2014 - 14:02

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It's my RH crank arm, I have tapped it and lost the first 5mm or so of thread. My other option is to get them Helicoiled which seems silly as they are FSA Gossamer cranks so an upgrade was on the cards anyway. Devil
I do figure I don't need an excuse to upgrade but as excuses go, I've stripped my threads, is quite high on the list Smile

Jay

posted by jasonm945 [17 posts]
30th January 2014 - 14:05

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I have 172.5 on one bike and 175 on another. Can't say I ever notice a difference.

posted by MattT53 [119 posts]
30th January 2014 - 15:44

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I had 175mm cranks on one bike 172.5mm on another and I did notice a difference injury wise, but I think I had my saddle too high; so whilst on the 172.5mm cranked bike my seat height was almost ideal the same saddle height on the other (175mm cranked bike) was fractionally too high. Gradually it felt like my calf was being pulled too much; I moved the seat down 2.5mm and forward 2.5mm and the feeling went away and I can't say I noticed a difference after that.

More recently I run 172.5mm cranks on my two bikes and 170mm on the fixie and I cant say I notice a diference there either.

Howl Like a Bianchi

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posted by HLaB [52 posts]
30th January 2014 - 16:04

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Your hip joints are articulated less on shorter cranks. If you are getting on a bit you might want to think about that. They do wear out in the end.

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posted by harman_mogul [88 posts]
30th January 2014 - 16:56

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harman_mogul wrote:
Your hip joints are articulated less on shorter cranks. If you are getting on a bit you might want to think about that. They do wear out in the end.

Is 43 getting on a bit?

posted by jasonm945 [17 posts]
30th January 2014 - 16:58

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Just to add to the chorus of no answers. I switched and no, I did not notice the difference. But then I did compensate by wearing four pairs of padded shorts.

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posted by sm [329 posts]
1st February 2014 - 11:41

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You could try running one side at 172.5 and the other at 175, on the basis that most people's legs are different lengths.

posted by vbvb [166 posts]
1st February 2014 - 12:51

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I read an article recently where they tested crank lengths to see if there was a performance difference, there wasnt any. The crank is only one part of the lever along with the gears themselves, the only difference was noted at real extremes, like 200mm cranks.
You might notice for the first hour, just because its different, but after that you'll be fine.

posted by lolol [103 posts]
1st February 2014 - 16:11

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Like many others here. I have run crank lengths from 170 to 175mm and can't say I notice any difference.
You might want to adjust your saddle height slightly if you did go from 70-75 but 2.5mm is about like a thick pair of socks, as mentioned. Have to say I do adjust my saddle height between wearing approach boots, sandles or bare feet though.

posted by Giles Pargiter [36 posts]
1st February 2014 - 23:10

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Just think if you moved your saddle 2.5mm forward.It feels like a foot.I have long legs and went from 170 to 180 and when climbing can push a higher gear with ease for the same heartrate.I think it's down to length of your legs I'm 6ft4ins if I was 5ft 165mm cranks would be better.

big mick

posted by big mick [165 posts]
2nd February 2014 - 14:28

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