Crank sizes 170mm vs 172.5mm

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Crank sizes 170mm vs 172.5mm

Postby dougalh » Wed Nov 28, 2012 2:11 pm

I'm currently looking at upgrading my drive train from 105 as my current setup is extremely worn, possibilities are just replace it and get a new 105 or ultegra, maybe even Di2.
While looking around the different options most come in either 50x34 compact or 53x39 standard I understand the differences there, compact you can get a higher cadence but not as much speed but then theres 170mm or 172.5mm

I presume this is the length of the crank.

What difference does it make and what do people have on their bikes? What does an extra 2.5cm in crank length do?
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Re: Crank sizes 170mm vs 172.5mm

Postby barefoot » Wed Nov 28, 2012 2:23 pm

dougalh wrote:What difference does it make and what do people have on their bikes? What does an extra 2.5cm in crank length do?


An extra 2.5 cm would make a heck of a difference :lol: , but a 2.5 mm difference is not trivial.

Remember that's 2.5mm on the radius your pedal moves around, which is 5mm on diameter. If you were to increase the length of your cranks by 2.5mm, you'd need to move your saddle down 2.5mm to reach the bottom of your pedal stroke - but then the top of your pedal stroke would be 2.5mm higher, which is now 5mm closer to your bum. That means your knee bends more.

Conversely, you get extra leverage when you pedal, because you're using longer levers.

Also, your downstroke is 2.5mm further forward with the longer cranks, so you might need to nudge your saddle forward by a fraction to be in the same position "on top of" the pedals.

2.5mm (or 5mm on diameter) isn't a massive amount, but people definitely adjust their bikes in finer increments than that.

It's all a matter of what's comfortable for you, which is largely determined by how long your legs are. I find 170mm cranks to be massively more comfortable to ride than 175s (have never ridden 172.5), and would consider going even shorter if they were readily available, but I have short legs.

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Re: Crank sizes 170mm vs 172.5mm

Postby Nobody » Wed Nov 28, 2012 2:29 pm

dougalh wrote:What difference does it make and what do people have on their bikes? What does an extra 2.5cm in crank length do?
The 2.5mm does little but suit a taller rider. If in doubt, get the 170s.

http://www.myra-simon.com/bike/cranks.html

http://www.pezcyclingnews.com/?pg=fullstory&id=8845

http://www.machinehead-software.co.uk/b ... lator.html
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Wed Nov 28, 2012 3:43 pm

Unless you are short with bad knees and don't like carbon :P ↑↑ get the longer cranks, they are probably faster;

Stolen from another cycling website, FWIW:




Jacques Anquetil 175mm
Lance Armstrong 175mm
Magnus Backstedt 177.5mm
Chris Boardman 170mm
Santiago Botero 172.5mm
Angel Casero 175mm
Mario Cipollini 172.5mm
Fausto Coppi 171mm
Malcolm Elliott 172.5mm
Tyler Hamilton 172.5mm
Bernard Hinault 172.5mm
Miguel Indurian 180mm (190mm for second Hour record!)
Laurent Jalabert 172.5mm
Greg Lemond 175mm
Brad McGee 175mm
Robbie McEwen 175mm
Nobody ACF 165mm
Eddy Merckx 175mm
David Millar 175mm (180mm in TT)
Francesco Moser 175mm
Marty Northstein 167.5mm in Keirin (170mm in kilo)
Graham Obree 175mm
Marco Pantani 170mm (180mm in mountains)
David Rebellin 172.5mm
Roger Riviere 175mm
Jean Robic 170mm
Tony Rominger 172.5mm (175mm for Hour record)
Oscar Sevilla 175mm
Jan Ullrich 177.5mm
Rik Verbrugghe 175mm
Erik Zabel 172.5mm
Alex Zulle 175mm (180mm in mountains)

Edit just thought I'd throw this in 177.5 :D :D



You can't have too much Fab on the forums :wink:
Last edited by warthog1 on Wed Nov 28, 2012 3:55 pm, edited 3 times in total.
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Re: Crank sizes 170mm vs 172.5mm

Postby TDC » Wed Nov 28, 2012 3:45 pm

I have both sizes on different bikes that I ride with some regularity. I have the saddle to pedal length, and tip nose to BB the same on both (also using the same saddle type on both bikes). Personally I cant tell the difference after the first few km. It feels slightly different at first, but after that I am just riding the bike.
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Re: Crank sizes 170mm vs 172.5mm

Postby rustychisel » Wed Nov 28, 2012 4:28 pm

Because you can use such things to prove or disprove any contention under the sun, let's have another look at that list...


warthog1 wrote:

Jacques Anquetil doper
Lance Armstrong doper
Magnus Backstedt 177.5mm
Chris Boardman 170mm
Santiago Botero doper
Angel Casero 175mm
Mario Cipollini doper (?)
Fausto Coppi 171mm
Malcolm Elliott 172.5mm
Tyler Hamilton doper
Bernard Hinault poss doper
Miguel Indurian doper (?)
Laurent Jalabert poss doper
Greg Lemond 175mm
Brad McGee 175mm
Robbie McEwen 175mm
Nobody ACF 165mm
Eddy Merckx doper
David Millar doper
Francesco Moser doper
Marty Northstein 167.5mm in Keirin (170mm in kilo)
Graham Obree 175mm
Marco Pantani doper
David Rebellin doper
Roger Riviere 175mm
Jean Robic prob doper
Tony Rominger doper
Oscar Sevilla 175mm
Jan Ullrich doper
Rik Verbrugghe 175mm
Erik Zabel doper
Alex Zulle doper (?)

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Re: Crank sizes 170mm vs 172.5mm

Postby mikesbytes » Wed Nov 28, 2012 4:43 pm

There is a small difference in foot velocity between 170 and 172.5mm. It is not that much and most could not tell the difference.

Gearing wise its roughly the difference of about 1/2 a tooth on the big ring
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Re: Crank sizes 170mm vs 172.5mm

Postby Nobody » Wed Nov 28, 2012 6:18 pm

warthog1 wrote:Unless you are short with bad knees and don't like carbon :P ↑↑
Can't escape genetics I suppose, but I'd probably love carbon if someone else was paying for it and replaced it regularly for me. Hmm, sound like a pro doesn't it? :P

warthog1 wrote:...get the longer cranks, they are probably faster;
Probably? I'm sure you've got lots of scientific evidence to back it up, right :?: How much faster did it immediately make you?
Here is an actual study which shows it doesn't make much difference.
http://www.plan2peak.com/files/32_artic ... hnique.pdf

Also you should take that loser "Nobody ACF" off the pro/doper list as he's wrecking your "stats". :lol:

warthog1 wrote:Edit just thought I'd throw this in 177.5 :D :D
Because it's now your size or Fab's, or both? It's amazing what skewed logic hero worship can produce. :P

warthog1 wrote:You can't have too much Fab on the forums :wink:
You can if he also turns out to be a doper. These days I'm very suspicious of the super-freaks (Bertie, LA etc).
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Re: Crank sizes 170mm vs 172.5mm

Postby usernameforme » Wed Nov 28, 2012 7:20 pm

I read somewhere that you should be optimising your cranks for power output (best fit) and not for gearing (longer cranks give you more leverage)

FWIW: I've tried 170, 172.5 and 175, I prefer 170, the main difference I notice is that spinning at 80 with 175mm cranks feels like spinning at 120 with 170mm cranks
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Wed Nov 28, 2012 9:22 pm

rustychisel wrote:Because you can use such things to prove or disprove any contention under the sun, let's have another look at that list...


warthog1 wrote:

Jacques Anquetil doper
Lance Armstrong doper
Magnus Backstedt 177.5mm
Chris Boardman 170mm
Santiago Botero doper
Angel Casero 175mm
Mario Cipollini doper (?)
Fausto Coppi 171mm
Malcolm Elliott 172.5mm
Tyler Hamilton doper
Bernard Hinault poss doper
Miguel Indurian doper (?)
Laurent Jalabert poss doper
Greg Lemond 175mm
Brad McGee 175mm
Robbie McEwen 175mm
Nobody ACF 165mm roper doper
Eddy Merckx doper
David Millar doper
Francesco Moser doper
Marty Northstein 167.5mm in Keirin (170mm in kilo)
Graham Obree 175mm
Marco Pantani doper
David Rebellin doper
Roger Riviere 175mm
Jean Robic prob doper
Tony Rominger doper
Oscar Sevilla 175mm
Jan Ullrich doper
Rik Verbrugghe 175mm
Erik Zabel doper
Alex Zulle doper (?)


You could say that they investigated all methods of gaining speed, including crank length and PEDs :idea:
Last edited by warthog1 on Wed Nov 28, 2012 9:44 pm, edited 1 time in total.
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Wed Nov 28, 2012 9:30 pm

Nobody wrote:Because it's now your size or Fab's, or both? It's amazing what skewed logic hero worship can produce. :P

warthog1 wrote:You can't have too much Fab on the forums :wink:
You can if he also turns out to be a doper. These days I'm very suspicious of the super-freaks (Bertie, LA etc).

He's no doper and I'll happily continue to hero worship him until he is :D .

He's given us some of the best moments in cycle racing I reckon. Cop that you wheel sucking sprinters :twisted:


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Last edited by warthog1 on Wed Nov 28, 2012 9:48 pm, edited 2 times in total.
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Re: Crank sizes 170mm vs 172.5mm

Postby Alien27 » Wed Nov 28, 2012 9:38 pm

I know bugger all about this but wouldn't longer cranks be for longer legs and shorter ones for shorter legs?
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Re: Crank sizes 170mm vs 172.5mm

Postby Byke » Wed Nov 28, 2012 9:48 pm

I went from 170 to 172.5 cranks 18 months ago. I'd be very surprised if I could consistently guess what length I was riding in a blind test.

The medium Giant OCR 1 I'd had for ten years had 170s. The medium Giant Defy Advanced 1 I bought eighteen months ago has 172.5s. I liked the new bike so much more than my old one that I bought a second-hand carbon TCR frame and built it up with 105 as my 'round town bike. Figured I may as well match the crank length of my 'good' bike, so got 172.5s.

But suspect if it had 170s I wouldn't be conscious of the difference. My MTB dually has 175s, and I'm not conscious of the length difference there either, but obviously the rest of the setup has a lot of more extreme differences so that's not that surprising.

Background info: I ride nearly every day - don't own a car - but my bike 'sizing' is simply a case of continually fiddling with the seat, bars and even cleat position for the first few weeks of ownership, and settling with what feels comfortable out on the road. I've never had a proper bike fit.
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Re: Crank sizes 170mm vs 172.5mm

Postby Nobody » Wed Nov 28, 2012 10:04 pm

Warthog1 wrote:
Nobody wrote:You can if he also turns out to be a doper. These days I'm very suspicious of the super-freaks (Bertie, LA etc).

Oh, so not only does he have a motor in his bike he's on the drugs also :roll: . He's no doper and I'll happily continue to hero worship him until he is :D .

I didn't specifically say he had a motor or he was a doper. I'm just not too trusting of pros anymore. Too much, too many...

LA was considered clean until it caught up with him over the last few years. Some were adamant that he was no doper either.

Bertie is still saying he was duped and was clean. Maybe he was, but they thought they had enough evidence to convict him.
http://road.cc/content/news/71156-alber ... ach-doping
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Wed Nov 28, 2012 10:17 pm

I took that bit off now I'll have to put it back in again. Making about 4 edits:roll:
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Wed Nov 28, 2012 10:19 pm

I know what you are saying, I hope he's never found to be a doper. Then I'll have to use short cranks. My career as a never was will truly be over.

At least my wife will be happy.
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Re: Crank sizes 170mm vs 172.5mm

Postby Nobody » Wed Nov 28, 2012 10:35 pm

warthog1 wrote:Then I'll have to use short cranks.
Don't forget the steel frameset, Brooks, mudguards and the minimal saddle to bar drop. :lol:

warthog1 wrote:At least my wife will be happy.
My wife is happy that I'm out of the house. So am I. :)
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Re: Crank sizes 170mm vs 172.5mm

Postby toolonglegs » Wed Nov 28, 2012 10:42 pm

180's on mtb, tt and road bike.
175's on CX and winter bike ( plus road bike if I need compacts ).
Hardly notice a difference... just like I hardly notice switching road pedals to mtb pedals on my cx bike when I want to race even though the cleats are all the way back on the mtb shoes.
The only thing I do notice is if I don't adjust my saddle height going from short to long... the extra 5 mm will hammer my heel after a few weeks.

I have long legs :P , don't spin, don't have knee problems ( except when I have to jump too far while running in CX races )... but do notice the reduced ground clearance on the mtb sometimes.
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Wed Nov 28, 2012 11:14 pm

Nobody wrote:My wife is happy that I'm out of the house. So am I. :)



:lol: thanks Nobody.

The steel frame and brooks saddle are becoming more inevitable the older I get. Im hanging on though :)
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Re: Crank sizes 170mm vs 172.5mm

Postby toolonglegs » Wed Nov 28, 2012 11:20 pm

warthog1 wrote:
Nobody wrote:Because it's now your size or Fab's, or both? It's amazing what skewed logic hero worship can produce. :P

warthog1 wrote:You can't have too much Fab on the forums :wink:
You can if he also turns out to be a doper. These days I'm very suspicious of the super-freaks (Bertie, LA etc).

He's no doper and I'll happily continue to hero worship him until he is :D .

He's given us some of the best moments in cycle racing I reckon. Cop that you wheel sucking sprinters :twisted:


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Great moments... but got to admit I cringed a bit when I heard Liggets voice commentating :| .
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Thu Nov 29, 2012 3:53 am

Yes the commentary on the second one, where I couldn't understand a word they were saying, was better.
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Re: Crank sizes 170mm vs 172.5mm

Postby Secret Squirrel » Thu Nov 29, 2012 10:02 am

warthog1 wrote:
rustychisel wrote:Because you can use such things to prove or disprove any contention under the sun, let's have another look at that list...


warthog1 wrote:

Jacques Anquetil doper
Lance Armstrong doper
Magnus Backstedt 177.5mm
Chris Boardman 170mm
Santiago Botero doper
Angel Casero 175mm
Mario Cipollini doper (?)
Fausto Coppi 171mm
Malcolm Elliott 172.5mm
Tyler Hamilton doper
Bernard Hinault poss doper
Miguel Indurian doper (?)
Laurent Jalabert poss doper
Greg Lemond 175mm
Brad McGee 175mm
Robbie McEwen 175mm
Nobody ACF 165mm roper doper
Eddy Merckx doper
David Millar doper
Francesco Moser doper
Marty Northstein 167.5mm in Keirin (170mm in kilo)
Graham Obree 175mm
Marco Pantani doper
David Rebellin doper
Roger Riviere 175mm
Jean Robic prob doper
Tony Rominger doper
Oscar Sevilla 175mm
Jan Ullrich doper
Rik Verbrugghe 175mm
Erik Zabel doper
Alex Zulle doper (?)


You could say that they investigated all methods of gaining speed, including crank length and PEDs :idea:


They sure did investigate all methods og gaining speed. 20 out of 32 are or suspected of taking drugs. Ha :lol:
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Thu Nov 29, 2012 1:01 pm

Secret Squirrel wrote:
They sure did investigate all methods og gaining speed. 20 out of 32 are or suspected of taking drugs. Ha :lol:


They are successful riders from an era where PED's were rife. In order to be successful unfortunately it appears that PED's were necessary :x But hey it looks like long cranks were too :P

Didn't post it with any intent to address drug use in cycling and I dont really see how it applies to crank length :? But then I'm hardly one to complain about going off on a tangent :oops: :lol:

Didn't know the Badger was implicated in any PED use :cry:

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Re: Crank sizes 170mm vs 172.5mm

Postby barefoot » Thu Nov 29, 2012 1:58 pm

warthog1 wrote:They are successful riders from an era where PED's were rife. In order to be successful unfortunately it appears that PED's were necessary :x But hey it looks like long cranks were too :P


Let's see a comparison of crank length against leg length on the pro circuit.

Most of those guys are built like stick insects. I'd be pretty sure most of them would have longer legs than me, even the diminutive climbers. It's quite possible that having long legs is a strong cycling performance attribute (and that's the main reason why I never turned pro... cough*cough).

It stands to reason that people with longer legs would ride longer cranks. If I had longer legs, I'd probably ride longer cranks too. But I don't, so I don't.

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Re: Crank sizes 170mm vs 172.5mm

Postby rustychisel » Thu Nov 29, 2012 2:50 pm

drugs and cyclists, who'd have ever made a connection? Yeah, sorry, my diversion, but I was merely seeking to illustrate that the information under review was proof of nothing at all, in isolation.

Obviously, generally, and taller cyclist uses longer cranks.
Based on that, a taller cyclist is more likely to win.
Yet, no, other factors are in play. Actually, crank length and comfort of an individual cyclist measured against power output /kg is more likely to be a function of femur/tibia length, which is a major speed determinant in the animal world (think wombat versus gazelle versus ostrich).


PS: my PED list was not exhaustive, just off the top of the head. As to Hinault, maybe, most likely... what about Robbie McEwen? I dunno.
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