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180mm cranks on a trail bike

buildyourown

Turbo Monkey
Feb 9, 2004
4,837
0
South Seattle
I'm building up a 140mm trail bike with a 13.5" BB
I'm tempted to run 180mm cranks. I've had them before on a hardtail years ago, and thought the felt great. Love the torque you get.
I'm planning on riding this bike hard. Am I asking for constant pedal strikes? I run 170mm on my DH bike w/o issue.

It also makes the math with the gearing work out really well. A single 30t front ring and 180mm arms should yeild a pretty decent low gear.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
You should know my thoughts on this already but I will list them again

If the crank length is right for your legs then run it, trail bike would standard out at 175, your adding five mm to that. If you can see a noticeable difference in pedal strikes with that small of a change something else is seriously wrong.

In all honesty 5mm really is not enough to give you any torque advantage either, not anything that should be a discernible difference.

In short, no your not asking for pedal strikes.
 

JRogers

talks too much
Mar 19, 2002
3,791
1
Claremont, CA
Agreed with Mike; it's not much of a difference.

I think too much is made of crank length given the small variances in length. 5mm will probably not make a difference between having a ton of pedal strikes and being fine.
 

Wumpus

makes avatars better
Dec 25, 2003
8,164
154
Six Shooter Junction
That is only 2.5mm per arm. <--- NO coffee=idiot. Yeah, yeah, it is five.

I run Profile 190s on the SS and have had them on the FS before. Didn't really have any issues.
 
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Jim Mac

MAKE ENDURO GREAT AGAIN
May 21, 2004
6,364
281
the middle east of NY
If you run flat pedals on your bike, you can always go to a thin version if said pedal strikes appear. I run 170 mm's on my trail bike (for uniformity/swappage needs with DH) and have gotten pedal strikes, but that's due mostly to sloppiness over moar east coast rox....
 

skunkty14

Monkey
May 29, 2007
175
0
Unless you have super long legs 180s on a geared bike are only going to make keeping a higher cadence difficult (wonder why most road bikes come with shorter cranks than MTBs?). Those who say the extra 5mm on each arm isn't noticeable in terms of strikes is either a far superior rider than most or errs on the side of never pedaling when anything is close to their feet IMO. My 180s on my SS see a lot more strikes than 175s on my geared bikes. Frames are identical as are tires and pedals between both setups so that 5mm does make a difference (TWSS). A lower stack pedal isn't going to make much difference, especially if it's a flat since the increased surface area & spindle length is going to hinder you if you're not dead upright.

180s on a SS however are awesome for climbing IMO. Spinning not so much.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
Unless you have super long legs 180s on a geared bike are only going to make keeping a higher cadence difficult (wonder why most road bikes come with shorter cranks than MTBs?). Those who say the extra 5mm on each arm isn't noticeable in terms of strikes is either a far superior rider than most or errs on the side of never pedaling when anything is close to their feet IMO. My 180s on my SS see a lot more strikes than 175s on my geared bikes. Frames are identical as are tires and pedals between both setups so that 5mm does make a difference (TWSS). A lower stack pedal isn't going to make much difference, especially if it's a flat since the increased surface area & spindle length is going to hinder you if you're not dead upright.

180s on a SS however are awesome for climbing IMO. Spinning not so much.
Ummmmm... Standard length for road AND Mtn is 175...... Think before adding, in the world of road cycling those who have understood teh true meaning of crank length will fit the crank length to the legs... PERIOD and no other information is used to determin the length.

I challenge you if you truly believe you can notice more pedal strikes with just 5mm difference..... let me put a set of cranks on your bike, you tell me how long they are by counting your pedal strikes.... I have a hundred dollars that says you will be wrong.....
 

Wumpus

makes avatars better
Dec 25, 2003
8,164
154
Six Shooter Junction
Not sure if serious....
or just measuring wrong....
I'm an idiot. No posting before my morning coffee anymore.


Ummmmm... Standard length for road AND Mtn is 175...... Think before adding, in the world of road cycling those who have understood teh true meaning of crank length will fit the crank length to the legs... PERIOD and no other information is used to determin the length.
The only problem is that bottom bracket height is pretty standard. Most folks will never need the cornering clearance of a road bike, but it wouldn't work for everyone.
 

skunkty14

Monkey
May 29, 2007
175
0
Ummmmm... Standard length for road AND Mtn is 175...... Think before adding, in the world of road cycling those who have understood teh true meaning of crank length will fit the crank length to the legs... PERIOD and no other information is used to determin the length.
Umm most off shelf road bikes are delivered with 172.5mm cranksets. Smaller frame sizes typically get 170mm cranks & some really small sizes receive 167.5s for kids & women's frames. Trying to fit the bell curve of people and carry over from crit racing history. Shorter cranks = pedaling out of turns.

I challenge you if you truly believe you can notice more pedal strikes with just 5mm difference..... let me put a set of cranks on your bike, you tell me how long they are by counting your pedal strikes.... I have a hundred dollars that says you will be wrong.....
Fly to Boston and you're welcome to perform said test, I'd be happy to lighten your wallet & mess up a pair of cranks on your dime. I need one GXP set & one BB30.

Maybe I'm just a hack (likely) or my experience is unique (not as likely) but I can tell you I strike 180s more than 175s. My teammate who ran 180s from an SS for a season on his geared bike bitched about it too & he's twice the rider I'll ever be.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
Umm most off shelf road bikes are delivered with 172.5mm cranksets. Smaller frame sizes typically get 170mm cranks & some really small sizes receive 167.5s for kids & women's frames. Trying to fit the bell curve of people and carry over from crit racing history. Shorter cranks = pedaling out of turns.



Fly to Boston and you're welcome to perform said test, I'd be happy to lighten your wallet & mess up a pair of cranks on your dime. I need one GXP set & one BB30.

Maybe I'm just a hack (likely) or my experience is unique (not as likely) but I can tell you I strike 180s more than 175s. My teammate who ran 180s from an SS for a season on his geared bike bitched about it too & he's twice the rider I'll ever be.
Um, check your facts.... most road bikes are spec'd with 175's......not 172.5's
I understand fully about crank length, remember I am fit certified from trek and speccy.... I have fit A LOT of people for road bikes. Yes the kids bikes have smaller cranks and a lot of the womens frames do to, still the standard is 175.

Last time someone took me up on this challenge on there m6, I installed one 165 and a 170 on the same bike..... they were told they were 165's.... they could not tell teh difference. Sorry but that small of a difference is in your head
 
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C.P.

Monkey
Jan 18, 2004
547
8
SouthEastern Massachusetts
A few SS mtb's come OEM with 180's in the larger sizes, long crank arms & SS MTB seems to be a good fit.
I have a 29er SS MTB that came spec'd OEM 180 cranks, they are a good fit for my 6'3" height.
On a somewhat separate note, I used to own a Specialized Stumpy HT (Splat owns it now) , and I ran some old Cook Bros 181mm cranks on it; pedal strikes were common, but I believe that was also b/c Specy BB height is a little lower than many other MTB's.
If you've tried 180's in the past on MTB & liked it, seems as though a 140mm travel with 13.5 BB height might work out nicely, (even with sag calculated in as part of the mix).
 

Banshee Rider

Turbo Monkey
Jul 31, 2003
1,456
10
Um, check your facts.... most road bikes are spec'd with 175's......not 172.5's
I understand fully about crank length, remember I am fit certified from trek and speccy.... I have fit A LOT of people for road bikes. Yes the kids bikes have smaller cranks and a lot of the womens frames do to, still the standard is 175.
It sounds like you used to work at a bike shop? Virtually no road bike comes with 175's <60cm these days. He was correct about 172.5mm. I can put my hand on over a 100 different bikes right now to prove that, but your post history tells me that's probably still not enough to convince you he (/we) are right.
 
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DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
It sounds like you used to work at a bike shop? Virtually no road bike comes with 175's <60cm these days. He was correct about 172.5mm. I can put my hand on over a 100 different bikes right now to prove that, but your post history tells me that's probably still not enough to convince you he (/we) are right.
Just walked in teh bike shop while i was at lunch.... two 58 and a 56 the first three i saw were all 175's.....

I have not worked in a bike shop in about two years now, but I still keep up with what is going on in the bike world....I have probably fit close to 3k bikes for people over the years, a lot of them were at the races in various locations here in so cal.........
 

CBJ

Turbo Monkey
Mar 19, 2002
10,991
1,291
Copenhagen, Denmark
Depending on how you sit on the bike too long cranks can also get your knees to high up when you pedal. Not sure if its the same problem on a mtb as on a road bike.

Specialized do not run the same crank length on their road bikes:

size 49 52 54 56 58 61
Crank Length 170mm 170mm 172.5mm 172.5mm 175mm 175mm

I think that is pretty standard.
 
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DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
I do actually stand corrected, just made a phone and yes there were changes in standard crank sizing on the roadies over the last few years..... Reasoning was too many guys like myself were taking off and replacing with different sizes........
 

CBJ

Turbo Monkey
Mar 19, 2002
10,991
1,291
Copenhagen, Denmark
Maybe I have no idea about the difference in stack height on pedals and shoes but I would think most of that is very similar these days. On a road bike drop on the bars, bar height I think is more important. My legs would hit my chest if my drop was bigger.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
Maybe I have no idea about the difference in stack height on pedals and shoes but I would think most of that is very similar these days. On a road bike drop on the bars, bar height I think is more important. My legs would hit my chest if my drop was bigger.
Actually you start with crank length, move to seat height and position, then move into bar reach/drop/roll....