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Hi all. I have an '09 heckler which i ride aggressively. I do a lot of long slow climbs, ending with rocky downhills.2 x 9 setup (22-34). I'm in the market for a new crankset. In the past I always ran the standard 175 mm arms but i was wondering if a 170 mm would better for my height ? (5'8" with shoes, and I have relatively short legs for my height-29.5" inseam)and if so, what the pros/cons would be. I know shorter cranks are good for downhill because of the better ground clearance, but I imagine it would raise your center of gravity a little? would climbing suffer or improve? Thanks,
 

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Metal
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From what I have read, longer cranks might help a masher be more efficient, and shorter cranks might help a spinner be more efficient. It seems to me that the 5mm (only about 0.2 inches) will not make all that much difference based on your height. If any advantage is to be had, it is probably in your riding style. If you've been happy with 175, then that there is a reason to stay with 175. But I would not fear 170 either. I am about 6-1, but with relatively short legs (though not feakishly so) and I ride 170 and I am happy.
 

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I have both on two seperate bikes, swapped them and could not tell the difference, I guess people that can are the really sensitive types.I bought 170s since they were on sale, recent info on mbt action thought longer cranks gives the rider more leverage on the down stroke and 175s will do for the vast majority, I have FSA mega exo's.
 
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i must be total screwed up

I am 6'1" with a 29 inch inseam without shoes. 175s work great for me, i once had a bike with 172.5 cranks and never really liked them, they always felt funny. look at BMX bikes. tall gears for little kids and they use 180's for low end grunt. many of the single speed guys are going for 180's now saying they get more torque.

Hope that helps a little. kimbo
 

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meow, meow.
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dwyooaj said:
5'8" with shoes, and I have relatively short legs for my height-29.5" inseam
My dimensions are about the same. I can both spin and mash, depending on bike, and prefer 175 mm. Definitely would not go below 170 mm for a trailbike. But I also run 1xN drivertrains and there are no real mountains around.

The only point I see in going to 170 mm is to try compensating for ground clearance on technical uphills on a FS trailbike.
 

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I'm 5-9 and use 175 on the geared bike and 180 on the SS. it depends on your riding style if you like to sit and spin or push a higher gear. If you like to sit and spin I would try the 170....but if you push hard or stand a lot I would keep the 175
 
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qkenuf4u said:
thats EXACLTY the reason for longer arms... simple and to the point.. :thumbsup:
No, it's much more complicated. Shorter cranks can help produce more power IF the rider is comfortable increasing his cadence to compensate. As for more "leverage", that's what gears are for. A shorter arm decreases leverage on the crank, thereby increasing pedal effort, but you adjust for that by changing the gearing. The best crank size for you depends on your range of cadence, your size, and fit issues like aero position for tri riders and ground clearance for off-road. Leverage is a red herring.
 

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175's on the DH bike, FR bike, and 4x/DJ bike. I've got 170's on my xc bike. You can definitely tell you have less leverage on the 170's.
I don't have a problem spinning the 175's at about 130 rpm if I have to.

I'm not a big/tall guy either. I'm 5'10 with a 32 inch inseam.
 
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One Pivot said:
this isnt road biking though, you cant just click down a gear and spin faster all the time on the trail unless you're a die hard fireroad rider or something.
Not sure what the point is of this comment. You choose your gearing beforehand just like you choose your crank length. If you can't shift at some point the penalty is the same regardless. The "leverage" of a crank arm is only one aspect of the overall gearing. Tell me, what provides more leverage, a 170 crank and a 18T cog or a 180 crank and a 17T cog? They are the same. The leverage argument is a red herring; that's what gears are for. If people didn't just slap on standard ring and cassette sizes they'd get this.

You should choose your crank length based on what suits you best, just like a roadie does and for the same reasons. You may need to adjust your gearing when you do so.

Road and tri riders care about crank length so helpful discussions can be found on their boards. SlowTwitch is good for that. To summarize what I've read there, there's a broad range of crank sizes where the power output per cycle is relatively the same but the smaller crank allows for faster cadence. From a power standpoint, you are best off reducing your crank size until you can't comfortably increase your cadence. For experienced riders this is generally smaller than 175mm. There are other concerns, though, since bicycle handling and aerodynamics are effected. I have adjustable cranks on my road bike and I've done this experiment. Even though I'm 6'2" I use smaller than 175mm. Prior to that I used 175mm and wondered I should go larger because of my size. That would have been a mistake.

If you just want your large crank assumptions validated I can't offer you anything, but if you are interested in the subject seek out some informed discussions on boards where there are experts. The question here isn't the basic mechanics (which are well understood), it's how they apply to mountain biking. Leverage isn't the answer.
 

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Hello OP...my dimensions are similar to yours and had a similar question to yours
http://forums.mtbr.com/showthread.php?t=493066
I was contemplating though on dropping down from 175 to 165. I went ahead and made the move to 165 and it was fine. More clearance(pedals hitting rocks less) and pedaling ergonomics felt better. As far as leverage is concerned, I agree with other posters that just drop down a gear. I did not notice any spinning or mashing issues that switching gears did not solve.
 

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craigsj said:
Not sure what the point is of this comment.
just a few short words.. lowest gear and highest gear.

what are you going to do, swap your cassette from a 32 to a 34 mid ride? change front rings? what about 1x9? you're stuck with your front chain ring and 32 or 34 high and 11 low. with longer crank arms its easier to push your highest and lowest gears. you made the assumption that you're going to be somewhere in the middle of your gear range the entire time you're riding anywhere..

its pretty easy to see the advantage of leverage. i spend most my time in the middle front ring and either 32 or 11 out back.. considering its just as easy to spin a longer crank at a normal trail cadence, ill take the extra leverage. most riders say the same thing, they're either in the middle or top/low range of their cassettes.
 
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One Pivot said:
just a few short words.. lowest gear and highest gear.

what are you going to do, swap your cassette from a 32 to a 34 mid ride? change front rings? what about 1x9? you're stuck with your front chain ring and 32 or 34 high and 11 low. with longer crank arms its easier to push your highest and lowest gears. you made the assumption that you're going to be somewhere in the middle of your gear range the entire time you're riding anywhere..

its pretty easy to see the advantage of leverage. i spend most my time in the middle front ring and either 32 or 11 out back.. considering its just as easy to spin a longer crank at a normal trail cadence, ill take the extra leverage. most riders say the same thing, they're either in the middle or top/low range of their cassettes.
Are you changing your crank length mid-ride? No, you fix your gearing when you change your crank arm and if you can't see how to change, say, a single chainring then maybe you shouldn't participate in the discussion. Idiotic comments don't strengthen your argument.

If you can't see that leverage is a mirage it's because you refuse to think about it. Gearing is gearing---the purpose of the crank length is to match your biomechanics, not to fix gears that are too tall. It doesn't really matter what most riders say, as though you speak for them, it only matters what people who've actually tried it have to say. A longer arm and a taller gear are the same as a shorter arm and a shorter gear. There's lots of research on the subject available online that disagrees with your closeminded opinion.
 

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awww did you get offended that someone disagreed with you? :lol:

22/34 is easier to spin with a 175mm crank than a 165mm crank. what happens when you're in 22/34 and the hills still difficult with your 165's? what can you do then? use longer cranks.

these are the most common, readily available gears. 44/11 is easier to spin with a 175mm crank than a 165mm crank. yes you can click down a gear and spin faster, your top speed is also limited. same story, this is probably what your bike is going to come with.

theres a reason 175mm cranks are pretty standard and 150mm cranks arent, and theres a reason why road bikers fuss about this a whole hell of a lot more.
 

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meow, meow.
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Also remember that we're pretty much stuck with 32T rings being the smallest ones that fit modern cranksets. Going too short on crank arm length can mean you're forcing yourself to shift to the granny more often. This is even worse if you're running a 1xN drivetrain.
 
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