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I currently ride 175mm length cranks on my single speed 29er and 172.5mm om my road bike with a 87.9 cm or 35" cycling inseam. I do like to spin. Is there any real advantage for more power for climbs going to 180mm cranks? I really struggle or just can't make some climbs but my gearing is perfect for the flat and going down.

Let the rock throwing begin!
 

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If you like to spin and you can't make some climbs, it might not be a bad idea to adjust your gearing if you want to clear everything. You said you like to spin so it might not be bad. If you increase your crank length you'll spin slower. It is unlikely that the added leverage would be enough to magically make you power up climbs. You're better off practicing better form and trying to keep more momentum if you want to keep your gearing. I've found that form is more important to clearing things than power.
 

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I recently went from 175mm to 180mm cranks on my single speed mountain bike. The difference was very slight. I could feel maybe a little bit more leverage on the downstroke, but as far as I am concerned, the difference is just barely perceptible and not really worth worrying about. If your gearing is "perfect for the flat and going down" then it might be too high. I'd recommend trying out some different gear ratios instead of changing crank length.
 

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So few who reply to these crank length threads actually have long term experience with long cranks. I'm not talking about the guys who've already replied to this thread (don't know), I'm talking in general terms.

Whatever.

I've been riding cranks between 195mm and 202mm for the past 14 years. I have a 36" inseam. Yes, you can utilize the leverage to climb things that would be more challenging to clean with shorter levers (cranks). But it's not a technique that comes overnight. After you've ridden long cranks for a season or so, the more subtle benefits surface. It's more than added power, it's traction, too. Kind like a cheater bar when you're breaking a bolt loose. You're less likely to bust your knuckles when you use a cheater bar, this is because the leverage makes power easier to modulate. Same with long cranks -- one can mete out the power in such a way that one not only has more power, but more traction and torque as well.

It's not as simple as putting on longer cranks and raising your gearing. There's a lot going on there and experience is really the only way to discover everything at your disposal. Not one single experience, but a season's or even several season's.

Sometimes I hear someone say, "I tried my buddy's bike with 180s. Rode around the block. Don't think I like 'em." Not fair. A bike is a machine. We get used to whatever tool we use a lot and then anything else we use briefly feels wrong -- even if it's in fact better.

Commitment to an extended term is the only way to find out.

My straight up opinion? If your inseam is 35", you ought to be riding 180mm (or longer) cranks.

Best of luck.

--Sparty
 

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My first single speed has 170mm cranks. I thought about switching to 180mm but found that I could still climb hills with the shorter cranks. My new bike has 175mm cranks and I think the leverage increase is only very slight. Percentage wise, this is a greater increase than going from 175 to 180. Overall, my physical conditioning made a larger improvement in my climbing ability.

You can spin shorter cranks faster since the circumference is smaller. 5mm longer cranks will increase the diameter of the circle by 10mm, which will change the angles your hips, knees, and ankles have to move through. This may have an impact on your bike fit/seat height since the bottom of the stroke will be lower....... You will not be able to spin longer cranks faster than the shorter ones. Given the same gearing, your max speed on the flats will be slower.

But, like Sparticus said, with a 35" inseam you should be able to use the longer cranks.

-Chuck
 

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You bring up an important point

Sometimes we have to shift our perspective / paradigm. The most common comment I hear about going to longer cranks is that they make one's pedals hit the ground more often. Depends on how one looks at the situation. Assuming a rider has the correct length cranks for his/her body, then if his/her pedals hit the ground too often, the frame's bottom bracket is too low.

I am saying that a custom frame is probably the correct way to deal with this situation. And it's not just BB height. If one employs truly long cranks, the frame will need a steeper seat tube angle (to maintain KOPS or some version of it), a longer front-center & shorter chainstays to compensate for the steeper seat angle, and finally perhaps a half-degree steeper head angle in order to compensate for the slightly slower handling that longer front-center bikes tend to suffer. So really, a custom frame is the ideal solution when going to cranks longer than around 180mm.

Personally I believe this is the reason so few crank manufacturers offer cranks longer than 180mm -- given the effort and cost of dealing with them, the average rider won't make the commitment. The market is small.

That doesn't mean the effort and cost are not worth the benefits long cranks provide for those who's legs are long enough to utilize them.

--Sparty

chuckjoga said:
My first single speed has 170mm cranks. I thought about switching to 180mm but found that I could still climb hills with the shorter cranks. My new bike has 175mm cranks and I think the leverage increase is only very slight. Percentage wise, this is a greater increase than going from 175 to 180. Overall, my physical conditioning made a larger improvement in my climbing ability.

You can spin shorter cranks faster since the circumference is smaller. 5mm longer cranks will increase the circumference by 10mm, which will change the angles your hips, knees, and ankles have to move through. This may have an impact on your bike fit/seat height since the bottom of the stroke will be lower....... You will not be able to spin longer cranks faster than the shorter ones. Given the same gearing, your max speed on the flats will be slower.

But, like Sparticus said, with a 35" inseam you should be able to use the longer cranks.

-Chuck
 

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Crank length choice is very particular to the individual. Inseam length is a very rough indicator, things like ratio of upper/lower leg ratio/ ratio of fast/twitch/slow twitch muscles, age (longer cranks as you age) all factor in.

Since it's too hard to figure all this out on paper, best thing to do is try 'em and see how it goes. Don't fall for the idea that proper crank length is like your shirt size, all you need is a tape measure to fit it right....

Back in the day story about crank length:
When I was younger in my roadie USCF days (late 70s), they tried to get me to use 172.5mm on the road, I died every time. Don't know why, don't really care. I always like shorter cranks, used 170mm on the track too, but I wasn't a sprinter. Now that I'm almost 48 years old, 175mm feel good on the road or trail. If I was a real roadie again, I'd start with 172.5mm and try 175mm on the road. I still run my 175mm 85-100 rpm, I'm a spinner.
 

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crank length should only be dictated by fit/feel...

there are folks on here all the time who want longer cranks for the "leverage" but in reality a gearing change and a leverage change are exactly the same thing, so if one wants a gearing change change the gears, it usually easier and cheaper.
 

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peanutbutter said:
...but in reality a gearing change and a leverage change are exactly the same thing, ....
Not exactly. It's all about the pedal's speed, linear speed (inches/sec), not rpm. A larger diameter circle requires faster pedal speed for the same bike speed if the gear isn't changed. If the crank is longer, then a larger gear is need to keep the pedal's linear speed the same for the same bike speed.

It's the slightly larger diameter circle that makes it different. With two different crank lengths, to go the same bike speed and keep the pedal's linear speed the same requires a different gear or different cadence, no matter which you choose, it's different.
 

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Not true

peanutbutter said:
crank length should only be dictated by fit/feel...

there are folks on here all the time who want longer cranks for the "leverage" but in reality a gearing change and a leverage change are exactly the same thing, so if one wants a gearing change change the gears, it usually easier and cheaper.
Your first statement is correct, but as for the rest, you're mistaken. Read what I wrote above. The stuff about torque.

If you think short cranks and a low gear are the same as long cranks and a tall gear, try getting on a kiddie tricycle with a tiny front wheel and then compare that to your bicycle. Four inch long cranks... not something anyone would want to do any serious climbing with.

--Sparty
 

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pursuiter said:
Not exactly. It's all about the pedal's speed, linear speed (inches/sec), not rpm. A larger diameter circle requires faster pedal speed for the same bike speed if the gear isn't changed. If the crank is longer, then a larger gear is need to keep the pedal's linear speed the same for the same bike speed.
Gain ratio.
 

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asphaltdude said:
Gain ratio = written tables & theory.

Personally I'll rely on my 14 years of experience on the bike riding 195-202mm cranks. I'm not saying long cranks are for everybody. But just think, some folks with long legs might find more comfort &/or power &/or torque &/or other benefits turning larger circles. That's it. Ergonomics that defy definition & go beyond spreadsheets.

No one really knows the advantages & disadvantages until they experience the real thing for themselves. And that's something I don't understand -- why some people who frequent these forums offer "advice" about how long cranks are no different than shorter cranks with a lower gear. Without experiencing both short AND long cranks, their opinions are little more than conjecture.

--Sparty
 

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In my time in fitting people,

another factor overlooked is the size of your foot (or cleat positioning to be precise). Peoples with big feet (for their size) tend to tolerate well an extra bump in crank length. We tend to pedal not with rigid ankles, but by keeping our feet at the same angle relative the ground regardless of leg position. I ride what I like, but I've been around some women (short legs) that managed to kick 175mm cranks over just fine if they had a good foot.
 

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Juanmoretime said:
I currently ride 175mm length cranks on my single speed 29er and 172.5mm om my road bike with a 87.9 cm or 35" cycling inseam. I do like to spin. Is there any real advantage for more power for climbs going to 180mm cranks? I really struggle or just can't make some climbs but my gearing is perfect for the flat and going down.

Let the rock throwing begin!
Back to your question, I would say your problem is obvious. If your gearing is good for flats and downhills, then it is too high. Start with the gearing that gets you up the hill, then you can play with the crank length.
 

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I am 5'6" (29 inch inseam) and I also have 175mm cranks on my mountain bikes and 172.5mm crank on my road bike. So I would agree with Sparty and others that you should adjust your gearing and try longer cranks. But the longer cranks would be addressing your fit, more than the leverage factor (although the ideal fit will probably give you the ideal leverage/torque results regardless of gearing).
 
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