Crank length for a 29er SS / gear ratio's

[KonaDupee]

Originally Posted by Chewyeti

Dupee... i will need some lessons on how you clean all them damn hills on that thing!

Chewy...here's the big secret: Climbing on a SS is actually so much easier than with a geared bike. I know it sounds counter-intuitive, but just ask anyone who single speeds.

[FoShizzle]

it doesnt matter...

like most things MTB, people over obsess over virtually non-meaningful things...0.197 inches on a crank makes no difference "on the trail". If you got or like 175s just use em....

if people suck ass with 175s they will still suck ass with 180s, and vice versa. Gearing changes are noticeable however

[Au575]

Originally Posted by durbish

I believe crank lenght has to do more with the lenght of your legs... think of it like do a knee bend... a shallow knee bend is easier to do then a deep knee bend... the longer the the crank the deeper the knee bend, I'm 5'10 and run 175mm with 32/18 on a SS 29"... if your 6' plus or long legged 180's shouldn't be too long, and gearing from 32/18 to 32/20 should do it. If your short legged stay with 175's.

I think this is the key - what fits biomechanically for your body. Take gearing out of the equation (just like you do when fitting a geared bike) and focus on the position and bend of your knee at the point where you initiate the power stroke. You want (a) a long enough crank arm so that your knee isn't bent "too much" and (b) a short enough crank arm so that your quads are in a good position to exert force - something slilghtly less than 90* for most of us. Any more bend than that, and I lose power and place too much stress on my knees. (As Durbish suggested, compare how much more easily you can perform a shallow knee bend than a deep knee bend / squat.)

Crank arm length also needs to be considered in the context of proper saddle position, to ensure that the knee is not too far forward with the pedals level. The old adage of a plumb-bob hanging off of the front of the kneecap should intersect the pedal axle (or be slightly behind the axle) with the forward crank level is still a good rule of thumb.

I think this is most important for the folks who stay seated when grinding up climbs - those who climb standing will be using a different and (if you're as sloppy as me) a more varied range of motion.

What gear you select has more to do with your strength/power and the terrain you ride. In combination with crank arm length the gear ratio defines the amount of torque you can apply for a given force/leg-strength. But since gear ratios are much easier to change and are terrain-dependent, I think the issue of crank arm length should be divorced from the concept of what gearing you run.

Disclaimer: I am not a professional bike fitter and I have never stayed at a Holiday Inn Express. Just been thinking about this a bit with my own SS... "I'm sure there's something on the Internets that backs me up."

[autoduel]

Originally Posted by Chewyeti

dang.. the monsters are using 20T cogs..... (so i should run a 21...or more?)

Run what gets you up the hills. SS'ers aren't going to win any downhill races anyway.

Originally Posted by tbowren

Oh I wanted to add one more detail. The longer your crank is, the lower you have to set your seat so your leg can reach it when it is all the way down.
This has the side effect of lowering your center of gravity AND making it easier to get behind your seat when standing on the pedals.

I disagree. Except when cornering, my pedals are always level, therefore crank length would not affect COG when going downhill. I would think having your forward foot 5mm farther forward of the BB would also reduce you ability to get behind your seat by the same amount.

Originally Posted by durbish

I believe crank lenght has to do more with the lenght of your legs... think of it like do a knee bend... a shallow knee bend is easier to do then a deep knee bend... the longer the the crank the deeper the knee bend, I'm 5'10 and run 175mm with 32/18 on a SS 29"... if your 6' plus or long legged 180's shouldn't be too long, and gearing from 32/18 to 32/20 should do it. If your short legged stay with 175's.

I tend to agree. If you're standing you may not notice it as much, but sitting.......it throws the conventional bike fitting alignment off. If you plumb your knee to the spindle, your opposite leg is 10mm farther behind.

Originally Posted by singleminded

I have always ran 180's on the singles. I am 5'8" and have no problems...hell you guys have seen me climb

Now I have reverse thinking...I think the smaller guys can use the longer cranks to make up for their lack of levers. As was mentioned you don't want to run them if you have a 25in inseam

So a stroker crank always increases torque and HP due to increased volumetric efficiency, but when you look at it the other way, your legs, like the pistons have to move farther, but requiring less force. The increase is in rotating weight you you can't rev as high....Duan?

I agree that we are highly adaptable, and we can get used riding almost any setup over time.

[foofighter]

i would agree w/ your analogy on that steve like big displacement motors dont have the ability to rev out as high as the smaller displacement brothers.

[onlyontwo]

Chew, I didn't know you got a 9er SS. Thats why you were asking me all the questions, huh? I run 32:21 and 175 cranks. You can try the SS out if you want.

Cheers,
Andy

[EBasil]

Well, I've been fantasizing about a niner SS to replace my aged singlespeed, and I've been riding 180mm cranks on my bikes (SS, boing-boing, beach cruisers) for a long time. One of the first things I thought of when looking at niners was that a nice set of 185 or 190 cranks might work nicely.

So, who even makes such a thing? External BB?

[foofighter]

i thought one of the complaints about the niner is that it had a lower BB height compared to other 29'ers on the market? that would make a big difference in your cranks striking

[DeeZee]

Originally Posted by foofighter

i thought one of the complaints about the niner is that it had a lower BB height compared to other 29'ers on the market? that would make a big difference in your cranks striking

That is only on the RIP9 (reason I didn't buy one). The NEW 08's have different geo

[Zippo]

I definitely vote for 180s on the SS. I have 2 SS 29ers and rode them last week back to back on the same trail, one with a Race Face Deus 180 and the other with a Race Face Deus 175. I definitely noticed the added torque on the steepest of climbs, but with either length you just adapt to the momentum and rhythm. Note that I've been riding 180s for the last 2 years or so, but the 175s feel small, the similar "smallness" you feel when you get off your 29er and get on a 26er. If you don't have the opportunity to ride different crank sizes back to back it's hard to decide which size to order up - I scratched my head over this for a long time but settled with the 180s. And now I like them just as much for the added leverage as for the feel of the bigger spin.

That said, I just pulled the 175s off my 2nd SS I just built up and installed my ENO 180s. So I have a set of Race Face Deus XC 175s for sale, along with a bunch of other parts. I'll post 'em up soon.