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Old 2006-04-27, 07:34 AM   #1
forget_your_life
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26x2.1 (w/127mm cranks) Vs. 29x2.1 (w/150mm cranks) Ping.Mikefule

hey there...

besides the bigger wheel of the 29er dealing better with road Irregularities, what am i looking at performance wise?

does 127mm cranks on a 26 offer better control than the 150's on the 29er? or visa-versa? things like that.

anyone is welcome to reply, i put Mikes name in the title because he is the champ of this stuff...
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Old 2006-04-27, 05:27 PM   #2
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Flattered.

Assuming wheel diameters of exactly 26 inches and exactly 29 inches.

(Real sizes may vary slightly, even for a given tyre section.)

127mm = 5 inches
150 mm = just under six inches.

Very simply, the 26 with 5 inch cranks has a crank:radius percentage of 38.5% (5/13)

The 29 with 6 inch cranks has a percentage of 41%

Or, for the 29er, the wheel is 29/26 = 11% bigger.
The cranks are 150/127 = 18% bigger.

So the 26 with short cranks will feel faster, but slightly less controllable in terms of mounting, idling and stopping.

In reality, the difference between 41% and 38.5% is negligible: about 6% which is less than one cog on a road bicycle.

If I were choosing the two unis, I would swap the cranks. Put the longer ones on the smaller wheel for that full-on tractor effect, and the shorter ones on the bigger wheel for that barnstorming unstoppable rolling death effect.
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Old 2006-05-16, 08:55 AM   #3
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how about a 26" with 114mm cranks Vs. a 29er with 127mm cranks?
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Old 2006-05-16, 04:41 PM   #4
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34.5
34.48

Almost identical in terms of ratio.
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Old 2006-07-30, 08:51 AM   #5
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you Da man!

Quote:
Originally Posted by Mikefule
barnstorming unstoppable rolling death effect.
all things being equal again with the tire (say 2.1) which will have the better "rolling death effect" a smaller wheeled 26" with 127mm's Vs. a large and in charge 29 with 165mm cranks?

the smaller wheel of the 26" falls into smaller holes (so to speak) thus slowing us down but is it still faster than a bigger wheeled 29 with "tractor" 165's? or does the roll over power of the 29" out due the smaller 26 with shorter 127's even though it has longer cranks (165mm)
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Old 2006-07-30, 04:15 PM   #6
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Well, I was criticised for posting it at the time, but this might help:

http://www.unicyclist.com/forums/showthread.php?t=50840

For riding cross country, with mud, long grass, short hills, gravel and general mixed terrain, 125s work well on a 28 with a skinny tyre, so should be magic on a 29er.

Given the choice of wheels and cranks you have specified, I would put long cranks on the smaller wheel, and short cranks on the larger. It would emphasise the differences, and give each a distinctive role. Otherwise, you end up with two broadly similar machines, about a gear or so different.

Most of my riding recently has been on a 28 with 114s. The terrain-crossing limits have been met by the tyre from time to time, but not by the crank:wheel ratio. (The tyre is a 23mm road tyre pumped to 130 psi.)
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Old 2006-07-30, 05:06 PM   #7
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The crank length : wheelsize ratios determine the "gear" of the unicycle, because the resulting number is proportional to the amount of "leverage" you have against the road. The higher the crank length:wheelsize ratio, the "lower" the gear: it'll be easier to turn the wheel but you'll go slower for a given cadence.

However, it's not the only difference: larger diameter wheels roll better over bumps, and also have more stability due in part to their larger mass. I'd expect you to go faster on a larger wheel given the same theoretical "gear" due to these factors (and because it's difficult pedalling fast on tiny cranks in my opinion).

For a concrete example:
My friend Alan has a 20" uni with 80mm cranks. I have a 29er with 127mm cranks, and a 36er with 150mm cranks. The highest theoretical "gear" is the 20" uni, but it's also the slowest of the three. The 29er is substantially (several mph) faster with me riding it, despite my being less fit - I'll hit, say, 13-14mph where he tops out around 10mph. Alan can take my 29er up to 15mph.

The 36er is faster again, with me topping out at a maximum of 17mph (so far), despite the wide hub, and long high Q cranks that I've got installed.

The ability to roll over bumps and be stable at high speeds (and have a decent stroke length when pedalling) makes the bigger wheels much preferable for any distance. However, they are also a bit more unwieldy, harder to turn, harder to thread through busy streets, etc. The 20" can easily go down to walking pace and thread through pedestrians.

For cross country offroad the bigger wheels will roll over bumps better than an equivalently geared smaller wheel (although it is harder to build up the necessary momentum due to their probably being harder to freemount offroad). If you wanted to do technical stuff you might find you need a smaller wheel.

I find the 36" easily best for road riding, and for XC offroad I'm liking it too. A 29er can make a good muni though - I'm going to put 150mm cranks on it for the purposes of muni, unless I'm doing really rough stuff that should roll over most things.
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Old 2006-07-30, 07:33 PM   #8
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you could get those cool kooka cranks that i think pdc is selling. that would solve your problems.
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Old 2006-07-30, 10:04 PM   #9
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Quote:
Originally Posted by mornish
you could get those cool kooka cranks that i think pdc is selling. that would solve your problems.
it would'nt solve the wheel size issue, we are taking about roll over ability here as well.

the wholy Kooka's are nice but they are alot of cash for a tapered crank and my uni's MUni hard..PDC sould get his machinist to broach the tapers to a 36 spline pattern for use on KH hubs like Steve Howard has done to a few cranks, then we would be in buisness...( of couse the price would be around $300 i bet)
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