magnify your your fun

General
1

Living on a flood plain, I don’t get too much opportunity to do ‘mountain unicycling’ but I do get to do plenty of ‘off road unicycling’ on a variety of surfaces.

With few steep bits, I seldom need the torque of long cranks, and I have been experimenting with very short ones. Today I did about 8 miles, mainly off road, on a 24 with 110 mm cranks. That’s a leverage of 36%… very similar to a standard Coker (33%). Yesterday I ordered some 102 mm cranks - that’s 4 inches old money - which will give the 24 exactly the same ratio as the Coker.

Results? Fun fun fun, and I recommend it to anyone who can’t get to steep hills easily.

On the flat boring bits, the cadence goes up, so you get there quicker, and, crucially, it feels like you’re getting there quicker. On the rough bits, it takes a lot more control than riding with longer cranks. It’s tempting to go too fast, then when the wheel hits a trap, things can happen very quickly indeed! Short steep bits can be swooped up with momentum.

Long steep up hills aren’t as hard as you think because the tiny diameter of the pedalling circle makes it like you’re going up a flight of very small stairs. Given a reasonably smooth surface, there are some hills I’d rather do on a 24 with 110s than a 26 with 150s.

Steep descents are more of a problem. It’s easy to let the pedal pass beyond ‘top dead centre’ unexpectedly, and you can find yourself flying!

So, a strong recommendation: if you are reasonably experienced at MUni, but can’t find any hills, put some short cranks on and magnify the hills you can find! And when you put the 150s back on, it will be so bloomin’ easy you’ll need to find some even bigger hills than you couldn’t find in the first place!

2

That sounds like fun. Riding MUni on flat bits with long cranks is a real drag.

Not much flat where I am, but I was thinking of doing something similar for racing, since I could probably run up hills as fast as I can MUni. (ie cyclocross style). What do you estimate is your difference in speed at roughly the same level of exertion? And also how much difference in gradient you can climb comfortably do you sacrifice with the shorter cranks?

We might be putting shorter cranks on our MUni’s for this weekends Taupo Day/Night thriller 12 hr mountainbike race. It’s quite flat and fast (for NZ).

Thanks,

Ken :slight_smile:

3

Ooh, technical questions! ;0)

It’s difficult to quantify the difference in speed but…
With shorter cranks, your top speed is higher, and your cruising speed is higher. As you ride on the flat without really trying, your cadence is naturally higher. It really does feel faster without trying.

Now my guess is roughly this: on the flat, it takes virtually no effort to propel a 24 inch unicycle. With 170 mm cranks, you would be in the same position as someone on a mountain bike in bottom gear. So it’s not a gearing problem in the sense of how big a gear you can push.

In fact, you probably use almost as much energy shifting the mass of your legs round and round/up and down as you do propelling yourself and the uni forwards.

So, go for a smaller crank and your legs don’t move so far, right? So my guess is that if you have a crank that’s, say, 25% shorter, and therefore your legs have 25% less distance to go, you tend to rev at about 33% faster.

(Note: adding 1/3 is the ‘opposite’ of subtracting a 1/4. I’m not sure what the proper mathematical term is, but I know I’m right.)

My 24 came supplied with 150 mm cranks and I’m running it on 110s until the 102s arrive. That’s 26.7% shorter cranks. I’d guess my cadence averages out something like 36% (say 1/3) faster. So, revving 1/3 faster, I go 1/3 faster. This is about what it feels like, but I’ve never tried to measure it.

As for steepness of hills, I’ve never been Mr. Mountaingoat himself, but I have found that as long as I don’t stall at top dead centre (which is a bit more likely with short cranks) the limiting factor is often the smoothness of the terrain rather than the gradient. Today I rode up some rough tracks which 6 months ago I would have failed on my 26 with 150s, and which would stop some bicyclists.

Going down it makes a lot more difference. Obviously the laws of physics (which ye cannae change, Captain) suggest that the effect should be about the same percentage wise. However, I tend to ride down steeper stuff than I ride up. I don’t use a handle. I do find that the short cranks make even short but steep descents a very challenging proposition.

There are so many subjective factors that I can’t be more precise except to reiterate: for riding undulating or flat tracks - rather than mountains - putting the shorter cranks on makes it faster and more fun. And moreover, it is good training for when you put the longer cranks back on.

Have fun trying. Mounting and idling are that bit trickier at first, and when you get tired, you get more UPDs, but on a 24 you won’t hurt yourself on the flat.

4

And technical answer- you’re not yet another engineer/ physicist/ rocket scientist by any chance? Seems to be a lot of of those people on this forum :slight_smile:

Thanks Mike, will give it a go this weekend!

Ken :stuck_out_tongue:

5

Re: magnify your your fun

On Wed, 9 Oct 2002 17:44:00 -0500, Mikefule
<Mikefule.ca31z@timelimit.unicyclist.com> wrote:

>So, go for a smaller crank and your legs don’t move so far, right? So
>my guess is that if you have a crank that’s, say, 25% shorter, and
>therefore your legs have 25% less distance to go, you tend to rev at
>about 33% faster.
>
>(Note: adding 1/3 is the ‘opposite’ of subtracting a 1/4. I’m not sure
>what the proper mathematical term is, but I know I’m right.)
I think you mean “reciprocal”. 1 + 1/3 is the reciprocal of 1 - 1/4.

>My 24 came supplied with 150 mm cranks and I’m running it on 110s until
>the 102s arrive. That’s 26.7% shorter cranks. I’d guess my cadence
>averages out something like 36% (say 1/3) faster. So, revving 1/3
>faster, I go 1/3 faster. This is about what it feels like, but I’ve
>never tried to measure it.
The way you phrase it, it almost sounds like a miracle. But it boils
down to footspeed being constant (with respect to a frame of reference
moving with the unicycle).

A few weeks ago Roger and myself discussed exactly this issue in
r.s.u. I should try it out for myself. I have 125 mm cranks on my 24"
Semcycle. I also have 150 mm and 170 mm cranks. Now to find the time
and motivation to do all the swapping (and getting used to) and then
measure maximum cadence. If and when it’s done I’ll post the results.

Klaas Bil

I posted only a single copy of this message.

6

Re: magnify your your fun

> 102 mm cranks - that’s 4 inches old money

Not 6? <threat to self-esteem looming> :wink:

I can barely stay on the 20" with my new 102s.
I’ll have to try 110s on the 24" though…