On Sun, 12 Mar 1995 d.kathrens@genie.geis.com wrote:
> I have begun the process of building my own MUni (Mountain Uni), planned
> to have a 26" wheel, 36 spokes, 175mm crankarms.
>
> A wide rim be stronger than a narrow rim & should provide better support
> for a wide tire than a narrow rim, right? Considering that more than
> double the load of the typical ATB wheel will be placed on the MUni wheel,
> I believe I should try to get the strongest rim possible.
Well, the carbon fibre uni was always concieved as a MUni, with a 26" wheel. The
rim I use is the bog standard Mavic M231, just like about 50% of all mountain
bikers. Its narrow compared to the steel rims that unicycles normlly use but
being ally, the strength to weight ratio is sooo much higher that strength is
not a major problem. On this rim I’ve done lots of hoping, curbs and
stair-riding with no probs whatsoever. However, the 17mm steel axle has just
cracked 
On a mtb, two things destroy rims. The first is the wearing through of the
breaking surfaces, not relevant on a uni. The second is impact loading out of
the plane of the wheel. This, to use that lovely american expression, ‘tacos’
the wheel. Unless you’re heavily into doing stairs while side riding I can’t see
that happening. On a uni the load is vertically down, through the wheel and
consequently its a very durable structure.
There’s also the effect of speed. At 30 to 40 mph+ the loading on a rim because
of rough ground is lots and lots higher than the loading in a Muni rim. Unless
you’re planning on that kind of speed, then I bow down before you oh mighty one.
As for tyre fit, mtb tyres are designed for the 20mm rims most mtbers use. It
looks odd at first but I’ve never had a tyre peel off, even when jamming tight
tarmac. (Well, tyre peel off road, but thats different.) My uni alternates
between a Specialised Nimbus semislick for road use and a Panaracer Smoke 2" for
the dirt. Don’t go for anything excessively knobbly like a Storm Control 'coz
you don’t need that much grip and the knobbles cause that ‘wheel advancing only
an integral no. of knobbles’ feeling.
As for Mavic 281’s, I use one of the back of my thrashy mtb. Unless you’re
planning on doing 2’ dropoffs then I think its overkill. Get a 231 'coz their
cheap and strong enough.
Jez jpw24@cam.ac.uk