In the past the NUM (National Unicycle Meet) allowed a rider to race
with one unicycle. This means that they couldn't switch unicycles
for differant races. Lately, this rule is changing. For the slow
races I perfer to use my 20" uni for more control. For the walk
the wheel race I use a uni with a wide tire and the seat higher then
normal. This makes it easier to walk the wheel. For all the rest
of the races I use my 'racing machine' uni.
IUF (UNICON) has always allowed the competitor to use any unicycle
they wanted as long it didn't go above the maximums and minimums.
So to answer your question: Slow race is the only benifit of having
a 20" uni.
Another big part of racing is not only the wheel size is the crank size.
The smaller the crank size the faster a person can go. The reason
for this is that for smaller cranks is that the leg doesn't have to
move as much making it easier to do high RPMs. I use a 5" cranks
on my 'racing uni' and I use 5 1/2" cranks for the obstacle course because
of the all the turning that is involved.
Although after the races last year I started to do the obstacle course
with my racing uni (high pressure tire, Miyata deluxe) and I found that
my times were the same as when I used my other uni with 5 1/2" cranks.
The reason I went to 5 1/2" cranks in the first place was John Foss
(World Champion n times over (where n is a large number)) said this
is best way to do it. John Foss currently holds the NUM record for
the obstacle course.
As long as I'm on the subject. When doing the obstacle course, a good
technique to reduce time is to have one hand on seat and one hand out
for balance. The hand on the seat 'steers' the uni around the cones.
Also holding on the seat stablizes the uni for all those starts and stops.
__________________________________________________________________________
Andy B. Cotter CAE UW - Madison
cotter@cae.wisc.edu Application Support