According to

  • Subject: racing
  • You can choose your own wheel size in the IUF races, but it must be <= 24".
  • I can’t imagine what the benefits of using a wheel size < 24 would be.

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 Application Support