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The Secret Set Up, Part 2:
Tire and Wheel Choices for 'Cross
In my last article, I introduced the idea of how difficult it can be
to find reliable information about cyclo-cross, and how the mysterious
cult of 'cross can be hard to infiltrate. There's a lot of folklore out
there, and a lot of old-school knowledge that not everyone wants to share.
If you've got a seat post in your garage that you drilled a hole in for
a brake cable to go through, or if you've ever glued tire tread to the
bottom of a pair of road shoes, then you're one of the insiders. But I
want to make those tricks available to everyone.
Even for people in the know, tire choices and pressure are a topic of
never ending conversation and debate. I would imagine that only motocross
racers stress about it in the same way as cyclo-crossers. There are so
many different options: skinny or fat? File tread or tractor tread? Clincher
or tubular? There is a different tire selection that, according to the
legends, will work best in each condition. Unless you've got an infinite
number of wheel sets (and believe me, the best guys do), you can't really
have a tire set up for each condition you might encounter. The best approach
is to have a standard set up that covers most of your bases.
Your first choice is probably going to be clinchers or tubulars. For training,
clinchers are great. There's an abundance of 'cross clinchers available
now, and it's nice to only have to change a tube when you puncture. But
clinchers are heavy, prone to flats and denting, and limit the amount
of pressure you can run on the low end before you bottom out and pinch
the tube. So, for racing, tubulars are far superior. The one advantage
to clinchers is that instead of bringing six sets of wheels to a race,
you can bring a couple different types of tires and change them quickly
and easily once you see the course.
Tubular rims are lightweight, stronger than clinchers, and don't dent
as easily. The tires are better because they're lighter, they pinch flat
less often, you can run very low pressure without puncturing, and you
have more tire choices. The only drawback is that they can be expensive
to replace. All things considered, though, it's a worthwhile investment
if you plan on racing.
In both cases, standard 32-spoke wheels are enough. You don't need to
go overboard and use 36, and many riders push the limit and go with 28
or less. Your tires should act as the suspension, so normal road wheels
will last if you're racing on true 'cross courses. Pre-built and specialty
wheels are also great for 'cross because they're light, strong, and their
aero cross-sections clears mud well.
The next thing to worry about is the width of the tires you run. The UCI
limit on tire width is 35 mm. Again, your tires act as shock absorbers
on a 'cross bike, so using 28 mm tires and pumping them up to 75lbs means
you might be fast on the pavement, but you'll get knocked around anytime
you're on the dirt. Using a wider 32-34 mm tire at a lower pressure, anywhere
from 30-60lbs, means you'll have traction in the turns, float through
sand, and you'll smooth out the bumps as you go. Skinny tires are good
is if the course is smooth and fast, if there's an exceptional amount
of pavement (in which case you could just pump your larger tires up harder
anyway), or it there's deep mud. In the mud, skinny tires can cut down
to the hard ground beneath, and provide more clearance in the frame. But
even then, skinny tires bottom out sooner and can't be run at the lowest
pressure, which would improve traction even more. With clinchers, you
almost never want to run skinny tires because the risk of pinch flatting
is too high. At either extreme, skinny or fat, there's always a compromise.
You need to make a decision based on the types of courses you race on
most, and the weather where you live.
With tread patterns, there are some general rules. A dot pattern is for
grass, loose dirt, and mud. The wide space between the tread allows your
tires to clear dirt or mud while still providing good traction. Square,
chevron knobs are good for hard packed ground and fast courses, and sometimes
as rear tire in the mud. File treads are good for fast, packed courses,
too, but are also great front tires in the mud, since they cut through
without picking any dirt up. For all around use, the best tread is the
arrow or tractor tread found on many popular tires. The tread is at once
aggressive, smooth, and open, so it works in a variety of conditions.
Many clincher tires that I've encountered tend to be over built, and look
more like miniature mountain bike tires with too much tread. That makes
for a heavy tire that rolls poorly and fills with mud easily. With a clincher,
look for something that has a large casing and shallow knobs.
The last thing to consider is tire pressure. On the road, the logic is
to pump your tires up as hard as you can get away with. In 'cross, the
opposite is true. You should always run your tires as low as you can get
away with. Lower pressure means a larger contact area and more flexibility,
which means better traction, better shock absorption, and more efficiency
(because you're not getting knocked around). I weigh 155 lbs, and on a
fast course, 60 lbs is my maximum pressure. If it's slightly bumpy, I'll
go to 40-50. If it's really bumpy, muddy or snowy, I'll go as low as I
can without bottoming out, usually 25 in the front and 30 in the back.
Do the thumb test: if you can push your thumb down on your tire with both
hands and bottom it out on the rim, then add a little pressure until just
past that point. With clinchers, you're always going to have to run 10-15
lbs. more pressure than a tubular, but the thumb test will work in both
cases.
Many of you responded to the last article with suggestions, questions,
or topics on cyclo-cross you'd like to see addressed. Keep them coming,
and I'll try to get to them all!
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