Pittsburgh Cyclocross

Pittsburgh Cyclocross interviewed cycling coach Chris Mayhew of JBV Coaching about proper tire pressure for Cyclocross bikes. Want to avoid DNFing a race due to problems with flats or rolling a tubular?  Then read Chris’ advice, then get out there and play!  Chris, thanks ahead for this interview.  Readers, just leave a comment below if you’ve got more questions for a coach or bike technician about cyclocross training or tech.

Q. Cyclocross racers typically run their tires at very low pressure compared to road or even mountain biking.  Why is that?

I’d argue road racers run too much pressure in their tires but I
suppose that’s an issue for a different website, huh?

Road bikes do not have and do not need suspension given the terrain
they ride on. MTBs have huge tires which are excellent suspension and
then of course most MTBs have suspension as well. On a cross bike the
only suspension is the tire. Also, if you haven’t noticed, most cross
tire treads are pretty lame. Part of that is by design [otherwise the
tire would have a lot of rolling resistance] and part of that is
tradition [mud tires are a fairly recent development].

The main way that most tires stick to the ground is by allowing  the
casing of the tire to conform to the ground. The goal is to get as
large a contact patch as possible while not pinch flatting or having
the casing roll in corners. The lower the pressure the larger the
contact patch and the more traction you get.

Q.  What is a typical PSI that you recommend for dry conditions? wet conditions?

That is a really common question but on for which there is not a
stock answer. It depends on your tire, weight, riding style and as you
mention, the conditions. In general you want to run a bit more
pressure on a dry course and a bit less on a wet course. But that’s
relative to what you typically run. To give a very broad answer start
with forty PSI and start working down.

Q.  Is there a “rule of thumb” for testing your tire pressure when you don’t have a pressure guage or digital tire pump handy?

There is indeed. We’ll call it the Powers method since he
introduced it to me. Take your left hand and make a fist. Now stick
your thumb out. Place your palm over your thumb. Now place your thumb
on the tire so your outstretched thumb is pointing to the side of the
bike. Using your body weight you should not quite be able to touch the
rim. That’s a good starting place for tire pressure and a good
technique in general for learning to check pressure.

Q.  What is the difference in pressures you can run if you have tubular tires vs. clincher tires?

Typically you can go a bit lower in a tubular, say 5 psi or more.
The reasons for this are threefold. One, the shape of tubular rim
means that you almost can’t pinch flat the tube. The edges of the rim
are much less sharp. That’s a big bonus when you’re flirting with the
edge of low pressure.  Secondly most tubulars will have a latex tube
in them. Latex stretches much better than butyl and therefore resists
pinch flatting better. Lastly, tubulars are glued on and not held on
by tire pressure.

12 to 18 PSI is not unheard of. I’ve played around on a bike that had
tubulars at 22psi for a 75kg ish rider.

Q.  When you show up at a race, what is your strategy for finding the perfect tire pressure for your event?

Hopefully by attending your local cross practice you’ve figure out
what tire pressure you can generally run. For me, on Challenge Grifos
it’s 30 PSI. When I get to the venue I inflate all my tires to that
pressure and do a few laps. As you ride you can let out a bit of
pressure till you feel you have it dialed in. It’s trial and error
backed up with a lot of data gathering from previous races and
training. And, as always, you can just use the cyclocross handshake.
Just squeeze the tire of someone you know who just raced and ask them
how that worked for them.

Q.  Do you have any other advice for a new cyclocross racer when trying to find the proper tire pressure to train or race with?

Go to your local cross practice. That’s the place to experiment with
tire pressure since there’s no penalty for flatting. Figure out what
you can run. Then start letting air out. Let it out in little bits
till you can feel the tire start to roll on hard corners. Add 2-3 more
PSI and figure that’s the bottom of your range. As I said that’s going
to vary with the tire, rider weight and style and environmental
conditions. That’s a lot of variables so always be trying a different
pressure and see what works for you. But the last thing you want to do
is experiment on race day.