I just found the following quote from John Childs in cyclingforums.com
archive. It seems to make sense and he offers several very helpful
guidelines. Another very succinct, but different quote from
"Krashin'Kenny", offers this formula: fill the tire with 1psi for every
10 ounds of body weight. That seems a bit low to me, but hey, what do I
know?
Here's the John Childs quote:
The ideal tire pressure for muni depends on a lot of different
factors.
It depends on rider weight, stiffness of the tire, what tire you're
using, how new the tire is, what tube you're using, what rim you're
using, your riding style, the terrain on the trail, how rocky and
rooty
the trail is, and other factors. There is no set rule for tire
pressure
that will hold for everyone for every situation.
I typically ride with something between 16 psi and 22 psi. It all
depends on the trail and whether I remember to check the pressure
before
the ride.
The basic concern is that you want enough air in the tire to keep from
getting pinch flats. You also want enough air in the tire so the tire
doesn't fold over when doing side hops or when pecking up a hill.
Here's a set of guidelines or a heuristic to help in determining ideal
tire pressure. This is a list that I posted back in 2000 and has been
copied to the 'tips section of Muniac Manor'
(http://www.muniac.com/tips.htm#pressure)
1) Ride right into a root or a similar obstacle. Don't try to hop over
it, just ride right into it and try to roll over it. If the wheel
bounces back instead of rolling over the root consider lowering the
tire
pressure. If you lose traction on the root consider lowering the tire
pressure.
2) Side hop up a hill. If the tire folds over increase the tire
pressure. Wider rims also help prevent the tire from folding over.
Tires
with stiffer sidewalls (like the Intense DH tires) are less likely to
fold over than tires with softer sidewalls.
3) Hop and jump on a log or similar obstacle perpendicular to its
length
(the length of the log will be to your left and right). Pick a log
that
is about 6" or less in diameter. A parking lot divider will also work.
If the tire bottoms out then increase the tire pressure.
4) If you get pitched off the MUni during a ride because the tire
bounced backwards (or upwards) after hitting an obstacle instead of
rolling over the obstacle consider lowering the tire pressure.
5) If you are going to be riding on fire roads or other similar "easy"
trails consider increasing the tire pressure to decrease rolling
resistance.
6) If you lose traction during a ride consider lowering the tire
pressure.
7) If you ever get a pinch flat consider increasing the tire pressure.
Also look for a thicker tube like the Intense DH tubes.
In the end it all depends on the rider, the terrain, and the style of
riding. The pressure that works for me may not be the pressure that
works for you.
--
john_childs - Guinness Mojo
--
terrybigwheel
Terry
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