Tyre Pressures

Dave195817

HI all!

I'm fairly new to cross racing, and seem to be struggling with getting my tyre pressures correct. I'm currently running 700x32 cross tyres with around 45psi, but seem to be loosing the back end whenever I come into contact with slightly greasy ground. The ground is still very hard, however the grass on top is wet/greasy.

Any thoughts?

DavidBelcher

Dave195817 wrote:

HI all!

I'm fairly new to cross racing, and seem to be struggling with getting my tyre pressures correct. I'm currently running 700x32 cross tyres with around 45psi, but seem to be loosing the back end whenever I come into contact with slightly greasy ground. The ground is still very hard, however the grass on top is wet/greasy.

Any thoughts?

You can probably drop it by another 5 psi - doesn't sound a lot but will make a difference. Best not to go too low, though, <35 psi in a CX clincher tyre leaves you very prone to pinch-flats, as well as the risk of a spill whilst cornering on harder ground (been there, done that) - the back end tends to slide too easily.

David

Monty Dog

It depends on your weight, riding conditions and tyre choice - often a case of trial and error to find a pressure that you can run safely without the risk of pinch punctures. I run clinchers at about 30psi and tubulars less, but I only weight 60kg.

Barbarossa

Ride the course at race speed - if your tyres never bottom out, they're too hard. If they bottom out regularly, too soft. If they bottom out once ore twice during the lap, they're about right.

Paul 8v

I'm a bit heavier than your average cycling cross whippet at 85kg and I only run them at 40 so it does depend opn your weight. Barbarossa is probably closest to the truth in what he says. Because the weight of a rider varies so much it's very hard to work out the pressure required, it's not like a car where the weight of the driver makes very little difference.

milese

I'm 72kg and ran 40 psi at the weekend on a greasy / increasingly muddy field and felt that they should have been lower as I slid around (and off) a lot with Schwalbe CX Pro tyres.

I've done very limited testing, but now certainly intend to.

Putting talc on your inner tubes is meant to reduce the risk of pinches.

FransJacques

Redbeard said it perfectly above.

BTW when he says "bottoming out" it means gently bottoming out the rim on the tyre when riding through a shallow depression on a trail and floating the bike onto the rim.

This doesn't mean ramming your front wheel up some sharp concrete steps or hitting a jutting rock. That's "bad" bottoming out and will likely pinch the tube.