Tyre pressures for clinchers and rear wheel drift!

othello

I'm running a pair of Challenge Grifo 32 Pro clincher tyres, and I'm struggling with the tyre pressure and feel when riding.

I had them pumped up quite hard before racing on Sunday (at Wessex league) -- I could press down with my thumb and make the tyre move a little. I dropped some air out of the tyres during the practice lap to get more grip, and could definitely press the tyre down with my thumb.

I got good grip on the short sharp banks etc.

BUT

On any bumpy ground I was bottoming out the tyre on the rim! I'm no lightweight, but at 13.5 stone I'm mega heavy either.

I also had a big case of rear wheel drift in the corners, where the tyre was squirming! To be honest was mega fun, and after a lap I had it almost like a power slide, but it was pretty disconcerting. It never slipped, so much as squirmed all over the place.

Is that how it is for everyone riding low pressure CX tyres? Or just a clincher problem? The bottoming out on the rim is the most freaky bit to be honest.

trek_dan

The rear wheel drift is normal, disconcerting at first but fun. I'm no expert but it definitely gets worse as the tyre tread gets clogged with mud. The rim bottoming out is the reason most people run Tubs over clinchers, nasty hit on a tree route or similar and it could pinch flat.

tgotb

You have to find a balance between babying the bike over roots (and possibly avoiding some of the bigger ones) and losing a bit of grip by having the pressures a bit higher. That's one of the interesting things about CX, you have to ride round the course, and figure out what pressure is going to work best for your riding style (and where to adjust your riding style to suit your choice of pressure). That could mean pumping them up relatively hard, bombing the wooded bit and having to run the power climbs, or it could mean running them softer, holding off a bit in the woods and having more grip everywhere else. The right answer is going to vary for every different rider, for every different course, and on every different day.

FWIW, I'm a similar weight to you, and was running 22psi front, 24psi rear on that course. I'm on tubs, but if I'd been on clinchers I'd probably have run them at a similar pressure. Of course that doesn't mean those pressures would be right for anyone else!

Don't trust the gauge on your track pump, you really want a digital pressure gauge.

Embrace the rear wheel drift, and get used to how it varies in different conditions, and when you put different amounts of power down. It can often be your friend!

othello

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19707657#p19707657]TGOTB[/url] wrote:

You have to find a balance between babying the bike over roots (and possibly avoiding some of the bigger ones) and losing a bit of grip by having the pressures a bit higher. That's one of the interesting things about CX, you have to ride round the course, and figure out what pressure is going to work best for your riding style (and where to adjust your riding style to suit your choice of pressure). That could mean pumping them up relatively hard, bombing the wooded bit and having to run the power climbs, or it could mean running them softer, holding off a bit in the woods and having more grip everywhere else. The right answer is going to vary for every different rider, for every different course, and on every different day.

FWIW, I'm a similar weight to you, and was running 22psi front, 24psi rear on that course. I'm on tubs, but if I'd been on clinchers I'd probably have run them at a similar pressure. Of course that doesn't mean those pressures would be right for anyone else!

Don't trust the gauge on your track pump, you really want a digital pressure gauge.

Embrace the rear wheel drift, and get used to how it varies in different conditions, and when you put different amounts of power down. It can often be your friend!

Awesome, thanks.

Yeah, I rode light in the woods (which was my best bit as I like my mountain biking a lot), and was glad for the lower pressure to ride the banks by the school.

Now I know the tyre drift is normal and expected I'll stop worrying about it. To be honest, it was a lot of fun and the more I went for it, the more the tyres wanted to grip. It came down to having the balls to do it!

I was still rubbish mind, but wasn't last and that was my aim for the race