Wipeout!

the_urban_spaceman

Hello CXers. A newbie here looking for opinions.

Today I went out on my CX bike. It was raining and wet in west London. Whilst turning right on a roundabout, at a reasonable speed the front wheel went from under me and I wiped out reasonably hard.

No harm done but I am baffled as to how it happened.

I am certain that under the same circumstances my road bike would have handled it fine, so why did my knobbly tires at about 60% of the pressure react like I was on an ice rink?

The tires are Vittoria Cross XG Pro II Folding 700x34mm which I was running at 60 psi. I'm about 71 kg.

Crap tires? (The reviews online wouldn't indicate so). Too high psi? (Not from what I've read - but happy to be told otherwise). Or are CX tires just generally worse on the road? (Which would make absolutely no sense to me).

Would love some thoughts

antsmithmk

Prob a patch of diesel

Jterrier

Cx tires have less grip on tarmac by a long way. The contact patch is way smaller.

the_urban_spaceman

Jterrier wrote:

Cx tires have less grip on tarmac by a long way. The contact patch is way smaller.

Okay this makes sense. I shall take care on the road, particularly in the rain. Thank you.

Jterrier

Actually also your pressures were way too high for knobblies. The tire would be balancing on its treads. Drop them down so there is more squash and deformation.

the_urban_spaceman

Jterrier wrote:

Actually also your pressures were way too high for knobblies. The tire would be balancing on its treads. Drop them down so there is more squash and deformation.

Ah okay, I was following a guide online but would much prefer some practical advise. Are we talking 50 psi or even lower? My understanding is that with clinchers I can't go too low.

tgotb

It's complicated...

Firstly, on the road anything above ~40psi should be fine for those tyres. If you push them to the limit they presumably won't have quite as much grip as road tyres, but they'll be good enough, and the bike handling will be fine. Don't expect anything special in the way of grip in the mud though.

At the other extreme, racing off road, you want to be much lower, maybe start at 25-30psi. A fairly good (and often-quoted) guideline is that if you're grounding out the rims (gently, with inner tubes) once a lap, you're about right. With tubeless and tubular tyres you can go lower; I have raced at 12psi in the past, and rarely go above 20 (I'm 85kg). However, ride on the road at these pressures and the handling will be terrible. Quite a few people have come to grief riding home after a training session. Racers learn to take tarmac corners somewhat gently.

As for your wipeout, sounds like bad luck to me; I use a pair of those for training, and at higher pressures they've been rock solid on the road.

ugo.santalucia

It happens in autumn and winter, often roads are wet and slimy and roundabouts force you to bend more than you should, if you aim for the apex... I don't know anyone who hasn't gone down at a roundabout at least once

bendertherobot

Yeah, I've never once struggled on road with those in the wet even at high PSI. One of those things. I'd not really make a habit of using them because it is also true that there is less contact.

the_urban_spaceman

That's all very helpful, thanks chaps. Will put it down to a fluke then.