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lhbernhardt 07-21-07 05:21 PM

Crashing on wet pavement
 
Hey, I just wanted to get some thoughts on why you think some riders were slipping & crashing while others had no problem with the wet roads on the Stage 13 ITT. (Let's ignore the fact that the roads were drying out towards the end.)

Like Kloden's crash. He was going at a reasonable speed, very cautious around that right-hand turn, then next thing you know, the bike just slips out from under him as if he's on a sheet of ice.

Is it the way the rider balances on the bike? Are the disk wheels too stiff? (Maybe having a bit of spoke flex helps the tire adhesion?)

Curious to see what you think.

- Luis

godspiral 07-21-07 05:33 PM

Kloden's crash did seem weird... didn't seem to be leaning very much or going fast. maybe he had very high tire pressure.

TYB069 07-21-07 06:16 PM

A bit of sand or gravel perhaps?

LWaB 07-21-07 06:27 PM

Oil or diesel from vehicles following earlier riders?

Jinker 07-21-07 11:16 PM

Another rider crashed in the exact same place suggesting something was up with the surface. Could have been sand, a bit of greasy asphalt, or something else.

TT bikes are pretty squirrelly compared to their normal bikes. They're also on the narrowest highest pressure tires which aren't very forgiving at all.

I as well was surprised by how conservative the lean angle on his bike was when it went down.

In terms of bump absorption, the difference between the stiffest and softest wheels is going to be less than the effect of going up or down just a couple PSI in tire pressure.

I would *love* to see some actual measured numbers showing that wheels make any difference to ride harshness. The tests I've seen online have indicated that even under several hundred pounds of load, a wheel will only compress on the order of magnitude of a sheet of paper. Far less than a tire. Vertical stiffness in bike frames is also incredibly high due to their shape. Forks may offer more bump absorption.

Running 18mm tires at huge PSI is much more likely to be a factor.

Sci-Fi 07-22-07 01:03 AM

Don't think it was raining hard enough to wash away the oil and grease from the road. Then there's the quandary of which air pressures to use..too low and you might add too much drag...too high and the bike will slip under you in the turns. Don't think there are too many tread patterns or tire compounds to choose from for those conditions. Forgot the name of the rider but I seen him with his legs spread out at that turn and it didn't look like there was a problem until he went off...so he probably felt the bike was slipping/sliding already, maybe one wheel locked from braking and that was the reason why he decided to go straight and catch it/recover when he hit the dirt on the other side of the road. In any case a lot of riders fell, the worse one was after going through that tunnel and making a sharp left hander.

meb 07-22-07 01:32 AM

Quote:

Originally Posted by Jinker (Post 4903093)
Another rider crashed in the exact same place suggesting something was up with the surface. Could have been sand, a bit of greasy asphalt, or something else.

TT bikes are pretty squirrelly compared to their normal bikes. They're also on the narrowest highest pressure tires which aren't very forgiving at all.

I as well was surprised by how conservative the lean angle on his bike was when it went down.

In terms of bump absorption, the difference between the stiffest and softest wheels is going to be less than the effect of going up or down just a couple PSI in tire pressure.

I would *love* to see some actual measured numbers showing that wheels make any difference to ride harshness. The tests I've seen online have indicated that even under several hundred pounds of load, a wheel will only compress on the order of magnitude of a sheet of paper. Far less than a tire. Vertical stiffness in bike frames is also incredibly high due to their shape. Forks may offer more bump absorption.

Running 18mm tires at huge PSI is much more likely to be a factor.

When under wet conditions like this, does anyone ever go a little wider i.e. 25mm tire with less pressure to play it safe? Would think for the domestiques and sprinters on a day like this just averting the crash would make a lot sense even if the rolling resistance might loose more than what you gain on the slippery corners.

Even some contendors you'd think a few seconds might be worth risking an injury, although maybe by then it was apparent there and with weather forecast access it was going to start drying.

SSIndyRider 07-22-07 07:00 PM

I don't know how long it was raining before the bikes were set up, apparently not long or not expected to stay - Ligget or Sherwin made comment that many riders may be caught with not having made air pressure adjustments for the wet pavement.

godspiral 07-23-07 04:50 AM

Chris Boardman was on VS/OLN during the stage and said he'd put "road" tires instead of TT tires in the rain... which I presume means 23 instead of 18.


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