hydroplaning

[Brett Dikeman]

At 11:19 AM -0500 5/28/04, Livolsi, Stephane wrote:
>This discussion is interesting - NAC - but interesting and so far no one
>has insulted anyone else...so far....:)
>
>Looking at a different example...how does a bike weighing say, 25 lbs,
>having 2 tires pumped up to 90psi exert 180psi on 2 little contact
>patches where the rubber meets the ground?  At 90 psi those tires are
>gonna be firm with very little contact patch.

Incorrect.  The tire contact patch will expand until it meets the 
load.  Under no weight load, the tire itself takes the load as 
tension stress.

At 90psi, to support 180lb, the front and rear contact patches would 
only have to be one inch square each.  Since bike tires are so large 
in diameter, the contact patch is fairly long.  Say, 3-4 
inches...which means the contact patch need only be about a third to 
a quarter of an inch wide.  Does that qualify as "very little contact 
patch"?


At 1:32 PM -0400 5/28/04, Mike Arman wrote:

>Comparing snow performance with rain performance will be misleading.
>
>Snow is a fairly compressible solid, and it can be squashed and 
>knocked out of the way.

The whole idea behind a narrow snow tire is to do all 
that(push/squash), instead of riding on top of the snow, which gives 
you absolutely zero traction.  The tread, particularly on the Hakka 
Q, is designed to do just this- pierce through the snow to contact 
the subsurface, via a spiral-siped tread.  The tread does little 
without enough pressure behind it to push it through the snow.

>I also think a lot of tire performance claims for CONSUMER grade 
>tires are mostly marketing hype - so just because some tire 
>manufacturer claims their tires are for rain, that doesn't mean they 
>are any good at it.

Yup.

>I'd like to suggest we take a look at F-1 or even Nascar race car 
>tire technology a little - those guys go blasting around WAY faster 
>than 49 mph on wet tracks - how do they deal with the hydroplaning 
>problem?

For the F1 guys, LOTS and LOTS of downforce and different tires. 
Much more so than they would use on dry track.  NASCAR guys don't 
"do" rain- they put out the caution flag and go for a sunday drive 
behind the pace car.

>  Is it tire compound

Yes- softer, designed for cooler running.  I don't know about F1/indy 
car tires, but many race tires like to run in the 200 degree 
range(varies quite a bit depending on the tire) which you'll never 
hit in the wet.

>, tread pattern

Yes- grooves to allow the water an escape route, and tiny holes in 
the tire surface to suck up the water into the tire(surface tension 
and pressure help here) and "remove" it from the track surface; the 
water is then thrown out of the tire while it's not in contact with 
the track.  Hence the giant rooster tails.

>  Or do they just close their eyes and pray?

Quite a bit of that as well, yes.

That's not all.  Ferarri's cars for example, I know have a big button 
marked "RAIN" which probably changes a whole bunch of stuff over at 
once.  They can change dozens of parameters in car / from the 
driver's steering wheel these days; Schumacher's wheel from 2001 
looked like a audio mixing board, and it got even fancier in 
2003/2004 with a high-resolution LCD display and whatnot.  F1 has 
turned into a video game, not a game of money, chance and driving 
skill.  Pretty sad- engine development and manufacturing is in the 1 
Billion dollar range per season.  No, that's not a typo- 1 billion 
dollars.

>  I know they have different tires for wet and for dry, anyone know 
>exactly what the differences are?

Pretty much everything that matters- tread and compound.  They also 
absolutely have to stay cool, or they self-destruct quickly.

>(I also like the idea that if my tires are flat (hence zero 
>pressure), the car is weightless - which means it can fly!)

The contact patch expands until contact patch x pressure = vehicle 
weight; obviously vehicle weight does not change to meet tire 
pressure(however, force on the wheel does change with weight 
transfer).

   Since zero would mean an infinite contact patch size, the tire 
expands out until you're riding on the rims, and after about 50 feet, 
your tires are now large, and expensive, doorstops- in part because 
several hundred pounds of weight is now spread across less than a 
square inch of surface area(ie, the wheel rim).

Brett
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