A usually reliable source wrote:
> Baaaaa...I guess Jobst said it, it must be true. I'm not a tire engineer but like I said,
> rain tires for motorcycles and racing cars, always have tread when compared to 'dry'
> tires..why is this??
>
> Also all aircraft tires I have seen on A/C I have flown have tread as well, so there is someplace
> for the water to go, under the tire.
>
> Why are all the 'rain' tires now produced for the auto industry treaded? Why not slick??
Because wide, low-pressure tires, traveling at high speeds, are at risk of a phenomenon called
"hydroplaning" in which the tire actually "surfs" on top of a layer of water.
Here's the relevant entry from my Bicycle Glossary:
"Hydroplaning
"When an automobile is driven fast on wet roads, especially if it has worn-out tires, a cushion of
water can build up under the tires, preventing the rubber from contacting the road. This is very
scary and dangerous, because it leads to a total loss of traction.
"Fortunately for cyclists, this cannot happen to a bicycle; they don't go fast enough, nor have
a large enough contact patch, nor do the tires run at a low enough pressure to make
hydroplaning possible.
"Even with automobiles, actual hydroplaning is very rare. It is a much more real problem for
aircraft landing on wet runways. The aviation industry has studied this problem very carefully,
and has come up with a general guidline as to when hydroplaning is a risk. The formula used in the
aviation industry is:
"Speed (in knots) = 9 X the square root of the tire pressure (in psi.) Here's a table calculated
from this formula:
[table snipped, 'cause it doesn't display well in ASCII, but you can see it at:
http://www.sheldonbrown.com/gloss_h.html#hydroplaning]
"An ill-founded fear of hydroplaning often leads people to buy bicycle tires with inefficient tread
patterns, when they would be better off with slicks."
Sheldon "Bald Is Beautiful" Brown +--------------------------------------------------------+
| Education consists mainly in what we have unlearned. | --Mark Twain |
+--------------------------------------------------------+ Harris Cyclery, West Newton,
Massachusetts Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com Hard-to-find parts
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