But those rain tires were made of moist bubble gum. The compounds were so soft that if the road dried you'd wipe the tread right down to the carcass in a few laps, assuming you could keep it from melting and sending you into the marbles. That effect overcomes what I'm talking about, and the hypermilers prefer hard compounds to minimize rolling resistance in any case.windshieldbug wrote:OK; I'll bite:tbn.al wrote:Subtract the savings on 100 tankfuls from the cost of repair after a collision caused by hyper inflated tires on a rain slick road and you are major screwed.
Racing in the rain meant you put on well-treaded tires pumped way up to drain water from the treads.
On a "rain-slicked" road, I'd think it would be more tread-wear than over-inflation causing major copulation.
The size of the contact patch is directly controlled by the inflation pressure. If you have a 1000-pound load on a tire, the contact patch will be 50 square inches at 20 psi and 20 square inches at 50 psi. It is true that the resulting friction force is not controlled by the contact patch, but rather by the normal force and the coefficient of friction. But that assumes that adhesion is linear, which it isn't. The small contact patch has less area over which to dissipate surface heat, and therefore will go non-linear (i.e., melt) when the rubber breaks down from heat quicker. Underinflation also causes heat, but that's heat back into the tread away from the surface as a result of hysteresis inefficiency caused excessive deflection through the contact patch (and high slip angles). Translated: Underinflation causes tires to get hot and are drag to increase. Overinflation causes tires to skid more easily especially with hard compounds and wet streets. Inflation that leads to even wear usually provides optimum traction in the widest range of conditions.
I also used high pressures when I raced cars on street tires, but the reason was to control the shape of the contact patch. The higher pressure would give me a patch that was wider and shorter (rather than longer and narrower), which would maintain proper tire geometry in hard turns. That would minimize wear on the corners of the tread, and performance and race tires are wide with square corners. Note that in round-tire applications, such as bicycle and non-fatty motorcycle tires, that does not apply--there are no corners on the treads.
There's a reason off-road drivers and skilled snow-drivers "air down" when driving in loose stuff. They need that contact patch as large as possible to provide traction rather than tearing the surface loose (for them it's the surface of the road or what's on the road, but for us it's the surface of the tire--but it's the same principle either way).
Another annoying trait of the hypermilers is that they coast down for about a mile approaching a stop to avoid using their brakes. I love it when someone driving a Pius--er--Prius does that--taking away much of the effect of regenerative braking. But it forces everyone behind them to slow down along the same coast-down curve as the hypermilers, which is always longer and more gradual for them because their tires are overinflated. That means everyone behind them is constantly cycling their brakes and throttles to maintain following distance.
But mostly its something that drives up the annoyance level of the typical psychotics behind the wheels of the surrounding cars, and that is exacerbated (no, that's not related to copulation) by the self-righteousness that the hypermilers exude. I wonder if they have figured in the cost of getting bumped into the ditch by a maniacal redneck in a Ford F-350 pickup.
Rick "finding balance between extremists" Denney
