Quote:
Originally Posted by IndyIan
Just thinking out loud here, isn't solo 1 racing a good sample set for how "over" inflated passenger car tires perform? Braking and acceleration to and from 100mph, powersliding sideways at 80mph? It may not be sustained for hours but the tires can be heated enough that they lose grip rapidly. Then they are pounded over curbs too?
I think this whole debate comes back to the fact that manufactures don't test their tires at higher pressures and therefore can't say they are safe at those pressures, due to legal issues etc.
We have lots of anecdotal evidence that tires can be over inflated from many people here, and people racing solo1 and 2, that tires don't have a problem being used at 40-50 psi even under extreme racing conditions, or coasting down the road at 50 mph.
We also have no official data on how 40-50psi tires perform for braking or turning, but again solo 1 and 2 folks don't inflate the tires to these pressures for fuel efficiency. These pressures result in faster times. Does this translate to the street? I think so but I'm not an independent tester.
I also think that some auto manufacturers pressure recommendations are probably pushing the envelope of safety due to underinflation. They want some vehicles to float along as smoothly as possible so people will buy them. The ford explorer fiasco showed this, if those people had started with tires at 38 psi instead of 28 psi their lack of maintenance would've been far less likely to result in a blowout.
Ian
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Ian,
Street tires used in racing and solo have short lives. While the issue about how a car handles at higher inflation pressures is supported by the experience of racers and soloists, there are some issues that aren't.
Above TEin mentions that Showroom Stock racers used to inflate tires to high pressures, too. But this was to overcome an inherent shortcoming of the cars - severe understeer - and the car went faster around the racetrack because of the balance was changed. It's quite possible that the reason this worked was because the rear end tires had lost grip and this was helping the vehicle pivot - but it's also possible that this was the result of the increased spring rate.
I think everyone would agree that racetracks and solo courses are not like the street in that the road surface isn't monitored for debris and brushed off every time some is found, not to mention there aren't any pot holes.
But you bring up 2 good points:
1) That the placard pressure has included in it ride qualities. The Ford / Firestone issue comes up constantly as an example that the placard pressure is somehow faulty. The way you've worded it is better - that the lack of maintenance is partially at fault - and it is certainly true that regular tire pressure checks would have helped the situation.
2) That tire manufacturers CAN'T say that tires are safe above what is written on the sidewall - so they are obligated to issue warnings pointing out the words "maximum". This is a valid point, but that doesn't take into account that the tires are designed for use at these lower pressures - or put a different way - NOT designed for use at these higher pressures (and they would be designed differently for higher pressures)
While I'm on this part let me address another response along similar lines:
Quote:
Originally Posted by jamesqf
Just a thought: Why is it that the skinny tires on my road bike, with sidewalls not much thicker than a stiff sheet of paper, can take - no, require - 100 PSI or more, but the much thicker sidewalls of car tires can't (in some people's opinion, at least) take more than 32 PSI?
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If you were to calculate the tension on the ply cords, you would quickly find out that the distance around the perimeter of the tire (in cross section) is a major player. Put another way, a little bicycle tire doesn't put much tension on an individual ply cord even at 100 psi. I'm going to take a SWAG, that plies used in bicycle tires are more limited by the ability to manufacture the tire than by the design of the tire - and that the limiting factor in the tire (as far as pressure is concerned) is the bead.