tyre pressures

[hiflier]

When I went on a 'speeding awareness' course recently the instructor posed the question, 'If you're going to embark on a long motorway trip would you change your tyre pressures?' Apparently the correct answer is yes, increase them. But is this really true? As a pilot I've seen aircraft tyres blow out (not thankfully blow up) because of excessive pressure, caused by overheating of the wheelbrakes, following one of the well-known gas laws (pv=rt, where p=pressure, v=volume (obviously fixed), R is a constant and t= temperature: ergo, higher temperature, higher pressure inj same volume. And car tyres get hot when driven fard and fast. So I maintained that the pressures should actually be reduced under these circumstances. But no joy from the instructor!

[Fitzer]

All car handbooks I've ever seen instruct higher tyre pressures for full loads/higher speeds. Increased pressures are required to withstand the higher forces generated at higher speeds or increased loads, the upper pressures are well within tolerance even allowing for the extra pressure generated by heat. Your crucial word is excessive, the increased pressures aren't excessive.

[TWR]

I usualy check my tyres weekly Hiflier, I keep them to 30psi including the spare, tyres do increase when warm / hot, there is obviously a difference in weight regards a plane to a car, HGV depending on make will blow out with over pressure but that due to the weight + what we used to call, Bandag Specials ( Cr@p) tyres, each to their own but I know what I would do, 50yrs +driving has taught me that. how long has that person been driving?

[tonyav]

TWR, weren't those Bandags remoulds if I remember correctly.

[TWR]

Hi Tony, you could tell them a mile off, the remoulds were all over the motorways.

[tonyav]

Yep, TWR them are the ones I had in mind.

[TWR]

The firm I used to work for tried these things out, the weight then was 32ton gross these tyres blew out as soon as looking at the, the firm quickly stopped using them.

[tonyav]

I'm not surprised TWR, but I suppose they were cheap.

[TWR]

In comparison to Good year/Dunlop, they were cr@p, the time issue also, at times you were on the hard shoulder waiting for either National Tyres to come out that in-turn at times made you late for deliveries

[tonyav]

Yeah, false economy I think TWR.

[TWR]

Are you from the B/ham area Tony?

[jomifl]

On a straight road I believe most of the heat in a tyre is generated by the flexing of the sidewall. If you increase the pressure of the tyre there is less flexing so the tyre runs cooler and saves energy. If the sidewall gets too hot it can delaminate.

[chas2008]

its recomended but in reality who does, especially in this day and age where so much driving can be 50% A roads 50% motorway all on the same day...as long as mine are at the recomended pressure im happy.

[Toureman]

The instructor is an idiot!

Why mention tyre pressures at all in a speed awareness course?

There is a big difference with aircraft and car tyres, why mention that?

Planes land at high speeds and the plane tyres are stationary at the time they land, how can they be compared with car tyres.

There's also a big difference between truck remoulds and good car tyres.

Keep your car tyres at the manufacturer's recommendations!

[MantaRay]

I've yet to see a car handbook recommending increasing tyre pressures for 70 mph motorway trips, though some indicate a higher tyre pressure for prolonged high speed driving c.100mph plus, presumably for the autobahn and a few other places where one can actually drive at high speed. Tyre pressures are normally varied according to the laden vehicle weight, i.e. number of persons onboard, amount of luggage in boot, etc.