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Old 05-28-2009, 06:49 PM   #11 (permalink)
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You can definitely go above the rating on the max pressure. This is what they assign to achieve. . . a safe boundary between normal operation and something bizarre happening.

I know people on here are all about going 50% above max sidewall sometimes. . .but I wouldn't do it. If your car drops through some of the potholes I've accidently hit(in NC mostly) that are 3-4 inches deep(maybe more) and rock my car chassis you can very quickly achieve burst pressure. Hypothetically its a warm day you've been driving for a little while, so your pressure is substantially higher(from driving and from the heat) and you hit a big pothole, at that point you've only got to jump up about 80 PSI in local pressure somewhere in the tire to achieve burst. Its not common I admit, but running above max sidewall is not common either. Its putting alot more molecules in the tire and making it behave in funny ways.

I would go with the 44 psi tires and only inflate to 49-50 and no higher.

Blow a tire off on the highway and I promise you guys will never go over that max rating again. Its honestly like driving on a solid sheet of ice.

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Old 05-28-2009, 07:11 PM   #12 (permalink)
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Sigh. Just found out from the UK's consumer report magazine and Germany's ADAC that the Firestone F590 has really high rolling resistance despite being a "fuel saver" and now I'm worried about the F580's (older version) having the same problem. So it's back to the EcoContact 3's but they are rated at 37 PSI which still worries me. The Fulda EcoControl is perfect (very good reviews, good price, fuel saver, rated at 51 PSI, everything I want) but the overall diameter is 5% smaller so the engine would spin 5% faster at the same speed, using up a little more fuel. Sigh.
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Old 05-28-2009, 07:20 PM   #13 (permalink)
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One other thing to consider is raising the PSI will increase your stopping distance. Raising the PSI puts less rubber on the road, putting less potential friction on the asphalt should you need to stop. Especially in a heavy car without ABS, this can become dangerous. Nothing like trying to do an emergency stop in a 2 ton vehicle on overinflated tires to make you lose a few PSI at your first opportunity.

And besides losing stopping power, you have decreased the cars ability to corner and, in extremely high pressure, can rattle your vehicle so badly it has the potential to cause premature wear on the body and suspension. So making your car roll easier will come at the cost of making your car stop and corner efficiently. Otherwise, we'd all be driving cars with temporary donut spares on all 4 corners.

On a front wheel drive car, I would be more willing to overinflate on the rear but not the front, since your front tires provide most of the stopping and all of the turning. To sum it up, use a bit of common sense.
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Old 05-28-2009, 07:24 PM   #14 (permalink)
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Quote:
Originally Posted by ShadeTreeMech View Post
On a front wheel drive car, I would be more willing to overinflate on the rear but not the front, since your front tires provide most of the stopping and all of the turning. To sum it up, use a bit of common sense.
Wouldn't that cause oversteer and the tendency to swap ends in a heavy stop?
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Old 05-28-2009, 07:28 PM   #15 (permalink)
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Eddles -

I use tirerack.com for all my tyre info. But you're SOL if they don't carry the tire you want. When I got my Continentals ContiProContact tires, I had to tell the tire-shop dude that they existed in 51 PSI. He called the warehouse and they had them later that day.

EDIT: If you get them from a shop, try to get the better quality tire valves. Supposedly you can get valves that are designed for higher pressure.

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Old 05-28-2009, 07:50 PM   #16 (permalink)
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Quote:
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EDIT: If you get them from a shop, try to get the better quality tire valves. Supposedly you can get valves that are designed for higher pressure.

CarloSW2
Cheers for help. Unfortunately, nearly all tires I'm looking at isn't in tirerack.com - I guess European tires isn't as common in the US.

But anyway. How do I ask for the valves? "Please fit better quality valves" is sufficient?

Thanks for your time!
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Old 05-28-2009, 08:19 PM   #17 (permalink)
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Eddles -

Quote:
Originally Posted by Eddles View Post
Cheers for help. Unfortunately, nearly all tires I'm looking at isn't in tirerack.com - I guess European tires isn't as common in the US.

But anyway. How do I ask for the valves? "Please fit better quality valves" is sufficient?

Thanks for your time!
Rats. I wish there were a "tyrerack.co.uk" for you.

I googled around, and I think the terminology would be "high pressure valve stems" :

SELECTING PROPER VALVE HARDWARE - May 6, 2002
http://www.techtirerepairs.com/tech_...0Issue%202.pdf
Quote:
...

Valve Stems – snap-in valve stems for passenger tires have a maximum air pressure rating of 65 psi (4.5 bars). This will allow snap-in valves to be used in all passenger and some light truck applications.

...

Valve Stems – TR600HP series valves for wheels with .453” valve holes and TR800HP series valves for wheels with .625” valve holes. These valves are designed for the higher air pressure of many of today’s light truck tires. These valve stems have a maximum rating of 100 psi (6.9 bars). Another alternative to a TR600HP valve would be a TR416 clamp-in valve. This type of valve must be used when using a metal extension and when the rim thickness is greater than .205” (5.2mm). The TR416 valve is used for wheels with .453” valve holes. Snap-in valve stems for passenger tires have a maximum air pressure rating of 65 psi (4.5 bars). This will not allow snap-in valves to be used in most light truck applications.

...
But, the above might not work if the *size* of the higher PSI valve stem is not compatible. I just don't know.

Let's wait for CapriRacer to chime in, he has the expert knowledge.

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Old 05-28-2009, 09:10 PM   #18 (permalink)
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Quote:
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Rats. I wish there were a "tyrerack.co.uk" for you.
There is. Tyretest.com

Thanks again re: valve stems, I'll ask them anyway.
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Old 05-28-2009, 09:24 PM   #19 (permalink)
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Quote:
Originally Posted by ShadeTreeMech View Post
One other thing to consider is raising the PSI will increase your stopping distance. Raising the PSI puts less rubber on the road, putting less potential friction on the asphalt should you need to stop.
Would you have the numbers on that? I've been hearing this for a few years now but am finding it impossible to find data on this increased stopping distance malarkey!

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Old 05-29-2009, 12:59 AM   #20 (permalink)
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Would you have the numbers on that? I've been hearing this for a few years now but am finding it impossible to find data on this increased stopping distance malarkey!
Drag racers use relatively low pressures to get more grip, but there's a world of difference between wrinkle-wall drag slicks and radial car tires!

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