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Old 01-08-2008, 12:21 PM   #11
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Originally Posted by Biffmeistro View Post
Upping psi won't necessarily give you worse handling or stopping. I remember an article that was linked from here that spoke of a police department upping their trainer vehicles to 60psi, and that gained quite a bit of performance in all aspects.

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Old 01-08-2008, 01:17 PM   #12
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If you want a quick and "dirty" contact patch tester, you will need: a few pieces of white paper, some dark paint, pen/pencil/crayon, tire gauge and a tire jack.

1) Air your tire up to max sidewall,
2) jack the tire up,
3) paint the bottom of the tire and put a clean sheet of paper underneath,
4) and release the jack until car is fully resting on the tires again.
5) Jack back up, remove paper and label appropriately
6) Lower tire pressure to next gradient, add paint and new sheet of paper, and lower jack again.

Lather, rinse and repeat.

-- Randall

McIntyre's First Law: "Under the right circumstances, anything I tell you may be wrong."

O'Brien's First Corollary to McIntyre's First Law: "I don't know what the right circumstances are, either."

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Old 01-08-2008, 04:54 PM   #13
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Good idea, I had a similar thought. It's raining lightly today, so I thought about dipping a dry tire in a damp spot in the driveway, then raise it up again and see how much area was wet. The problem is with my car the rear wheels rotate slightly when the car is jacked up/down. The front tires slide in/out when raised/lowered. So the inkblot would squirm and look larger than it really is. hmmmm...
Dave W.
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Old 01-08-2008, 07:40 PM   #14
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That article isn't correct. Seriously - a) the tire pressure on a Crown Vic CRUISER is 44 PSI. Likely closer to 35 on a regular vehicle, some even 32.

I AGREE that tire manufacturers are stressing smoothness of ride. But do braking tests on your own vehicle (recommended stretch of closed road) - overinflate by say 35 PSI and you risk sidewall blowout and you WILL have increased braking distance. This on STOCK tires. Better tires will have better characteristics.

The article also notes *increased stopping distance with underinflated tires - and their reasoning IS correct. Easy to hydroplane - and patch is REDUCED because basically the middle pops up. But the steel belt will NOT keep the contact patch the same size. If it deflects in one direction, it will deflect in the other. It will HELP, but anyone can test this. Overinflate tires OFF the vehicle - you can see it bend, and eventually it WILL blow up with enough pressure.

Given the example - 100 PSI Crown Vic Cruiser tires - anyone know the rating on Cruiser tires? They are NOT standard tires. Closer to racing tires, because they have to be rated higher for high-speed chases, etc. Exactly how many miles did the guy run on the sidewalls? Just because it can be done doesn't mean it SHOULD be done. Let's see 50,000 miles run on those sidewalls and see if they pop. Got a twenty that says LONG before then.

If it were TRULY better handling and better stopping power, don't you think police departments would be rushing out to make a law that no passenger vehicle could have over 50 PSI in their tires, but law enforcement could? Don't you think there would be a special tire that only police were allowed to own? There are already laws that say the general public can't have lights, sirens, what have you.

There are different temp ratings, traction ratings, temp ratings on tires. I have another twenty that bets that Crown Vic Cruiser tires have better traction, temp and speed ratings than those on a stock Geo Metro, for instance. Gee - tougher tire, likely to be easier to pump up higher, and with more base PSI ratings! You have to compare apples to apples.

Now it's possible to redesign a set of tires for maximum FE - but there would be trade-offs. You can't have better FE AND better stopping distance AND better price AND better handling. Pick 2.

There's also handling - may increase with pressure increase, but there IS a point at which it starts getting worse. Think racecars. Ever see the pressure LOWERED in the pits for better handling? Every single race. It happens at some point.

Looking to trade for an early 1988 Honda CRX HF (Pillar mounted seat belts)
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