Re: Tire pressure vs ride

Retired VIP wrote:


I can't find any. Tire dealer had no recommendation other than "30 pounds each", which they recommend for all cars to all people (great, huh?). If you can find a recommendation for TripleTreds on an '89 Grand Marquis I'm all ears.

The weight on my rear axle is definitely less than the weight on my front, I'm pretty sure even with the trunk and passenger compartment loaded to capacity. The manufacturer specified a bias of 4 PSI rear for all loads.
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Do you know who manufactured the tires? If so, contact the manufacturer and ask for a chart.

I keep 40 front and 35 rear on my 2000 Grand Marquis. That seems to give the best tire wear but the ride is a bit rougher. The tire sidewall list 45 psi at max load.
Jack
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Might be a handling thing; more pressure in the rear = more grip in the rear = more understeer than oversteer = safety on the road; and, no offense, but I would guess the Grand Marquis doesn't get inherently excellent handling from chassis design, so tire pressure tuning is probably in order.
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Understood. But just because one plus-sizes their tires, or, keeps the same size tire but goes up a speed rating or two - IE from S to T or V-rated, does not mean all common-sense goes out the window and the new tires are automatically set to the max. pressure placard on the tire. I just had an alignment done and the car was riding smooth - too smooth, in fact the tires were barely gripping the road! (sure enough, the alignment shop had inflated them to 35psi - I checked - they were 38-39psi hot). So basically NOBODY in this country knows how to set tire pressure!
I know my "new" Malibu(Saab-based) has a pretty hard suspension and actually rode better with the original S-rated tires. But I went ahead and got H-rated tires of the same spec. With the S-rated tires, I could inflate them up to 3psi over the door sticker(30psi), improve my rolling, and still have a smooth supple ride; with the H-rated Yokohamas - 31psi. Anything higher and the whole damn car rattles like Arlen Specter's jaw!
-CC
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_____________________
*Posted two days ago but disappeared into cyberspace* <sigh> here we go again...
Just because one plus-sizes their tires or goes up a speed rating(IE from S to H or V rated) doesn't mean to throw common sense out the window and fill the tires to their maximum pressure as listed on the tire.
My 2005 Malibu(Saab based) came with S rated tires. The door placard said 30psi. I could go as high as 33 and still be comfortable with them and get better gas mileage. I recently upgraded to the same size tire, a Yokohama, but H-rated. Now I can go up only a pound or two over the door placard pressure. The Malibu has a hard suspension already, and going significantly above GM's recommendations is like riding the Coney Island Cyclone. Fun, but not as fun. 31psi is where they'll stay.
-CC
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wrote:

I know of one vehicle for sure where the factory recommended pressures aren't the best to choose even for the OE tires and that car is the '01-'03 Prius. The factory recommends 35 front 33 rear but many owners have noticed underinflation wear patterns such as edges wearing faster than the center at the factory pressures and have used higher pressures instead such as 40/38 or 42/40. Some have even foolishly exceeded the sidewall max cold ratings but I have not yet heard of anyone showing overinflation patterns such as center wearing faster. A side bonus to this seems to be increased fuel mileage
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On Oct 28, 3:15 pm, Bruce L. Bergman

__________________ Not if you owned a 1996 Ford Contour GL as I once did, size P205-60R15. Front: 31psi Rear: 34.
Try ta figger that one out!
-CC
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Back in the days when dinosaurs which came from Detroit ruled the Earth, it was pretty much a given that the recommended pressure was way low for reasons of ride comfort, and "serious" drivers would pump another five or so pounds in. The advent of compacts and Japanese cars has made this wisdom unreliable, but by the same token, you still can't rely on the recommended pressure to be the best performance (excluding comfort) wise. A little trial and error may be in order.
Elsewhere, I saw a rule of thumb **for an approximate starting place** for trial and error: Pressure in PSITotal weight of car/100 + 2 lbs extra on the heavier end of the car + 2 lbs if car has stock suspension
(Notice that trial **and error** should take care that the error part isn't too bad.)
That said, my experience is that with pressures at recommended or a few lbs higher, I've never seen excess wear on the centers, indicative of overinflation.
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That's the thing on my truck - I feel my tires are WAY overinflated, but the ride and traction say otherwise. unfortunately, it's going to snow here soon, so I'll see how the grip compares vs normal pressures.
I've been meaning to do that in the winter anyway - run my tires at 5 pound increments from 20 to 50 and see if I can determine any difference in handling or traction. I know on my Trans Am, I can feel the difference between 30 and 35. The tradeoff is 35 gives a sharper turnin but there's more traction at 30 - the back tires spin easier at 35.
Ray
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Interesting; normal recommendation is more inflation to prevent hydroplaning; might be a difference in tread pattern. I assume your tread pattern is pretty "aggressive" and therefore probably doesn't need help channeling the water out, compared to the close-treaded allseason car tires?
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z wrote:

I can see too low also allowing water to get under the center of the tread and causing trouble.
I do have large tread lugs which channel water although some folks cuss these tires in the wet. They behave for me. Most seem to be running them too hard though. They seem think larger tire means larger pressure.
We use a 'chalk' test to see. That is running some chalk marks across the tread and drive a short bit straight, then seeing how much chalk is left. On my style of tire, the best footprint for traction and handling leaves about 1/4" on each edge not touching.
Running either too low or too hard is pretty bad on large tires in particular and in certain conditions can cause big trouble.
I even remember the Volvo 240 GLT I used to own also didn't like hard tires either, they would hydroplane bad. They were 60 series, so 'wide' tires.
Mike
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Oh yeah, good idea; I'd forgotten about that. A while back I got enamored of trying to take the tire temps across the tread like the pros do and wasted a lot of time and effort trying to get usable readings with the crappy equipment I can afford on no budget; should have remembered the simple old techniques.
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EdV wrote:

I sometimes drop the pressure in Winter, to maybe 34, but I think the tire itself matters more than the pressure.
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Built_Well wrote:

35 is fine if you aren't sure your readings are accurate. 38 is probably best of you can get it.
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