Pressure - more is better

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That is quite a study. Very interesting. I keep all my tires on all vehicles at 35psi cold. The thing that I don't like about going to 40+PSI is that is beats the living [censored] out of front end and suspension components. I think it makes the tire so hard there is no give and the front end takes the brunt of potholes and expansion joints, etc.

Anyone else care to chime in about their experience with 40+ PSI in their tires.
 
I tried it for a short time, it was bone jarring. I eventually settled on +3 psi over recommended pressures which brought it up to 35 front and 33 rear.
 
I do 40psi in all my tires. I think it helps the tires last longer and keeps the tire more stable in a panic stop. I have used a contact pyrometer and for a given speed on the freeway the temps were a bit lower and more important more even across the width of the tread. This I tested a bunch of times. I don't have any cars that really required different pressures from fron to back.
 
I run 40psi on my 255/45/20 tires, but its pretty stiff, especially with the already stiff suspension of my car.

My daily commute is only 5 miles back and forth. If it was any longer I probably wouldn't be able to stand it.

Its kind of amazing the difference that it can make though. My car is fine up to 38.. then as soon as you cross over 38 it almost instantly becomes unbearable.
 
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My jeep rides awfull with 32 psi in them or more. Around town I run around 24psi and they wear fine.

My pickup ate a set of tires @ 35 psi. Wore em out in the middle very fast. Been playing with the pressure since then. 18 in the rear and 22 in the front. Got 60K on them and they are wearing good.
 
Here's the down side to more pressure:

1) Ride quality (as mentioned above)

2) Dry traction (footprint is smaller)

3) Wet traction (discounting hydroplaning)

4) Reduced resistance to impact damage (up to the point where the tire bottoms out against the rim, lower pressure creates less force input to the tire.)
 
How high you can/should inflate depends on the maximum rated pressure of the tire. I like about 85-90% of the maximum, for best fuel economy and handling. If the sidewall says 51 psi max, then I aim for about 40-44 psi. If the sidewall says 44, then I aim for 37-40 psi.

If the rated maximum pressure is 35 or less, I probably won't buy it because I probably won't like the soft squishy handling.
 
Under no circumstances should you reference the pressure listed on the sidewall of a tire - except, of course, to use it as it says - a maximum. (There are a few exceptions!)

The reason is that the government regulation that requires this value is a bit vague and there is disagreement as to what is supposed to be imprinted on the sidewall.

Some folks read the regulation to mean the pressure at which the maximum load carrying capacity occurs. For Standard Load passenger car tires this would be 35 psi. The Michelin group (Michelin, Goodrich, and Uniroyal) are in this camp for their S and T rated products. Everyone else seems to feel that the same tires ought to say 44 psi - the maximum as recommended for handling and / or high speed usage.

Many tire manufacturers also recognize that V and higher speed rated tires are allowed to use 51 psi for standard load tires. nevertheless the load carrying characteristics are the same for all these tires.

The net effect is that the sidewall pressure is not a consistent value. It would be better to reference the vehicle placard pressure. This at least has the benefit of being reasonably consistent - and tested. If you want to use a slightly higher value than the placard value - say 3 to 5 psi more - that's OK. In many cases you get the same value as 85 to 90% of the sidewall pressure, but this is just a coincidence.


If you want to know more about tire pressure vs load and why what I wrote above is true, here's a longer version:

http://www.geocities.com/barrystiretech/loadtables.html
 
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I tried 40 psi in my Michelin LX4's on a Gramp Marquis...didn't like it. It "twwappped" too much over expansion joints, I could feel the larger bumps shake the front end, and it tended to wander in the lane more. At 35 psi, it's much better. These tires tend to be a bit harsh anyway. But, since I'm averaging over 25 mpg on this dinosauer, I'm satisfied that 35 psi is as high as I'll go.
 
Originally Posted By: Titan
I tried 40 psi in my Michelin LX4's on a Gramp Marquis...didn't like it. It "twwappped" too much over expansion joints, I could feel the larger bumps shake the front end, and it tended to wander in the lane more. At 35 psi, it's much better. These tires tend to be a bit harsh anyway. But, since I'm averaging over 25 mpg on this dinosauer, I'm satisfied that 35 psi is as high as I'll go.


Not a bad decision. Someplace here, I think maybe from Capriracer there were links to some hard to read rolling resistance curves that showed the reductions in rolling resistance became smaller the higher in pressure you went. 40psi was better than 35, but not nearly as much of an improvement as going from 30 to 35.
 
I use nitrogen and go with two lbs under the recommended pressure.
I like a bit softer ride.It's worth the tenth of a mile I may lose MPG wise.
 
Originally Posted By: Colt
I use nitrogen and go with two lbs under the recommended pressure.
I like a bit softer ride.It's worth the tenth of a mile I may lose MPG wise.


Colt,

Are your statements about nitrogen and 2 psi under the recommended connected in some way?

Also, when you say "recommended", what recommendation are you referring to?
 
Originally Posted By: Titan
I tried 40 psi in my Michelin LX4's on a Gramp Marquis...didn't like it. It "twwappped" too much over expansion joints, I could feel the larger bumps shake the front end, and it tended to wander in the lane more. At 35 psi, it's much better. These tires tend to be a bit harsh anyway. But, since I'm averaging over 25 mpg on this dinosauer, I'm satisfied that 35 psi is as high as I'll go.

Heh, I have these exact tires on my CV, and I like it at 40psi. I dont mind the harsher ride. In fact its still to soft. Thats alright though, it can be fixed. :) Police springs, Pol. Front swaybar, Pol. shocks, Marauder rear swaybar, and 05+ Mustang GT Premium Pkg. 17" wheels are on the exceedingly long todo list..
 
Originally Posted By: CapriRacer
Originally Posted By: Colt
I use nitrogen and go with two lbs under the recommended pressure.
I like a bit softer ride.It's worth the tenth of a mile I may lose MPG wise.


Colt,

Are your statements about nitrogen and 2 psi under the recommended connected in some way?

Also, when you say "recommended", what recommendation are you referring to?


The recommended was the door sticker pressure.
I'm wondering if the nitrogen's keeping the pressure when hot down compared to just air,a lb or two when hot,actually means I'm like 3-4 lbs under door number.
As a tire with regular air heats up and increases pressure more than a nitrogen fill.
 
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I keep tire pressure as reccomended by manufacturer and it's fine. I tried playing with different pressures but I like 30 psi. When tire is overinflated it reduces stability due to traction lose. Besides 1 MPG is not that much of a gain. If 1 mpg is that big of a deal for you try a bus, or getiing a better job, or more fuel efficient car.
 
Originally Posted By: Colt
.....

The recommended was the door sticker pressure.
I'm wondering if the nitrogen's keeping the pressure when hot down compared to just air,a lb or two when hot,actually means I'm like 3-4 lbs under door number.
As a tire with regular air heats up and increases pressure more than a nitrogen fill.


This is a myth that is being spread by the makers of nitrogen generators. Nitrogen behaves just like air according the Ideal Gas Law: PV=nrT.

Even if it behaved differently, air is 78% nitrogen, so it's unreasonable to think it is going to behave significantly different that air.
 
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