Re: tire pressure

The tire manufacturer's say to run them at the vehicle manufacturer's specs. The number of the sidewall is an industry standard for a given size of tire and type of tire. It is the tire pressure for the maximum safe loadfor that particualr size and type of tire. Surely you understand that the same size and type of tire can be used on very different vehicles. Do you think all of these vehicle have the same optimum tire pressure?

Regards,

Ed White

Dave Mundt wrote:

The tire manufacturers say to use the Ford pressures as long as the tires are the same size and type as the original tires. If you change eweither the size or type of tire, then the Ford numbers are no longer valid, but I doubt that the maximum pressure listed on the tire is either.

Regards,

Ed White

moli n ny wrote:

The tire manufacturers suggestion is to use the pressures recommended by the vehicle manufacturer. No tire manufacturer recommends blindly inflating the tire to the pressure listed on the sidewall. This is not a "recommended" pressure. It the pressure for the maximum safe load. Very few vehicles laod tires to anywhere near the maximum safe load. If they do, then they will specify the max pressure listed on the sidewall.

Regards,

Ed White

Steve Barker wrote:

o please.

If ya want to know the "correct" PSI for yer tires......

First.......go to a set of scales and get your rig weighed........a separate weight for each of the axles.......if ya have a regular ole PU.......get a separate weight for the front wheels and then for the back.......

Second......go to the tire manufacturers web site and do a search for inflation tables.........look up your tire size.....enter the table with weight and inflate accordingly at cold PSI.....Michelin has some good tables at their website for various tire sizes.

This should alleviate all concerns and cause your tire/treadwear to be even.......

Another option is to "play" around with inflation pressures and measure treadwear by a depth guage and adjust accordingly over time........

Fred in AZ

|If ya want to know the "correct" PSI for yer tires...... | |First.......go to a set of scales and get your rig weighed........a separate |weight for each of the axles.......if ya have a regular ole PU.......get a |separate weight for the front wheels and then for the back....... | |Second......go to the tire manufacturers web site and do a search for |inflation tables.........look up your tire size.....enter the table with |weight and inflate accordingly at cold PSI.....Michelin has some good tables |at their website for various tire sizes. | |This should alleviate all concerns and cause your tire/treadwear to be |even....... | |Another option is to "play" around with inflation pressures and measure |treadwear by a depth guage and adjust accordingly over time........

Or a good tire pyrometer.

Shame I did not save my tire so you could see one, or actually a pair.

Blair

They may have said that, but I find it fairly absurd. Over reactions to what? Changing the tire pressure is not going to make *that* big a difference on steering response, and from personal experience, I would think the vehicles with the higher pressures would still be more stable overall in a "reaction" scenario. I think this statement is just one where they are trying to cover their butts with wives tails and other jibber jabber intended to deflect the safety issue over to firestone. An over reaction would be a driver issue more than vehicle. They need to brush up on their driver skills if overreacting is a problem.

Furthermore, Firestone executives admitted under oath

Again, they may have well said this, but I think they must have been high at the time. Whatever it is they are using, I wish they would send me some... I suppose ambient temp never entered their minds....I wouldn't be half surprised if they did most of their testing in Michigan where it usually doesn't get that hot. You try running a fairly heavy SUV with 22 lb inflated tires on scorching pavement that is baking from 100 degree plus wx, and high speeds to top that off, and I bet their tune would change a bit. Seems to me it did eventually...

The media never bothers

I could care less what the media thinks. I'm mainly going on common sense. If I had a tire on an exploder that was at 22 lb's, it would be my opinion that I nearly have a flat, and need to find a air station before I half ruin my tire. But this would be the case even on my fairly medium weight monte carlo. Overall, I think ford screwed the pooch giving out bad tire pressure advise in those years, and firestone ended up being the scapegoat. Ford probably has more money and lawyers than firestone. Money and lawyers talk, common sense took a walk. Firestone may have had a few quality issues, but they were severly aggravated by ford's fairly absurd "to me" tire pressure recommendations. But this is just my opinion. MK

Everyone is entitled to have an opinion but I do think people form opinions on tire pressure based on incorrect or misleading information.

Here are some point I consider important -

- The tire pressure listed on the side wall is the tire pressure associated with the maximum safe load for the tire. This value is an industry standard for tires of a particular size and type. For instance all P235/70R13 will have the same maximum load and tire pressure no matter who made the tire or the exact construction details used. So, the idea that this pressure represents any sort of tire manufacturer recommendation is wrong. It is an industry wide design goal and should represent the minimum acceptable tire design for a given size and type.

- People like to claim that tire pressures are solely set to achieve the best ride. This is a silly idea these days. Years ago, it was common for manufacturers to specify radically lower tire pressure than in recent years (my Mom's 1972 Full Size Ford Station Wagon specified 22 lb front,

27 rear when unloaded and it weighed at least as much as a late 90's Explorer). Today manufacturers are willing to take extraordinary steps to increase fuel economy by small amounts. Ford has recently switched to 5W20 oil for most of their vehicle to increase the CAFE average by less than 1%. It is illogical to believe that Ford would specify low tire pressures if they significantly decrease fuel economy. Ride quality can be affected by springs and shocks and therefore lower tire pressures are not required to improve ride quality at the expense of fuel economy. Outside of the US, vehicle manufacturers usually specify a range of pressure for different speed and load conditions. Within the US, most passenger vehicles specify only one set of pressures. I assume this is done because the vehicle manufacturers want to force the EPA to do the fuel economy testing with tire pressure that will be most advantageous for fuel economy.

- Tires of the same type and size are used on a variety of vehicles. It is illogical to expect that all of the vehicles that use the same size and type of tires have the same ideal tire pressure.

- Tire pressures are often different front to rear. This should not be surprising since the loads on front and rear tires are usually very different. This difference in tire pressures also helps promote handling characteristics that the manufacturers consider advantageous.

- Since most passenger vehicles only specify one set of pressures for a given size and type of tire, it is reasonable to assume that these pressures are on the high side since they must handle the maximum loaded condition and the maximum speed condition. I have seen a few US vehicles that do specify an increase in tire pressure for high speed driving.

- Recently I have seen statements in Owner's Guides warning owners not to over inflate tires. The following statement is from a recent Ford Owner's Guide - "Do not exceed the Ford Motor Company recommended pressure even if it is less than the maximum pressure allowed for the tire."

- Every tire manufacturer that I know of specifically warns against treating the maximum pressure listed on the side wall as a recommended pressure for any particular application. See the following references:

If you take a look at these references, I think you will see that all of the tire manufacturers represented recommend following the vehicle manufacturers recommended tire pressures (for OE size and type of tires).

- If you have access to the Load / Inflation Tables for your tires, and you know the load on your vehicle, I suppose you could pick your own tire pressures. However, I'll bet if you strictly go by the load / inflation pressure tables, you would inflate your tires to a lower pressure than recommended by the vehicle manufacturers. For instance:

Many Explorer were equipped with P235/75-15 S105 Tires. The industry standard load inflation table for this tire size follows:

Cold Inf. Pressure Load

20 1543 23 1653 26 1753 29 1852 32 1940 35 2028

This is a tire industry standard, not a Ford Standard, or even a Firestone Standard. A P235/75-15 Tire inflated to 26 psi is rated to carry 1753 psi at it's maximum rated speed. Since the Explorer used "S" rated tires, the maximum safe speed is 112 mph.

The late 90's Explorers were rated for a total maximum rear axle weight of 2950 lb max. This mean each rear tire should not be loaded more than

1475 lb. This is well below the maximum safe load of 1753 lb. Even if you derate the tires by 15% for severe service and an unbalanced load, the tires are still rated to carry 1490 lb. each. A properly loaded Explorer should not cause the failure of a good quality tire of the correct size and type if inflated per the original recommendations (26 psi).

Regards,

Ed White

Thanks. This is a very interesting response. It makes a lot of sense.

HR.

For Ford trucks, there's 2 types of tires possible. Small trucks like a Ranger will probably have Passenger car tires installed. Passenger car tires start with P in the part number. Trucks like a F350 will come with Light Truck tires. Light truck tires start with LT in the part number. These 2 tires are built to different standards and have different pressure requirements. Passenger car tires have a max inflation pressure listed on the sidewall. Light truck tires do NOT have a max pressure listed on the sidewall. Go outside and look at one; it only has a max load at a listed cold pressure. My comments following apply to Light truck tires.

The label on the door jamb is assuming a truck is loaded to the GAWR's (Gross Axle Weight Rating). If you are operating at a lower weight, you can reduce the pressure for better tire wear, smoother ride and better traction. The label is also assuming you have stock tires as delivered from the factory. If you have a different tire installed, you need to use the correct pressure for the tire installed.

Here's the proper way to determine what pressure to run in your tires. Weigh your truck, getting individual weights for each wheel (or at a minimum each axle). Then consult the tire inflation chart for your brand/model of tire. The chart will tell you what pressure to run based on your weight. If you got individual wheel weights, use the heaviest wheel on an axle to determine what pressure to run on all tires on that axle. If you weigh your truck unloaded you'll need to do this again with your normal load. If your load fluctuates all the time, it's probably easier to just keep the tires inflated to handle the highest load you anticipate.

In my case, I carry a 4000 lb slide-in camper occasionally. I keep the truck tires inflated for unloaded driving most of the time. Then before I load the camper, I pump them up for the extra weight. That way the truck rides smoothly with good traction and even tread wear while unloaded. If I was loading and unloading the camper daily or even weekly, I'd probably just keep the tires pumped up. Changing tire pressure daily on a dually would get old real quick.

It's a good idea to read the footnotes and fine print in tire inflation manuals also. For instance, in the Firestone manual it says that if you are driving for long periods at 65 to 74 mph, you should increase the tire pressure 10 psi (provided the wheels are rated to handle the pressure). In the case of the Firestone Steeltex 265/75-16 tire that would be 90 psi if you are at max load. This means that the 80 psi listed on the sidewall is not the max pressure. If you want to drive 75 to 84 mph , you still need those extra 10 psi, but you also need to reduce you max weight capacity by

10%.

You can view a tire inflation table for LT235/85-16 tires at

. Here's the inflation table for the LT265/75R16 Firestone Steeltex tire

Weight Pressure

1910 35 2100 40 2280 45 2470 50 2625 55 2790 60 3000 65 3105 70 3260 75 3415 80

If you are driving at higher speeds for extended periods, you need to add more air:

65-74mph add 10psi 75-84mph add 10psi & decrease max load 10%

The sticker on your door jamb is set for the original equpt tires put on by the manufacturer to maximize ride and handling. if you overinflate tires it will cause center to wear out. 32 all around is good for 1/2 tons.