Dare I Ask? Correct Tire Pressure for a 1997 Explorer

[BigBear1987]

Our 1997 Explorer 4.0 V6 XLT Auto 4x4 AWD shows 26 PSi for the oem std 235/75R15
Also found them better on 30 psi according to recall.
Have since fitted L T 30 x 9.5 R15 Bridgestone Dueler A/T 6 PR Side wall Max 50 PSI
Running them at 34 PSi ride is very hard and handling not great when hitting bumps.
30-32 PSi
Ride, Comfort and Handling is a lot better.
Can't Imaging how hard the ride and unstable it would be @ 10% of Max ie. 45 PSi

 

[jadatis]

Give Gross Axle weight Ratings (GAWR) front and behind and the maximumload and pressure written on the sidewalls .
"maximum load xxxx lbs AT 50 psi( cold) " on the sidewall.
And I will calculate for you the lowest save pressure for the tires , when fully loaded and not overloaded.
If you give empty weight and weight division front/back, and how you load it normaly ( persons and load) , I can estimate the normal axle loads , and calculate the pressure for that.

The problems with the Firestone tires on the Ford Explorer , to my opinion , where because the sidewalls bended more then was save for those tires, with profile blocks going a lot over the sidewall.

 

[koda2000]

32-35 psi cold should be fine. as far as new shock recommendation, i'm very happy with my KYB Gas Adjusts. good ride (considering) good control.

 

[coco944x4s]

I run Yokohama 31x10.50x15 tires on my 94. The sidewall of the tire shows 50 psi MAX. I run them in the 42-44 psi range and find it works best for me. It rides better on the highway and side roads. I live in the mountains of North Carolina and drive curvy roads quite often, and sometimes I am running late for work which usually involves me traveling a little above the posted speed limit on bumpy, uneven, ill-maintained roads. The tires had gotten down to around 36 psi with temperature changes and I had not kept a check on them. With them at this low pressure I experienced more roll in corners, less stability and a greater loss of traction on concrete and asphalt paved surfaces. After pressurizing them to the level that I felt more comfortable with, all or my driving issues were solved. I no longer break traction on pavement(even under high revving clutch "dumps" to try), I have less roll in the corners of mountain roads, and I feel as if the explorer has more stability. All these ride improvements are taking into consideration that my explorer is equipped with spacers under the coil springs and longer shackles in the rear. Since we all know that lifting a vehicle makes it handle worse in many situations (i.e. on road) then if running higher pressure makes handling worse (as a few members have stated) then my explorer should be condemned and removed from the roadways, when in actuality I feel more safe with higher pressure in my tires.

One could argue that my point is completely moot due to the suspension geometry being "non factory" and that my tire size is also "not within manufactures safety specs". However in my experience having worked for a Ford/Chrysler dealer for many years, and working on a wide variety of vehicles, I found that the majority of truck/suv owners would buy bigger tires for their trucks (most often due to small factory sizes not giving them the truck look they wanted) and the majority of all vehicle owners RARELY replaced their previous FACTORY tires with the exact same size, brand, and line or tires. Particularly because the Continental tires that were used(by Ford mostly) wore unevenly and produced vibrations and ride comfort issues. Given this information to be from actual observation, then we can assume that most of the vehicles on the road are unsafe for usage on public thoroughfares because they are no longer operating under the vehicle manufactures tested and assessed vehicle safety specifications and therefore should be ruled unsafe.

I will end this post simply by saying this: Buy whatever tire brand, model line, and size you would like. Then adjust your tire pressures according to however you feel safest doing them, or consult with your trusted automotive professional.

 

[MNgopher]

I don't own my '97 anymore, but noticed several posts with bad advice in this old thread. Be very careful when switching between P series tires and LT tires. In order to carry the same load in the same size, the air pressure in the LT tires MUST be be inflated to higher pressures. This is due to the construction of the tire itself. The idea that they hold the same volume of air and thus can support the same load is incorrect.

I'd be very leery of only inflating an LT tire to the low 30 psi range as posted above. One really needs to refer to the inflation tables from the manufacturer to determine the correct pressure if you convert sizes. As an example, I switched from P series tires to an LT series tire on my F150. To carry the exact same load, the LT tire must be inflated to 41 psi in that particular size versus 35 psi in the P-series tire. The result is that when running unloaded, the truck rides like well, a truck. When running loaded with a trailer and weight in the truck its better though.

As an example of the information available from tire manufacturers (and note the recommended pressures for the LT tires!)

http://www.yokohamatire.com/assets/docs/tsb_070302.pdf
https://nittotire.com/Content/pdf/Replacing Tires on Light Trucks - Technical Bulletin.pdf

The reality is that LT series tires sometime just are NOT the right tire for an application if the ride quality and handling is of importance.

And again, the simple answer to the OP's question is 30 psi is the recommended pressure for the stock P235 75 15 tire size.

 

[SoNic67]

I will end this post simply by saying this: Buy whatever tire brand, model line, and size you would like. Then adjust your tire pressures according to however you feel safest doing them...

That's one of the most irresponsible/bad advice EVER.
You think that the average Joe gut is better than the manufacturer on deciding what pressure the car tire should have. You do that when you are sick too, go with your gut feeling?

 

[coco944x4s]

That's one of the most irresponsible/bad advice EVER.
You think that the average Joe gut is better than the manufacturer on deciding what pressure the car tire should have. You do that when you are sick too, go with your gut feeling?

I am not gonna get in a pissing contest with you here because it would seem that I am nothing more than a raving lunatic with no sense at all in his head and deserves to be placed in an assisted living facility so that I can no longer be a danger to myself or anyone else. However, had you finished the quote, "or consult with your trusted automotive professional", you would realize that I covered both sides of the equation here; the knowledgeable individual who does their research and their own testing and finds what is best for them, and the unknowing "average Joe" who usually has a shop or mechanic that they trust and could refer to. If you feel sound in your own knowledge and abilities, I see no problem why you cant do your own research and testing (as I myself have done) and find what works best for you. On the other hand, if you have doubts in your own tire judgement, then ask a professional who deals with this stuff everyday and is a valuable resource. There again some common sense is involved here too. If the tire manufacturer recommends 35 psi cold, and you put 45 in it because you think you get better mileage, that is just unsafe and irresponsible, no room for debate there.

Since I obviously have not put any time, thought, or research into how I run my own vehicles, professionally repaired them, or advised the unknowing public on how to run their vehicles, if you tell me to delete my posts because I am nothing more than a hell raising, rebel rousing, redneck, shade tree country bumpkin, then I will respect your opinion that I am a complete nincompoop and remove what I believed to be helpful and insightful information based on first hand research and real word findings.

 

[jadatis]

I don't own my '97 anymore, but noticed several posts with bad advice in this old thread. Be very careful when switching between P series tires and LT tires. In order to carry the same load in the same size, the air pressure in the LT tires MUST be be inflated to higher pressures. This is due to the construction of the tire itself. The idea that they hold the same volume of air and thus can support the same load is incorrect.

I'd be very leery of only inflating an LT tire to the low 30 psi range as posted above. One really needs to refer to the inflation tables from the manufacturer to determine the correct pressure if you convert sizes. As an example, I switched from P series tires to an LT series tire on my F150. To carry the exact same load, the LT tire must be inflated to 41 psi in that particular size versus 35 psi in the P-series tire. The result is that when running unloaded, the truck rides like well, a truck. When running loaded with a trailer and weight in the truck its better though.

As an example of the information available from tire manufacturers (and note the recommended pressures for the LT tires!)

http://www.yokohamatire.com/assets/docs/tsb_070302.pdf
https://nittotire.com/Content/pdf/Replacing Tires on Light Trucks - Technical Bulletin.pdf

The reality is that LT series tires sometime just are NOT the right tire for an application if the ride quality and handling is of importance.

And again, the simple answer to the OP's question is 30 psi is the recommended pressure for the stock P235 75 15 tire size.

A LT tire with its higher maxloadpressure of 50psi because 6 ply indeed needs higher pressure for the same load then a P-tire with its maxloadpressure of 35 psi.

This maxloadpressure is called the reference-pressure ( further Pr), and is the pressure at wich the maximumload can be carried up to a speed of 99m/160km/h or if lower the maximum speed of tire, without damaging the tire by driving alone, and then especially the sidewalls.
This is not the maximum pressure of the tire, as many think.
On P- and XL-tires only the maximum pressure is given on the sidewall mostly, From C-load/6ply the Pr is given in the sidewall like this "maximum load xxxx LBS AT yyy PSI (cold)". The maximum pressure is 1.4 times as high.


The 10% loadreduction for a P- tire on SUV is originally done to compensate the wrong calculation in America before 2005. But adding 10% to the real actual load is for every car a good advice,to cover uneven loading R/L, pressureloss in time, misreadings of weight and pressure-scale, incidental extra load, etz. Determinating that real actuall load thouh is not that simple.

But the calculation for LT tires is still wrong in America, Only for P-tires and XL the calculation chanched since 2006 , saying it was to come to a worldwide same system, but why not chache the LT tires calculation either then?!

so the pressure/loadcapacity-lists that are given in America are still wrong for LT tires , beter use the European lists for the same tire, or beter even make your own list with spreadsheet I made.
https://skydrive.live.com/?cid=a526e0eee092e6dc#cid=A526E0EEE092E6DC&id=A526E0EEE092E6DC!601
In this map use the 8th document , load it by right clicking on it, then choose download, after eventual virus-check open it in Excell or open office Calc to use it. The right power and construction load are already put in , you only have to fill in from part D and give the wanted roundings and if per axle or tire.
If you only fill in Psi part , only the psi lists are given.
Mind to set the kg/lbs selection cels right.

 

[ponkotsu]

Manufacturers develop the "correct" tire pressure based on averages. There is no magic mathematical formula that provides the correct tire pressure for everyone. In the case of the 2nd gen Explorers I think they chose 26psi, which was chosen out of ride comfort. I think we all know by know that is way too low. If you are going for fuel economy, you probably pump them up. But studies have shown that depending on the vehicle, once you get beyond about 30psi on a radial tire, there is little fuel economy to be gained. I've tried anything from 32psi to 38. I think 36-38 gives too hard of a ride. 32psi seems about right for me.

 

[MNgopher]

You are correct - vehicle manufacturers select tire pressures based on several factors, including load capacity, tire wear, vehicle handling, fuel mileage, etc... However, one fact that remains constant is that the manufacturer will not select an air pressure and tire combination that does not handle the load imposed upon it.

Thus, the general premise is that one should never select a replacement tire with a lower load capacity, period.

And no offense jadatis, but between a language barrier and different techical standards from the respective north american and european tire agencies, I have a very hard time calling one method right and the other method wrong. If I were selecting a tire for use in the North American market, and selecting the air pressure as well, wouldn;t it make sense to use the load tables and ratings that are the same as the designer of the vehicle used? Switching to the Euoropean tables on a vehicle designed on North American design assumptions doesn't seem like a smart choice in my book.

I'll end with the same note: The correct tire pressure as recommedned by Ford for a P235 75 15 equipped ford explorer in 1997 is 30 psi.

 

[jadatis]

If you want to read it from an American IR , who worked for a tire-company you can follow the next link
http://www.dawsengineering.com/linked_files/tirepressureatreducedloads.pdf
Mr. Daws describes there a new way of calculating and compares it to the , by the tire-makers used formula with a power in it.

His site's link
http://www.dawsengineering.com/

Especially look at the conclusions and discusion on page 7 and 12.
I first also hovered over it to get the for me usable information.
Even did not agree with "his " system and made my own universal formula, from wich "his"formula and the old power formula can be made by filling in the right construction load ( my own input this word Lc further ) and X ( power in the equation).

The american lists are made with the old power-Equation with power 0,5 ( = root)to calculate loadcapacity for a sertain pressure, for standard load tires , before 2005 , and old list are often still refered to in fora.
This gives at 75% of the Pr that more deflection that they stopped there and did not advise lower the 0,75 times 35 psi=26 psi . In Europe the power 0,8 is used for decades wich only gives as low as 60% of the Pr a to much deflection so you have to stop = 21 psi.

So if you calculate the European power, and fill in the max load and Pr that is given on the sidewall of the american tire, you have a saver calculation then the old American way

 

[alohamonte]

I run 36 PSI in a 31" tire

 

[ponkotsu]

However, one fact that remains constant is that the manufacturer will not select an air pressure and tire combination that does not handle the load imposed upon it.

Except for the case of the gen 2 Explorers where Ford chose the pressure based on comfort. My 2000 has the pressure on the door jam of 26psi. And when I bought it used from a dealer that's what they set the tires to. Good thing I know more than the dealer and Ford, or I might get myself killed.

 

[ponkotsu]

If you want to read it from an American IR , who worked for a tire-company you can follow the next link
http://www.dawsengineering.com/linked_files/tirepressureatreducedloads.pdf
Mr. Daws describes there a new way of calculating and compares it to the , by the tire-makers used formula with a power in it.

His site's link
http://www.dawsengineering.com/

Especially look at the conclusions and discusion on page 7 and 12.
I first also hovered over it to get the for me usable information.
Even did not agree with "his " system and made my own universal formula, from wich "his"formula and the old power formula can be made by filling in the right construction load ( my own input this word Lc further ) and X ( power in the equation).

The american lists are made with the old power-Equation with power 0,5 ( = root)to calculate loadcapacity for a sertain pressure, for standard load tires , before 2005 , and old list are often still refered to in fora.
This gives at 75% of the Pr that more deflection that they stopped there and did not advise lower the 0,75 times 35 psi=26 psi . In Europe the power 0,8 is used for decades wich only gives as low as 60% of the Pr a to much deflection so you have to stop = 21 psi.

So if you calculate the European power, and fill in the max load and Pr that is given on the sidewall of the american tire, you have a saver calculation then the old American way

I'm glad you are using facts and science to make a decision. Seems to be a serious shortage of that in the world. But the calculations are just that, calculations. Only actual testing can determine if the tire pressure is correct or not. And even then, there will be an accaptable "safe range" that the end user can freely select from to suit his individual preference.

 

[buzz]

I've searched and cannot find a definitive answer. What is the correct tire pressure for a 1997 Limited, AWD-V8? 235/75/15, stock size tires. The Ford recommended 26 PSI cannot be correct... IMO.

Thank you in advance for any input!

Look for the sticker on the door jam. It has the info.

 

[MNgopher]

The 26 psi ford originally recommended was safe and within the load capacity of the tire. The problem was the average motorist is a moron who can't be bothered to check their tire pressure periodically, and 26 psi left little margin for underinflation. Now I'm stuck with a TPMS system on my 07 that means spending an extra 300 bucks to keep the tpms warnings off with a set if snow tires. amazing what a $2 tire guage could do if only people had common sense...

 

[GJarrett]

Wow, over fifty posts and no one has mentioned the chalk test. I guess it's time to dredge up old long-lost wisdom from this site that evidently has been lost in the last decade.

For the perfect tire pressure, we had the answer on this site way back in the '90s ( I posted this in Herc's registry entry in July 1999 - I'm not the originator of the method and learned it here on the Explorerforum way before I posted it in 1999). There is a very simple answer. By the way, this method works with any set of tires, on any vehicle, with any modifications resulting in added or removed weight, on any tire whether front and rear,.... period.

Finding the Perfect Tire Pressure - the Chalk Test
There is a trick you can do to determine precisely how much pressure to keep in your tires for your particular vehicle. It will give you the best tradeoff possible between mileage, tire life, and comfort. Make sure you use an accurate tire gauge so that once you learn this pressure you know it is correct.

With a cold vehicle and cold tires, air them up over pressure - 40 psi or so. Take a chalk and mark a chalk line sideways across the tread of a front and rear tire. Drive your vehicle several yards in a straight line (30-40 or so should do it). Now look at the chalk marks.

You should see the inside of the chalk marks worn off but the outsides should still be showing. In other words, the bowed out overinflated tire was wearing the middle of the tread and not touching the outside of the tread.

Release a couple of pounds of pressure from the tires and repeat the experiment. Continue until the complete chalk marks wear evenly. (Once there, you might want to then release another pound of pressure to make sure the entire tire is bearing down across the tread with weight). You have now determined the tire pressure at which you are keeping the entire tread on the road.

Under this pressure you are wasting available fuel economy, generating excess heat, and prematurely wearing the tread. Over this pressure you will get better fuel mileage but it will come at the cost of comfort from the rougher ride and decreased tread life from wearing the middle of the tread out prematurely. Keeping at this pressure will wear the tire evenly and thus extend its life to its greatest extent and offer the best compromise possible between gas mileage, comfort, and safety (you'll have your whole tread on the road). The pressures may be a couple of pounds different between front and back for your particular vehicle application.

A caveat: this needs to be done on NEW tires as soon as you buy them. If you have already logged 25,000 miles on overinflated tires all you will be doing is verifying the excessive pressure you have already been using (in other words, the chalk line will wear evenly even though the middle of the tread may be quite a lot shallower than the outside tread).

Hope this helps answer the question.

 

[jadatis]

Except for the case of the gen 2 Explorers where Ford chose the pressure based on comfort. My 2000 has the pressure on the door jam of 26psi. And when I bought it used from a dealer that's what they set the tires to. Good thing I know more than the dealer and Ford, or I might get myself killed.

Also for that I found an article of someone who cals himself Capriracer at many fora
http://www.barrystiretech.com/fordfirestone.html
Calculating this trough with the GAWR's mentioned and the tire-specifications,
I came to even lower pressures, so first blamed the overloading ( blew out often happened at one rear tire). But seeing the tipical tire damage I came to the conclusion that such a tire, with large profileblocks at the side, wich go even a part over the sidewall, makes the sidewal less bending allowed , so lesser deflection then a "normal"street tire with the same dimensions.
So lesser deflection means lesser maximum load of the tire.
The maximum load, the tire-maker calculated ( this also is calculated with a much more complex formula) then is to high.
If you would fill in the naturally right maximum load in the formula , the needed pressure would come higher then.

This also is the case with low Aspect Ratio tires ( Further AR= fi the 40 in 235/40 ZR 18), I once made a spreadsheet to calculate how much such a tire may deflect in ratio to a 80% AR tire and wrote Mr. Daws about it.
Already had earliër contact with him, been as brutal to contact him , and he gave usefull information every time. He sended me a graphics about it in wich a low AR tire gave even 27% deflection of the free flexible part of the sidewall. A 80% AR tire only 20%, with maximum load and referencepressure ( Pr)on it . I calculated the low aspect ratio tire only to may have about 17% deflection to get the same amount of bending as a 80% Ar tire.
Calculated from that a much lower maximum load.
For a bit the same reason the Firestone tire on the Ford Explorer should have a lower maximum load.

My temporary endconclusion is that this to high calculated maximum load the tire is the real reason of the Ford/Firestone accidents, and this is the reason for why in America you got those anoying TPMS systems. Also not giving normal use advice in Europe ( 3 persons and little load) after 2000, and the extremely high advice-pressures for normal cars in Europe, is the endproduct .

The goal of all the calculations is to keep the deflection of the tire the same as when maximum load and Pr on it. But when the deflection is already to much , after calculation with the ever to be constructed ideal formula, to wich my formula comes close ( i think), you still have to much deflection.

But most of this is my own thinking, I am not a tire-specialist, so draw your own conclusions of the information I gave.

 

[ponkotsu]

I love annoying TPMS. Have you ever had a flat tire? Wouldn't it have been nice to know it was going flat before it happened? They absolutely save lives and tires. Unless you are checking your tire pressure every time you get in they are very useful. And no, you can't tell by looking at a tire if it is losing pressure until it's too late.

 

[ponkotsu]

PS, I'm starting to think that tires are like religion. Everyone thinks theirs is the best, and they don't want someone else's tire belief's pushed on them.