31" Tire Pressure on 89GW

[igd]

Hi all,

I just put 31"x10.5" tires on my 89 Grand Wagoneer. What do you think I should set the tire pressure at for normal everyday highway driving? Does it remain the same as with the original tires?

THX

[Veepster]

you want to keep your tire pressure as high as you can without negatively effecting ride quality......low pressure is good for handling characteristics and ride quality, but high pressure will help fuel mileage. so you need to find a balance.....I am guessing it will be in the 30-38psi range......play with it and find what you like

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Peace.............BartG

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[Darin]

With the 31 x 10.5 do get any rubbing? When I need new rubber I would like to go with this size, but only if it is clean with stock suspension.

[bignblue]

31s SHOULD rub at full lock or under articulation. The 235/75 (or whatever came stock) is about 29" across, and Wags have that funky rear fender skirt thing happening. From what I can gather 31s or even 32s will fit with no rubbing if you use a 3" lift, but I haven't tried it myself.

[SpruceMoose]

i've been running 30x9.5 bfg a/ts for 3 years. they have about 45000 miles on them now, and look like they will get about 10k more. they have a 40k treadwear warrantee. been running 40-45 psi since i put them on. max is 50 psi at full load. nice ride, but firm, not squishy.

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88 Grand Wagoneer
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[This message has been edited by SpruceMoose (edited May 22, 2001).]

[BobBarry]

You will probably have to run lower pressure than the factory-recommendation for the original-size tires. I started running my 30" tires at the factory-spec 35psi, but found the center of the tread wearing more than the outer. I've gone down to 28psi, and may go down even further as the tread is still wearing faster in the middle than the outer edges.

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Bob Barry<UL TYPE=SQUARE>* '78 Cherokee 4-door
* '88 Grand Wagoneer[/list]http://studentweb.providence.edu/~rbarry/wheels/

[243]

When you are running tires that have actual tread width wider than wheel width, you may have to run a lower pressure than is optimum to get a proper footprint. A narrow wheel will pull the tire bead in and pull the edges of the tread away from the road.

To arrive at a correct tire pressure on my Dodge, I aired up to the 65psi and drove on a dusty road and then onto pavement. I lowered pressure until the pavement cleaned the tread completely and then reduced it by 5psi. I had to lower the pressure in the rear to 25-28psi to get a full footprint because I ran a 285/75/16 on 6.5" wheels. The fronts needed 62psi but mostly because of the weight...4300lbs vs 2380lbs in the rear.

I consider this to be the highest pressure I can run on this vehicle with these tires, on the factory wheels with no payload. The pressures would probably change a bit if I switched wheels, tires sizes or tires.

The same concept will work fine on the Wagoneer and the pressure will probably not be the same front to rear. The difference won't be as pronounced as it would be in a truck, but it probably won't be the same either.

If tire life is not a concern then you can just air up per the owners manual or the tire mfg's recommendation.

My comment is, tire mfg's make tires that fit hundreds of vehicles so they can't be exactly right. The recommendation in the owners manual is for a specific size and tire or possibly an alternate or two and they can't be exactly right. The problem is compounded with our Jeeps because tires have changed in the last thiry years...

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243

Ol'e Blue
79 Wagoneer 401/T400/QT

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[This message has been edited by 243 (edited May 22, 2001).]

[desert_freak]

Has anybody done the trial and error thing with pressures on a J-10??? You could sure save me some time when I put tires on my beast, assuming I am able to get the thing registered (Read "If I only had a brain...).

I'm not sure on the width of my rims yet but they are the alloy mag style (not the later wag style though) and I plan to probably put 31x10.50 on them.

Thanks in advance,

Patrick

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The fun has just begun! Resurection began on 4/8/01.

[This message has been edited by desert_freak (edited May 22, 2001).]

[Veepster]

ful footprint going straight is not always desired.....it increases roll resistance dramatically(read: kills mileage)....and with the weight of our beasts once you turn a corner the contact patch will increase significantly....

[243]

Veepster,

I have to politely disagree with that logic http://www.ifsja.org/ubb/smile.gif

If mileage is a "real" concern, stock size tires and 2.73 - 3.08 gears would be better.

I see no benefit at all to running over inflated tires; conversely, it increases wear and in some cases causes handling to be twitchy.

243

[Veepster]

243...I agree with you!and if not I always love a good debate! ;) over inflated can cause twitchiness AND a harsh ride......my response was to the statements that you want to lower the pressure until you have a complete tire footprint......

for example: my brther has a CJ with 35's( and he used to follow the theory of "total footprint"....he made a trip down to my house(500 miles) he got something like 15mpg, I suggested he put an extra 5psi in his tires for the trip home.....he got 18mpg on the way home!!

point is there is a balance in there somewhere where you can get maximum mileage and maximum safety and maximum tire wear....

and my last set of T/A's on my Ranger got 50,000 miles



------------------
Peace.............BartG

the Green Flash!
360ci
Custom 4v TBI
Edelbrock Performer Manifold
TH400, QT with low
4" skyjacker suspension lift, 3" body lift Rancho 9000's
33x12.50 BFG KO's 8" American Racing Baja Rims
Thorley headers, 3" exhaust, Dyno Max
Infiniti power leather seats
Custom billet shift knob by Millerluck
50%Luxury Car, 50%Tractor
http://www.teamgodspeed.com

[243]

Veepster,

We are on the same page...lowering air pressure to get a full contact patch will "kill" fuel ecomony; especially, if you are running wide tires on narrow rims.

Wonder if igd's question has been answered???

243

[graham]

<BLOCKQUOTE>quote:</font><HR>Originally posted by igd:
Hi all,
I just put 31"x10.5" tires on my 89 Grand Wagoneer. What do you think I should set the tire pressure at for normal everyday highway driving? Does it remain the same as with the original tires?
THX<HR></BLOCKQUOTE>

Biggest killer of tyres is heat build up, and the way to control the heat build up is by pressure. The same princible as the coolant systeme. Radiator caps increase the pressure therefore reducing the operating temperature.Ever noticed the temp gauge when you have a leak in the cooling system?

One method of determing the correct pressure for normal running is to obtain the manufacturers spec's and find out the recommended "rolling radius". From this inflate your tyres, on a smooth surface, measuring from the centre of the wheel to the
ground, correct pressure is when the "rolling radius" is achieved. Loaded or unloaded the "rolling radius" should stay constant, just add/reduce pressure as required. With higher speeds add more pressure to over come the sidewall movement. Because the tyre is spinning more times for a given time period, = more side wall flex,= more heat build up, = increased tyre wear and in severe cases tyre blowouts.
All the above assumes that you have a rims width which fits within the tyres spec's.

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Graham
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[irbob]

I haven't done this yet but heard that it's a full proof method of having the proper psi in tires.

Air up to the max recommended psi. Borrow a piece of your kids sidewalk chalk. Find a good stretch of road where you can get up to 55mph and stop without turning the wheel. Chalk the full width of the tread for about a foot on each tire. Being easy on the gas and brake peddles, go down the road getting up to 55 then stop and check the chalk marks. If there is too much psi the center of the tire will have more chalk missing than the outer edge and vise-versa if there isn't enough psi.

If you look at the side of a tire, it says something like "MAX LOAD (2149LBS) MAX PSI (35LBS)". There aren't many times when a tire is driven with max weight on it so this would lead me to believe that the max psi shouldn't need to be used either.

The recommended psi given by the auto manufacturer is for the tire that was on it when it was purchased new. I'm sure they perform tests to find the correct psi for that car with that tire. We need to perform some sort of test to determine the correct psi when other that the original tire is used.

Hopefully someone here has an input on what test a manufacturer uses to determine psi.

Everyone is going to air up to what suits them. My Buick recommends 32 in the fromt but that feels to floaty for me so I put 35 in them. The back recommends 34 but that feals to hard so I use 30.

My educational guess is to air up to what suits you the best.

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[ClarkGriswald]

Ive been running BFG AT's 30x9.50x15 for about a week and a half now.. I was running them at 40 , but after airing down for the sand dunes this weekend.. I put the full 50 in that the tire suggests. It did roll better but became twitchier. So I think im goin back to around 45 or so. Like it has been previously stated its different for every vehicle and how its loaded. I think my favorite spot is between a flat profile and the rounded curve that the tire recomended psi makes. so im splittin the difference.

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[Va-Rob]

The PSI stamped on the tire is only the maximum psi the tire should be inflated and should not be exceded. Because most of us a running oversize tires there is not a recomended pressure to go by. common sense should should dictate, but in the absence of that I think 30-36 would be a reasonable psi. I Air down to 20-25 depending on conditions.

Rob

[ClarkGriswald]

I air right down to around 12 and mabye less depending on how it goes from there.

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88 Grand Wagoneer
D44's front\rear
Warn 20990 Lockouts
AMC 360
TF 727
NP208
BFG AT's 30x9.5x15
http://www.btc-bci.com/~jaserb/images/WAGG1.jpg
"Hail to the Jeep"

[irbob]

Air down, hummmmmm, sounds like a new thread. http://www.ifsja.org/ubb/wink.gif

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