recommended tire pressure

[kraulto]

I recently installed BFG Rugged Trail T/A, 31 x 10.50R15, max psi is 50. All four is @ 32 psi right now, is that good I used to have Michelins that were of the same size. I did do a search but there was so much variance on the recommended psi and most were using 16 " rims.

 

[CJF]

I think you should closely watch the wear patterns and customize.

That said, 32psi seems a little low on a 91 to get even wear. I think I'm around 40psi on mine (little more in front, little less in back), with 31x10.50x15 BFG AT's.

Too much wear on the edges=too little pressure; too much wear in the center=too much pressure

Welcome,

Curtis
91FJ80

 

[psfpilot]

There should be a sticker on the driver door that shows the factory recommended tire pressure, if you are looking for Mr. Toyota's recommendation. There is also a section in the owner's manual regarding pressures.

edit:IIRC, my door sticker says 29 front/41 rear psi (w/3rd row seats)

 

[IdahoDoug]

Go with the door sticker's recommended pressures. On my FZs I believe it's 29/29 (f/r). There are a lot of tire pressure recommendations flying around here on the forum but I think people need to stop tossing out numbers without mentioning the serious consequences of making your own inflation choices. These are SUVs and they handle very poorly in emergency maneuvers. Toyota knows/knew that and these trucks were tested on the track to determine inflation pressures that will handle daily tasking and also unexpected emergencies. Stray from them dramatically and understand that you have dramatically changed what will happen in an emergency maneuver.

I'll pick on PSF here for a second. Having the rear tires so much harder (29/41) than the fronts will encourage the rear of the truck to come around in an emergency evasive maneuver. I've personally done testing of this nature, including track time, instrumented testing, testing on artificial ice, and high speed under track photography of tire contact patches at various pressures, speeds and braking conditions. That's not a winning pressure combination.

Note that recommended f/r pressures frequently vary on most vehicles. Whatever that ratio is (it's 1:1 on the FZJ) it is almost more important to preserve that ratio than it is to have the pressure be the same. So, if you run an FZJ at 41 in the rear, you make darn sure the fronts are also at 41. That's the ratio that will determine what's going to happen in an emergency - which end will break loose first and how quickly it will grab again, etc. So, never run f/r pressures that are not in the same ratio as the door sticker.

This is for everyday driving and stock size tires. I run stock size tires at around 34/34. When I tow, they're at 40/40 for better dynamic control of the total weight of the trailer and truck. When I wheel, I run 20/20 or so. So, things can vary.

So, your best bet for wear and for safety is to stick with the door sticker on your truck with changes made only if the vehicle is going to be subject to dynamics well outside the envelope of normal driving, and only after consulting with someone familiar with what the changes will do.

Those who know me well here know that I'm not trying to get anyone's nose out of joint here - just wanting people to be safe and informed. Tire pressure is a big deal in terms of emergency handling and the only time you're going to realize you've made a bad choice is when you lose control of your vehicle because it suddenly behaved in a way you've never experienced due to a sudden maneuver. That's a very bad time to realize you've made a bad choice.

Generally, the door sticker pressures will give you very good wear and traction as well. Personally, I'm OK with up to 4psi increases from the factory recs to get a little crisper daily handling and fuel economy. But wide variances take you into the unknown, and changing the f/r pressure ratios is definitely a bad thing.

DougM

 

[-Spike-]

I'll be the dissenting voice on this one. Go with what the tire manufacturer recommends first, then make your adjustments from there for uneven tire wear. Different tires are constructed differently, thus the wide range of tire pressures. The sticker in the door is great if you have stock tires on your rig, most of us don't.

-Spike

 

[CJF]

Go with the door sticker's recommended pressures.

I'll pick on PSF here for a second. Having the rear tires so much harder (29/41) than the fronts will encourage the rear of the truck to come around in an emergency evasive maneuver. I've personally done testing of this nature, including track time, instrumented testing, testing on artificial ice, and high speed under track photography of tire contact patches at various pressures, speeds and braking conditions. That's not a winning pressure combination.

Trouble is, I'll bet he's correct about his door sticker. For example, 91 FSM (can't check my door sticker as it, along with the rig, along with the wife, is out of town) says 30 front and 40 rear with 3rd row seats in and 31x10.50x15 tires.

Curtis

 

[psfpilot]

Doug, I understand your concern, but that is what the factory recommends as nearly as I recall. I don't have the knowledge or experience to recommend straying from factory guidance, so I'm just letting him know what the factory says for that (stock) tire size. I don't have my cruiser available for reference, so others will have to check their door stickers and owner's manuals and post up.

Interestingly enough, IIRC the Owner's Manual lists lower rear pressures if one does not have the 3rd row option. My WAG is that this is due to lower potential max weight on the rear axle without three extra people sitting over it. It also lists different pressures for metric versus english dimension tires, but I have no guess on the reasoning behind that.

Spike, as I understand it the tire manufacturer pressures listed on the sidewalls are listings of maximum loads at maximum cold pressures, but not necessarily recommendations to run that high of a pressure (assuming stock tire size). For instance, my 1/2-ton pickup has 35psi maximum pressure tires, but GMC recommends 32 psi front and rear.

Regards,
Jon

 

[-Spike-]

Spike, as I understand it the tire manufacturer pressures listed on the sidewalls are listings of maximum loads at maximum cold pressures, but not necessarily recommendations to run that high of a pressure (assuming stock tire size). For instance, my 1/2-ton pickup has 35psi maximum pressure tires, but GMC recommends 32 psi front and rear.

Regards,
Jon

I absolutely agree. However, because tires are constructed differently, the vehicle manufacturer's recommendations are not necessarily relevant to aftermarket tires. For instance, say the vehicle sticker says 32 psi, and the stock tire had a maximum inflation of 35. You put an A/T tire on the truck that has a maximum inflation of 55 psi. It's very unlikely that the truck is going to behave the same with the aftermarket tire inflated to 32, or just over half of it's maximum pressure, as it did with the stock tire at nearly full maximum pressure. However, if the tire is rated for a 5000lb load vs. the stock tire at a 2500lb load, that also has to be taken into account. My point is that unless someone has the exact same tire on the same truck, 'recommendations' by board members are nothing more than guesses and very possibly misinformed ones at that. Tire wear is truly the best indicator at our disposal for correct tire inflation. Car and tire manufacturers have more knowledge to draw from for their recommendations, but they don't study every possible car/tire combination. The 'safest' option is to replace stock tires with exactly the same tire and go with the car manufacturer's specs, but few people around here are going to do that.

-Spike

 

[psfpilot]

I recently installed BFG Rugged Trail T/A, 31 x 10.50R15, max psi is 50. All four is @ 32 psi right now, is that good I used to have Michelins that were of the same size...

Assuming he previously had factory-issue Michelin LTX M/S 31x10.5R15, 50psi max, would kraulto be better off with the door sticker pressures, since his new tires have the same dimensions and max pressure?

 

[Nay]

The 'safest' option is to replace stock tires with exactly the same tire and go with the car manufacturer's specs, but few people around here are going to do that.

-Spike

Did you really just say that the safest option is to replace the garbage that comes on most vehicles with the same garbage?

The safest thing is to buy tires with the necessary traction for your driving. Running tires that do not provide the necessary traction for your conditions is far more dangerous than choosing between 30 and 32 PSI.

I run Load Range E tires that have a max load of 3,500 lbs each. The load capacity for a tire like this at 30 PSI is completely different than a 31" "touring" tire at 30 PSI. What people need to do is understand that load capacity increases with PSI, size, and load range, and adjust accordingly for proper handling and wear.

Nay

 

[kraulto]

The door sticker indicates 29 for the front and 41 for the rear but based on 235/75R15 tires, clearly different from what i currrently have on. I appreciate everyone's advice on this issue but i kinda hesitate to use the values on the door sticker just because the wheel dimensions are slightly different. The prior tires were Michelin LTX M/S 31x10.5R15.

 

[ElJefe]

As per Michelin's website for LTX's...

235/75/15 = 9.4W x 28.7H
31x10.5R15 = 11.1W x 30.8H

In my experience, ideal tire pressure goes down nearly proportionally with an increase in width, and slightly with an increase in diameter. Going to a wider tire will require less air to prevent the tire from crowning and wearing unevenly in the centers. Going from a 9.4 inch wide tire to a tire that is 11.1 inches is roughly 15 percent. As a starting point I would dial down the pressure 15% from what is stated on the doors.

The best way that I have found to really figure proper air pressure for non stock tires is to get a can of water based spray paint at home depot etc. and spray a lite stripe of paint across the width of the tire tread a few inches high. Let it dry and drive for a while trying not to make any turns when the tires when you are not rolling at speed. A long straight street is best. Run a while and check the paint. If it is wearing off the tread in the center of the tire faster than the shoulders, the tire is overinflated. If it is wearing off the shoulders faster, the tire is underinflated. I usually shoot for an indication of being slightly overinflated because the shoulders will scrub slightly during turns, as well as a margin for loading up with the crap I usually carry around. When I put a new tire size on any of my trucks, it takes a few tries to zero in on the right pressure, but the results will be long even tire wear.

 

[-Spike-]

Did you really just say that the safest option is to replace the garbage that comes on most vehicles with the same garbage?


Nay

Perhaps I gave the wrong impression, although looking at it now that's exactly what I said. What I should have said was that the car manufacturer has only given you the information for tire inflation that they know is safe for the tires that came on the vehicle from the factory. If you are looking for someone else to tell you what is safe, that's the only technically researched data available. If you want to put tires other-than-stock on the vehicle (which I highly recommend, which is what I meant by 'few people around here are going to do that') then you have to take in to account other variables when you make a decision on what pressure to run.

Sheesh, this has gone on long enough. My fault though.

-Spike

 

[CreeperSleeper]

I know that I've posted this before, but let me try again: Every tire is different, so the way that I figure out the best street psi is I go to my local truck scale. I wiegh the front of my truck (just the front tires on the scale) then the back of my truck. Then I read the sidewall of the tires I'm running. The will say "Max XXpsi @ XXXXlbs" From there I make a line graph with 0psi and 0lbs meeting and then end of the graph with the max psi and lbs. Take the weight of the front of you truck and divide it by 2. (The weight is spread over two tires) From that you can figure out what psi to run with the wieght of your veh. I will try to get a diagram up so the graph makes more sense. HTH

 

[Tapage]

29 PSi F/R in my HDJ-80 with 285

 

[IdahoDoug]

Wow - the door stickers on FJ80s are for 30/40 front/rear. That's interesting. The handling must have changed considerably from the suspension changes for 93+ models driven by the engine.

DougM

 

[KliersLC]

Little more weight up front as well perhaps???

 

[ashooter]

Wow - the door stickers on FJ80s are for 30/40 front/rear. That's interesting. The handling must have changed considerably from the suspension changes for 93+ models driven by the engine.

DougM

The 91/92 came with 15" wheels, didn't they? Would that make any difference?