33" tire pressure

FH212 · August 6, 2014

Trying to get a feel about tire pressures. Discount Tire likes to run my 33" Toyo MT's at 40psi with a 66 cold psi max. To me 40 is waaaaay to low. Does it ride good? Heck ya but it also unnecessarily wears the nice sharp edges on the MT's. So I run mine between 50-55 PSI. I argue with them all the time. What is everyone else doing?

thewhitestallion · August 6, 2014

66 psi max? that is odd... what ply tires are they? usually 8 ply tires are 50to 65 I can remember now (been a while since I worked there and also depending on the tire size) and 10 ply tires are 80 psi max. just because the tires sax 66 psi cold does not mean you run that in the tire. the amount of air you run in your tire depends on your set up. honestly I would try running 35 and see how they start to wear and then if they start to cup or chop out a little you could try bumping it up to 40 or so. honestly if you run 66psi in those tires it's going to ride like a wooden wagon. also the tire will not wear evenly still. the tires will wear more in the center of the tread then the edges, but probably start to chop out.

honestly most of the time that mud terrains chop out is not because of the tire pressure it's b/c the shocks cannot handle the extra weight. moral of the story is if you want to know the recommended tire size look in your door jam of the door and not the tire. but when you put m/t's on a truck you have to find a happy median.

EDIT: I have 275 70 18 bfg a/t's and they are LRE 10 ply tires with a 80 psi max and I run 35psi in mine with even wear and a decent ride for 10 ply tires.

surebuttercringe · August 6, 2014

I've been moving mine around to find the sweet spot. I am running Open Country AT which are also 10 ply in my size. Right now, I am running 43 psi cold. I tried 45 psi cold and found the ride a little harsh. Tried 40 psi and it just looked low. 43 psi cold seems to work well. Usually gets up to about 45 or 46 once hot.

FH212 · August 6, 2014

66 psi max? that is odd... what ply tires are they? usually 8 ply tires are 50to 65 I can remember now (been a while since I worked there and also depending on the tire size) and 10 ply tires are 80 psi max. just because the tires sax 66 psi cold does not mean you run that in the tire. the amount of air you run in your tire depends on your set up. honestly I would try running 35 and see how they start to wear and then if they start to cup or chop out a little you could try bumping it up to 40 or so. honestly if you run 66psi in those tires it's going to ride like a wooden wagon. also the tire will not wear evenly still. the tires will wear more in the center of the tread then the edges, but probably start to chop out.

honestly most of the time that mud terrains chop out is not because of the tire pressure it's b/c the shocks cannot handle the extra weight. moral of the story is if you want to know the recommended tire size look in your door jam of the door and not the tire. but when you put m/t's on a truck you have to find a happy median.

EDIT: I have 275 70 18 bfg a/t's and they are LRE 10 ply tires with a 80 psi max and I run 35psi in mine with even wear and a decent ride for 10 ply tires.

Yes they are load range E. I am not suggesting to run them at 66psi I would never do that, but 35psi on a mud tire will wear the crap out of the edges on the front every time you turn. These tires are too damn expensive for that. I was just curious what other people ran theirs at.

FH212 · August 6, 2014

I've been moving mine around to find the sweet spot. I am running Open Country AT which are also 10 ply in my size. Right now, I am running 43 psi cold. I tried 45 psi cold and found the ride a little harsh. Tried 40 psi and it just looked low. 43 psi cold seems to work well. Usually gets up to about 45 or 46 once hot.

My ride is a little harsher with the higher PSI too. I need to find the right spot also. I had them at what Discount recommended 40 and my fronts already have the sharp edges wearing down. I never turn harsh or sharp. Its frustrating.

TXS Heat · August 7, 2014

I am running the toyo mt 33s and keep 43lbs right now - they only have 3k miles on them.

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CAtaylor · August 7, 2014

This will get you very close.

-Load rating of the factory tire divided by the recommended air pressure, that will give you what each tire is carrying.

-Take the new tire load rating and divide that by the tire max psi; that will give you about what the new tire carries per psi.

-Take the number you came up with the factory tires and divide it by the lbs per psi on the new tire.

*this isn't exact but it will get you very close, it isn't linear across the board. Or do the first step and look at the inflation table for your tires. Toyo offers this on their Web site if that is what you are running.

thewhitestallion · August 7, 2014

Yes they are load range E. I am not suggesting to run them at 66psi I would never do that, but 35psi on a mud tire will wear the crap out of the edges on the front every time you turn. These tires are too damn expensive for that. I was just curious what other people ran theirs at.

also another consideration is how wide the tire is compared to the wheel. i.e. if you have a 33 x 12.50 17", 18" or 20" wheel, the tire is going to bulge on the sides which could be causing the sides wearing irregular. just play around with the tire pressure until you find the "sweet spot" G.L.

Spurshot · August 7, 2014

Who drives their truck with cold tires all the time?

Let's talk hot tires. It's really all that matters and with TPMS we can see the actual running temps. It changes in the winter for you guys in the 'snow belt. Guys in the hot areas need to know what the running pressures are when the tires are on the highway.

00Silverado4x4 · August 7, 2014

Who drives their truck with cold tires all the time?

Let's talk hot tires. It's really all that matters and with TPMS we can see the actual running temps. It changes in the winter for you guys in the 'snow belt. Guys in the hot areas need to know what the running pressures are when the tires are on the highway.

This is true but when checking your tires, you should always check the psi when the tires are cold to keep a more consistent readings to start with. Then adjust as needed for climate, season and so on.

thewhitestallion · August 7, 2014

Who drives their truck with cold tires all the time?

Let's talk hot tires. It's really all that matters and with TPMS we can see the actual running temps. It changes in the winter for you guys in the 'snow belt. Guys in the hot areas need to know what the running pressures are when the tires are on the highway.

what 06sierraz71 said. you should always check when tires are "cold" meaning they have been sitting a while and are around the lowest possible temperature depending on ambient temp outside. because if you check your tires when they are "hot" and adjust the air then, when they cool down you are going to loose some psi causing your tires to run "low" and causing some bad wear and/or handling. always check pressure when tires are "cold" and obviously as you drive on them the air will expand some and make the readings go up in the dic.

Spurshot · August 8, 2014

You guys have been drinking the water.

Come to the desert and try that. You'll end up with over inflated tires driving on summer days. The only pressure that matters is the stabilized driving pressure. You just need to know what that should be.

00Silverado4x4 · August 8, 2014

You guys have been drinking the water.

Come to the desert and try that. You'll end up with over inflated tires driving on summer days. The only pressure that matters is the stabilized driving pressure. You just need to know what that should be.

Um, I have, Phoenix, Arizona in summer. Once the tires heat up they will always read higher, that's why you start out with properly inflated tires when cold. Your owners manual, the stickers inside the door jam, even the sidewall of the tire itself will tell you what the psi is suppose to be "cold". Stabilized driving pressure will never happen as it fluctuates from mile to mile, degree to degree and MPH to MPH, hence setting pressure when cold.

Example you set your tires to 35psi while rolling in the desert at 102* while driving at 70mph, your tires will be under inflated by time you stop driving and the temps drop down by as much as 3-4psi maybe more. So when you start driving again unless you go 70mph and ambient is 102* your tires will never reach 35psi again. Tire and auto manufacturers take this idea into account when they set the psi for a certain range.

Spurshot · August 8, 2014

The mfrs give you a pressure for a factory tire. Their recommendations are based on averages of vehicle loading, road temperature variations, etc.. The OP has 33" tires and his question was 'what tire pressure should he run?'.

GM gives a "cold" pressure. They base this on an estimated average rise in pressure when driving. I've seen as high as 7-8 psi rise when hot. Even more if the "cold" reading was taken in a cold morning and driven at highway speeds in high heat days. Around my town, it's more like 4 psi.

With the advent of TPMS, we can monitor pressure at road temperatures. This is one of the more valuable features of late model vehicles for me. I check my tire pressures all the time, especially on long road trips covering days and thousands of miles. So, I have a good familiarity with the tire pressures at running temperatures on my vehicles and adjust pressures based on running pressures. I also know approximately what the pressure will be at "cold" temperature.

You don't drive your vehicle with "cold" tires. Figure out what pressure works best for your particular tires (especially oversize tires) and wheels using pressures from your TPMS at running temperatures/pressures. Once you know that, the cold pressure estimate will be known as well, if you've been using that TPMS enough to be familiar with your particular tire pressure variations where you live and drive.

I'm running my 33" tires at 46 psi @ road temps. They are LR E tires and I could run them as high as 80 psi. But I'm trying to balance tire wear pattern (center vs edge), handling, and lastly, ride. I know that I'll get better handling at 50-55 psi, but the center of the tires will go long before the outside.

00Silverado4x4 · August 8, 2014

The mfrs give you a pressure for a factory tire.

Actually that would be manufacturers of ALL tires, as I said look at your sidewall. There will be a psi rating and it will say "COLD". Yes you can run them lower than max but all I am saying is that it has always been stated that you check your tires initially at "cold" temps. The tires psi will go up from there but the tire manufactuerers have already taken that variable into account.