33x9.5 tires - How many PSI do you run?

[JCruse]

I'm really curious about this because this is my first "truck" (FZJ80) and I recently went up in size from 31" to 33" tires. The 31's were set at the factory 32psi so that's where I set the new 33's at. The ride felt a bit squishy, especially on tight turns, so I bumped it up to 35psi. That felt better handling wise and I noticed a couple more MPG as well. But when I noticed that my new tires were wearing down on the fast side, I dropped it back down to 32. As you can see I'm totally clueless on this, I'm used to running 225/40/18's on sporty cars, not great big truck tires. So I thought I'd take a poll - what do you guys run your 33" tires at? Maybe I'll take the average and set my tires to that!

 

[gaijin]

I'm really curious about this because this is my first "truck" (FZJ80) and I recently went up in size from 31" to 33" tires. The 31's were set at the factory 32psi so that's where I set the new 33's at. The ride felt a bit squishy, especially on tight turns, so I bumped it up to 35psi. That felt better handling wise and I noticed a couple more MPG as well. But when I noticed that my new tires were wearing down on the fast side, I dropped it back down to 32. As you can see I'm totally clueless on this, I'm used to running 225/40/18's on sporty cars, not great big truck tires. So I thought I'd take a poll - what do you guys run your 33" tires at? Maybe I'll take the average and set my tires to that!

If those are 33x9.50-15's, then "the book" (Yearbook of Tire and Rim Manufacturers) says you should be running them at 42psi.

 

[Fast Eddy]

That's a lot of truck for that little tire. 42 may be about right.

Are they 16s? Never heard of 33/9.5-16. My 15" rims don't fit over my fzj80 rear brakes.

 

[LDowney]

I'm really curious about this because this is my first "truck" (FZJ80) and I recently went up in size from 31" to 33" tires. The 31's were set at the factory 32psi so that's where I set the new 33's at. The ride felt a bit squishy, especially on tight turns, so I bumped it up to 35psi. That felt better handling wise and I noticed a couple more MPG as well. But when I noticed that my new tires were wearing down on the fast side, I dropped it back down to 32. As you can see I'm totally clueless on this, I'm used to running 225/40/18's on sporty cars, not great big truck tires. So I thought I'd take a poll - what do you guys run your 33" tires at? Maybe I'll take the average and set my tires to that!

Are you certain that they are 9.5" wide? The wheel on an 80 is wide enough that a 9.5" tire might be too narrow regardless of what pressure that you run.

 

[cody c]

As long as the max rated pressure is over 42 psi

I usually drive by tread wear and not by book or rated pressure (as long as its below max). If the tire wears in the center more, pressure is too high, if it wears on the outside of the tread, too low.

with 37's on fjcruiser wheels, driving by pavement performance for me is kind of an oxymoron though.

 

[JCruse]

Ooops, I screwed up! I put down the rim size for some reason. Disregard that. The tire is a 33" 305/70/16 on a 97 80. This is what I'm asking about. A fairly standard tire for an 80. I keep fiddling with the pressure, I was just wondering what others run in this size tire on an 80. Maybe I should have put it (correctly) on the 80 board.

 

[gaijin]

Ooops, I screwed up! I put down the rim size for some reason. Disregard that. The tire is a 33" 305/70/16 on a 97 80. This is what I'm asking about. A fairly standard tire for an 80. I keep fiddling with the pressure, I was just wondering what others run in this size tire on an 80. Maybe I should have put it (correctly) on the 80 board.

That makes a lot more sense.

Assuming they are "LT" tires and not "P" tires, the correct Cold Tire Pressure for you is 35psi Front/Rear.

This gives you a Load Limit of 2,270 pounds/tire and a flat contact patch with a normal load.

Source: 2012 TRA Yearbook

 

[JCruse]

Thank you so much gaijin! Yes they are LT's. If 35psi it is then 35psi it will be! That's where I'll keep them. Thanks again.

I wonder, does your chart cover passenger car tires as well? I've never been clear on what my VW tires should be set at since changing sizes. They were 185/60/16 but I upgraded to 235/40/18's and there's no authorative source I'm aware of that tells you what to set a tire to that doesn't actually belong on the car. It weighs 3225lbs and stock tires were set to 27psi I think. I have the new size tires set to 36psi but that's really just a shot in the dark!

 

[gaijin]

Thank you so much gaijin! Yes they are LT's. If 35psi it is then 35psi it will be! That's where I'll keep them. Thanks again.

I wonder, does your chart cover passenger car tires as well? I've never been clear on what my VW tires should be set at since changing sizes. They were 185/60/16 but I upgraded to 235/40/18's and there's no authorative source I'm aware of that tells you what to set a tire to that doesn't actually belong on the car. It weighs 3225lbs and stock tires were set to 27psi I think. I have the new size tires set to 36psi but that's really just a shot in the dark!

You're welcome - always glad to help

The "authoritative source" you seek for tire pressures is the Tire and Rim Association Yearbook - it contains Load Limit / pressure charts for all kinds and sizes of tires.

If you can give me the OEM tire size, the factory recommended tire pressure(s) Front/Rear, the GAWR Front/Rear and the tire size you want to run, I can figure out the correct pressure for the new tire.

 

[JCruse]

Stock tire size was 195/60/16 - tire pressure is 28F 28R half load and 30F 39R max load. And the GAWR is 2315 front and 2161 rear. The new tire is a 235/40/18. Is that it?

 

[gaijin]

Stock tire size was 195/60/16 - tire pressure is 28F 28R half load and 30F 39R max load. And the GAWR is 2315 front and 2161 rear. The new tire is a 235/40/18. Is that it?

The 235/40-18 tires should have the same Load Limits as the stock tires when inflated to 29psi F/R for Half Load and 32psi Front and 38psi Rear for Max Load.

 

[JCruse]

The 235/40-18 tires should have the same Load Limits as the stock tires when inflated to 29psi F/R for Half Load and 32psi Front and 38psi Rear for Max Load.

Oh so I can run stock pressure then. Thanks.

Everyone I see on modding websites say that you should increase tire pressure 2psi or 4psi for every inch in wheel increase. I assumed this was to protect the rim from potholes with those narrow sidewalls.

 

[gaijin]

Oh so I can run stock pressure then. Thanks.

Everyone I see on modding websites say that you should increase tire pressure 2psi or 4psi for every inch in wheel increase. I assumed this was to protect the rim from potholes with those narrow sidewalls.

Not exactly.

You said your stock pressure for half load was 28psi.

I said you should be running 29psi - that's +1psi from stock.

For max load I suggested +2psi from stock for the Front and -1psi (or you can run the same as stock) for the rear.

The max load rear tire pressure is unclear because above the pressures I recommended you are NOT increasing the Load Limit, just firming up the sidewall - if it appears to need it.

 

[JCruse]

Not exactly.

You said your stock pressure for half load was 28psi.

I said you should be running 29psi - that's +1psi from stock.

For max load I suggested +2psi from stock for the Front and -1psi (or you can run the same as stock) for the rear.

Minus one? I think you goofed somewhere . You previously put down THIRTY NINE psi max load rear. 11 more than stock.


As for the rest I stand corrected and thank you so much again for your time in helping me out.

 

[gaijin]

Minus one? I think you goofed somewhere . You previously put down THIRTY NINE psi max load rear. 11 more than stock.


As for the rest I stand corrected and thank you so much again for your time in helping me out.

I goofed?

Here's your original post about your tires/specs (emphasis mine):

Stock tire size was 195/60/16 - tire pressure is 28F 28R half load and 30F 39R max load. And the GAWR is 2315 front and 2161 rear. The new tire is a 235/40/18. Is that it?

YOU said 39psi Rear for Max Load.

I said 38psi Rear for Max Load.

I may not be a rocket scientist, but that looks like -1psi from the stock pressure you gave me.

 

[JCruse]

I goofed?

Here's your original post about your tires/specs (emphasis mine):



YOU said 39psi Rear for Max Load.

I said 38psi Rear for Max Load.

I may not be a rocket scientist, but that looks like -1psi from the stock pressure you gave me.

OH! I didn't know you were referring back to the max load pressure. Sorry.






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