Tire pressures

[Salteen]

Hey, its me. What was the factory tire specs, Metric P or LT tires, and what load range and what is the PSI for F/R? 1987 Dodge Power Ram 50. I have LT 235 75 15 tires on range E load (M/T tire) and all i know if factory is 225 75 15 for my truck. Idk about load range and P/LT ratings. I have factory full size spare to look at

[Salteen]

I know this: my new tires are Forceum 08 Plus M/T tires LT 235 75 15 C load range 6 ply Q speed rating 99 mph max. Dad had a pair of 30 x 10 i think on his yota and boy did they scream. I think it woke up anyone we drove by at night, we had to turn the radio to max to hear it at all. Idk why but i find tire droning to be a thing of the south : a status symbol for real american trucks

[camoit]

Go off of what the pressure on the side of the tire says.

[geezer101]

Go off of what the pressure on the side of the tire says.

...the man's not wrong (unless it's a first run Ford Explorer. Did Ford screw up badly that time :shakehead:) I have a tendency to run 2-3 psi higher though. Tires wear more evenly, less rolling resistance (better fuel economy over the long run) and tires last a little longer.

[Salteen]

well I would, if a tire pressure were there! I can't find one, I have went over it with a white sharpie looking for a tire pressure.

[Salteen]

i looked into the manual and it says that the factory tires were P225 / 75 / 15 and that I should not go with a lower load rating. now if i need to run like 50 PSI to keep the same load as the factory tires then I can't use my truck to its potential.

it also said to air the tires to 35 psi with cargo in the back, and to air them up to 30 psi for high speed driving, which I can't really do with a q rated tire, which kinda goes against my plans I am about to post on my build thread.

here is what I have:
Factory tire diameter is 28.3 inches. my new ones are about 28.9 inches
factory tire width is 8.9 inches. my new ones are about 9.3 inches
factory sidewall is 6.6 inches. my new ones are about 6.9 inches
I am turning 14 less revolutions per mile a significant decrease. 20:20.4 40:40.8 60:61.3 80:81.7 (MPH)

the top of the tire to the fender well is .3 inches closer than factory, the inner sidewall to the suspension and frame is 2.95 inches farther away and the outer sidewall is 3.35 inches farther out. this is because I went from a positive 50 offset rim and 225 tire to a negative 30 offset rim and 235 tire

my old tire pressure of 26 psi needs to be umped to 39 PSI for normal driving, 43 PSI for high speed driving, and 47 PSI for driving with a load.

here are some pictures

24495

24496

24497

24498

24499

24500

24501

[charger_john]

Salteen, doesn't your truck have an ident plate like this, inside the driver's door jamb?

24503

Going with what this says should be right, or you can go higher, up to the max shown on the tire sidewalls.
You say you can't find this on your sidewalls, that's surprising, I always see the max load & pressure on every
tire I've had..... (the ram is at least my 30th vehicle I've owned)

Also - the chart you show above shows a dramatic increase (from 30 to 43, etc.) due to going from a 225
tire to a 235. I don't buy it - that's a small change in tire size.

[Salteen]

i would just look but I am about 10 minutes from my truck and I don't feel like a 20 minute drive just to take a picture of the plate in the door jam

[SubGothius]

The sidewall pressure spec is the maximum that the tire can safely stand up to; it's usually not the proper pressure for the specific vehicle they're on.

The owner's manual for my '87 Ram 50 lists these tire specs:

P195/75R14 - 26 psi*
P205/75R14 - 26 psi*
LT195/75R14(D) - 36 psi*
P225/75R15 - 26 psi*

*W/o cargo for all tires. If carrying cargo, rears should be 36 psi (P-metric), or 65 psi (LT).

If you rarely carry heavy cargo, go with P-metric, but LT tires will hold up and drive better if you frequently carry heavy cargo, at the expense of ride quality and tread noise.

[MrPaco]

The sidewall pressure spec is the maximum that the tire can safely stand up to; it's usually not the proper pressure for the specific vehicle they're on.

The owner's manual for my '87 Ram 50 lists these tire specs:

P195/75R14 - 26 psi*
P205/75R14 - 26 psi*
LT195/75R14(D) - 36 psi*
P225/75R15 - 26 psi*

*W/o cargo for all tires. If carrying cargo, rears should be 36 psi (P-metric), or 65 psi (LT).

If you rarely carry heavy cargo, go with P-metric, but LT tires will hold up and drive better if you frequently carry heavy cargo, at the expense of ride quality and tread noise.

I'm running one size bigger than stock, 235/75R15, and rarely carry heavy cargo. Any thoughts on proper psi? Should it be the same, lower or higher than the 225/75R/15 size?

[MrPaco]

I realize this is the same question Salteen had, just wondering if anyone has some thoughts on appropriate pressure adjustments when going up in size.

[Salteen]

here, this is how I found out: https://tiresize.com/pressure-calculator/ factory is P225/75/15 26 psi and SL load range (102)

mine says that max load is at 48 psi, but I wouldn't run it with a 6 play tire. I am putting a 3.3L V6 in it and I will be towing a small trailer from time to time, it weighs about 2000 lbs with the rzr on it, my tires are 104 load range. so it said that 39 is best for daily, and ill air the rear up to 47 or 48 when I am pulling the rzr behind it.

the rzr is a side by side atv: a 4 wheeler with bucket seats and fully independent suspension and a steering wheel and pedals.