Tire pressure?

[Silver]

The contact patch should be 125% of the max PSI rating of the tire in mm at an ambient temp of +/- 7 deg F of the average temp during your drive.

 

[George Bynum]

I'm make a road trip to Florida Friday with a fully loaded [weight wise] 98 RAM 1500. We're bringing a small lathe, tools, 60 gallon compressor etc. The tire placard says 41 psi, the tire says 80 psi. What pressure do you tire experts suggest?

You've had some intelligent (and some less intelligent IMO) suggestions. The reference to Bridgestone's booklet is very good.

I want to add what some seem to have missed. The WHEELS also have load limits, although they are not easy to find. Whatever pressure you decide to use (I'd guess in the 50-60 psi range without good knowledge), you want to consider the AXLE limits that should be on the vehicle sticker. Factory wheels should be good to axle ratings.

 

[OVERKILL]

The truck in question is my brother's, I'm helping him move this weekend so I'm not 100% certain of the tire sizes. IIRC it's 245/75R16 on the placard. I'm not sure on the LT tire size on it now, only that it's a 16" tire with 80psi on it.

OK, so, let's use this document from Toyo:
https://www.toyotires.com/media/3729/application_of_load_inflation_tables_20200723.pdf

We see that that size of tire, at 41psi, has a load carrying capacity of 2,469lbs:

So, we divide that by 1.1 to get the load capacity per the OEM, which is 2,245lbs.

Now, if we go to an LT in the same size:

We see that we get 2,335lbs at 55psi. So, your proper inflation pressure is 55psi.

 

[demarpaint]

@OVERKILL Thanks.

 

[OVERKILL]

@OVERKILL Thanks.

You are quite welcome.

 

[CapriRacer]

What is very likely here is that the original P245/75R16's were replaced by LT245/75R16's - and in that case, the pressure would be 15 psi MORE than the placard pressure = 41+15 = 56 psi.

 

[jadatis]

My calc with LT american formula comes to 58 psi to carry the 2470 lbs as maxload is of XL P-tire LI 112
With European calc 60,5 psi.

But 41 psi is most likely a not calculated vallue, yust reference pressure of XL in american system. So most likely calculation with use of GAWR'S would give lower pressure.

So give those, and maximum technical carspeed, and I will calculate what it would need.

Best would be real axle-weights , and max epeed you use , and wont go over for even a minute.
Determining the real weights in use, is the most tricky part in it all.

 

[SwampSurvivor]

OK, so, let's use this document from Toyo:
https://www.toyotires.com/media/3729/application_of_load_inflation_tables_20200723.pdf

We see that that size of tire, at 41psi, has a load carrying capacity of 2,469lbs:
View attachment 102178

So, we divide that by 1.1 to get the load capacity per the OEM, which is 2,245lbs.

Now, if we go to an LT in the same size:
View attachment 102180
View attachment 102181
We see that we get 2,335lbs at 55psi. So, your proper inflation pressure is 55psi.

Woah I need a link to that!

 

[OVERKILL]

Woah I need a link to that!

Link is the first one there, should be able to download the PDF.

 

[OVERKILL]

What is very likely here is that the original P245/75R16's were replaced by LT245/75R16's - and in that case, the pressure would be 15 psi MORE than the placard pressure = 41+15 = 56 psi.

Nary identical to what I got using the load tables

 

[Rmay635703]

A word to the op, it’s extraordinarily rare that you can have too much pressure as long as it’s in spec with the tire rating.

Less heat, better fuel economy and more even tire wear are worth it despite the bumpier ride.