Tow vehicle tire pressure

[Tireman9]

Originally Posted by Jim Smyth

So as a tire engineer I have a question for you. Say for discussions sake my tires are rated at 2500 lbs each max load at 80 psi cold. So if I inflate them to 75 lbs to start and they warm up to 80 lbs after 15 minutes of being on the highway which always happens to me via my TPMS. So do tires that warm up to 80 lbs from 75 lbs still have the 2500 lb load rating and if not why?

Load capacity is determined at the cold inflation pressure. If you have 2500# and start at 75 psi you are driving the tires in overload. This does damage to your tires.


I would also hope that you have some load margin. Check the load tables. Find the load for 75 psi and that should be your goal as if you go exactly to 100% of rated load how do you know the scale accuracy and the pressure gauge accuracy. and you have zero allowance for wind loading or road crown or road camber or that extra Big Mac you just bought.
I would like to see a minimum margin of 10% of the load capacity because your tires are not brand new. Old tires have some internal structural damage (pot holes curbes etc) I cover this in my Blog.

[Jim Smyth]

Originally Posted by Tireman9

Load capacity is determined at the cold inflation pressure. If you have 2500# and start at 75 psi you are driving the tires in overload. This does damage to your tires.


I would also hope that you have some load margin. Check the load tables. Find the load for 75 psi and that should be your goal as if you go exactly to 100% of rated load how do you know the scale accuracy and the pressure gauge accuracy. and you have zero allowance for wind loading or road crown or road camber or that extra Big Mac you just bought.
I would like to see a minimum margin of 10% of the load capacity because your tires are not brand new. Old tires have some internal structural damage (pot holes curbes etc) I cover this in my Blog.

I just recently put on New Goodyear Endurance tires on my 5th wheel. The tires are ST235/80R16. Max load via this Manufacturers charts shows 3420 per tire at 80 psi cold.


Here is the graph.


https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf


So at 75 psi my tires have a rating of 3260. Times that by 4 and I have 13,400 lbs of towing capability for my 5th wheel tires. Last time I scaled my 5th wheel it scaled at 8200 lbs on the trailer tires.


This is the entire point I was trying to make that you dont have to run at max cold pressure. I am sometimes running in very hot weather and get a 10+ psi rise after 15 minutes on the Highway. I dont like exceeding any numbers and would rather err on the side of being a little more cautious.

[RKHengst]

I recently went to a 2017 Nissan Titan XD SV which has all the packages. It tows my Jayco 31QBDS well with great stability. (Towed with a Duramax for 16 years before switching).

I am delighted in how stable the XD is and how well that engine handles the additional load. My tow behind is a little lighter than yours, and we never tow “wet”. I checked the regular Titan specs and determined the tow limits to be too close to the limits for my liking. Since you also chose the gasser (great engine), load capacity is less of an issue, but may be once you hook up.

Am loving the Titan so far, hope to get back out camping soon!

[Tireman9]

OK we may have some confusion in this thread. We started out with a question on the TV and now we have the trailer tires and weight mixed in.

Inflation guidelines are different because of the high level of Interply Shear experienced by tires on trailers.

TV tires can inflate based on scale reading, consulting the Load Inflation tables to learn the MINIMUM COLD INFLATION.and adding 10% to that number to avoid having to chase your tail with minor changes in ambient temperature.

Multi axle trailers experience Interply Shear forces that are trying to tear the belts apart that are about 24% higher than an identical tire would experience on a TV. As I cover in my blog TT tires should shot for a MINIMUM of 15% Reserve Load with 20% or higher being desirable. Also increasing the tire inflation to the inflation shown on the tire sidewall can decrease but not eliminate the Interply Shear force. I have a number of posts explaining the technical aspects of Interply Shear or you can see the Google search on the topic HERE.