What Tire Pressure Is Recommended On 4.80/4.00-8 Load Range C Trailer Tire For Highway Speeds

Updated 01/09/2026 | Published 07/29/2010

Question:

I just bought this boat and trailer 14 alum Grumman / galv trailer Tires are 4.80-4.00-8 K371-006 Max rating 90 psi 745 lbs What tire pressure should I run for highway driving? 90 psi seems like a lot. Thanks!!

asked by: Greg

Expert Reply:

The tires should be inflated to 90 psi on the highway as well as other roads, regardless of load size. The problem is that under inflating a trailer tire will lead to degradation of the tire.

On trailer tires, the side walls are thicker than on car tires so they can handle more vertical load. An under inflated tire side wall will heat up more often and quicker and will lead to early wear and possible failure of the tire. The best thing to do is to follow the rating on the tires and inflate them to the maximum recommended psi. Also, trailer tires are speed rated for 65 miles per hour maximum.

i have incldued a link to our tire FAQ article for you.

expert reply by: Michael H

Thomas S.

6/17/2020

I have a set of carlisle 4.80-8 2 ply load range b on my trailer that I tow behind my motorcycle and am wondering what should the air pressure be. The trailer empty weighs 100 pounds and the max would be 300 pounds so right now I get a lot of bounce and only see about 2 inches of the center tread making contact with the pavement if even that amount and by the way this trailer is about 30 inches wide. Can you help me out here?

Chris R.

6/22/2020

For that size tire in a Load Range B you're looking at a max psi of 60. I really can't recommend inflating them to less than this because it would essentially lower their capacity to an unknown number. Is there any way to add some more weight/cargo to the trailer?

Thomas S.

6/22/2020

@ChrisR The trailer is being towed behind a motorcycle and it would be better on the motorcycle with the lightest weight possible. The trailer weighs 100# and I'll be putting in a 5 gallon gas can, 5 gallon water can, and standard camping gear so I don't see it topping 250 lbs. The other choice was strapping all this to the bike or using the trailer and since my bike is a modified 1950 Harley I want to carry spare parts and tools. lol

Willie

1/9/2026

There is a minimum tire pressure spec for 4.80x8 tires and its 10-15psi based on its ply rating. This is an ST tire specification that specifically targets "very light trailers". There are online calculators that can help you calculate the mathematical ideal pressure, but the min pressure is 10-15psi. All these people telling everyone on the internet to "inflate to the max psi" are just saying the safe answer for the 99% of people who cant do the measurements and math to calculate the RIGHT psi for their specific trailer, tire, temperature and load - because overinflation is safer than under-inflation. However there are cases - such as yours, where a specific pressure needs to be calculated and utilized for the proper operation of the tire on the trailer... just keep it above the minimum and monitor for for excessive heat. Also remember using this specific and low of a pressure means it will have to be checked and adjusted MUCH more frequently - even day to night if there is a significant change in the ambient temperature. Over-inflating the tires washes away most of these variables and that's why doing so it recommended for the general public