Trailer Tire Pressure?

[Russ]

I've got a dual axle aluminum trailer (I added the second axle) and I don't know what tire pressure to inflate them to. The sidewall said 65PSI max.

Over the winter ONE of the four tires lost most pressure down to 18PSI. Which got me thinking again how much should I inflate these tires?

What say you hive mind?

[kmclemore]

I've got a dual axle aluminum trailer (I added the second axle) and I don't know what tire pressure to inflate them to. The sidewall said 65PSI max.

Over the winter ONE of the four tires lost most pressure down to 18PSI. Which got me thinking again how much should I inflate these tires?

What say you hive mind?

Russ, I usually run with them fully inflated because I have a single axle and they need to be at full pressure to hold that amount of weight. However, if you want to find the really correct pressure for your trailer, you can do what I did when I was racing. There are two methods - chalk or masking tape - and both work the same way. With chalk, you use sidewalk chalk and draw a heavy line across the tread of both tires... then go for a short drive, with mild curves if necessary (no high speeds or fast turns). Once you stop, have a good look at how the the chalk wore away on the tread. If it's gone in the center but still evident at the edges, the pressure is too high... if it's worn off at the sides but chalk still remains in the center, the pressure is too low... and if it wears evenly across the tread width, then you've got it right. The tape method can then follow the chalk method, or you can just do tape. With tape you tape across the tread and up onto the sidewalls (to ensure it stays on). Then go for a longer and more varied drive. The wear pattern should be even across the tread, and if it isn't, follow the instructions for the chalk method.

This should get you to the correct pressure for your tires. The correct pressure allows the full width of the tread to be evenly applied to the road surface. That being said, with trailers, I tend to err to the over-pressurized side, because the tire needs to stay cooler and it also has to withstand hard bumps with no shock absorption.

[Starscream]

I've always run mine at 50PSI cold. My logic is that the 65 PSI is required for the max load of the tire, but with four of them on there I'm well under that. I've done a lot of trailering in the last 15 years of MacOwnership, and never had an uneven wear problem.

Losing air over winter should be addressed. I had a similar issue and it turned out to be a valve stem that needed replacing. The problem is that slow leaks can rapidly develop into fast leaks, and of course I that happened on a road trip.

[Be Free]

An underinflated (or overloaded) tire will get hot and and according to the Sturgeon General heat is the #1 preventable cause of early trailer tire death.

Seriously though, I've never had an issue with a tire at the maximum design pressure but I've lost several due to under-inflation and one due to seriously overloading a trailer. This is particularly important if you have radial tires on your trailer. Under-inflated radials are prone to tread separation and that almost always happens at highway speeds (in my experience). Even bias ply tires will die if you abuse them enough but they will put up with a lot more than a radial will.

Check the maximum load rating for your tire (marked on the sidewall). There will be two numbers: one for a single axle and another for dual axles. Pick the one that applies to your trailer. If the weight of your boat (and everything in and on it) plus the weight of your trailer minus tongue weight divided by the number of tires is less than this number then even if you have 99 problems an overloaded tire ain't one.

If you have dual axles you may be surprised to learn that you have to reduce the load rating for your tire. This is to account for the fact that when you go over a bump part of the weight is transferred to the other axle for a short time. A load range E tire (for example) can carry 2830 lbs on a single axle but only 2470 lbs on a dual axle.

It's a good idea to do the math yourself (or go to a scale and have the whole rig weighed). Unless you are a racer and are very careful about the weight of your boat, you will probably be surprised at how close your tire loads are to the maximum.

[Russ]

This is to account for the fact that when you go over a bump part of the weight is transferred to the other axle for a short time. A load range E tire (for example) can carry 2830 lbs on a single axle but only 2470 lbs on a dual axle.

Interesting.

My logic thinks adding the second axle doubled the capacity, yet the original axle still must carry the entire weight if needed.
Right now, the trailer is sitting on a slope and the two rear tires (back axle) were not touching the ground until I jacked up the front.

I'm thinking 50PSI minimum at this point. I don't know why I'm afraid to pump them to the max PSI of 65. It just seems like a lot of air.

Well, hopefully the boat will melt today and I can get back to prepping her for launch.

[Hamin' X]

Somewhat related to the discussion at hand; what kind of springs does your trailer have if it is a tadem axle trailer? Generally speaking, leaf springs are a better choice for more than one axle. The reason for this is that leaf spring axles share the load equally between both axles via the equalizer arm/beam.

This is why, with torsion axles, it is vitally important that your hitch height is such that your trailer frame is level with the road surface. This directly affects both load factor and wear on the trailer tires. With torsion axles, it does not take much of a difference in levelness to drastically increase the load on one tire over the other. It is why, when I was in the tire business in the '80s, in the earlier days of trailer torsion axles, I reccomended that trailer tires be kept at max rated inflation for that application.

Here is a webpage from someone with more letters behind their name than I have.

[Russ]

Some interesting info in that link,

Yes, I have torsion axles (Mac Aluminum trailer).

I try to keep the trailer level when towing.

[kurz]

I keep my trailer near 4bar (4 wheels).

Most important anyway to check on tour often if bearings get hot...

[Be Free]

Assuming that the other portions of the trailer can support the additional load, adding an extra axle does effectively double the capacity of the trailer. On level ground that load is carried approximately 10% on the trailer hitch and 22.5% on each tire. If you have leaf springs, most of the time when you go over a bump the equalizer will keep the load equally divided between the axles. This is not the case with torsion bar axles.

I would humbly like to offer one correction to my previous post. The de-rating for dual use is for dual tires, not single tires on dual axles. It's still a good idea to avoid running your tires at their maximum load just in case you have to temporarily run on three tires instead of four.


Sometimes it's better to have a spare axle than a spare tire. Because I don't run my tires at their maximum loads but I do run them at their maximum pressure I was able to safely return home on three tires after breaking an axle about 30 miles from home.

[Hamin' X]

I would humbly like to offer one correction to my previous post. The de-rating for dual use is for dual tires, not single tires on dual axles.

The proper terms are: Tamdem, for two axles and Dual for tires side-by-side. Not uncommon for the terms to cause confusion. As far as I know, the two different load ratings are only used on LT (Light Truck) tires.

Speaking of LT tires, they should not be used for trailers. I know that I have covered this topic in the past, but it is still important. The following link has a good explanation and I will only add that the heavier sidewalls on ST (Special Trailer) tires gives more protection in the event that the trailer tire rubs, or strikes a curb when turning.

Different Classes of Tires

[Be Free]

They are definitely used on trailer tires as well. No argument about LT tires on a trailer. Just Say NO!