1. I have just bought a 26.5' fifth wheel weighing about 7000lbs. I have Toyo MT's 285/75/R16 (E) tires. What tire pressure should I use for towing?

2. Do I need to add an auxiliary trailer brake? I'm wired with a bumper/ball hitch and just had the fifth wheel installed.

 

you should hook up a brake controller in the truck, always better to be able to utilize more braking power, for towing I'd run at least 75 psi,

 

Most states require trailer brakes on trailers over 2000#'s.

Since your pin weight should be in the area of 1400#s, 70-75 psi would give you plenty of load capacity. But more important for proper handling, while towing, stiffer tire side walls. The stiffer the sidewall, the less sway you will feel while towing.

 

If you are going to be doing a lot of towing, you might think about changing out your "R" tires for "LT" tires.

 

The OP is already running E rated tires - I think it was a mistake when he put the R in front of 16, the tires he has are LT.

75 lbs would make sense for a fiver. The max you should ever be at is 1,400lbs of pin weight (about 20%) and you should run full recommended tire pressure.

Definitely get a full trailer brake wired in. I have the integrated system, so not sure what most people recommend for an aftermarket unit, but someone will chime in.

 

You do not want to pull that 5th without trailer brakes, especially where you live. You'll end up on a runaway ramp (if you're lucky) coming down the back side of the first mountain pass you hit.

Install a good trailer brake controller. Test the trailer brakes before you pull away with the trailer. If you're going to tow often, seriously think about installing an exhaust brake on your PSD.

 

I live in BC so I am not a stranger to mountain towing!

A trailer brake and/or exhaust brake, not only make the trip safer but a whole lot more enjoyable too, unless you like the adrenalin white knuckle towing LOL.

With my exhaust brake, I have had the same service brakes for 4 years and they are still roughly 70-75%, service brakes are just for complete stops now.

 

Toyo labels their tires as LT285/75R16, so he probably just left the LT off (I know I do, mine are techincally 35X12.5R20LT). His tires are rated for 3740lbs at 80psi.

According to the tire inflation tables for his size tire he should run the following pressures at for the corresponding load on each tire.

35psi - 2130lbs
40psi - 2340lbs
45psi - 2540lbs
50psi - 2755lbs
55psi - 2925lbs
60psi - 2110lbs
65psi - 3305lbs

The inflation table I have access to stops at D rated tires in his size so I can't say wha the load ratings would be for 70 or 75psi.

You need to find out the front and rear axle weights of your truck when you have the trailer attached and you are fully loaded. Divide that weight by 2 and use the numbers above to figure out the correct tire pressure. These numbers are for single rear wheels, if you have dual rear wheels they run about 200lbs less for the same psi.

 

Great info guys, thanks for all of it...I'm calling to get booked in for that brake install right away

 

Who is doing the install, by any chance is it Malcolm at Harbor City Diesel?

He is a great diesel guy on the island!