Rear Tire PSI when towing?

Do you increase rear tire pressure when towing? My tires are the stock 245-75-16, speed rating S (112 mph), max psi 51. Current psi at manufacturer recommendation of 32. When camping the trailer tongue weight on the hitch is about 150 lbs and cargo in bed will be about 400 lbs. Taco is 2020 SR V6, 4WD, double cab. Total weight of camper + gear + people close to 3,000 lbs.

 

No. I’ve towed dozens of different boats and trailers over 50 years and never adjusted the tire pressure just for towing. If there was a need to do that your owners manual would so state.
But trailer tires are different. They should be run at max pressure all of the time.

 

I do find it odd that Toyota has nothing to say in the manual about adjusting tire pressure for increased load. I wonder if that’s because the correct adjustment may vary by manufacturer, but don’t know.

Scientifically speaking, increasing vehicle load while the tire PSI is constant increases the surface area of the tire patch contacting the road. This can cause a rise in tire temp, a decrease in mileage, more wear on the drivetrain, and uneven wear on the tire. Highly unlikely that any of this will lead to a catastrophic failure, you’re just getting an increase in wear and tear over time. It also makes the vehicle a bit mushier to drive.

When I tow my boat any further than say 15 mins, I do increase the rear PSI on my stock size tires to 40. Tongue weight is around 500 lbs.

 

I always check trailer tire psi and lug nut torque before hitting the road.

But there's a lot of chatter on the interwebs about reducing heat on the rear tires as well as increasing mpg when towing by increasing psi to max or just below shown on the sidewall. I'm wondering if this just a lot of hearsay or if anyone has actual data or official tire manufacturer guidance on this.

For example a booklet from UHaul:
"Air pressure in the rear tires of some tow vehicles may be increased to accommodate the additional weight of the trailer. Inflate rear tires approximately 6 psi above normal pressure (normal is usually 30 to 35 psi) but do not exceed front tires. Incorrect tire pressure can cause poor stability, an uneven ride and poor gas mileage. Check pressure when tires are cold, as pressure will increase with heat when traveling. Do not bleed off (release) this increased pressure."
https://www.aphis.usda.gov/mrpbs/fmd/downloads/SafeTrailering.pdf

What do they mean by "some vehicles". And if you do increase psi, by how much? And what about "do not exceed from tires"? Everything I read seems to create more questions.

I've gone both ways, Toyota spec vs max psi. I definitely notice better gas mileage with max psi. However I haven't done a scientific test to measure actual mileage difference. Some say that there will still be more heat when towing so you shouldn't go to max because the additional heat will send the psi over the intended max limit. So they recommend 10% under the max. For my tires that would 46 psi when loaded.

 

Max pressure sounds like a great way for a blowout, especially considering the pressures go up after you start driving.

 

I do the same. Max sidewall pressure on my tires is 42 and I bump up to 40. Truck drives great and I get decent mpg, but I don't have anything to compare it to as I've always done this.

 

Sprig is referring to trailer tires and trailer tires are another matter. They should be at the trailer manufacturer's spec, which on my trailer just happens to be the max listed on the sidewall. Trailer tires are constructed differently.

 

Standard load or P metric don't benefit much from inflating past spec. That said I still would bump up rear tires to 40psi on tacoma if I'm hauling at the top end of capacity.

LT tires need more pressure with weight, so 44psi is recommended with tacomas and hauling.

TW recently brought this calculator to my attention and I use it as a rough guide line for suggesting pressures when trucks have LT tires over SL. @BasicPainter You could use this towing as an excuse to buy some cool LT tires to match your new truck. I prefer the heavier tires for hauling and they'll last longer.

 

What does the tire placard on the driver's door jamb indicate for maximum tire pressure at maximum load????

 

That doesn't sound like a great combination. Air is air and expands when heated up. I am just wary because I've seen A LOT of blowouts this year. They were never me but it had me wondering if people were overloaded, going too fast, the tire was too old, or the tire was overinflated, or any combination.

 

Oh great, a new excuse to buy more stuff for the Taco!

 

Trailer tire blowouts are from under-inflated tires. More contact patch equals more heat and that leads to belt separation. That and tires are just old. Trailer tires should be replaced every 3-5 years regardless of milage.

 

Nothing about "maximum load".

 

I noticed your motorcycle. Specs on my Honda moto say increase the rear tire to 35 from usual 29 when fully loaded. No such guidance from Toyota on the Taco.

 

Then it is a reasonable conclusion that the published tire pressure is suitable for all loads within the limits of the truck.

In other words, no need to play around with tire pressure.

Personal example. I was hauling multiple loads of brick/block/mortar debris in 1100-1300 lb loads to a landfill 30 miles distance. This was just over the maximum load for my Tacoma. Didn't adjust the tire pressure, tires didn't squat or bulge or overheat. Rambled thru the landfill in loaded condition to reach the dump face. Tires didn't sustain cuts or punctures. This load only depressed the rear (stock) leaf springs by 2 inches.

My point, stay within the truck capacities and you don't need to fiddle with "enhancements" for loads. The truck is already set up.


<edit> Yeah, motorcycles are more sensitive to loads due to cornering and handling requirements are different. Not many trucks lean in corners.
<end edit>

 

Even in engineering there are gray areas. In this case Toyota has an interest in safety. So telling owners to increase tire pressure on rear tires when towing would certainly lead to cases of people leaving the rear tires at towing spec unloaded which would lead to accidents because of reduced contact patch yada yada yada.

But this is mod city right? My next trip will be 8,000 miles. If I can even modestly increase my mileage with a few more pounds in the tires, and do it safely, I’m most likely going to do it.

 

The new tundra is going to sense load, Toyota is very concerned with law suits and people simply don't know how to tow anymore.

You see so many overloaded trucks with headlights in the sky. (or upside down in a ditch)

It's my dream that you need to have a secondary license to tow ANYTHING

 

That makes sense as well

 

Trailer tires are way different than car/truck tires. If trailer tires aren’t run at max pressure it causes excessive heat. The number one cause of catastrophic trailer tire failure is under inflation.

 

The placard is an industry standard NHTSA requirement. It’s 100% CYA, as in, run these pressures up to max vehicle load and you won’t blow out your tires. It is NOT a solid guide to what tire pressures are optimal at various speeds and loads.

Other manufacturers actually list different pressures based on speed and/or load.

The placard is best utilized as a guideline for optimal pressure with minimal load in normal paved road driving conditions. Other than that, various conditions dictate adjustments to the PSI.

For example, if I asked what’s the best pressure for good traction in loose sand on the beach, the correct answer is not “see the placard”. It’s always situationally dependent.