E rated tires and air pressure?

[Advmoto18]

I run 50 on my front and 55 on the rear. By the table above I would be running under 35 pounds of pressure on my front. No WAY am I going to run that low. The tires would heat up like crazy. Gas millage would tank, and every time I went around a corner the truck would lean. No thanks.

Make sure you're using the correct chart!

Do not use the TRA P Metric chart. Scroll down to the TRA Light Truck Inflation Table.

 

[rubberlegs]

Calculating the pressure using the Toyo tables for different types of ties has been greatly simplified with this website:
https://tiresize.com/pressure-calculator/.

Using that for our Tacoma (265/70R16), which has a placard pressure of 30 psi for P-rated tires, any LT tire (C, D, or E) change to 42 psi. This gives it the same "safety factor" of capacity/load of about 150%

Why such higher pressures? I suspect it's due to not overheating the tire, but haven't found the smoking gun after much web searching. Maybe it takes more pressure to "poof" out the tires. Does it take into account braking and cornering performance, ride quality, wear, etc.? I think it only tries to match the "safety factor" but could be wrong. Was the most critical component in the engineer's decision the tire load safety factor, instead of those other factors?

Our dealer would consistently put 35 psi (instead of 30) during the two-year free service period. Maybe they had the same new tech doing oil and tire rotations. From the tire pressure website: 35 ==> 46 psi for LT tires. (30 ==> 42 as a comparison)

Why does Toyota recommend 30 psi on all four wheels? Our empty truck with two people and full gas tank is 2700 lb front axle, 2000 lb rear axle. Are the rear tires over pressured? With a camper, our rear axle goes from 2000 lb to 3200-3600 lb. Why is there no advice on rear pressures? Is it too complicated for the average consumer, who probably doesn't check tire pressures more than once or twice a year (if that). Or maybe they tried to average what most people load in their truck. (Most trucks I see on the road are empty!). Maybe they figure a 700 lb load over the rear axle evens out the two axles, so 30 on both axles seemed like a less fussy compromise pressure.

Our tires are at end of lifetime. During that time we've used about 45psi front, 60 psi rear, with the thought to match the "safety factor" front and rear, based on the Toyo tables. They seem to wear evenly with rotating every 5000 miles. But that's only one data point and not conclusive. It seems intuitive that the rear axle should need more tire pressure.

In considering 265/75R16 upsized tires that supposedly fit our truck (1" more diameter), the pressures according to the tire pressure website (and Toyo tables) are: 30 ==> 39, 35 ==> 43 psi.

Edited to add: considering "pizza cutter" 235/85R16 tires: 30 ==> 46, 35 ==> 50

 

[K7MDL]

The Toyo link in earlier posts appears to not exist. I found the Toyo chart here. The calculator above is interesting.
Application of Load Inflation Tables Version 2020-7 (toyotires.com)

 

[rubberlegs]

Here's another way to think of tire pressure, and a very easy way to measure front to rear. I'm not convinced a tire engineer would agree... Anyway I measured ours and we were pretty close on all four tires.
Adjusting tire pressures

 

[Wandering Sagebrush]

Here's another way to think of tire pressure, and a very easy way to measure front to rear. I'm not convinced a tire engineer would agree... Anyway I measured ours and we were pretty close on all four tires.
Adjusting tire pressures

That is an interesting method, I’m curious what a tire engineer would say.

 

[rubberlegs]

I wrote to the YouTube guy and he agreed, but said it was a good rule of thumb.

 

[CPT Davenport]

Silverado 1500

50 front
55 back

 

[rubberlegs]

I've been using 47 front, 67 rear on our overloaded Tacoma.

 

[Vic Harder]

3500 Silverado, Puma/Grandby. I was running 65/65. Seems to be wearing even, maybe a bit more on the outsides (I corner aggressively). Trying 70/70 now.

 

[rubberlegs]

I've been using 47 front, 67 rear on our overloaded Tacoma.

Looks like we can't edit our posts after a certain time interval. Anyway I forgot to say the pressures are for our "pizza cutter" narrow and taller 235/85R16 tires.

 

[ski3pin]

Looks like we can't edit our posts after a certain time interval.

Perhaps we cannot edit pre software upgrade posts?

 

[rubberlegs]

I saw something about a limited time that you can edit (new forum software). But I don't recall where I saw that of course!

 

[JHanson]

I've been using 47 front, 67 rear on our overloaded Tacoma.

Sixty seven?! That's crazy. We run 55 on the rears of our Land Cruiser Troop Carrier when it has 71 gallons of fuel and 29 gallons of water onboard for a two-week no-resupply route in Australia. What do you carry? Have you done a chalk or paint test?

 

[Wandering Sagebrush]

I saw something about a limited time that you can edit (new forum software). But I don't recall where I saw that of course!

Initially, new posts and their titles may edited. I don’t know the specifics, but I believe length of time for the title is less than the body of the post.

 

[Tom n N]

Don’t want to loose track of the original question, but since the subject of the new software came up, what happened to the signatures that used to be on the bottom of posts? Was very handy during discussions like this when the poster showed what kind of rig they had, helped put answers in context.

As far as the original question:
I’m currently running 40 front end 60 rear on my very much overloaded 93 Toyota w/ FWC running 235-85R 16’s. Still experimenting, so keeping an eye on this thread.

Tom

 

[Wandering Sagebrush]

Tom, members need to edit their profile to re-establish their signature.

 

[rubberlegs]

Sixty seven?! That's crazy. We run 55 on the rears of our Land Cruiser Troop Carrier when it has 71 gallons of fuel and 29 gallons of water onboard for a two-week no-resupply route in Australia. What do you carry? Have you done a chalk or paint test?

Bottom line: I've not found good guidance on tire pressures based on axle weight. There's lots of opinions but I'm not sure they are science based. Tires are complicated and have non-linear characteristics. Rules of thumb may be ok in a small region of axle loading, but in our case the rear axle has 33% more load than the front. A guy I used to work with has a PhD in landing gear design. I should get off my duff and ask his opinion.

I suppose the chalk/paint test is a more involved, but a similar method to the video linked in post 44. It measures the contact area super quickly -- it takes about a minute to check all four tires.

There are standard calculations for E-rated tire pressures, so I use that for the front based on the placard pressure (in our case P-rated is 30psi, E-rated 47psi). For the back I use the same "safety factor" as the front, using the line per the Toyo tire tables.

I gotta admit 67 seems super high, so at first we did 45 front, 55 rear (different size tire though, 265/70R16). But I decided to follow the tire pressure curves and "inched" up to the higher pressures after a couple years of trips.

There are truck scales close to home, so we often weigh at the beginning of a trip. Have you weighed your two axles when carrying all that fluid?

 

[JHanson]

There are truck scales close to home, so we often weigh at the beginning of a trip. Have you weighed your two axles when carrying all that fluid?

Yes, we weighed it in Australia fully laden; I can't remember offhand what the result was. It's written down somewhere. We're right on GVWR for an HZJ75 when fully loaded.