Tire pressure observations

[mickier]

I needed to tow a 7000lb trailer a couple hundred miles with my 2018 tahoe (which has the 18" tires). I pumped the trailer tires to their rated number and checked the Tahoe - my tires (Pirelli Scorpion III) says max pressure is 51psi - so I pumped them up to that.

I immediately noticed a pronounced increased stability - (the trailer wasn't wagging my tail anymore). but that's not what this post is about.

After I dropped the trailer, I left my tires at 48psi for a while - noticed harsher ride of course, but it looks like I'm getting a couple MPG better than with 35 psi... Has anyone else tried or noticed this result?

I'm going to do a longer test, I'm also going to have to watch that I'm not wearing out my tires faster in the middle too but I drive 400 freeway miles a week, so even a couple more MPG helps especially at $4/gallon for gas(!) (looks like i'm a bit over 24mpg with 48psi vs. 22ish)

 

[Doubeleive]

 

[KMeloney]

A lot going on here...

First, you've posted in the '21+ section (which doesn't much matter here, since your post is about tires), so you might want to throw this post in the pre-'21+ section for better accuracy.

Second, and maybe it should be first, the "max pressure" markings are exactly that -- a MAX that shouldn't be exceeded. Your tires should be inflated to a certain PSI WHEN THEY ARE COLD because the pressure in them will increase as the tires are driven on and heat up. If you're starting with them at the max pressure, then the pressure in them is only going to increase as you drive. You could quickly exceed the max pressure, and that's not good.

Otherwise, yes, it takes more energy to roll under-inflated tires (just like riding a bike with under-inflated tires). So, you should see a fuel savings with properly-inflated tires. However, running at the pressure max is a bad idea. Also, as you suggested, you'll likely start wearing out the center of the treads and decrease your contact patch as you over-inflate the tires.

 

[Joseph Garcia]

^^^^^x2^^^^^

 

[Stbentoak]

I'm good with running them up to 5 PSI over the placard if it makes anyone feel any better....But I start getting pressure warnings if I'm more than say 3-4 PSI under. Some mileage difference, but mostly negligible.....

 

[Marky Dissod]

Has anyone else tried or noticed this result?

Everyone.

Whaddaya mean, 'everyone'?

EV-ERY-ONE!

Yes, everyone.

 

[Marky Dissod]

Seriously, though, the civilian Tahoe air pressure spec is lower than the Tahoe PPV air pressure spec for several very good reasons.
Autocrossers also know better than to settle for the air pressure on the placard.

YO: read the following carefully ...
Very generally speaking, it's better to slightly overinflate tires vs underinflate your tires.

 

[mickier]

A lot going on here...

First, you've posted in the '21+ section (which doesn't much matter here, since your post is about tires), so you might want to throw this post in the pre-'21+ section for better accuracy.

Second, and maybe it should be first, the "max pressure" markings are exactly that -- a MAX that shouldn't be exceeded. Your tires should be inflated to a certain PSI WHEN THEY ARE COLD because the pressure in them will increase as the tires are driven on and heat up. If you're starting with them at the max pressure, then the pressure in them is only going to increase as you drive. You could quickly exceed the max pressure, and that's not good.

Otherwise, yes, it takes more energy to roll under-inflated tires (just like riding a bike with under-inflated tires). So, you should see a fuel savings with properly-inflated tires. However, running at the pressure max is a bad idea. Also, as you suggested, you'll likely start wearing out the center of the treads and decrease your contact patch as you over-inflate the tires.

DOH!

my bad

 

[Fless]

DOH!

my bad

Thread is moved to correct MY section.

 

[TheBigCheezeBall]

I have always run mine between 40-42, depending on the season. If I have expect to make a long trip in rain / snow / sleet, I will drop them back to 35. The only thing negative I could mention is that my tires appear to be cupped on the inside, but that might be due to blown struts I had for a while.

 

[Marky Dissod]

I have always run mine between 40-42, depending on the season. If I expect to make a long trip in rain / snow / sleet, I will drop them back to 35psi.
The only thing negative I could mention is that my tires appear to be cupped on the inside, but that might be due to blown struts I had for a while.

Your tires cup on the inside because excess psi wears out the center sooner than the edges, like mine do; I run similar tires pressures.
You (your tires) could likely benefit living @ 36psi for more even treadwear. Or, you could do what I do:
take every turn as if running 10min late, rotate tires every oil change, & use the following alignment specs:
*As much positive caster as reasonably possible, so long as they're within 0.5 degree or less of each other
*No positive camber, 1.0 degree (or less) of negative camber EACH / -2.0 degrees total
*No toe-out, 1.0 degree (or less) of toe-IN EACH / 2.0 degrees IN total
Be sure that they check to keep the Z-angle in spec (specific to GMT800s if I'm not mistaken)

My tires wear out the middle first as well, but by the time it's clearly evident it's almost times to replace my tires anyway.
In the rain I drop to 36psi (resistance to hydroplaning slightly improves with more psi). In winter conditions I drop to 30psi.

 

[mickier]

Just an update - I have 153k miles on the truck, and with 48psi front and rear (and with new plugs), I drove 160 miles from georgia to Knoxville - cruise set to 78, & hit slow traffic a few miles along the way - I clocked (according to the computer) 26.4 going up and 24.4 on the return trip. That's maybe 1.5 or 2mpg better than I was getting before but some of that might have been the spark plugs which had been in since 70k. Next week I'll try again with like 42psi.

Note that the 2018 Tahoe computer doesn't complain about 48psi

 

[RST Dana]

Vehicle computers used for fuel mileage are not fully accurate. I’ve logged all my mileage/fuel purchases for the last 8 years with 16,17,20 and 21 Tahoes. The first 2 were 5.3 and the last 6.2. Try manual calculations and let us know the “rest of the story”.
Good Day