LT tires; pressure and MPG

I have 2 questions. Please keep this on topic and assume I'm talking about a tire that is similar to stock, not a 30" p to a 44" MT.

1) How do I calculate correct pressure when using LT tires for general on road driving? If the tire size was stock is the pressure still the same on an LT tire? Are these values different from for example a D and E?

2) i know hese tires can weigh more and the increased sidewall material adds to the rolling resistance. Assuming they do require more pressure, is any of the fuel economy gained back or should I just assume that fuel economy will always be worse with an LT tire?

 

LT pressure is the same often on these trucks. Google "Tire Chalk Test" and it will help set tire pressures.

I ran 29 psi on my E rated Duratracs. Usually set customers LT trucks to 32-34psi unless they tow or haul a lot.

Less side wall and load dictate higher pressures. Towing 2000-6000lbs I would set the rear tires to 40psi.

You are right about weight, rolling resistance and size. No amount of tire pressure can counteract these factors. You will lose about 1-2 mpg on a LT tire vs a SL tire.

 

The tire store put 50 PSI in my E rated tires, the ride home was stiff. That is about right for an unloaded 3/4 ton truck or a heavily loaded 1/2 ton. But on an empty Tacoma was too much. I had to do some experimenting but found that the same recommendation on the door sticker for P series tires was a good starting point. In fact since the E's are stiffer they need less air in them to carry the same loads. My truck says 29 and 32 PSI for the P rated tires that came on it, but I always ran about 38-40 PSI. With the E's about 35 is working well for me. I can't detect any ride difference between the E's @ 35 PSI and the P's at 40 PSI.

The sidewall on P series tires calls for 44 PSI when loaded heavy. That is the main reason I tend to run a bit more air than the sticker on the truck call for. When I have to load the truck I don't have time to stop and air up before carrying something in the bed. So I prefer to keep it closer to the max. It also will improve fuel mileage. But if you put in too much air it will wear the center of the tires early. I've never had an issue with this. I still get 55-60K out of a set of tires and it is always the outside edges that wear out 1st. The only time I change PSI is off road. Airing down makes a huge difference, just remember to air up again when back on pavement.

A word of caution. The sidewalls of E rated tires call for 80 PSI when loaded heavy. That is for heavily loaded 3/4 and 1 ton trucks. No need for that on a 1/2 ton or Tacoma. For one thing the rims aren't designed for that much pressure. You risk wheel damage if you put that much air in them. I'd put no more than about 40 PSI in an E rated tire on a Tacoma.

You have it backwards. The stiffer tire reduces rolling resistance, that is what you do when you increase PSI. Reduced air pressure, wide tires, and tires with aggressive mud tread increases rolling resistance and hurts fuel mileage since you spend less time coasting. I've driven trucks where I had to keep my foot on the accelerator to maintain speed going down hill.

The weight of an E rated tire alone makes zero difference in fuel mileage for most people. The heavier tire will require a little more power to get moving, but that weight will also keep it moving once underway. You MIGHT see a fraction of 1 MPG loss in city driving, but on the road and overall none. When MOST people move up to E rated tires they also go to a larger diameter, wider tire with a more aggressive tread. It is those factors that reduce fuel mileage, and it could be 2-4 mpg. It is just a coincidence that those tires tend to be heavier.

I went from a mildly aggressive P rated AT tire that weighed 38 lbs to a similar tread on an E rated tire in the same size that weighs 53 lbs. My truck gets exactly the same fuel mileage today that it did 12 years and 200,000 miles ago with the factory tires.

 

There are several factors here. The one I was referring to is "Hysteresis".

This is the same reason super expensive road bike tires ditch kevlar for Vectran. Adding different plys does add rolling resistance but I was wondering if the increased pressure was able to offset that. It sounds like there really is no increase in pressure so even if it was true, it wouldn't apply to the Tacoma. I didn't realize the economy change was so large.

Do you still think the 2-4 mph would apply to an A/T tire with similar tread to stock?

 

I just put on Duratrac 265/75/16 E"s on a 2019 Pro. Cold psi set at fronts 35, rears set at 32. After 4 tanks of gas (91), I have got 18.6 mpg everytime. No chalk, but I drove in light dust dirt and can see both treads lie flat, full patch contact. Very little road noise, after driving for an hour, fronts at 38, rears at 35. This it where I will stay until a little mall, I mean off road action comes up

 

What were you at (mph)before the change? We're you on stock wheels?

 

I had the stock kevlars, 260/70/16, I ran 30 on all 4. I got about 19.2 mpg before

 

3% difference sounds like it's within the margin of error. That's less of a difference than others have made it out to be. Thanks for the info

 

I do have the E tires, compared to the C, that most run. I can run the E a little bit lower due the the strength of the stiffer sidewall

 

It's all about the inflated load weight. PSI is just a means to achieve that.

3d gen Tacomas have a inflated load weight of 2,149 lbs-2,172 lbs
Examples:
265/70/16/112 @ 30 psi = 2,149 lbs(Offroad)
P265/65/17/110 @ 29 psi = 2,149 lbs(Sport)
P245/75/16/109 @ 32 psi = 2,172 lbs(SR)

The vehicle manufacturer de-rates euro-metric and P-metric tires for use on trucks and SUVs.
If you switch to LT tires, the new inflated load weight is 2,149/1.1=1,954 lbs.
Use the LT load charts to find the PSI that attains this weight for your particular size.

You can try inflating for mpg, but you lose footprint; mostly longitudinal. I'm not a fan of the practice.


TOYO PDF
https://www.google.com/url?sa=t&sou...Vaw0zaHumL9xB01d0CRYFLPCS&cshid=1562890063059

NITTO PDF
https://www.nittotire.com/media/152964/TechBulletin_NTSD-12-011.pdf


https://www.tiresafety.com/en_us/choosing-tires/sizes-and-classifications/light-trucks-and-suvs


https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=195


https://www.moderntiredealer.com/article/311494/lt-or-p-metric-tires-for-light-trucksuv-applications


https://www.tirereview.com/tire-types-and-load-capacity/

 

Way over thinking this.

 

I dig the science behind it actually....

 

I’m running General ATX (E) set at 38lbs cold, getting 21 to 23 mpg. 101 miles round trip daily commute but, that’s on relatively flat terrain and really good ankle valve control.
Oh and size is 265/75/16

 

And getting full tread patch contact? I can get better mileage by pumping in more air, but what about tread contact?

 

Yes sir, tread wear is even side to side. I’ve got around 33k on tires started with 16/32nds and was just rotated (done every 5k) and they gauged at 13/32nds, outer/middle/inside gauge points.