Light truck LRR tire question ...

[lasitter]

Of course most of the posts here are not about old F-150 trucks, but that's what I have, and one of the mods I've been studying for a long time is the switch to LRR tires.

I have this sense that the size of the rubber patch on the road matters in terms of fuel economy, and so I was wondering what the difference might be (same LRR brand, etc.) between a tread width of 7.2" vs 6.2"?

General makes the "Grabber HTS" which is about the only option for LRR on my 1996 Ford F-150 in the 235/75R15 size.

I think it should be required, but there is still no coefficient of rolling resistance available on a tire by tire basis.

[oil pan 4]

Do you have to run the 1980s classic 235/75R15 tire size for any particular reason?
That is what my suburban should have, I put 31 inch tires on it.

[lasitter]

Originally Posted by oil pan 4

Do you have to run the 1980s classic 235/75R15 tire size for any particular reason?
That is what my suburban should have, I put 31 inch tires on it.

Generally, larger tires mean lower fuel economy, so replacing my 28.9" standard with the 31 would result in lower mileage. You might think otherwise since the larger tire size acts like a differential reduction, but most everything I've read suggests this.

[Cobb]

I got 235 75 r 15 yoko touring s on my sidekick. Love them. I had Continental that sears sells, they sucked.

[lasitter]

I got these on right now. Very affordable. Just wondering about potential LRR improvements:

Kumho Solus KR21
235/75R15 108T XL 2183lbs./50psi

[JRMichler]

I have Nokian WR size 235/75R15 tires on my truck. Nokian claims these are LRR, and my gas mileage agrees.

[rmay635703]

On my 2wd diesel suburbans I used to always run car tires on the front of the truck and properly load rated tires on the rear (or sometimes car tires all the way around)

The issue you will experience is even if the load rating appears to be appropriate you will have more tires fail, likewise though you get better gas mileage and probably spend less overall on tires.

It helps a GREAT deal if your truck uses 15" tires as your LRR choices are much better.

Good Luck
Ryan

[oil pan 4]

Originally Posted by lasitter

Generally, larger tires mean lower fuel economy, so replacing my 28.9" standard with the 31 would result in lower mileage. You might think otherwise since the larger tire size acts like a differential reduction, but most everything I've read suggests this.

The mileage stayed the same on my suburban, it may have even trended up a tiny bit. I expected fuel economy to go down by full numbered MPGs. But lucky for me everyone was wrong.
Going to 31 inch load range C tires gave me tires that didn't look like clown car tires and about 1000lb more weight capacity which I do use.
The "hit" to fuel economy was well worth it.

Originally Posted by rmay635703

On my 2wd diesel suburbans I used to always run car tires on the front of the truck and properly load rated tires on the rear (or sometimes car tires all the way around)

I am about to do something like that to mine. I have 30x9.5 inch tires to put up front, replacing the 31x10.5 tires that are on there now.
I only have four 31 inch tires now that one went bad. So instead of buying a new 31 inch tire I got three 30 inch from my friend who bought them and then decided later he didn't want them any more, before he ever even put them on.

On a 2wd diesel suburban the axle weight is very close to 2800 per axle. Make sure the Pmetric tires can handle that much weight after you derate them 9% for being on a tall SUV.

[Joggernot]

Consider 6-ply tires (4 on tread and two on sides). They can run at 80 psi. If there is an LRR 6-ply tire, all the better.

[CapriRacer]

Originally Posted by lasitter

Generally, larger tires mean lower fuel economy....

Actually, No! Larger tires generally give BETTER fuel economy for 2 reasons:

1) The rolling resistance is lower - all other things being equal. This is a pretty small difference, but it is there.

2) The larger diameter tires is like reducing the axle ratio. You get more distance per engine revolution.

But the real problem is that things are hardly ever equal. When you change to 31" tires, you are also changing the type of tire - P type to LT type - and LT's are typically not designed for fuel economy.

Also, there can be more difference in fuel economy between different tires (meaning make and model) than the difference between different tire sizes. Careful selection of the exact make and model can pay dividends.

And lastly, LRR is a relative term, not an absolute one. LRR means better fuel economy compared to other tires with similar wear and traction characteristics.

Put another way, a LRR tire doesn't necessarily have a low rolling resistance. It's just lower than similar tires. It is quite possible for a tire NOT labeled LRR to have a better RR level.

*****************************

Originally Posted by Joggernot

Consider 6-ply tires (4 on tread and two on sides). They can run at 80 psi. If there is an LRR 6-ply tire, all the better.

Ah ...... Mmmmmm ........ not exactly .......

Most tires are built with a 2+2 construction. That is, 2 body plies (typically polyester) and 2 steel belts. When listed on the tire's sidewall, this will come out as:

Tread - 2 steel plies and 2 polyester plies
Sidewall - 2 polyester plies.

Please note the 2 polyester plies are the same ply, just listed differently. That tire would NOT have 6 plies.

Sometimes a nylon cap ply is added over the belts. Sometimes 2 nylon cap plies. These would be listed under "Tread" on the sidewall stamping.


The 2+2 construction can be used in a 35 psi max tire or a 95 psi max tire. It's a little complicated about how many plies a tire needs - mostly because the cords can be made out of many things - including steel cable. But you will find plenty of examples of tires NOT built with a 2+2 construction.