Tire size vs mpg with an LS

[Billett]

This sort of goes along with my other thread, but I thought it was different enough to deserve its own. I've been considering purchasing an extra set of tires for the truck and had a few questions.

Current tires are 285 wide 28" tall cooper cobras. They are essentially a large passenger car "all season performance" tire. I've had them on plenty of vehicles and like them in general.

Question is, who is running larger 33" or so tires on the street? I know generally a larger tire will cause a loss in mpgs due to more rolling resistance and more aero drag and the larger torque required to move it from a stop. However, these engines are torque monsters, would a larger tire really matter that much if it werent too radical in the tread department. The aero of these trucks is also shot already so I don't think that could hurt a ton... also a larger diameter means lower rpms.

Has anyone here done a tire size change like this? Similar treads, passenger to a/t, anything really. I'm just kind of curious now before I buy another set.

[BR3W CITY]

Originally Posted by Billett

This sort of goes along with my other thread, but I thought it was different enough to deserve its own. I've been considering purchasing an extra set of tires for the truck and had a few questions.

Current tires are 285 wide 28" tall cooper cobras. They are essentially a large passenger car "all season performance" tire. I've had them on plenty of vehicles and like them in general.

Question is, who is running larger 33" or so tires on the street? I know generally a larger tire will cause a loss in mpgs due to more rolling resistance and more aero drag and the larger torque required to move it from a stop. However, these engines are torque monsters, would a larger tire really matter that much if it werent too radical in the tread department. The aero of these trucks is also shot already so I don't think that could hurt a ton... also a larger diameter means lower rpms.

Has anyone here done a tire size change like this? Similar treads, passenger to a/t, anything really. I'm just kind of curious now before I buy another set.

My rear "preferred" tire is the MT DOT Street in 325/50/15, which ain't small but ain't huge...on a 12in wide steel wheel. I switch off to a 235/75/15 for longer trips since its narrower, and MUCH cheaper to replace (standard truck/suv size). I lose traction, but driving normally its not an issue, and I get another 1-2mpg on the freeway since that combo is also on an aluminum wheel. (my front tire is another size entirely, a much harder to find 235/60/15)

[crazy longhorn]

The 6 .0, should have plenty of tork....my question, would be what are you running for rear gears? Longhorn

[BR3W CITY]

Originally Posted by crazy longhorn

The 6 .0, should have plenty of tork....my question, would be what are you running for rear gears? Longhorn

we both have 3:73's (he just happen to post it on his other thread lol)

[crazy longhorn]

Originally Posted by BR3W CITY

we both have 3:73's (he just happen to post it on his other thread lol)

Yup, 28" for fun! On a cruiser, you might think 29-30" on the height? My 02 Silverado, runs a 29" tire, with 3.73 gears. I like the combo, much better than the 3.42's that were in the truck! I lost about 1/2 mpg in town dropping to the 3.73's, & really nothing on the hyway? If you look at the 4x4 trucks, in a 1500 series, they run a tad taller tire (30-31), with that 3.73 gear. I wont opt for the larger tire, as I am running a 4.8 in that DD. You might find the "sweet spot" in the rpm range (hyway cruise), then play with a calculator to find the tire size that you need @ the speed that you like to cruise? You already know that a "brick in the wind", has a bunch of drag I tend to cruise 65-72mph...anything slower, tends to lug& eat fuel, & anything faster....the wind tends to get? I don't think 33" on the tire will help you....to hit the "sweet spot" on the revs, I feel that you will be pushing too much wind, to realize it. Longhorn

[BR3W CITY]

Don't forget that just like with my steel wheels, a larger tire will add rolling mass, which will have an effect on mpg regardless of the gearing. Going too big to alter the "final" gearing ends up with an awkward combo at times, the same goes for the "tiny" tires that lowriders and the such end up with.

[crazy longhorn]

Originally Posted by BR3W CITY

Don't forget that just like with my steel wheels, a larger tire will add rolling mass, which will have an effect on mpg regardless of the gearing. Going too big to alter the "final" gearing ends up with an awkward combo at times, the same goes for the "tiny" tires that lowriders and the such end up with.

Totally with you on that Longhorn

[Billett]

Yeah the rolling mass is definitely a consideration, but with the mass already on these trucks would that little bit make such a large difference? Although I suppose the same could be said for the slightly larger tire size haha.

[Jon01]

Maybe I missed it, but what is your goal in having 2 sets of rear tires for the truck?

I run a -80E, 4.10's and 28" tall tires and mine goes down the interstate fine at 75-80. Turns around 27-2800.
If you're worried about turning some RPM, don't be.

[68GMCCustom]

I have a pair of MT 315/60-15 drag radials on a 15" pair of steel rims for better traction at the track, are roughly 30" tall. Taller tire to increase the footprint helps traction along with a wider one. The street tires are Nitto 275/45-17 and 29" I think? A higher speed with lower rpm is what works best for mpg... to a point. Keep your cruise rpm at or below 2000rpm and you'll typically find your best mileage. Our LS2/4L70e powered TBSS has 4.10's and 30" tire and returns 13-15avg or at 2400-2500rpm 17 or so highway mpg.

Truck never had its mpg checked.

[Billett]

I'd pick up a full set of 4, but there wasn't really a goal, just interested. I was worried that the rpms might be too high, but 27-2800 like you mentioned seems average for these engines at highway speeds.

Still curious whether the decrease in rpm vs more weight and rolling resistance has more affect, but I'd imagine it about evens out.

[BR3W CITY]

with thin tires in the back, and the aluminum wheels, my truck changes COMPLETELY. The light wheels and tires make it twitchy when your on the throttle..too much tq. With my big tires, its way more tame.