village idiot

When I first got the car, I was getting an easy 30mpg at 70mph. If I reset the average mpg, I'd get 31 or so, maybe a touch higher.

This road trip I was at 26.

Only thing that changed was runflats to Hankook V12 Evos- same size.

2008 z51.
14.5k on the clock w/ 31mpg
17k on the lock with 26mpg

No CEL or running rough or anything.

C7 BOB

Stickier rubber
More friction
Less MPG

Mad*Max

Pinky...

New tires. More rolling resistance. Wait for them to wear down some.

hawkandersonjr

Mine dropped from 29-30 to 24-26 when I dumped by Goodyear run flats and went to Firestone 500 non-run flat.

Boomer111

The RF tires are stiff with less resistance, the softer riding tires have more resistance.

I am expecting the same with my new Potenza Pole setters non RF.

village idiot

I guess it's normal then

It's really strange because it was misting out, and the roads were wet. They should have far less traction in wet than RF did in dry. We're talking 15-20% mpg drop. That's huge.

HOXXOH

I've experienced a 2 MPG (instant mileage) drop just from a rougher road surface where a different county did the paving/maintenance on a flat interstate. After passing that county and the road was smooth again, the MPG went right back up. I was surprised it was that much.

Triumph Jerry

Time to wax that vette.

FortMorganAl

Traction is only incidental. The road could have had a layer of oil on it and mileage would have been even worse due to moving the oil out of the way. If the road was wet you were using gas to move water. Primary cause is your non-RF tires flex more and get hotter. That heat comes from the gasoline you burn. You could also have had a head wind, more ethonol in the gas, lower tire pressure, rougher road, increasing altitude, and 1,000 other things that are different. A single trip isn't enough to get a good feel for real mileage. I was shocked the other day to see my average that I reset with every tank was down to less than 15mpg. I normally get in the low 20's except on the Interstate where I get 29-31. Maybe summer gas? Maybe depleted uranium foot? Who knows.

village idiot

well, in theory, the friction between the tires and road, wet or dry, should be identical and identical speeds. I'm guessing it has very little impact as no car I've ever owned changed much in the rain.
Also, it was the same exact road in the same exact direction. I bought the car in Houston and in the last 45min of the drive to Dallas, checked the MPG. I did the same thing on this trip. I even checked on the way down there too. Same thing- 26mpg.

Flame Red

Another factor could be that you filled up with a tank of Al Gore-ahole ethanol. I know of quite a few gas stations in my area that seem to have more of that crap than others and my mileage drops that much if I make the mistake of getting that crap.

Boomer111

I experienced a near 2 mpg drop when I went from stock GY size RF to Invos in the 275/305 widths. Went back to stock GY sizes and the mpg returned.

Now I have the 4:10's, for 3 years now, with the newly mounted non RF S0-4 Pole Setters so I guess I might as well give up caring about fuel economy....now I am more concerned about best tire operating temps.

Always something to fret around with with me..

C7 BOB

Tire diameter is not always the same, even when the "size" is the same. Also, new tires have a greater diameter than worn tires. That means your speedometer is off a few MPH. I believe the MPG is calculated based on a specific tire diameter. Thus, the discrepancy. (Go to http://www.tirerack.com/index.jsp and check the diameter on both tires.)

carpe dm

APACHEDR1V3R

Even though tires are listed with the exact same size specs, you can still run into the tread depth being different. That tread depth difference will affect the tire revolutions per mile.

ie: Using my GS specs for the front tire, my stock GY RoF G2 has a 5 RPM difference from the Hankook V12 Evo K110 even though all the listed specs are the same...except for the tread depth.

This difference affects the computer's ability to calculate fuel consumption accurately. It will also change the accuracy of your speedometer and odometer.

My truck is where I first came to learn this after I bought different brand replacement tires with all else remaining the same.

truckplay

try adding 2-3 lbs of air to the tires. are you using the DIC or a calculator? still going to the same station ? maybe they are cheating you.

frogman1

Never rely on the computer. Always check with a calculator. I've seen my computer read 5 mpg higher than the actual. Also alcohol will lower your mpg.

phileaglesfan

Regardless where he is checking it if he is using the same thing for both checks then he has good info. He knows his gas mileage is dropping.

I noticed a 10-15% drop on my 08 when I switched to Michelin A/S ZPs and they gripped a lot less than the Goodyears.

With Michelin Super Sports I noticed a 10% increase over OEM Goodyear Supercars. Non run flats should give you better mileage unless it is heavy tire to start with.

I don't know the weight of Hankooks but they might be heavier since they are cheaper.

Could also be the driver since I'm hoping you are willing to power up the Corvette to test the new tires.

A tire change can cause decreased MPG though. As much as I hate Goodyears they are generally efficient tires for MPG. I had a MPG drop in all my swaps to Michelin on various cars over the year. However if the Michelins last twice as long are you really wasting money? $1-2k of gas is a lot of miles.

THE MOUTH

Did you take out the spare tire????? There's a few extra pounds lost!!!!HEHHEHE