I went from Conti Runflats on my MCS to regular BFG G-Force tires on my MCS. It rides SO much better now, but I've noticed that my MPG has taken a hit. On average, I'm getting around 2 MPG less than I did with the run-flats.

Has anyone else noticed this? Is it because there is less rolling resistance with the hard sidewalls that the run flats have?

Just looking for ideas.....

Also, I'm running around 36psi in my G-force tires.

Thanks

 

Never noticed. We replaced the dunlop runflats with Michelin Exaltos when the dunlops died. On a brand new set of Michelin Super Sports as of yesterday. Highway mileage is around 29 ( Way over 55 mph ).

 

Were the Conti RFs also summer tires? Nothing else changed (e.g. size)?

 

I did go up in width....went from a 205/45/17 to 215/45/17. I think the width only increased 1/4" or so. Would that slight increase in width knock that much mpg off?

 

Every tire will be a little different with respect to rolling resistance. That said, I could certainly see a stiffer sidewall that doesn't flex as much offering less rolling resistance than a more flexible sidewall. But, of course, that's not the only factor. I wouldn't worry about it and just enjoy the car. Mileage will vary from other factors as well, aside from tires.

 

When I went from 195 to 205 and changed from the all-season RFs to summer non-RFs, I lost a couple mpg. So your results may not be unusual.

 

You have increased you overall diameter by 1.5%
Would that have changed the mpg?

 

yes, it takes more gas to make your car move now.

First, think of it as having to hold out a bowling ball (and swing it around in a circle), but with your elbow bent. Takes a pretty good effort, right?

Now, extend your arm and do the same thing. Takes a lot more work to move that ball, huh? Larger diameter tires are the same thing as extending your arm. That larger diameter takes more work for the car to twist that axle (which is connected to that larger tire) to make the car move. More work = more gas.

I went to a larger width tire on my pickup (255 x 16 to 285x16 I think) and went from 20mpg to 16 on the highway. That is because widths are a percentage of the height, and so the larger width creates a larger diameter too..

Just enjoy the better ride. At these mileage rates, I smile everytime I think about how much money I'm saving over driving that pickup.

 

There I thought it was just more fun to drive now!
The worst part about my car are the Run Flat Dunlops, rock hard, no grip. Trying really hard to wear them out!

 

In theory, you could lose some due to higher rolling resistance. I wouldn't expect it to be that much. I would have expected some of that to be offset by the lower weight of the non-ruflat tires, unless your non-runflats are actually heavier.

 

I had Dunlap run flats, Replaced them with Michelin Exalta PE2's summer only 215/45/17 tires and don't see any less MPG then I had with the Dunlap's.

My car does ride a lot smoother and way less tire noise with better wet traction.( These just never hydroplane like the Dunlap's did)

The Michelin's are about the same exact weight as the run flat dunlap's were even though the Michelin's are larger.I still get 28 to 30 around town and 36/38 on the interstate at 75mph.

I run 36PSI all around in the Michelin's

 

Yes. More rubber on the road = more rolling resistance.

 

However, the larger diameter tire should also yield better mileage going down the road. Therefore, it may depend more on the kind of driving that's done. Larger diameter tires, stop and go driving, accellerating at the same rate as before = less mpg. Larger diameter tires, freeway cruising as same speed as before = more mph.

 

I got rid of the run flats from my 05 MCS. I tried to sell them and nobody wanted them. Two are real good and two are just good. I had them on Craigslist for $170 for all four (w/o wheels) and nobody called. Speaks volumes about runflats doesn't it? I love my non-RFTs. Much quieter,softer and more fun.

 

Do you measure with GPS, or with the odometer? Since your diameter increased, the odometer will incorrectly show lower miles traveled than it did before. If you weren't using GPS, you will need to correct your new mileage before figuring mpg.

BTW, wider tires = more wind resistance, as well as potential rolling resistance. Wind resistance is a constant, but rolling resistance varies from tire to tire. Also, the increase in diameter could theoretically INCREASE your actual MPG's due to less engine RPM for the same speed.

My thoughts are that the bulk of the 2mpg difference you are seeing is due to not correcting for the ODO error, if that's how you are doing it.