Do brand new tires decrease MPG? [Archive] (2024)

nickdaddyg

30th August 2013, 15:32

Hi everyone,

All of my fill-ups since new BFG Gforce Sport Comp 2s, have been down 1.5 mpg.

Does the extra grip require more oomph & gas to move the car?

Also just changed the spark plugs, and no loss of power, so the plugs aren't the issue.

I am curious because I want to know if I should be concerned with another problem is causing the decrease in MPG. This is the first time, I've bought new sporty tires. I'm hoping their grippy-ness is the factor.

Thank you all,

Jesus Freak

30th August 2013, 15:52

Billy

30th August 2013, 16:15

....Does the extra grip require more oomph & gas to move the car?..........

Yes.

It may more noticeable depending on what you were running before.

Any size changes?

Are they properly inflated? (most aren't when you get them from the tire shop)

mongrel

30th August 2013, 16:56

It is mostly hysterisis (and imagination).

I recently put new tires on one of my cars and noticed, well, nothing.

So, lets accept that new tires do react in such a way that more effort is required to get from A to B (where A is anywhere and B is anywher else) but that 'loss' is offset by the fact that the tires are complete and have a marginally higher profile than the bald ones they replaced.

Thats my story anyway.

Miniata

30th August 2013, 17:00

Jesus Freak

30th August 2013, 17:49

If its not the tires or the plugs, maybe it is this:

171410

Coaster

30th August 2013, 18:28

Does the extra grip require more oomph & gas to move the car?...I'm hoping their grippy-ness is the factor....

Softer rubber = higher rolling friction. I get 24 MPG on my Star Specs (running 29 psi cold) and suspect I would get better w/ ordinary tires. But what a shame it would be to trade my E ride for a C.

TheSmokingMan

30th August 2013, 18:42

Softer rubber = higher rolling friction. I get 24 MPG on my Star Specs (running 29 psi cold) and suspect I would get better w/ ordinary tires. But what a shame it would be to trade my E ride for a C.

Ding! Grippier rubber has higher rolling resistance and less mpg's.

Mr. Sound

30th August 2013, 19:48

Dennis Nicholls

30th August 2013, 20:10

Mr. Sound

30th August 2013, 20:55

A new tire has a slightly larger circumference than a worn tire....I'd expect slightly larger mpg with a new tire because it's spinning at lower RPMs for a given speed.

Too bad the odometer does not know that you have gone farther, and the resulting mpg calculation is low ... :eek:

Chas H

30th August 2013, 21:05

Too bad the odometer does not know that you have gone farther, and the resulting mpg calculation is low ... :eek:

But the engine has made fewer revolutions to get there, and possibly used less fuel.

Mr. Sound

30th August 2013, 21:15

But the engine has made fewer revolutions to get there, and possibly used less fuel.

Possibly a good answer IF the OP asked "Do brand new tires increase MPG?" ... ;)

Chas H

30th August 2013, 21:24

Possibly a good answer IF the OP asked "Do brand new tires increase MPG?" ... ;)

Well from what I've read in this thread, it could go either way.
We have new softer tires offering more rolling resistance and possibly less fuel mileage, while the same tire has a larger circumference and possibly greater fuel mileage. ;)

Mr. Sound

30th August 2013, 21:54

Chas H

30th August 2013, 22:15

Having used the words "grippy" and "sporty" in his question possibly the OP is simply using a little more gas by driving with a little more conviction on his new and not bald tires ... :dunno:

This may be the true explanation.

nickdaddyg

3rd September 2013, 17:30

Thanks for all the responses, everyone.

Having used the words "grippy" and "sporty" in his question possibly the OP is simply using a little more gas by driving with a little more conviction on his new and not bald tires ... :dunno:

No, I drive the same: slow acceleration, shifting at 3500 ... (always trying to get that 30 mpg)

I'll check the air filter... it's been on for the year I've owned the car and who knows how long prior. The air filter is quite protected though... Jackson Racing set up...

nickdaddyg

3rd September 2013, 17:33

Yes.

It may more noticeable depending on what you were running before.

Any size changes?

Are they properly inflated? (most aren't when you get them from the tire shop)

Same size, only difference is going from BFG g-force to BFG g-force comp 2.

I've keep them at 28 psi cold, per Miata.net members recommendation (on previous tires I maintained 31 psi).
The fronts show a bit of sag due to the engine wait. The sight of it really makes me want to inflate them more.

MMoondog

3rd September 2013, 20:34

Same size, only difference is going from BFG g-force to BFG g-force comp 2.

I've keep them at 28 psi cold, per Miata.net members recommendation (on previous tires I maintained 31 psi).
The fronts show a bit of sag due to the engine wait. The sight of it really makes me want to inflate them more.

I just bought the same tires as you did. I haven't even used a tank of gas yet. These tires, like all tires need about 500 miles of non guts hanging out around the corners driving to break them in.

After that would be the time to check your mileage. Sure, I can see that different tires, different inflations, change in driving habits could effect the mileage. So would things that are not quite right with the engine, like worn plugs, old wires, and so on down the line.

I haven't had much of a chance to really drive on these tires yet, but so far, I really like them. I am going to patiently wait the rest of the 500 miles and then really drive them and find out.

Ask me the question again at that time. :dunno:

RobertC

18th September 2013, 23:09

I believe that I once read on the Tire Rack site that new tires have more rolling resistance because of the depth of tread. Supposedly the surface of the tire squirms more because the height of the tread elements.

Often times OEM tires on new cars have somewhat less tread depth than after-market tires in order to improve the mpg that the manufactures can claim.

TheSubaruGuru

27th September 2013, 00:19

Simple physics dictates that: squishy tall new tread has higher drag than a smooth tire surface; the new tire is taller, so odo reads LOWER than a bald tire. Both these result in a lower "apparent" mpg calculation. But the former is real, the latter a calculation bias.
The comment that taller gearing efficiency offsets drag loss is a small effect, I believe.
We're only talking 1-2% taller gearing from new to old tires at most, and that's much too small a change in gearing to yield an efficiency difference based on lower engine revs alone.
I AM intrigued by the comments that sticky max perf tires have higher drag than harder rubber types. Could that be as much as a 5% difference (1mpg or more)?

Fuel eco on my NC 6AT used to be 28-30mpg average. After change to 235/40 17 Star Specs AND the Cosworth/Magnusson with 3.2" piulley I see only 22-24mpg (mostly fast highway).
Anyone venture to parse out how much of the 20% drop is due to: 205/45 to 235/40 (they're equal height, so this isn't a calibration diff)? the SC? RE050 to Star Spec?
I made ALL changes at the same time, so don't have comparative incremental data.
Thanks.

Farther

28th September 2013, 13:57