Lost 8MPG with New Tires!

[emsvitil]

Air pressure too low

Directional tires mounted backwards (don't think it would affect mileage, but maybe)

Alignment (new tires have squirmier tread blocks, which may be more rolling resistance with an alignment problem)

[aarfocus]

Thanks to all for the replies and help! I am planning to do some experimentation this week, probably leading to having the TPMS sensors installed in the new tires eventually.

Just to cover some things mentioned:

Pressure: Actually raised it to 35psig in the new tires to see if I could improve the MPG-no significant change.

Alignment: New alignment with new wheels/tires, plus a recheck-no change.

Direction: New tires are directional-proper direction.

Weight: Possible increase, I will check. (doubt this would have much effect, especially "over the road", once up to speed the effects are minimal.)

Driving style: Again possible, but the "OTR" (highway) numbers are mostly with cruise on and it still goes down. When I first noticed the reduction, I figured that it was my being more agressive, but after a couple of thousand miles, I know it isn't.

More later!
Thanks,
Ned

[elsolo]

I lost 1-2 mpg when I went from 205/55/16 to 215/45/17.
Same brand and type of tires.

It was worse at first, but not 8 mpg worse, I attributed it to more aggressive driving style with the new wheels and tires.

[BigRed03]

tire width and tire compound can have serious influences on mpgs. i consistently get 2-3 mpgs less highway with my z rated tires (<30k miles) than friends with 60k+ mile rated tires, and i drive at slower speeds (~77 vs ~80)

[iminhell]

I'm going with weight and diameter.

Diameter will alter the calculation for MPG. OP really hasn't said much about the new tires/wheels so I can't offer much in the way of how much error.
Thought I'd made a thread discussing tire diameter errors, but I can't find it.

Rotating weight is always in play, even at sustained speeds. It takes more power to keep it at speed.

[Malibooya]

Originally Posted by iminhell

Rotating weight is always in play, even at sustained speeds. It takes more power to keep it at speed.

This was my thought too. How much do the 17s weigh?

[Slo86GT]

I went from stock sized 2008 SES snowflake wheels with 205/50/16 Yokohama S-Drive's and got about 32-33 mph with pretty passive driving.

Now, no matter how gramps I drive my car with the 6 spoke 2004 SVT wheels and 215/45/17 Kuhmo's I CANNOT get over 30 mpg on the exact same trips.

I'm a bit aggravated and thinking of getting an intake/tune to help with this a bit. :-\

...It's worth it, though. The car looks 100x better on the new wheels.

http://i178.photobucket.com/albums/w...s/e5d304e0.jpg

[elsolo]

I just did another 2000 mile roadtrip, this time with svt 17" wheels and 215's.
Mileage is the same if driving with cruise control compared to the 205's on 16"

[Phokus]

Most likely the wheel weight man.
I went from 15" stockers to 17" 15 spoke stockers and 17" motegi 5 spokes I lost a handful of mpg I could never regain at least not very easily.
I never weighed them to compare but it was noticeably heavier when I was picking up the wheels to bolt on. I lost about 5-9mpg by going to 17s but oh well.. you gotta pay to play. lol

However, Since my Ti I just got is starting with 18s I wonder what I'll gain from going to 15s in the winter.

[lilpup2022]

if you increased the rolling diameter of the tire you will lose mpg. also the tire can change mpg all by its self without even changing the size. I work with tires and have seen it a million times. a hybrid will come in getting 40= mpg and not want to pay for the tires designed for eco cars and want a cheaper tire. well that cheaper tire doesnt have the same rolling resistance and weights several pounds more than the eco tire. i personally switched my stock tires (continental) for a bridgestone turanza with serenity plus which is a low rolling resistance eco tire. i average 41.8 mpg on the hwy now.