Stock tires give good fuel economy
 

Switching to Michelin Pilot Sport A/S 3 in 225/45x17 size changes the indicated average fuel consumption on my BRZ by about 10% (more fuel used) of which only about 1.3% is due to slower wheel rotation (fewer miles recorded than actually travelled).

Food for thought if you are fitting non stock tires, that's quite a cost penalty so those new tires better be good.

The stock tires are pretty light too.

Just don't grip too well compared to the ability of the chassis.

Thanks?

Yeah, I know. Sorry. As if we needed another reason to keep those stock tires eh?

They're fun to slide around in

Not surprising since the stock Primacies are low rolling resistance, i.e. good mileage.

I just received my new wheels / tires (18x8.5 wheels 225/40 tires) and as it turns out they are exactly the same weight as the OEM setup.

They are going on after my next track day, at which point I am pretty sure my Primacies will be cooked. I'll be curious to see how my mileage changes.

You're increasing width... which means increased rolling resistance.

Yep, just curious how much.

Yes, and I'm driving faster, much faster. Nobody said I was on an economy run and I'm definitely not claiming to be scientific about this. Still, those Primacies are actually pretty good tires...on the right vehicle.

Increasing width does not increase rolling resistance. In fact, a wider/shorter contact patch should generally have less rolling resistance than a narrower/longer contact patch if all else is equal, as the middle of the narrow/long contact patch is undergoing a lot more deformation and hence loses more energy to hysteresis.

FWIW, my best tankful in my 530ish hp FD, on 255/265 Dunlop StarSpecs, was 29mpg. 465 miles on 15.8 gallons :)

There are compromises to performance when optimizing for rolling resistance, and there are compromises to rolling resistance when optimizing for performance, BUT there are also some factors that are good for both. Essentially, both high performance and low rolling resistance tires benefit from generating as little heat as possible. For LRR, obviously energy lost to heat is bad, but also for high performance generating heat is bad because the tire will overheat sooner. Less heat generated means a softer more grippy compound can be used.

TL/DR: Wide high-performance tires don't necessarily have high rolling resistance.

http://i.imgur.com/siRikUa.jpg

First 10,400 miles were on stock wheels, without track events.

Subsequent 13,500 miles were on mostly 245/255 Toyo T1Sport, with some on 235 Falken Azenis RT615R (track use).

-alex

Rolling resistance aside, wider tires also have more surface area which creates more wind resistance and a decrease in fuel economy.

Curious, did you mount the 225/45's on the stock 7" wide wheels? Any pictures of the fitment? I just picked up some 225/45's and planned on getting 8" wide wheels, but may just slap them on my 7" wheels for now and spend the money on suspension (if the fitment isn't awful).

here's the fitment of 225/45-17 Michelin Pilot Super Sports on the stock wheels. I don't have a view straight along the side, this is the best I got.

http://i.imgur.com/wjZBmYw.jpg

Physics aside (contact patch size, width, weight, etc), I've gone from LRR tires to normal tires on several vehicles (same size, as well as wider).. fuel eco suffered by 7-10% in all cases.

Any fuel economy I lost switching to AS/3's were negligible and more than compensated by the confidence I feel going around curves, braking, and accelerating.. all of which are amplified when it's raining.