Road & Track: 5 minutes to a faster FRS (/BRZ) via Tires

[Suberman]

Originally Posted by jarviz

Just did a little bit of research and found that the DW weighs about ~27lbs and the OEM tires weigh about ~20lbs. Does anybody know how much of an effect this has on fuel efficiency?

Not much but the ride and handling will be adversely affected. R u sure? That's a very heavy tire for the stock size.

Tire Rack quotes the weights for these two tires as the same 20 lbs.

[Gary in NJ]

Originally Posted by jarviz

Just did a little bit of research and found that the DW weighs about ~27lbs and the OEM tires weigh about ~20lbs. Does anybody know how much of an effect this has on fuel efficiency?

This is off topic from the original post. But as Suberman pointed out the DW weighs 20 pounds. The Dunlops run around 25lbs. Unless you're boosted, a 25 lb tire is a bit porky for our cars.

[jarviz]

Originally Posted by Gary in NJ

This is off topic from the original post. But as Suberman pointed out the DW weighs 20 pounds. The Dunlops run around 25lbs. Unless you're boosted, a 25 lb tire is a bit porky for our cars.

Sorry this is defintely off-topic. I prob had a couple of tabs open and responded in the wrong one but thanks for the input.

[kurbkilla]

Originally Posted by 7thgear

All of this should be no surprise to people who understand contact patches and all that stuff. Wider/larger is not always better.

So for people that don't understand "all that stuff" why would a 17x8 or 17x9 (wider tire) be bad for performance? I understand that a 18x or larger tire is bad because of the larger diameter; it takes more time for the wheel to go around, but for a wider tire/wheel the only problem i could think of is weight.

[CSG David]

Originally Posted by kurbkilla

So for people that don't understand "all that stuff" why would a 17x8 or 17x9 (wider tire) be bad for performance? I understand that a 18x or larger tire is bad because of the larger diameter; it takes more time for the wheel to go around, but for a wider tire/wheel the only problem i could think of is weight.

I don't think you should focus too much on the width of the wheel. The idea of running a 225 EHP tire on a 17x9 is for the fact that you can run a larger tire size in the future when your setup permits it. Some EHP tires have a softer sidewall, so the 17x9 maximizes the sidewall stiffness and allows the tire to do its job completely.

Overall, going wider than 225/45/17 tire is going to give you diminishing returns. Why? Simply because you don't have enough power to overcome the extra grip. In return, you may have faster turn in, but your exit speed will decrease due to scrubbing. Everything is a balance.

[kurbkilla]

True, it is all a give and a take. In the long run I was thinking of doing a 17x8 225/45/17. IMO 225/45/17 is perfect for the power mods I'm looking at (vortech supercharger) and still usable with stock power.

[Suberman]

Originally Posted by kurbkilla

So for people that don't understand "all that stuff" why would a 17x8 or 17x9 (wider tire) be bad for performance? I understand that a 18x or larger tire is bad because of the larger diameter; it takes more time for the wheel to go around, but for a wider tire/wheel the only problem i could think of is weight.

Larger wheels don't have larger running circumference because the car runs on tires, not wheels. Fitting a larger diameter wheel doesn't, and usually shouldn't, mean fitting a larger diameter tire. It is the rolling circumference of the tire that affects gearing.

Larger diameter wheels are usually heavier and almost always put extra weight further out towards the road surface. Air weighs next to nothing and tire sidewall is very light compared to tread weights. This means larger wheels and lower profile tires will be heavier and have higher rotational inertia per unit weight, both adversely affect acceleration.

Finally, contact patch shape has very little effect on braking or acceleration, other than taller tires probably brake and accelerate better than lower profile tires most of the time. Lower profile tires of the same rolling circumference have shorter and wider contact patches which corner at lower slip angles for a given cornering speed. They also transition more quickly from left to right and vice versa. They rarely deliver higher cornering speeds at the limit without also breaking away much more abruptly.

Paying for tread compound yields performance improvements in dry conditions. Not much else is worth paying for. For these cars a "rain" tire with wet weather tread compound optimized would be a foolish modification for most areas of North America. I am seriously considering Michelin Sport Cup or Pirelli PZero Corsa for mine as I'm confident the chassis can benefit. However, the fun factor will not improve for most situations so my most serious contenders for "summer" tires are Michelin a Pilot A/S3, Continental DWS or Pirelli PZero Nero A/S.

Paying for more grip than your car can use is not smart. The trouble is this car can corner faster and faster with tires using better tread compounds. Changing tire size much above 225/45x17 or maybe the equivalent 18 is pretty pointless. Buying the grippier tread compound you can afford in those tire sizes will definitely deliver cornering and braking improvements. Acceleration improvements will be limited by engine torque and grippier tread may actually slow you down a tad off the line.

No free lunch for tire designers.

[fatoni]

Originally Posted by CSG David

I don't think you should focus too much on the width of the wheel. The idea of running a 225 EHP tire on a 17x9 is for the fact that you can run a larger tire size in the future when your setup permits it. Some EHP tires have a softer sidewall, so the 17x9 maximizes the sidewall stiffness and allows the tire to do its job completely.

Overall, going wider than 225/45/17 tire is going to give you diminishing returns. Why? Simply because you don't have enough power to overcome the extra grip. In return, you may have faster turn in, but your exit speed will decrease due to scrubbing. Everything is a balance.

i think its also worth noting that a wider rim will provide more air in the tire and that makes it much easier to control tire temps. maybe not a huge issue at an autox but on a road course its important imo.

[BRZ NA]

So in another word,go with stock size with better grip tires will be better than going with 255 wider tires when running in stock on the track ?(both with same grip tires )