Full Report: Road & Track tests stickier FR-S/BRZ tires

[Justin.b]

Originally Posted by miodculae

for the most part, air rolls across and over the body. if the wheels are aligned and/or tucked in the wells, there should be no additional drag.

rolling resistance may increase with a higher UTQG (250-300+) but the difference in MPG would be negligible.

Unless the car is lowered to the ground, wider tires are still going to present more frontal area to the wind. It's not going to make a difference at low speeds and at high speeds it's about the difference of having larger mirrors on the side of the car.

Rolling resistance generally goes the other way. Stickier tires will have lower treadwear ratings and higher rolling resistance.

-Justin

[D1cker]

Originally Posted by UncleFester

I was told the 17x9's will be +45.

This would make more sense. I have a set of 17x9 +35 RPF1's on my car now and the front sticks out a bit (stockish height and no camber adjustment yet.)

[Want.FR-S]

Originally Posted by Jdogg180

The larger diameter 18" rim will have it's weight farther from the hub that the same weight 17" rim so it's very likely the straight line performance was reduced as well as braking. It would be a very small amount but the margin as pretty small. So lighter wider 17's would give you more grip and if you can stay under or very close to the weight of the stock wheel tire combo you will see that wider is in fact better.

Originally Posted by LSxJunkie

That is entirely untrue and completely misses the difference between a 215/17 and a 235/18.

See below.

So what you are saying is to keep the 17" rim with wider track, while reducing the profile to keep the same rolling diameter and you should see the performance increase. Is this correct?

[LSxJunkie]

Originally Posted by Want.FR-S

So what you are saying is to keep the 17" rim with wider track, while reducing the profile to keep the same rolling diameter and you should see the performance increase. Is this correct?

Yes, most likely. A 235/40/17 or a 245/40/17 are within .1" of the diameter of the stock 215s. However, that is not an absolute. The contact patch, depending on the weight of each corner, may grow laterally and shrink longitudinally.

[rice_classic]

Originally Posted by Allch Chcar

You can see that it slowed acceleration going to the wider tires. They use G-meters to monitor acceleration and grip.

I've seen this same phenomenom in Forza (they use a good tire physics system) so I'm not surprised.

Plus it just makes sense, unsprung rolling mass is multiplied compared to sprung mass. Plus bigger tires have more rolling resistance. On modest HP, it makes a significant difference.

Exactly, thus why I used the words "almost" and "within reason".

[Matt Andrews]

Originally Posted by feldy

That's cool. I want to know what kind of times they would see with a 17x9 wheel with dunlops or even hankooks. Keeps the wider tire but not the gearing issue of the 18s.

I also have a set of 225/45/17 dunlops and kooks that I autocross with.

I've run the test you are curious about. You can see it here.

http://fecompetition.wordpress.com/

While I respect that they tested, its pretty hard to say a thinner tire is faster when the wider tire they tested has a larger overall diameter. Only think they learned is that a taller tire is slower. surpise...

[Turbowned]

In layman's terms, upgrade to wider rubber when your car makes enough power to warrant an increase. There is such a thing as "too much tire".

[Supergoji]

Originally Posted by mike2100

Why do you need bigger brakes?

One would need larger rotors for shorter stopping distances and for keeping heat down for fade free braking on track.

[SkAsphalt]

Or switch out the stock pads for a better track pad - I am sure that would improve the 5 lap average over the stock set up as well

Originally Posted by Supergoji

One would need larger rotors for shorter stopping distances and for keeping heat down for fade free braking on track.

[Justin.b]

They went with 18s because a 'Plus 1' upgrade it pretty common for wheels/tires. I think a lot of guys new to cars would assume that the larger setup would improve everything. I'm not surprised it didn't, and I'm glad they took the time to document it (I's rather not see the Toyobaru become the next stance car tucking 22's while the owner thinks he's made the car faster).

-Justin

[No Limit Motorsport]

Originally Posted by D1cker

I bet the car would have been fastest on the 235/40/17's because it would actually slightly increase the gearing...

This is my guess as well. As soon as my wheels get here I will let you guys know.

I am trying 17x9 +35 square setup (Weds TC105) with 235/40/17 star specs. I think ideal offset would be +38/39 though.

Adam

[Jdogg180]

^ 3mm is peanuts

[Touge Factory]

This video brings up a very good point.

We have driven on few tracks where our car's gearing was not at its max potential.
Instead of changing gears in your drive train, you can increase or decrease tire size to maximize the gearing for that particular track.

Smaller, and more technical track... the car would benefit with slightly shorter sidewall.

We have also noticed that just because you have Huge tires, you're not always faster.
You may gain cornering speed, but you also gain drag from the additional rubber on the straightaway, and don't forget the extra weight of the tires.

Just being able to drive the car smooth with less corrections will put down a faster lap then a guy with much larger tires that's just throwing the car into a turn and hoping the tires will stick...constantly correcting.

[D1cker]

Originally Posted by No Limit Motorsport

This is my guess as well. As soon as my wheels get here I will let you guys know.

I am trying 17x9 +35 square setup (Weds TC105) with 235/40/17 star specs. I think ideal offset would be +38/39 though.

Adam

with that tire I think you're right. My wheels are the same size but I'm running 225/45/17. Ideally the go fast wheel size for this car is +42 or so to fit a 255.