17" vs 18" Wheel Track Performance
 

17" vs 18" Wheel Track Performance

Hey Racers & Racettes

I've been kicking around the idea of buying new wheels and tires for summer use for my FR-S.
I don't want to knock the tail happy action of the OEM green rated Primacy HP tires, but nice sticky summer tires sound like fun too.
My conundrum is this:
18" wheels pushed closer to flush look waaay cool. :party0030:

HOWEVER, I think the car is actually faster on 17" wheels (with a sticky tire retrofit).

The physics support the conclusion.
Demeris of large diameter wheels
1) Unsprung Mass: 17" wheels are typically lighter than 18" wheels, reducing unsprung mass.
2) Rotational Inertia: 17" wheels have less rotational inertia. In other words, they are easier to spin up compared to an 18" wheel with more metal as outward mass.
3) Diameter / Gearing: The OEM tires 215/45x17" tires roll out 844 revs per mile (24.7" Diameter)
A comparable 18" fitment @ 225/40x18" roll out 830 revs per mile (25.1" Diameter) which is a GEAR UP from OEM (harder to accelerate).
Though in rare cases you could possibly fit: 225/35x18" which would roll out 860 revs per mile (24.2" Diameter) which would gear down (should improve acceleration).

Or course the merits of 18" flushed tires would include:
1) Stance: Improve outward stance by dished out tires (wider vehicle)
2) Contact Patch: Improve contact patch with a wider tire
3) Cornering / Sidewall: Improve cornering with a smaller / stiffer sidewall (lower profile).

Also, Road and Track agrees. Lap times as follows:
Reference this test:
http://www.roadandtrack.com/special-...transformation
* OEM 17" tires @ 1:29.3
* Sticky 17" tires @ 1:27.0
* Sticky 18" tires @ 1:27.6

So the question is. What is your opinion? Do others agree the FR-S / BRZ on sticky 17" tires is the best set up for track (or street use?).

Or is the performance 'crutch' of the bigger 18" wheels worth the bling?:drool:

Let me know your thoughts.

For the same reason that you have established 17s are better than 18s on the track, is why 16s are better again.

Lower COG, better aero because of lower ride height, the gains are there.
The only thing that sucks about 16s, is the tyre selection.

If you're really keen, go 15s. Tyre choice is excellent (well, it's certainly better than 16s) and you can still get decent brakes under a 15.

16s bad tire selection makes me sad :(

18s look really nice, but you can still have a good looking 17 inch wheels!!!

http://dudesphotography.smugmug.com/...frs-gt86-M.jpg

Here are some Rota Titans. They are similar style(exact copy) of Wedssport tc105n, which are super light(15.8lbs for 17x9). Smaller wheels will always provide better performance. While you may think it will help acceleration, the truth is that it will also help braking and steering response. If you are looking into doing any sort of autocross or track days, then you definitely have to go smaller. If you still want to keep some style go with 17s.

17's are faster, period, until you're pushing some serious power.

Flushed tires DO NOT WORK. You won't ever see that at the track, except on perhaps a novice's car.

When's the last time you saw Our car with flush tires? Or Evasive? Or Element Tuning? Or Robispec? FT86Speedfactory? Crawford? Modbargains? There must be a reason :)

Are these rotas super light as well? 15.8lbs 17x9?

No the Rotas aren't quite as light. They aren't heavy either. I want to say they are 18lbs, which is pretty good. Gram Lights 57xtremes are heavier for the same size but they also are better quality wheels.

GREAT thread! I've been pretty set on keeping my stock wheels and replacing them when I have the money with another set of 17's.

Thanks for the feedback guys.


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I'm pretty sure these look like 18s... @wheeldude can you chime in on the size and tire specs?

http://www.ft86club.com/forums/showp...51&postcount=8

So I guess I am wrong...

There's flush, then there's hellaflush. :D

But seriously, do you guys run the same offset as stock or slightly less, i.e. not enough to be flush but a little less than stock to get a just a little bit wider stance?

I've been looking for this forever :thanks:

Edit: do these need camber bolts with a slight drop like a eibach prolines

Slightly less, but because we need to clear the suspension.