For last gen, 225 were fastest on track. 245 were better for autocross.

 

so im looking at BRZ/GR86 cup car wheels setup, enkei rays advan all proposes 17" 7.5J wheels.
that is setup perfect for 225/45/17, looks like that is the setup i'm getting. the offset varies tho +40 to +45.

my GR86 cup car basic is only ready for delivery april 2023

 

hi guys,

consideration for the weekend track warrior, assuming using same semi slick tires, lets say RT660.

medium length track maybe 1.5-2km, top speed ~180kmh.

stock engine & just coilovers.

is 225 sufficient? using rpf1 8j for light weight tires & wheels.

or 245 required? using rpf1 9j.

thanks in advance for your inputs!

For the track you will want the 245 tire. I also use the Falken 660 on 17x9 RPF1 +45. They fit well with coilovers and alignment. (micro rub on inside fender liner at full turn) with the bigger/stickier tires you will benefit from bigger anti roll bars (I have whiteline I think 24 F and 18 R) and of course better pads (project mu club racer advanced from Counter Space Garage) and brake fluid. This is a great article: October 2007 - Make It Stick

 

For the track you will want the 245 tire. I also use the Falken 660 on 17x9 RPF1 +45. They fit well with coilovers and alignment. (micro rub on inside fender liner at full turn) with the bigger/stickier tires you will benefit from bigger anti roll bars (I have whiteline I think 24 F and 18 R) and of course better pads (project mu club racer advanced from Counter Space Garage) and brake fluid. This is a great article: October 2007 - Make It Stick

Interesting note about the ARBs. I’m on 245/35r18 340tw tires and front camber bolts and I have not even considered sway bars as it’s still fairly loose in some situations on track, even with a slight rear toe in. My next tire set will be a 200tw set. Maybe then I’ll be able to spot some weaknesses? Did you do the coils or the ARBs first?

My background is more with older STis and some FWD vehicles, so I’m still learning about setting up a RWD car.

 

Your'e welcome. If you join Grassroots Motorsports about $16 per year, then you have access to all articles from all years. At higher speed tracks, VIR I stay around 33 F and 34 R. At shorter/slower tracks 31F 32R. This is a great article on tire pressures with good science.

Falken Azenis RT-660 Tire Test: Autocross and Track

Will the new Falken Azenis RT-660 measure up in our Miata-based, SCCA-style tire test?

grassrootsmotorsports.com

 

Interesting, thanks again. I’ll give that a shot next time I’m out - but living in CO that might be a while!

 

I plan on mounting 245 width tires on an 18"x9.5" wheel. I am interested in trying out autocross with my car and wanted to know if this is a risky set up. It's my daily, so the wheel choice was mostly aesthetic.

 

You should do this at your local tire/wheel dealer because the 245 will be very close to rubbing the upper shock perch (depends on brand of tire Falken 660 is wider than most.) Why the 9.5 wheel?

 

My opinion: stock power, stock wheel size.
I would even consider 17“ wheels for the track.

 

While I think it’s a fair point, every one of the BRZ / GT86 drivers I have talked to / ridden with / been instructed by at the “instructor” level are on wider, stickier tires. I don’t think any of them are running anything beyond headers, with most of them being bone stock engine.

 

@Argo thanks for the link, good info. I think they hit the nail on the head when they mention the gearing change resulting from the 235/40R18. It was almost and inch greater in total diameter, which certainly hurts acceleration

I think with carefully selected wheels and tires, we can achieve a setup that has more grip and width, the same overall diameter for torque delivery, and less weight than stock. If we can achieve all that I don’t see much downside.

 

For what it's worth you can fit a 245 on a 8j wheel, so you don't necessarily need to decide between 225 8j vs 245 9j.

 

Wouldn't perform as well in corners though.

 

What is your driving level? At my level I’m trying to be the fastest I can be with the tires I’ve got. So I’m trying to get what I can out of the stock PS4 then move up to 225 width and gradually move up in stickiness. Judging from other peoples lap times I’m still apparently 5s off =( but I haven’t actually seen any laps of people on stock PS4 setting the times they claim the car can do and my corner speeds seem in the ballpark.

 

There’s a lot of variance in actual real-world tire sizes compared to their spec. I currently have 245/40 V601s mounted on 17x9.5 +40 EC7Rs and while I haven’t gotten them on track to properly test, i couldn’t make any rubbing happen even while deliberately tanking big bumps. Before these wheels I had 225/45 RT660s on 17x8 +45 T6Rs, with a 15mm spacer. The old setup was 9 millimeters further inset compared to the new setup, but despite this, I had rubbing on the rear fender tab just due to the profile of the RT660s.

 

after watching videos of stock GR86 on the Nurburgring, easy decision to go 225/45/17.
Most likely will pair it with RPF1 8J +35 square setup.

focus on improve driver skills 😅

 

after watching videos of stock GR86 on the Nurburgring, easy decision to go 225/45/17.
Most likely will pair it with RPF1 8J +35 square setup.

focus on improve driver skills 😅

It was on stock, doesn't necessarily prove 225 is better.

In NA/NB Miatas on track, 225 and 245 are about even for lap times. People used to think 195-205 sized tires were better, but these days that has been proven false.

The GR86 is 400-500 lbs heavier with double the whp of a early Miata. It’s going to be fastest with a much wider tire than a Miata, which means wider than than 225

It's going to be trial and error to find out which work out best. For previous gen, 225 were fastest but lots of things has changed. Tires are grippy, how 2nd gen handle, as you said power.

 

In NA/NB Miatas on track, 225 and 245 are about even for lap times. People used to think 195-205 sized tires were better, but these days that has been proven false.

The GR86 is 400-500 lbs heavier with double the whp of a early Miata. It’s going to be fastest with a much wider tire than a Miata, which means wider than than 225

 

the difference between a sticky race tire and a wide street tire has to be driven to understand. A 340tw (street) vs 200tw (performance) vs 50tw (race) in the same dimension will a substantial increase in handling.

If you are starting out, get an 8" wheel and put on 225. Look for a tire with the section width & tread width within a inch of each other. Tire rack is good about showing this data. It will also give the optimal wheel width.

If you want more traction get a better tire not a wider tire.

A smaller diameter tire will accelerate quicker but require shifting sooner. On track, a smaller tire gets you out of the corner quicker so you have a higher starting speed for the straight.

In autox, a smaller diameter wide tire will accelerate quicker and have less tendency to slide so you can stay on throttle longer.

A bigger diameter (taller) tire will have a higher top end speed and extend the maximum speed per gear. However it'll be slower to accelerate. Unless you are planning on 150mph on every straight, a taller tire isn't really helpful on track.

Stuffing the maximum size tire in the wheel well is for aesthetics. Getting the lightest stickiest stiffest tire will have the biggest effect on track. Having a properly tuned suspension will enable using every millimeter of that tread width.

If you can only buy one set of wheels and tires, buy for your 90% use case. If you start tracking alot, your consumables cost will convince you of the wisdom of having a track only setup.