Square Set-up Or No?

[17RubyShelbyGT350]

Ever since I found out about the 31 lb boat anchor wheels on my '17, I have been considering moving to a true forged wheel set-up (saving approximately 9 lbs of unsprung rotating mass per wheel and upgrading to the newer, improved Michelin PS4s. I have zero desire to run the Sport Cup 2's on a car that spends 95% of its running time on the street. The Sport 2's IMHO are ridiculous for the street for so many reasons most of you already know.

So, I called tire rack yesterday, and asked about the availability of these new Michelins in an "R" configuration. The 305s are available, but the 315s are not. "Maybe they will be available in the Spring, maybe a year or so after that." :doh:

I know some of you have run the square setup - 305s all the way around - perhaps on 11.5 inch wide rims? I could always mount the 315s on the rear wheels if and when they become available. I am looking at doing this next Spring - waiting a few more months to see if Michelin releases the 315s?

Also plan on replacing/upgrading the trunk mounted handling module.

Comments are welcome!

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[firestarter2]

This is a good question on the street I do not see the 10mm making a difference. On the track at the limit it might but I find even that suspect.

 

[MrCincinnati]

Ever since I found out about the 31 lb boat anchor wheels on my '17, I have been considering moving to a true forged wheel set-up (saving approximately 9 lbs of unsprung rotating mass per wheel and upgrading to the newer, improved Michelin PS4s. I have zero desire to run the Sport Cup 2's on a car that spends 95% of its running time on the street. The Sport 2's IMHO are ridiculous for the street for so many reasons most of you already know.

So, I called tire rack yesterday, and asked about the availability of these new Michelins in an "R" configuration. The 305s are available, but the 315s are not. "Maybe they will be available in the Spring, maybe a year or so after that." :doh:

I know some of you have run the square setup - 305s all the way around - perhaps on 11.5 inch wide rims? I could always mount the 315s on the rear wheels if and when they become available. I am looking at doing this next Spring - waiting a few more months to see if Michelin releases the 315s?

Also plan on replacing/upgrading the trunk mounted handling module.

Comments are welcome!

I believe there's a thread a few pages back with recommendations on a square setup with ps4s and it was either 305s or 295s I think.

 

[mkonrad]

There are surprisingly few 315/30/19 fitments for track and competition tires. Most of them are 305/30/19 unless you stick to the Pilot Sport Cup 2's. Using 305 all around opens up options, but then you get into all the black magic about more tread, car balance, understeer and oversteer as you start changing things.

But with only PSC2 and some slicks available in 315, I'd look at other options unless you know you want them specifically, and you just said you did not require the PSC2.

FWIW, Bridgestone RE71R in 305 square for me on 11" Forgeline.

 

[xray16]

I switched to the project 6GR R spec wheels. When time for new tires, PS4, would folks go 305 30-19 square or 325 Rear and 305 Front? Mostly street driving.
Probably going to switch P51 wheels when get new tires since 21 lbs each

Thx

 

[TDC]

I'm setup for 305 all around for both my street/autox and Track. IMO tire poke with 325 is not attractive.
Grip is good with a handful of regional 1sts in class. This is on factory non-R rim widths.

 

[Trackaholic]

IMO a little added oversteer (via a square setup) wouldn't hurt the GT350 much.

I'm not a great driver, but I've found the car to understeer a little, so I've been trail braking to adjust the balance. It actually works very well, but some added front grip would probably be fine.

Many people go square for tire rotation purposes, but keep in mind that the front/rear offsets are very different, so you'd need to run spacers if you wanted to easily rotate tires F/R, or just use dedicated wheels and forget the rotation aspect.

-T

 

[AutoX R]

I ran the RE71R 305 square on the stock 11.5'' wheels all season long with no issues. I do have a bigger front bar though.

 

[nastang87xx]

IMO a little added oversteer (via a square setup) wouldn't hurt the GT350 much.

I'm not a great driver, but I've found the car to understeer a little, so I've been trail braking to adjust the balance. It actually works very well, but some added front grip would probably be fine.

Many people go square for tire rotation purposes, but keep in mind that the front/rear offsets are very different, so you'd need to run spacers if you wanted to easily rotate tires F/R, or just use dedicated wheels and forget the rotation aspect.

-T

Get yourself a front swaybar my man. Softest setting for track. Firmest for autocross. If your autocross surface sucks with a lot of imperfections, go medium.

 

[nastang87xx]

I ran the RE71R 305 square on the stock 11.5'' wheels all season long with no issues. I do have a bigger front bar though.

Same here. I run 11 squared with factory-like offsets. 25+ front. 60+ rear.

 

[EF300]

I have 305 30 19 square on stock non R rims. I immediately noticed a bit more oversteer in the front as compared to stock. It seems ridiculous but the car felt a bit loose at the time. After driving for a few days everything seems to have settled down and the car feels more neutral. Probably it was just my noobness not being used to such a big tire up front.

 

[xray16]

thanks for the input. I will probably go PSS4 305 30-19 square, agree the 325 just look a little too big. . One follow up, how much difference does it make with the speedometer if any? If so, did anyone reprogram for the change in tire diameter? Thx

 

[mkonrad]

thanks for the input. I will probably go PSS4 305 30-19 square, agree the 325 just look a little too big. . One follow up, how much difference does it make with the speedometer if any? If so, did anyone reprogram for the change in tire diameter? Thx

Check the Forscan sticky, it has answers to that recently. Once you change the tire height data in the body control module, you'll get a non-MIL error until you use the new Forscan command to cause the PCM to re-fetch parameters from BCM. But it works (error is no longer present) - it was added sometime in October.

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