[addyb0y5]

Hi Guys,

I recently started doing HPDE events with SLICKS on 18s Forgeline GS1Rs.
The tires I run - Pirelli's DH 305/660/18 in the fronts and 315/680/18 in the rear. Got good use out of them. 3 track weekends. The only reason I moved to slicks is to make the sport little cheaper on consumables. Not to improve my lap times. Before moving on to slicks, I have gone through 4 sets of 3Rs.

I ordered tires from used racing tires website and by mistake I ordered two different brands of fronts and rear. In my defense, I ordered by the size not by the brands. So I ended up getting Dunlop's 305/660 in the fronts and Pirelli's 315/680/18s in the rear. I can returns the fronts and try getting the Pirelli's DH for the fronts in 305/660 size but they aren't available any where.

So the most obvious and probably dumb question -
has anybody driven with two different brands of slicks in front and rear ?
If not, what is you opinion on it ? I know you shouldn't mix different brand of tires. but these are slicks so they should have similar amount of grip, right ??

Also, please let me know other website to get scrubs. I only know one website i.e usedracingtires.com

Thanks in advance for all the inputs.

Cheers
Addy.

[TheRealJA105]

I'd run them. One time when i tried out the DHs, i melted a rubber valve stem on my front wheel from brake heat and swapped back on my Goodyear Supercar 3s just in the front and ran the rest of the day.

Look up GTracingtires.com

[NorthGeorgia]

With sub 100 treadwear tires, i run different brands on front and rear with no issues. if there is a material difference in compound, I try to keep softer lower rated treadwear in rear. Also there is some safety understeer bias in a staggered 305/315 setup versus square. It still crosses my mind when I put a fresh set on the front and the rears are on their last legs. Last month had harder compound in front and dealt with more understeer in certain sections. Just had to adjust driving style to compensate.

[SFV1LE]

I would run the Pirelli DH 315 front and rear. 315 in the front should definitely fit and this will give you more contact patch, the GT4.R runs 305 square so running square should be ok.

But here's another site with Pirellis in 325/680/18 listed so this might be the best option: 315/680/18 front and 325/680/18 rear (more like stock ZLE):
https://usedracingtires.com/collecti...-pirelli-slick

EDIT: just realized that was the site you already bought from, these guys also list Pirellis in 305/680/18 and 315/680/18. But dont seem to have the Pirellis in 325/680/18 listed on usedracingtires.com
https://gttrackdays.com/tire-specs/?...12243652343750

[addyb0y5]

Thanks for all the inputs. Appreciate it!

My wheels are 18x10 in the front and 18x10.5 in the rear. I don't know if it is okay to mount 315 on the 18x10 for the front. ??
And another interesting thing I have heard from folks working in GM - PTM is calibrated for 5% rpm difference from Front:Rear ratio. Hence I chose the 660 in the fronts and 680 in the rear (similar to stock setup). Don't want to mess with PTM.

@any one who is running 18" square slicks - found any changes how car behaves on PTM(RACE) mode ?

[seanblurr]

These cars don't like square set ups w/ PTM. As you stated, the electronics get all out of wack. You will definitely want to run w/ everything turned off if you ever go to a square set up.

[addyb0y5]

Originally Posted by seanblurr

These cars don't like square set ups w/ PTM. As you stated, the electronics get all out of wack. You will definitely want to run w/ everything turned off if you ever go to a square set up.

Hey Seanblurr, What is your wheel setup for running the slicks ?

[seanblurr]

I have a few sets of stock wheels I have run slicks on, as well as 18" wheels w/ stock specs.

[SFV1LE]

Originally Posted by addyb0y5

Thanks for all the inputs. Appreciate it!

My wheels are 18x10 in the front and 18x10.5 in the rear. I don't know if it is okay to mount 315 on the 18x10 for the front. ??
And another interesting thing I have heard from folks working in GM - PTM is calibrated for 5% rpm difference from Front:Rear ratio. Hence I chose the 660 in the fronts and 680 in the rear (similar to stock setup). Don't want to mess with PTM.

@any one who is running 18" square slicks - found any changes how car behaves on PTM(RACE) mode ?

No I definitely wouldn't try to mount a 315 on a 10" wheel, 11" min I think.

Stock ZLE 3R diameters are 26.3" F (305)/26.7" R (325)

660/680 converts to ~ 26.0" F/26.8" R