Randy turned a 1:36.83 in the 2019 GT350 during MT's BDC.

[FastCarFanBoy]

Didn't see this mentioned anywhere. He turned a 1:36.11 in the R during 2016's BDC for reference.

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[NorthernBeast]

Didn't see this mentioned anywhere. He turned a 1:36.11 in the R during 2016's BDC for reference.

The 2019 GT350 now comes with the Sport Cup 2's so what you're seeing is the advantage the tires gave the R cars. The other upgrades on the R (aero, etc) make up the remaining gap in lap time.

 

[Droopy1592]

I always thought there would be less than a second difference between the R and Non-R with the same tires.

 

[newmoon]

I always thought there would be less than a second difference between the R and Non-R with the same tires.

The difference now is likely the advantage of the CF wheels, with the improvements to the 19 aero and cup2 tires I would guess it is now very close to the R

 

[Demonic]

The Cup 2's on the R are a different tire compound than the Cup 2's now on the GT350, per Billy Johnson. The name was used more for marketing.

 

[Droopy1592]

The Cup 2's on the R are a different tire compound than the Cup 2's now on the GT350, per Billy Johnson. The name was used more for marketing.

I got chastised here for asking for the tread rating between the two same-named tires for comparison purposes. I think there’s a letter or symbol difference between the two and I think expected mileage is closer to 10k (vs 2k for the R version). It’s still impressive that even with less sticky tires the non-R is that close. I’m guessing the R version may have a slightly improved time as well.

 

[mkonrad]

The tread rating is a government thing. It's the way you can see a 200 tread-wear rating on an RE71R, yet they are softer than another 200 tread-wear - which is used for classing purposes in autocross, so there's a reason to "cheat" and stay at a certain rating of 200. The tread-wear is measured under controlled government testing, and the test cycle doesn't include timed laps at Laguna Seca by a prepped race driver. For the purposes of government ratings, the tread-wear will will probably remain at 180 (PSC2) even with a different compound as the load rating changes.

Billy also seemed to hint that the PSC2 on the GT350R is about the softest available. Porsche PSC2 has a higher load rating, and the GT350 PSC2 has a 35 aspect ratio.

Randy runs Laguna Seca this all the time, but across a different day ... and in 2016, hard to compare to now. There's no shortage of people here trying to figure out which of the tires, wheels, weight, aero actually makes the difference, but they'd have to be tested in the same conditions to satisfy the skeptical crew here and put this to rest.

 

[Hack]

The GT350 also has different programming for the anti lock brakes, different spring rates, and I think they changed the advancetrac setup as well.

I agree tires are probably a big improvement to times, but I would be willing to bet these other changes improve lap times as well.

 

[Austinj427]

This was also on a completely different day.

There are a lot of variables to take into account.

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