Give me your best guess? Advice needed

[dlct3]

2018 PP car for road course. Factory wheels and Tires weigh 60lbs up front and 64 in the rear and of course the standard factory 19" widths on Michelin 4S. I'm considering a set of forged 19x10.5 fronts weighing 20lbs each and rears 19x11's same weight of 20lbs each plus a set of Michelin Sport Cup 2's for on track and some road use. Those in a 305/30-19 weight 26lbs so I figure with wheel weights & sensors mounted approx. 47lbs +/- Saving around 13lbs each corner up front and 17lbs out back. The car has upgraded brake pads, stainless lines, springs, suspension, semi-track alignment fluid, etc for handling.

My big question. On a 2.07 lap time around a road course how much is this added braking, acceleration, & grip worth in time?

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[ddozier]

All your gains will be from the tire change, wheel & tire weight change is less impactful then proper tire pressures and alignment to make best use of your new combo.

these are number from Michelin on comparable tires and times. Glean from it what you will.

1. Based on internal dry circuit lap time tests comparing the MICHELIN® PILOT® Sport 4 S (39.25 sec. avg. lap time) versus the Bridgestone® Potenza™ S-04 Pole Position™ (40.70 sec. avg. lap time), Continental® ExtremeContact™ Sport (40.03 sec. avg. lap time), Pirelli® P ZERO™ PZ4 (40.24 sec. avg. lap time), and Goodyear® Eagle® F1 Asymmetric 3 (40.44 sec. avg. lap time) in tire size 235/35ZR19 91Y using a 2015 BMW 328i. Actual on-road results may vary.
   
   
2. Based on internal dry braking tests from 60 mph to 0 mph comparing the MICHELIN® PILOT® Sport 4 S (106.0 ft. avg. stopping distance) versus the Bridgestone® Potenza™ S-04 Pole Position™ (119.4 ft. avg. stopping distance), Continental® ExtremeContact™ Sport (115.9 ft. avg. stopping distance), Pirelli® P ZERO™ PZ4 (118.3 ft. avg. stopping distance), and Goodyear® Eagle® F1 Asymmetric 3 (115.2 ft. avg. stopping distance) in tire size 235/35ZR19 91Y using a 2015 BMW 328i. Actual on-road results may vary.
   
   
3. Based on internal wet circuit lap time tests comparing the MICHELIN® PILOT® Sport 4 S (37.23 sec. avg. lap time) versus the Bridgestone® Potenza™ S-04 Pole Position™ (38.65 sec. avg. lap time), Continental® ExtremeContact™ Sport (38.87 sec. avg. lap time), Pirelli® P ZERO™ PZ4 (39.42 sec. avg. lap time), and Goodyear® Eagle® F1 Asymmetric 3 (38.52 sec. avg. lap time) in tire size 235/35ZR19 91Y using a 2015 BMW 328i. Actual on-road results may vary.
   
   
4. Based on internal wet braking tests from 50 mph to 0 mph comparing the MICHELIN® PILOT® Sport 4 S (97.0 ft. avg. stopping distance) versus the Bridgestone® Potenza™ S-04 Pole Position™ (112.6 ft. avg. stopping distance), Continental® ExtremeContact™ Sport (108.5 ft. avg. stopping distance), Pirelli® P ZERO™ PZ4 (112.9 ft. avg. stopping distance), and Goodyear® Eagle® F1 Asymmetric 3 (108.4 ft. avg. stopping distance) in tire size 235/35ZR19 91Y using a 2015 BMW 328i. Actual on-road results may vary.
   

Dave

 

[NightmareMoon]

Agreed, the biggest difference will be in grip from the MP4S->SC2 change. The rotational inertia from the weight of the wheels and tires factors in mainly at lower speeds, and won't have a huge effect on lap times on a road course.

Times from the tire change could be significant. Maybe 2 seconds or more if I had to guess.

 

[wmfateam]

 

[BmacIL]

His way
My way

 

[Austinj427]

I bet you pick up 5-6 seconds depending on how technical the track is. Don't overheat those cups.

In my experience, lighter wheels and tires are quite helpful.

 

[Hack]

I bet you pick up 5-6 seconds depending on how technical the track is. Don't overheat those cups.

In my experience, lighter wheels and tires are quite helpful.

I agree. The main differences between the R and regular GT350 are the lighter wheels plus better tires.

Reduced rotational mass really improves acceleration and deceleration. I have no idea how much faster the car will be around the track with the change the OP was talking about, though.

 

[Rodan]

You might want to check out this article: https://grassrootsmotorsports.com/articles/are-lighter-wheels-really-better/

It's the only article I've seen where this has actually been empirically tested. Smaller, lighter car, but a decrease in wheel weight of over 25% which is more than we're talking about with Mustangs.

There's definitely a benefit to be had, but as noted, the difference in rubber will make a bigger improvement.

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