Here is what reducing 50 pounds of un-sprung weight (and better tires) do

I replaced the OEM Pirelli's (255/40 F, 275/40 R) and rims (19x9 and 19x9.5) on the 2015 GT-PP (which collectively weigh F-60.6lbs / R-64.3lbs) after driving around in them for over 2 years (and putting in 5 autocross days as well!). I felt the Pirelli had three strengths: decent steering feedback, even wear and high limits in the dry heat (but with a sudden drop off). I wont go into the negatives on those tires as many of you already know them. Changing those wheels and tires out was harder than I expected it to be as they were so goddamn heavy that lining those with the hub studs was hard (I need to do more core workouts!)

I went with Firestone Indy 500s (285/35 F and R) and square Advanti Hybris wheels that were wider on the front and rears (19x9.5) and MUCH lighter (19.6-20 pounds each). This combo weighs 49.6-50 pounds each.

I also added 5mm hub centric spacers in the front so the wheel caps can clear the hubs!

So changes in specs:

• Totals a savings of 50 pounds of rotating unsprung mass.
• Slightly wider tires in rear (275 Vs 285), much wider in front (255 Vs 285)
• Newer more advanced rubber.
• Improvement in front and rear track (not measured)
• Reduced sidewall, especially in rear (0.8 inch)
• Really reasonably priced wheels and unusually cheap tires (I purchased from CARID which had no sales tax and beat Tire Rack by 100-150 for the 4 set!)
• I like the design of the wheels and aggressive tire tread look. The wheels have a nice concave design that doesnt show in photos.

Here are the improvements I have noticed driving around in the street and freeway for 200 miles. I have not auto crossed the new combo yet or driven it hard on mountain roads. To be clear, I was expecting benefits from the weight loss but was skeptical of the FireStone brand. I did a lot of research and the reviews on Tirerack for these tires were really good - apparently they are re-branded Bridges tones Potenza S003's (sold abroad). Worth mentioning - there is no bulge with mounting 285 tires on 9.5 inch wheels (measured width is 10 inches, range is 9.5-11 per TireRack).

• Car feels much lighter. Especially in the front. It feels like I removed the V8 and put a lighter engine in there! I suspect this is because of the lighter front wheels and improved track in the front, which improves steering response.
• Steering effort is greatly reduced. I suspect this is because of lighter wheels and tires that have a smoother tread. Normal has the effort of comfort now.
• Car responds to smaller steering inputs (better response). This is likely because of wider front track.
• The ride is noticeably better even though the sidewall is smaller in the rear. I think this is because the tires have a softer sidewall? Potholes and issues in the road are dealt with without impacting the body much (its like the dampers are better) and overall the ride is less busy.
• The car is controlled less by wheels and tires. Before, a mid corner bump would disturb the car more than it does now. To be fair, the S550 is MUCH better than the S197 in bumps. I should also add, the mid corner bump situation got worse when I installed stiffer rear sways and poly bushings/cradle bracing in the rear IRS (so I made a trade-off here when I stiffened the rear in order to get less wheel hop and more rear feel). With this tire and wheel combo, I can carry the car with more confidence much faster on ramps and its NOT because of improved grip (I have not explored that limit yet).
• The car grips way better in the cold (40-50 and rainy days). Before, I would assume anything but babying the throttle would result in spin. Now I couldn't really get much spin even in moderate throttle in those conditions (I haven't tried full throttle in the cold wet conditions).
• Car feels like it accelerates faster up the rev range (its a minor change). I would say it almost feels like a lighter fly wheel. This is def due to reduced rotating unsprung mass.
• I have experienced no tramlining. This was unexpected. It might be because these tires have a smooth tread design that doesn't catch and softer sidewalls.

These are all subjective benefits, which are important to me. My build philosophy is a daily driver and fun car for autocross and twisties with balance, handling and feedback/feel = confidence and enjoyment . I am not building a drag car or race car. I expect actual objective benefits when I autocross and take her to the twisties, resulting mostly from the improved rubber compound, wider fronts and lighter wheels. Not that I have had an issue but I'm curious if braking will improve given lighter wheels, better compound. Additionally, the wheels have big gaps between the spokes - this could improve brake cooling.
More on that when I get a chance to test those out.

Some snaps showing the wheels, gaps, wider track, tread etc. The wheel gap needs to be reduced - I have GT350R springs and Pro Action adjustable shocks waiting for me to find some time to install! Unfortunately, when I autocross next I will have these new tires, wheels and shocks and springs, camber plates etc so it will be difficult to tease apart what caused what improvements.

Nice! I'm planning on that exact tire setup myself when the currents are done. Can't wait to hear your thoughts on the springs and dampers.

Nice write up! I need lighter wheels and better tires :tsk:

Nice write up. I just put the same set on my 2015 GT / PP but used the stock tire measurements. Night and day difference compared to the stock tires. I actually like the steering response so much better. Few heavy rain days in Northern California and they did well on freeway and surface roads.

I put about 20,000 miles on the OEM Pirelli's. Zero track time but a few long hauls to Vegas, LA, and then back. It will be interesting to see how the Firehawks compare.

Edit: No track events with my car although I'm looking for something down the road at Sears Point (or whatever it is called these days) or Thunder Hill for beginners.

How are those tires in the rain?

DoubleX said:

How are those tires in the rain?

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I can't speak for the OP but I went through a few heavy rains with my new tires and they did fine. To be fair I never had an issue with the OEM Pirelli's either. But the Firehawks have a real good feel to them. Response maybe? Not sure, but it was a very noticeable difference between the two. Mine are stock profile.

Thanks for the info. I'm looking to get a 'trackday/autoX' set of light wheels and tires in the near future. Subscribed.

Nice lookin rims and great info!...so how much do the pp wheels weigh without the tires?.. Anyone?..Very intersted in knowing this as I get serious this year about getting some aftermarket rims.

Excellent info. Thanks so much for sharing.
As much as we all might guess about the benefits of losing unsparing/rotating mass, rarely does anyone take the time to lay down the specifics and provide first hand experiences.

saf1 said:

I put about 20,000 miles on the OEM Pirelli's.

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Those rear tires must have been damn near bald. I had better wear with my nitto dr's than these damn Pirellis. 12K miles and I'm down to the wear bars. No burnouts, no track time...just daily driving.

hiccup said:

Nice lookin rims and great info!...so how much do the pp wheels weigh without the tires?.. Anyone?..Very intersted in knowing this as I get serious this year about getting some aftermarket rims.

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Fronts are 31 lb, rears 33.

Definitely reducing unsprung weight is a good thing, low profile gains depends on what kind or roads you have and how hard you push on a track....

Great write up and info!

Since you went square with the same size tire front and rear, did you change to PP rear bar to a standard GT bar keep the balance?

The PP has different rear bar because of the staggered tire size.

valentinoamoro said:

Here are the improvements I have noticed driving around in the street and freeway for 200 miles.
Car feels much lighter. Especially in the front. It feels like I removed the V8 and put a lighter engine in there! I suspect this is because of the lighter front wheels and improved track in the front, which improves steering response.

• Steering effort is greatly reduced. I suspect this is because of lighter wheels and tires that have a smoother tread. Normal has the effort of comfort now.
• Car responds to smaller steering inputs (better response). This is likely because of wider front track.
• The ride is noticeably better even though the sidewall is smaller in the rear. I think this is because the tires have a softer sidewall? Potholes and issues in the road are dealt with without impacting the body much (its like the dampers are better) and overall the ride is less busy.
• The car is controlled less by wheels and tires. Before, a mid corner bump would disturb the car more than it does now. To be fair, the S550 is MUCH better than the S197 in bumps. I should also add, the mid corner bump situation got worse when I installed stiffer rear sways and poly bushings/cradle bracing in the rear IRS (so I made a trade-off here when I stiffened the rear in order to get less wheel hop and more rear feel). With this tire and wheel combo, I can carry the car with more confidence much faster on ramps and its NOT because of improved grip (I have not explored that limit yet).
• The car grips way better in the cold (40-50 and rainy days). Before, I would assume anything but babying the throttle would result in spin. Now I couldn't really get much spin even in moderate throttle in those conditions (I haven't tried full throttle in the cold wet conditions).
• Car feels like it accelerates faster up the rev range (its a minor change). I would say it almost feels like a lighter fly wheel. This is def due to reduced rotating unsprung mass.
• I have experienced no tramlining. This was unexpected. It might be because these tires have a smooth tread design that doesn't catch and softer sidewalls.

These are all subjective benefits, which are important to me.

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Looks great. The wheels, the tires, the over-all look.

Keep in mind, 99% of your impressions are due to comparing 2 year old, 5 auto-cross, worn out, used up, and wrecked OEM tires, to brand new tires.
If you put brand new OEM tires on, you would have basically the same experience.

I keep seeing people making the same comparisons, and I remain baffled.