Ranger

I’ll save you some time and expense if you’re considering buying the Goodyear Supercar ROF Gen2 rear tires for their straight-line traction on dry pavement, including the drag strip. Forget about it. The Gen2 fairs poorly compared to the Gen1. Details follow.

I took the plunge on a pair of 325.25.19 GY F1SC ROF Gen2 tires for the rear of my bone-stock C6Z. Bought them from the TireRack. Total cost of tires and shipping was around $1000. Local mounting and balancing on a Hunter GSP9700 was another $85.00. To do the A-to-B test, also had to buy a new pair of stock comp gray C6Z rear wheels on which to mount the tires ($490 shipped) and the TPMS sensors to make them solid with the car’s nannies (another $85). All told, a $1660 test.

At the same time I bought a new pair of F1SC SuperCar EMTs, the Gen1 that came from the factory on 2006 to 2010 Z06s. Those I had installed as replacements for my second set of rears that were just about to the wear bars at 22.5K miles.

Broke in both sets of new rears for at least 300 miles, with plenty of hear cycles and moderate driving.

Then I did my owner-testing, all involving straight-line, no curves. All tests were done with tires warmed thoroughly by driving (street) or burnouts on the drag strip.

On the street, the Gen2 rears at a road surface temp (not air temp) of 70F, would not hold a throttle-squeeze to wide open throttle from a roll in 2d; a quick shift to 3d at 5500 produces excessive spin that required a lift completely off the throttle. I was shocked. At the torque peak in the mid-4000s in 2d, the tires broke loose. I repeated that test on roads I know to provide good traction. Results were the same.

Took the Gen2s to the drag strip (Maryland International Raceway) and ran 11 passes with pretty good surface prep and a track surface temp in the 70s. Results were poor, even with varying psi ( 27-24) and burnout durations. Best 60’ the Gen2s produced was 1.83. Average was high 1.9x In addition they spun excessively on the 1-2 shift, losing nearly a tenth just on that shift in the 60’-330’ increment. Again I was shocked.

The following day, I swapped to the Gen1 F1SC EMT rears and returned to MIR. Made eight passes in conditions very similar to the previous day. Best 60’ was 1.74, nearly a tenth better than the best on Gen2. Average 60' was low 1.8x, about 1.5 tenths faster. In addition, the Gen1 produced 60’-330’ incrementals (that include the 1-2 shift) more than another tenth quicker than the Gen2. Back to normal performance. I was reassured.

I earlier had tested the Gen1s on good-traction road surfaces at 70s F (surface) temp. They held 2d gear roll-ons well and hooked the 2-3 shift near redline with just a small amount of spin. Repeated the test with the surface temp in the low 60s F. Results were pretty much the same. Bottom line. The Gen1s substantially beat the Gen2s in straight-line street traction.

I readily acknowledge that straight-line acceleration is a secondary concern to some owners, but for many of us, it’s central. I also have no way of knowing whether the pair of Gen2s sent to me are representative of the full production runs in terms of performance. My assumption is they are, since they passed GY production QC.

I’ll keep the Gen2 and run them on the street in Florida where their wet-weather performance may be beneficial. But I’ll be saving the Gen1s for the drag strip.

BTW. Anyone buying the Gen2s ought to weigh them before mounting. The ones initially shipped to me by TireRack…the right rear weighed 32.5 pounds, the left rear weighed 31.0. Again I was surprised at that degree of production variance on a $500 tire. Fortunately, TireRack was quick in shipping me a replacement for the left rear. The new left weighed 32.0, within a half-pound of the right.

I’m sure companies would/did do more comprehensive testing than mine. But the results I got are conclusive enough for my purposes. The Gen1 F1SC EMTs are the ones I’ll be running at the drags on my bone-stock C6Z.

Ranger

u1arunit

Very good info Ranger. Thanks for taking the time to post all this for us!

Lawdogg

I hope the lack of forward grip you document is offset by better lateral grip. As you know, lateral grip is the most important characteristic for some of us.

NORTY

Thanks for the analysis, Ranger. Do you suppose these GENII tires were more designed for the less powerful Gransport? Surprising findings for sure though.

Ranger

Not sure, NORTY. The Gen2 is stock on the C6Z. So I assumed GM had done acceptance testing that would have included straight-line grip. We've read here posts of a favorable test of the Gen2 on a road course. Those factors were the basis of my initial assumption that Gen2 straight-line performance would be better than the Gen1. That turned out to be wrong and vindicates my decision to simultaneously get a new pair of Gen1s, just in case.

I suspect someone at GM and/or GY will speak up in the thread some test results defending the Gen2. Hoping so, anyway and would be interested to read their basis for concluding the Gen2's dry straight-line traction is not worse than the Gen1's.

Ranger

PatriotZ

As per usual the Ranger has some good information here....Thanks for taking the time.....

383vett

Nice write up Ranger. Now do a test comparing the Michelin PS2ZPs to the Goodyears.

Ranger

I'd love to do an A-to-B comparing the Gen1 to the Michelins that come on the 2011 Carbon, 383vett. But that would require four wheels/tires that aren't in my current budget forecast.

Ranger

obzidian

Interesting... much appreciated.

383vett

Just put it on plastic. You won't have to pay it until next year.

JoesC5

Thank you, thank you, thank you. I've just crossed the GEN2 tires off my list of possible replacement tires for my Z06. I'm not running on the drag strip or doing any road courses, I'm just looking for a tire that will tame the beast on the street. I want a tire that will hook if I get on it in first or second gear. Appears the GEN2 tire failed miserably in that test.

Ranger

Anyone know the GM or GY test regime for measuring straight-line grip. I'm wondering if the test spec conditions are confined to surface temperatures substantially higher than 70F I was at on the street and mid-70s on the drag strip surface. If they test at say 90F or higher, perhaps the Gen2 behaves better.

Ranger

JoesC5

Since both tires are designed for the same application and both are rated as summer tires, then I would think a comparison between the two at any temp would be a fair test. 40 degrees, 70 degrees or 100 degrees, just as long as the comparison was done at the same temp between the tire tests.

3LZZ06

If that truly is the case, the LS7 will probably be pulling a fair amount of timing at that temp, thus defeating the advantage of a "heat friendly" tire...

Thanks for the very costly experiment Ranger, it's greatly appreciated.

Gearhead Jim

(tagged)

shifter77

Awesome. I would like to see a comparison between the Mich vs GY. Iam not a fan of the gys. Would like to see manufacteres produce more street/track tires in C6ZO6 sizes with emt.

D-Rod

In spring I will bring a set of PSP ZP's to MIR for you to test. Wish I could make the rental in a couple weeks but already have plans.

Were you going to be there when they rent MIR next month? A guy from my area is going and may be able to have him take the wheels/tires down to you.

BTW- they are on repo spyders so I dont know how true the test would be. Just leave a little life left for me.

jschindler

I just put the new Michelins on my car last week. If you are in the Houston area PM me and I'll let you drive my car. Right now I can tell you that they hooked very well for me last weekend from a roll in first and second gear in 68 degree ambient temps. They spun in first gear some, but not in second from a roll.

But I'm the first to say that its been over a year since my factory tires hooked as new, so I am not willing on making a comparison of new-to-new.

As to your comparison above, you are the second person on the forum to say the exact same thing about the new Goodyears....

see post 114...
http://forums.corvetteforum.com/c6-z...post1575916169

Dr.Ron

As I have mentioned before on the forum, I AM a fan of the stock GY runflats, as they have over performed for me both on the drag strip (1.68 60') & the road course, where in bone stock form I was ALL OVER advanced group drivers in mostly road race set up heads/cam/etc. C5Z's.

After reading about the Gen2's and the results the Bondurant driving school had with them, I figured they'd be a nice replacement for my 15,000 mile GY F1's that were road raced on & drag raced on that are currently on the car. The front's have about 2/32nd's left & the rears are pretty much down to the wear bars.

I DO however notice with this set that once they passed the 13,500 mile mark that they got more slippery AND more noisy. More then I noticed in the past with previous GY F1's.




Ron

CTYANK2