Installing new Michelin tires
 

I have a 2017 Grand Sport I am going away from run-flat tires and have decided to go with Michelin 4S Pilot Sports. The new tires on the rear are not exactly the same size as the origional factories. I can go with
325-25-20 (a little smaller then the factories) or the 345-30-20. Any body have experience with this or opinions?
Thanks

With the 325-25-20 you have a difference in diameter of -0.8%. At 60 mp/h on the speedo you will actually be going 59.5 mp/h.

With the 345-30-20 you have a difference in diameter of +5.6%. At 60 mp/h on the speedo you will actually be going 63.4 mp/h. Not sure if this is enough to impact traction control / PTM etc.

That's well within the tolerance of a speedo (I believe spec is +/- 5% error)

Odd that Michelin is replacing the PSS with the 4S but doesn't offer the correct size for the GS....?

The 4S aren't OEM for the C7.

Hmm?
 

I don't think the 4S is a run flat so it wouldn't have a C7 spec.

I'm truly surprised that GM keeps sticking with run-flats. They are notorious for riding harshly, and having a lot of NVH. Lots of cars run with "inflation kits", no spare, and standard tires. I wonder what makes GM not do the same.

OP, please share with us your impressions of the tires (versus the OEM tires) once you have them installed. I am hearing fantastic things about the MPS4s.

Also; no thoughts on using the Continental Extemecontact Sports? These are available in the correct sizes, and I also hear a lot of great things about them. In fact a member here got them, and was amazed at the reduction in NVH over the OEM tires.

That is true but Michelin announced they are replacing the PSS with the 4S. So at some point in time down the road we won't have the option of the PSS unless they continue to produce it just for the C7.

Ok guys, thanks for the comments. I ordered my new 4S's today and should be in next week. I got the 295-30-19 for the front and 325-25-20 for the rear.I will let you know how I like them when I get them installed. Now I have a set of Michelin SS run flats for sale with 3000 miles on them!

I have had the Michelin 4Ss on my Stingray for about 1 year now and love them. I think you will too. :thumbs:

You are a decade out of date, and ZP technology has changed dramatically in that period. The ride quality of today's Michelin ZPs is the same especially on the very low profile tire sizes on C7s. I have a ZP and non-ZP set, and there's no difference in ride quality. I prefer the ZPs.

It's too late for the OP now, but one of our semi-pro track wizards tested the PS4S against the OEM Michelin PSS ZPs on a race track, and his lap times were slower on the PS4S. The OEM PSS ZP tires were specifically designed by Michelin for the C7.

If GM were to start offering non-ZPs on Corvettes they'd have a whole bunch of pissed off people because the majority of informed customers now prefer the ZPs.

I just went from Alpin PA4 to A/S3+ ZP and boy what a difference. The stiffness and noise is greatly increased going to the ZP. The ZPs have this thud whenever hitting a bump whereas the PA4s were quite. The ZPs are definitely at least twice as stiff. Both sets were brand new and driven in the same temps on the same roads.

Hey Foosh, how's the Sebring Orange going ? you were having a problem a while back... all okay now? I haven't been here in a while

"I'm truly surprised that GM keeps sticking with run-flats. They are notorious for riding harshly, and having a lot of NVH. Lots of cars run with "inflation kits", no spare, and standard tires. I wonder what makes GM not do the same."

Of course, GM did not ALWAYS use RunFlats exclusively; as OEM on the C5 Z06 were not. I still have the OEM Z wheels (2nd series from Italy that didn't break) and nonRun-Flats on my C5 coupe.

When my C7 needs tires, I'm going nonRunFlats, too. All the best with your new tires. :thumbs:

Some of us aren't interested in going on the track and PSS or 4PS would be sufficient.

When I replace my tires on Z51 I am leaning on going NON Run Flats. I would prefer a slightly smoother ride, and I don't plan on running mine on track.

Ken

Tire replacement
 

Take this for what’s its worth. Have New Z06. Just swapped out the STOCK Michelin PSS for the AS3+. Great tire. It’s cold out and I have less then 40Omi on them. They say you need about 1000mi to break them in. I immediately notice how much of a more comfortable ride these are. Also there quieter. I wouldn’t say it’s a drastic difference but it’s notisable.

Bondojohn,
Thanks for the comment. You guys up north have a whole different set of problems with the snow and cold. I am lucky to be in Austin TX where we have mild winters.
I am looking for a better ride but also of great concern is the bending wheel issue. I want a more shock absorbing side wall so it will reduce the possibility of bending my wheels. I think the AS3's are a good choice for your climate!

To be clear, we're talking tires for the Grand Sports, in particular.

I have read here of folks switching from the Michelin ZPs to the Contis and reporting dramatically reduced NVH. Having owned performance cars for quite some time, it is very obvious that the tires that manufacturers choose to fit to their vehicles are always compromises, and Chevy is all about performance over comfort right now. The frustration for GS Corvette owners must be that there are so few choices in tires for their cars.

With so few choices out there for tires, GS Corvette owners don't know what they don't know. Right now the GS choices in OEM sizes are the OEM tires and the Contis (setting aside all-seasons and the Cup 2s), so basically 2 choices. There is a world of performance tires out there, each with their own strengths and weaknesses, and GS Corvette owners don't get to sample from that massive pool, they're very limited in their choices.

My being here is about investigation, considering if a Corvette is right for me. One thing that has popped-up in my investigation about Corvettes (other than the Grand Sport) is that they are twitchy at the limits of mechanical grip. The Z06 and ZR1 in particular, but also the Z51 Stingrays. And their levels of NVH has led some vendors to offer interior insulation packages to quiet them down. So I'm led to wonder if these concerns are due to the ZP tires. And when a member here reports that switching away from the ZPs dramatically lowered NVH, that really catches my attention.

Since I'm considering a Z51 car, I am very glad to see that there is a lot more choices in tires for that model, many of which aren't run-flats. Including my beloved Firehawk Indy 500s, which are a little-known but amazing tire.

Yes, all is well and thanks for asking.

It was a bank 1, position 1, intermittent, O2 sensor malfunction that showed up at 900 miles. It took the dealer it was flat-bedded to (not Criswell) two days without finding anything, but once they called GM tech support, they were instructed to replace that sensor because they'd had a potential bad run of 02 sensors that were intermittently malfunctioning. That corresponded to the codes it was intermittently throwing pertaining to bank 1. It was a simple 15 minute fix once diagnosed.

I've had zero issues in the 8K miles after, except for 2 punctures, and 2 PSS ZPs replaced free of charge under my Tire/Wheel policy. I'm happy to be on ZPs.

Glock,

Narrow vs. wide-body sizes are irrelevant to this discussion.

Yes we have a few people reporting better ride quality on non-ZPs, but contrast that with the vast majority who report no difference. This is one of the most discussed topics on this forum with dozens of threads over the last several years. The Michelin ZP design is entirely different than the old Goodyear F1 Supercar ZPs with the stiff inner and outer sidewalls. Both the PSS ZP, and the AS3+ ZP run the same compounds and outer sidewalls as the non ZP version. The difference is an extra inner band next to the inside sidewall, which is only there to support the tire at zero pressure. At full inflation it does not stiffen the ride.

It's not 2005 anymore.