AW

I started using my Cup car with Dunlop slicks which worked well but did not last very long. I only managed to get about 10 heat cycles from the dunlops.

Many cup car owners told me to switch to Michelin because they last longer and also, because they have been designed for the car. It all made sense and I quickly started to order some Michelin Cup tires.

I will spare you with all the details of this adventure, but basically, I got some inconsistent results with Michelin slicks. The good news is that this inconsistency appears to be connected with the fact there are 3 different types of rear tires in the 27/68-18 size:

1) the "real" cup tires which is a 27/68-18 with a yellow "Porsche cup" label. This tire works very well. It is in my experience as fast or faster than dunlop and last longer.

2) the "S8A" tire in 27/68-18 size, which has an "S8A" yellow label. S8A means medium compound. I have not tried these yet. I'm not sure if they are identical to #1 or not. The ref numbers are not the same, however, “real cup tires” (#1 above) are documented by Michelin to use an S8A compound.

3) the "S9A" tire in 27/68-18 size. These have a "S9A" label. S9A means hard compound. To go to the facts, these tires suck. For me they were at least 3 seconds slower and then got a lot worse after 4-5 heat cycles.

When I ordered, Michelin slicks for my 996 GT3 Cup car, I received either #1, #2 or #3. Some tire vendors appear to have no problem shipping S9A (hard compound) tires when someone orders a cup tire! So, if you switch to Michelin, it is important to specify that you want S8A compound tires. I don’t think I’m the only amateur racer that got abused that way. Some competitors at PRC were using S9A on the rear.

Here is what I’m trying to understand:

1) What is the purpose of S9A tires? Everyone says, hard compound to run in extreme heat but really I would love to hear a better explanation. If that’s the explanation, when should one use an S9A versus S8A?

2) Are tires with an S8A yellow label really identical to the one with a “Porsche Cup” label

I would appreciate if anyone with real knowledge of Michelin slicks could cast some light on this.

Thanks

Arnaud

95m3racer

Are you racing with these, or just doing track days?

AW

I'm racing with Nasa/PRC and ARC. Do you mean that S9A are "good enough" for track days?

A

earlyapex

The track may simply have been too cold for the hard compound tires.

When's your next track day?

AW

> The track may simply have been too cold for the hard compound tires.

Sure. But the big issue, and the point I'm trying to make besides asking these questions is that some companies ship S9A compound when people order "cup tires" A cup tire is S8A (medium compound), not S9A (hard compound). I'm also not sure when it would actually make sense to use S9A tires. Different car? Dead hot track? but if so how hot?

Next PRC race is early may.


AW

Geoffrey

I believe there is also an S7A (soft) compound available and I was told by JD Motorsports (Michelin slick USA distributor) that the Cup specific compound is between an S7A and S8A and as you mentioned, built specific for the GT3 Cup Car.

analogmike

Your info is wrong, the non-cup tires are SOFTER than the cup tires.

The CUP tires are S8 front (medium) and S9 rear (hard). These are required for IMSA GT3 cup and other supercup series. They hold up really well on these heavy cars. The S7 (soft) and S8 (medium) sets are cheaper, but not quite the same construction. Best for use at lower track temperatures, on lighter cars, or lighter wallets

I corded an S8 rear at Atlanta Saturday morning after only about 6 sessions.

4 Kurves

This makes sense. I have 3 sets right now and the set I received which were supposed to be Cup tires are S9's (couldn't see any marking on the fronts) and I have 2 non-Cup sets which are the S7/S8 combos.

Funny thing is that most I've talked to say the "Cup" tires are supposed to be faster yet they are harder? This is consistent with Michelin's website which lists the S9's as harder.

It makes sense for a spec series that IMSA would go with the harder tires but what is preplexing is why do they cost more and why do some people say that they are supposed to be faster. Could it be the construction is different accounting for the lap time varience?

AW

As far as I know, there are 4 compound for michelin slicks:

S6 Very Soft
S7 Soft
S8 Medium
S9 Hard

This is documented on Michelin's web site here.

Cup tires are S7A front and S8A rear. S9 are not cup tires. Further, I heard and would love if someone could confirm that the cup tires have a stiffer sidewall. I got this information from the Michelin documentation. Here is a grab:



Now, what I'm still not sure is what the actual difference between a rear cup tire and a rear S8A tire. Further, what is the actual purpose of the S9A tire?

Thanks

AW

4 Kurves

Could it be that what Michelin calls the GT3 Cup tire (for Carrera Cup and Super Cup) is NOT what IMSA determined to be the spec tire for the series over here?

It still makes sense to me that IMSA choose the hard S9 - plus my source for the "Cup" tires I have turned out to be the S9's.

As for their use it seems that the only reason would be extremely hot temps and extended wear although your own test seems to disprove that.

Judging heat cycles vs. wear length are two different things aren't they?

kev

AW,

I read the chart differently. The S7A/S8A listed is the "customer" tire that, yes, will fit a GT3 Cup and is listed as such. The "Cup" tire is list as a SI compound. Which may be S8A/S9A?

BTW, I have a set of "Cup" tires and they don't have S9A stamped on them for the rears.

analogmike

you think you guys are confused?? Horst Farnbacher (winningest supercup team leader, Hi Konstantin, nice meeting you in Atlanta!) was at our 1st IMSA race and even HE was confused by the markings on the tires... It seems the 7 8 9 markings do not always show up on the PORSCHE CUP tires. But they are medium front and hard rear.

I stand by what I wrote above but would add that now there are new CUP tires for the 997... further confusing things. PLUS speedway/oval tires...

AW

Kevin, I agree. I got one set of Michelin cup tires that had (for me) better performance than dunlop. There was no S7, S8, or S9 yellow sticker on them. Instead, there was a Yellow "Porsche CUP" sticker on the side. The 2 sets of S9 rears I got, in my experience were significantly slower. I will try and report on the S8.

Do you have any Michelin documentation about this SI tire compound?

Mike, yes this is very confusing. I spent thousands of dollars is poor tires and posted this thread to make sure everyone is informed. Do you have Michelin documentation showing that rear cup tires are S9 / hard? All the documentation I have (some of it posted here) represent cup tires as being medium/intermediate or S8

AW

karlooz

did you do Thill this weekend w/ NASA? PRC was there. racing was... exciting between these guys



it sucks it turned out like this




more pics of the race HERE

Geoffrey

All wheel steering - cool option...