pepinozaur

Hi guys,

I have used Cup2 N2 265/35/20 paired with rear 325/30/20 M0 (AMG), they run so GOOD, so FAST, and they LAST for many events.
Then I thought I should go with a faster combo and put on 245/305 Trofeo R, my car started to understeer and Trofeo times or the same or slower than wider cup2. Then I increased front camber and now the car is neutral, but only slight decrease of timing, also I like Cup2s more as they seem to keep the performance better throughout the longer sessions of tracking.

I have bought also 265/305W Hoosier but didnt have time to test those, but as these are more of tracking only tire I was contemplating what our options are for more street friendly tires, and the following 3 options come into my mind:

1. TROFEO R 265/315
2. CUP2R 265 and either 315/30 (K1 - Ferrari) or 335/25 (AMG-M01) still no specs as rolling diameter etc for these rear tires, hope at least one of them is ok for our AWD system.
3. CUP2R 265 + 325 CUP2 M0(AMG) and maybe do some tricks to improve rear grip to decrease the potential of oversteering due to increased front grip.


I am considering 1 or 2, as 1 is already available to order, but seems 2 to be the faster choice and guess will be available soon if not already out.

I do mainly track and spirited driving with my car, so more into the Cup2R to be honest.

hcvone

My Z06/Z07 and ZR1 came with cup tires, yes great traction on the track, but on the street they pickup every stone and throw it down the side of the car, and are not good in the wet, and really suck in the cold, now on an all wheel drive you can get away with that problem to a point. I just have track wheels and tires, and my street wheels and tires, go to the track I put the different wheels on, with a lift it takes 15 minutes, works for me.

pr-s

I'm also more into waiting for Cup2R, don't think they're out so far. Also, don't know if they'll hook any better for spirited street driving than the Toyo 888R it has right now. What are your thoughts?

pepinozaur

I am waiting too for Cup2R as after some research here in the European market seems the rear 315 and 335 TorfeoR arent available or even producing by any of the production facilities.
Seems that early April, Michelin will produce the tires we are looking for, at least the fronts 265/35/20, guess also the rears will be available. Stil dont know any specs, but guess 335/25/20 M01 will be exactly or really close to 325/30/20 Cup2 M0 and great pair for 265s fronts.

Consideting Cup2R might be as fast as R7s at least for few sessions, but also really streetable, that would be my first choice from now on if their price will be not more than 2500Euro including all taxes.
Here I can get a pair of Cup2 N2/M0 265/325 for like 1350Eur, Trofeo 245/305 for 1850Eur and Hoosiers 265/335 for 2400Eur.

nolimits

Anyone tried the new true width 335/20" R7 vs last years narrow? I just got a set of them and C2 MO in 325/20", both to run with respective 265s. The R7s are definitely wider than C2s now, hope I can make em work. Diameter is less and works with 265's. OEM springs and ride height except for alignment impacts. Will mount in a month or so and post results in Tracking thread.

Jean

PepinoAzur,

I can feel your pain in trying and testing the different brands and sizes, we get entangled with maximizing rolling diameters and widths only to find out lap times do not follow the theory. I am sure you are aware of all this, several parameters impact the contact patch besides the diameter or width.. One of the most impactful are tire pressures, sidewall stiffness, wheel width, tire ratings, camber and of course tread depth.. When it comes to grip, even more parameters than contact patch come to play, rubber coefficient of friction, stability, sidewall stiffness in cornering etc.. Of course I am considering spring rates and suspension, weight, load transfer..all assumed being irrelevant here.

991 turbo full weight with 70Kgs driver (~1680Kgs)..

1) Front Wheel 9", Trofeo R 245/35 x 20".. @2.5Bar --> Contact patch length 101mm, contact patch width 240mm, total contact patch area 243 sq.cm.
2) Front Wheel 9", Trofeo R 245/35 x 20".. @ 2.0Bar --> Contact patch length 114mm, contact patch width 244mm, total contact patch area 275 sq.cm
3) Front Wheel 10",Trofeo R 245/35 x 20".. @2.5Bar --> Contact patch length 95mm, contact patch width 258mm, total contact patch area 245 sq.cm.
4) Front Wheel 9", Trofeo R 265/35 x 20".. @2.5Bar --> Contact patch length 101 mm, contact patch width 242mm, total contact patch area 246 sq.cm.

Impact of tire pressures offsets any difference in tire width or diameter in terms of contact patch, example 2 above gives you a +13% increase in overall contact patch vs. example 1.. Given that Trofeo R love 30PSI hot while Hoosier like 37PSI, you can quickly tell which tire will give you a better contact patch effectively, regardless of advertised sizing or rubber Mu. A wider 10" wheel with Trofeo 245s will give you the widest patch and theoretically highest cornering speed, but under acceleration in straight line, you will have less tire grip than a 9" wheel at 2Bar because of the shorter contact patch.

Choosing the right tire combo and size depends a lot on the type of track you have, power, etc.. and where do you need the most grip, in cornering or acceleration.

Sorry if the above was a bore .

IMI A

Do you run stock tyres sizes Jean?

Jean

I run full slicks for time attack on 19". 275/675 front and 315/705 Rear.
Or 265 front and 325 rear Hoosier on 19" for track days.
But I have full racing suspension on the car, makes it easier to setup.

IMI A

I was looking at 265 and 325 for road use with Cup 2s but N rated not available yet for the rears

pepinozaur

Get the M0 spec Cup2 for the rears, thats AMG GTR tire... grips like N2

pepinozaur

Hey Jean! Your posts are as always really good, so thanks for such a long but yet informative post.

I am aware of almost if not all of the variables above and of course we have to find the sweet spot that works well for each setup. In my case, I was telling myself (now I regret it) I am never going to use slicks for this car, as this will imply also some more modifications to suspension, braces, R19 rims etc.

And I decided to go with a separate set of 20". Again I wasn't brave enough to risk 9.5" or even 10" wide wheels in the front, and did only OEM ET 9" ( guess the ET is 51), and for the rears I did 12" ET56. For these tires I decided to use Hoosiers R7 265/305w(new design 305). And most probably for the next set of Hoosiers will do 265, but 335w in the back.

Now, for some time atack events, the organisers will consider R7s as slicks, PASM as racing suspension and so on, and my car will have to compete vs real racecars, guess not vert competitive there in the lightweigt&big aero department, so I was wondering what would be the best tire to choose from? The Hoosiers if going to like 37psi, might run narrower as you said, I have never tried a pair of R7s yet, so will come back with my feed-back afterwards, and will have to use them only to hunt down my own personal track records.

My experience with Cup2 N2/M0 265/325 is they are quite as fast if not a bit faster as Trofeo 245/305, car feels more neutral(265 front- real life maybe 272mm or so), they last longer and seem to be able to put more fast laps/session than Trofeo. With Trofeo I start @1.8-185bar, do the warming up lap and then I can run 2 fast laps and thats it... they need serious cool down time to be able to achieve the same times again. Cup2s are a bit better here...

Now, for all the variables above, some of them are just fixed values I run Trofeo only @2bar as I see their performance drop above 2.2bar or so... I have a specific set of rims, springs, max camber etc ... And I have seen that the tire compound is something that matters maybe more than anything else in achieving good lap times. Also as you mentioned with a huge importance is the sidewall stifness.

For me, I feel the TrofeoRs arent such a good and fast tires as lots of guys are saying... the wide Cup2s are faster than narrow TrofeoRs and GUESS the Cup2Rs wide will be MUCH faster than wide TrofeoRs and will also last more(but at Cup2N2 grip level after few sessions).

Time will tell, but guess the wide Cup2R should be as fast as Hoosiers but be also 100% street legal and way way beter in the rain etc.

I feel our 4wd system is doing its work really nicely, so looking more into impoving cornering grip vs acceleration. My local track is technical, trying to set-up the car for it as my first choice and then will see about the faster ones.

My last alignment was -2.3 all four corners and regular toe and caster... I felt the car a bit over-steeering with TrofeoR, but using cup2 n2 265/325 the car was neutral with -1.7F/-2.0R, same settings on trofeo R and the car was understeering. I see everybody like to do -.3 to -.5 degrees less on the rear compared to fronts, I am lost For me this combo 245/305 is the last set to buy/use for this car. I feel the key is to use at least 265 in the front as this car is asking for more grip.

My final plan is to try to use some shims and setup like -2.8F/-2.5R as I did some front GT3 LCAs, still driving me crazy the front as not being able to achieve more than -2.3 with small shims.. will have to look for the right combo.
Will add also the DSC paired with my freshly installed new stiffer and lower springs (H&R now vs Eibach before) and pretty much thats it. I might give one last chance to 265/315 TrofeoR if going to be released before Cup2R, other than that guess the Cup2R 265/335 will be my next combo

Bruce H.

Are you also analyzing tire wear and temperature readings for different width, inflation, camber and tire selection decisions or using more lap times and subjective feel?

Bruce

pepinozaur

Yes, sometimes I measure those interior/center/exterior values and I have seen 65-80C immediately after sessions, but as you suggested I was using more lap times as the ultimate method of choosing one setup over the other.

In my case tire wear was perfect even with lower camber, for both Cup2 and Trofeo, but since now I have used -1.6 till -2.3 degrees only, will try more for the next track days. Even -1.6camber, it didn't affect the exterior of the tire.

Bruce H.

Okay, thanks. Always good to record as much data as possible.

pr-s

Sorry for the ignorance but can anyone explain to me the different N ratings on those Cup tires?