I'm looking for a good 18" track tire and I'm not having any luck finding anything. Sport Cup 2, R888, R7 . . .nobody seems to make anything that fits the back and most of the load ratings look pretty low. Any suggestions?

 

Re-11 are awesome.

 

RE11s are not R compound though. If that's what you are looking for the Toyo Proxes R888 would work in 18 inch. You need at least 92 load index so would have to go 245 in the front and take 265 or 275 in the rear to be staggered.

 

Thanks for the R888 info - I overlooked part of the TireRack tables and missed the sizes we need. I'm currently on 245/265 MPSS and like the balance it gives, so that's a great option.

Merc63, have you had the RE-11 on a road course much? It's 200UTOG makes it look like an excellent choice for the stock classes in autocross, but my experience with the MPSS has me questioning the ability of a street tire to handle the abuse that comes from a heavy car on a road course.

Any other suggestions?

 

I run the R888's too. 245's in the front and 275's out back. Start them out cold 28 psi in the front and 30 in the back. You will probably get about two days out of a set. Where are you going to run?

 

this ^^^^

 

I've never started that low, but may try that. What do you run hot at? My car seems to you like 41, 42 hot.

 

Toyo R888 seems to be the universally accepted choice for a "street" C63 that's being driven on the track - they come in the right sizes and seem to perform well with a heavier vehicle like the C63. Optimal hot pressures are somewhat on the high side for an R-comp (around 43-44 psi front / 41-42 psi rear). Fronts are 245/40ZR18 93Y (Toyo p/n: 159490) and rears are 265/35ZR18 93Y (Toyo p/n: 172770) and fit quite well on the OEM 18s. You can also get them in the OEM 235 & 255 sizes like I originally did as well. The load rating is not an issue even on the 235s - 91Y is just fine. And, if you're not going to drive them in the wet, get them shaved if you can - shaved to 4/32" they will last twice as long as running them with full 6/32" tread (less tread squirm and thus less heat).

If anyone is interested, I have two brand new Michelin PSC 265/35ZR18 93Y rears that I'd sell for $450 US + shipping, but the only matching PSC fronts that would fit the C63 would be the 235/40ZR18 91Y which you'd need to source from elsewhere.

 

Great post, Diabolis! I like posts with info more than opinion, and this one is very useful!

 

Great post, Diabolis! I like posts with info more than opinion, and this one is very useful!

 

Glad I could help. And, I'm getting the 44O enhanced cooling package installed on Tuesday (IIRC from the AMG PL you already have it on yours), so I really look forward to finally getting some 'liberal' use of the car...

 

For me the best tire i have ever used no a track si the BF Goodrich G Force R1, they are really amasing and stick to the track like glue. Come in the right sizes and last. i used the for a year going to track days once a month in a short track, 2.5 km.

 

Diabolis - you really need that 44O upgrade - hope you saw my post from NCM - got the car up to 250F oil temp WITH the cooling upgrade at 100F track temp. Boy was I glad I had it! Enjoy - that upgrade really makes a big difference!

 

So . . . it looks like the BFG R1 DOES come in sizes we can use:

P245/40ZR18/LL 88 W 1235@51psi

P265/35ZR18/LL 85 W 1135@51psi
P275/35ZR18/LL 87 W 1201@51psi

However, load range looks pretty light. They rate the fronts at 1235@51psi and the rears at 1135 for the 265 and 1201 for the 275. That's well below the Michelin Mercedes-specific PSS ratings for the same size tires:

245/40ZR18 97Y XL - 1,609 lbs. @ 50 psi

265/35ZR18 (97Y) XL - 1,609 lbs. @ 50 psi
275/35ZR18 (99Y) XL - 1,709 lbs. @ 50 psi

I guess the proper comparison would be against stock C63 tires:
235/40ZR18 (95Y) XL - 1,521 lbs. 50 psi
255/35ZR18 (94Y) XL - 1,477 lbs. 50 psi
The R1 shortfall isn't as large but is still close to 20%. Is that cause for concern?

 

Unfortunately I do not know either where the lower limit is for required weight capability, but one other datapoint is that the 19 inch Contis my C63 507 came with, only had a rating of 92 in the front, at 235 width.

 

Guys, when I run R888's hot ~40 psi the tires are super slick and the wear pattern is not ideal. The centers are worn more and the temps are higher there as well.

I struggled with it after I got this car. But I kept lowering the pressure and the tires started to grip much better in the low to mid 30's (depending on track conditions) and they were not rolling over. With the lower pressures, you can start to use the big shoulders on these tires to combat the heavy car.

I'm a PCA instructor and this is the technique that I teach my students. I get more emails from them about how effective finding the sweet spot for tires using this technique is.

 

Bigtickets - another (ex-) PCA instructor here (UCR, Zone 1). I'll have to try that next time I'm out as I do recall that Toyo themselves indicated that the R888s like 2-3 psi less than the RA1s, which were my usual tires of choice on the 951 Cup and the E30 & E36 M3 track toys I had before. Mind you, all three of them were properly dialed in, gutted and purpose-built track toys weighing less than 2,600 lbs, so I found that on the street C63 I was rolling over the front R888s too much at anything less than 42-43 psi hot - but in all fairness that may have been before I readjusted my driving style to moving as much of the weight to the back as early as I could. Thanks for the sugggestion - will definitley try that next time I'm out (and now I can do it in August after the cooling package gets put on tomorrow - last time I did a track day in late July at 33 C ambient, the oil was starting to overheat after two laps no matter how gentle I was trying to be so I gave up on the Benz early on in the day and an hour and half later came back with my old 928GT. It doesn't have anywhere near the power of the C63, but at least I could drive it at 8/10ths instead of doing cool-down laps).

Cheers,
Doug


P.S. Seeing as this tread is more or less along the same lines as the other "negative camber" one here (https://mbworld.org/forums/c63-amg-w...rack-cars.html), I am just cross-posting the link for posterity as there's related information on the subject in both if someone else decides to have a read at a later date.

 

Jc63 & zcct - seeing as you'll be running them at the track - in other words, (1) high speeds, (2) lower pressures and (3) very high lateral loads, I'd err on the side of caution and go with the Toyo R888s in the 245 (93Y) size. The BFG R1s may be great for a Lotus, Miata or S2000 but I would think them dangerous on a C63. A front blowout is the last thing you'd want when entering a 160 km/h corner. Stickiest tires I've ever run were Hoosier R6s (I've never run the BFG R1s), but that was on a purpose-built 2,300 lb track cars (the tires have mid-80s load ratings), not a 3,900 lb C63. The Hoosiers also come in sizes that will mount on the C63 rims, but I would strongly discourage you from using them.

Besides - if you're over-driving the car, there's much more gain to be had by getting the tire pressures right and modifying your driving style as opposed to moving to better equipment. In other words, the limiting factor is that you're not extracting all of the available performance out of the equipment that you already have, not the equipment itself. In identical cars and on the same track, really good drivers can lap on street tires as fast as I can on R-comps, and I've been doing this on and off for 13 years. We're talking a 2-3 second a lap difference here on a ~1:40 lap, which is huge. While I have no racing expreience, on a familar track in a familiar car I can lap consistently (< 1 second difference lap to lap) all day long driving at 8/10ths - in other words, giving myself a little bit of room for error, if I hit an oil patch or a large chunk of rubber mid-corner. If I push to 9/10ths I might go another second a lap faster, but then occasionally I make a mistake and have to wrestle the car back under control, losing several seconds in the process. At 10/10ths - driving on the limit - when I get it right I might gain yet another second, and while I have pushed it at 10/10ths in the past and might still do it for a single lap now and then, the consequences of losing it are dire as you usually end up in the wall or run-off area if you're lucky seeing as you're on the edge and have absolutley no room for error (which I have also done numerous times, the worst one at the expense of writing off my first M3). Now, my 8/10ths may be only 6/10ths for a better driver, so even with the stickier R-comp tires I am lapping at the same rate (s)he is on street tires driving at his/her 8/10ths. And, as I said, while the R-comps are worth 2-3 seconds a lap over good street tires, getting the tire pressures right and adjusting your driving style is easily worth 5-6 seconds a lap, with the added benefit of you not destroying the tires in the process after a single session.

Bottom line is - forget about the guy in the CTS-V, get your tire pressures right, don't over-drive and wrestle but rather feel and gently and smoothly balance and guide the car, and chances are you'll gain a lot more than by going with more negative camber or even sticker and less forgiving tires. You'll then realize that your knuckles are no longer white, your heartbeat is down to 120 from 150 bpm, and there is this moving obstacle on the track in the form of a CTS-V that you repeatedly have to drive around when he signals you to pass.

 

I'm really puzzled about tire pressures.

- The door sticker on my '12 coupe recommends cold pressures of 42F/46R for high load and track use generates hot pressures of +6 to +8 psi, putting me in the neighborhood of 50#.

- Over-pressured tires would be hottest near the center and cooler on the edges. I'm seeing a center temp that is, as expected, lower than the outside and higher than the inside.

- My prior experience is mostly autocross where the tires don't have time to get so hot. SOP is to bump pressures up about 5# over the street pressures in order not to roll the edges, also suggesting a driving pressure in the neighborhood of 50.

- Load rating doesn't change with pressure once above about 43#, but load rating declines linearly as pressure is reduced below 42#.



I'm hearing from all corners that 50 is way too high for these tires. It just feels WRONG to drive to the track on street pressures and then let air out into the thirties in order to get more performance out of the tires. Since I seem to be the only one with this perception, I must be missing something. Can someone help me with the logic here?

 

zcct - while track tires have to deal with higher lateral loads and generally flex more than street rubber due to the lower pressures, they are constructed differently and do not need to protect your rim from pothole damage, be able to eliminate water at the same rate as a street tire or be perfectly safe at both 40F in the wet and a scorching 100F dry environment without you having to adjust the pressures, so what the nominal "all-around all-weather all-temperature street driving" tire pressure recommendations are on the fuel filler door has little to do with what you'd run on a dry track without raised or sunk manhole covers.


At autocross events you're not going to get them anywhere near the speeds that you would at a track and thus they won't heat up nearly as much by themselves while you repeatedly exceed 140 mph, so you need to start with a much higher pressure to begin with especially on a heavier car. At a road track on the other hand, you are setting the pressures for that particular track and those particular conditions on that particular day, and the trick (especially with R-comps) is to find the sweet spot at which they give you the best grip without you rolling them over too much. If you're driving in the wet, you need to add 8-10 psi from your baseline and have the full 6/32s of tread just to eliminate the water. If you're driving on a fast, sweeping course like Mosport on a dry and sunny day, you may need to drop the pressures by an extra 4 psi from the baseline to get them at their ideal temperature and grip levels after they warm up. If you're then also going to drive on the same tires at legal speeds on public roads on the way back home (so on R-somps well below the temperatures at which they're made to work), you need to add pressure to bring them back up and drive very carefully even in the dry as R-comps have about as much grip at those temperatures as a bucket of wet eels. In other words, the recommened pressures for street tires are realy for the "jack of all trades - master of none" tires and scenario, whereas your R-comps are the most brilliant and best single-puprose tools but only perform well within a very small window, which is different for any set of specific circumstances.

 

Thanks Diabolis - good explanation.

For those of us not yet equipped with spare wheels and R-comps, what would y'all suggest doing with pressures when running a street tire like the MPSS? Does going down below MBZ street pressures make sense?

 

Diabolis nice tech write up and cheers to UCR Zone 1!

zcct, have you done any road course driving before? What track experience do you have? Also, what are your expectations? These factors will greatly affect how you deal with your tires and overall set up as well as your driving style. If you have a hundred track days under your belt, you will be able to feel the difference with a single psi move either direction. If you are just getting started, you will want to worry more about traffic and your driving line first. Just get it around the track safely and concentrate on whats going on around you. As I'm sure Diabolis will back me up, your instructor should be a good source of info to set your car baseline with you if you are new so that you can concentrate on the items I mentioned earlier, ie getting safely around the track and learning the line. Once you've got some sessions under your belt and you are running consistently, THEN start to work things like tire pressures and set ups more heavily into your routine. A good way to look at it is to remember that at first, you as the driver, are the limiting factor. The car will do much more than you are initially capable of being able to make it do. As your skill set progresses, then the car begins to become the limiting factor. At that point you will start to realize the subtleties of the car and the way it responds to the way it's set up and you'll begin to make a tweak here and a tweak there to get it dialed in. About the same time you will start to realize that the way you drive the car also has a huge affect on how things come together on the track. Your setup and your driving style will start to compliment each other and at that point you are starting down the pathway to track zen!

 

Thanks for the sermon, Rev Bigtickets. :-)

While I'm not as experienced as the PCA instructors on here, I've been autocrossing for decades. I've only starting tracking the car recently but I've got several hundreds laps under my belt. At least at this particular track, I know the line. My last session was with a new Z06 and a GT3 and I'm running right with them. I don't know whether that's more a reflection on their driving skills than my expertise, and I know that I have much to learn, but I'm not a complete newbie. So forgive me for wanting to better understand tire pressures and track setup. Its the engineer in me and I can't help it. If you have useful info to share, I'd be most grateful.

 

zcct - at the track, yes. Your tire pressures will likely go up about 6-8 psi instead of 3-4 on the street. On a dry track you'll get the most grip when your contact patch is the largest, which is at lower pressures - so the "chalk mark wear indicator" is your best friend. At the AMG DA events I seem to recall that we were running the OEM 19" 235 & 255 Continentals on the 507s around 40 psi F and 38 psi R hot. That probably means that you want to let them out to about 33-34 psi cold F & R and start from there (I assume you've got the TPMS sensors so you can see what the tire pressures are in real time). Don't push while they're cold, give them a full 4 or 5 laps to properly warm up instead of just 2 or 3 as otherwise the thread portion of the tire gets up to temperature and start to stick but the tire carcass rubber is still cold and hard, and you end up chunking the tires.

The recommended cold pressures on the fuel door take into account the fact that you may be driving the car with four passengers in it at ~40 km/h in December at near freezing temperatures when the tires will never warm up and the ambient temperature at the shop or in your garage where they were checked may have been 24 C so you will actually lose 4 psi from what they were set at. As a general rule of thumb, slightly over-inflated tires are safer than under-inflated tires as they are less likely to blow out, so if you are going to err, err on the high side. Maybe only let them out to 36 psi cold to begin with (in which case they likely won't go over 44 hot), drive your session and on your cool-down lap check the readings. On the heavier cars like the C63 you don't want your hot pressures to dip much below 40 psi, but running them at, say, 38F and 36R even if that means starting with cold pressures of 30 psi is OK for as long as you don't do 280 km/h on your first three laps. I suspect that at anythign below 38 psi or so you'll be rolling over the sidewalls on the fronts a fair bit, so I think you'll find the sweet spot on the PSS somewhere around 40 psi.

 

zcct - to Bigtickets defense, I was aware that you've done a fair bit of auto-x and some track days before from your earlier posts in different threads, but that particular bit of information was not stated here and is not apparent. I am sure he didn't mean to be condescending, but without prior knowledge of one's experience level my primary concern would also be about your and everyone else's safety, by making sure that you are completely comfortable with the basics before moving onto extracting more performance out of the car. In every single situation where I didn't know what the driver skill level is, I too had to assume that they were beginners until they demonstrated otherwise seeing as our primary responsibility is looking after everyone's safety, and the consequences can be very grave indeed if one becomes distracted with the details before the basics become second nature. In other words, you don't get into heel and toe shifting and going faster before you're 99.9% certain that the driver is not going to miss braking points and go in too fast because (s)he is now concentrating on something else but is not yet ready to take on the additional workload becuase they are still at the stage where they need to concentrate on slowing down and turning where they should. He is just being responsible and wants to make sure that you stay safe and go back home in one piece. At least that was my take on it.

Cheers,
Doug