Wobble64

Hey, I resent that - doofusing me just 'cause I am an engineer..... :-)

But yeah - in god we trust, everybody else please bring data!

zcct04

Weight rating question: The R888s in stock sizes are rated 1,356 front (91Y SL) and 1,477 rear (94Y RF) per the Toyo website. The NT01s are not available in stock sizes but the 245 front is rated 1,433 and the 265 rear is rated 1,819 per the Nitto web site. What is the OEM rating for our cars?

And what is the SL and RF suffix about on the Toyos?

Wobble64

I was never able to find an outright weight rating requirement for our cars. However, lower cross-section tires have lower weight rating - so those delivered with 19 inch wheels have tires with a lower weight rating than those that came with 18 inch. My 507 came with a 1365 lb (91 index) weight rating on the Contis it came with.

So as long as a tire has at least 91/1356 lbs, I would not think twice about it. If a tire has a lower rating, then it is something to keep an eye on. I would not stray too far below.

The Toyo R888 in 235/35/19 only has an 87 rating (1201 lbs).

Diabolis

Wobble - there's no way that any Benz - and especially a 507 that weighs 3900 lbs dry and reaches speeds in excess of 280 km/h - came with a 91 load index tire from the factory. Even if the "equivalent" streeet tire (same make and model as what you saw on your Benz) had a load rating of 91, the OEM tires likely had an "MO" suffix - Mercedes OEM - that incorporates additional plies and a much stronger tire carcass than the "regular" model of the same tire.

Due to the considerably lower tire pressures and much higher sustained and/or repeated speds and loads that a tire is subjected to in a track environment, I would respectfully suggest that the LOWEST load rating for a tire on a ~4000 lb, ~500 hp vehicle should be around the 650 kg mark, or 93. The higher the better.

Diabolis

Hard to say what the OEM rating is as the OEM tires (Contis or Yokos - whichever came on your car) were specifically manufactured to Mercedes' own specs, using additional reinforcing plies. They are all "XL" rated indicating the presence of additional belts, but how much the "MO" rating adds to the tire's load rating and thus ability to withstand sustained high speeds and cornering loads is something only the engineeers at Daimler (and possibly Continental and Yokohama) know.


SL means Standard Load - you don't want these anywhere near your C63. RF is Reinforced - same as XL.

zcct04

Diabolis - If I've copied the right numbers from the Toyo website, the R888 in 18" stock size front tire (a 91Y SL) is NOT a good choice? I'm a little surprised - I'd heard that the R888 was the track tire of choice for the C63.

Further check - upsizing widths on the R888 provides higher load ratings: 245/40ZR18 and 265/35ZR18 are both 93Y SL with a load rating of 1,433.

However, despite the higher load ratings, both are still a SL tire. Do you feel that, even with the higher load ratings, the SL should be avoided?

Diabolis

Zcct - correct, I ran the R888s in 245/40ZR18 F & 265/35ZR18 R and both are 93Y. A 91Y would be borderline acceptable on slower tracks, but I don't know that I'd want to spend much time pushing a C63 well in excess of 220 km/h aropudn a fast, flowing track on them. You can actually get a different R888 rear in the same 265/35ZR18 size (different part #) with a 97Y load rating, but I'd probably only give those more thought on a 911 where both the weight of the car and the driving style places greater demands on the rears, as IMHO on our C63s the fronts are the bigger problem.

You might also want to look into the new Pirelli Trofeo Rs - in an 18" diameter they make them in 235/40ZR18 (95Y), 245/40ZR18 (97Y), 265/35ZR18 (93Y) and 265/40ZR18 (101Y) sizes. I tried a set of fronts only (jumped the curb with the L/F and got a bulge in the sidewal, and the trackside tire shop had those in stock so I got a set of fronts to try out for the rest of the day). They were quite sticky but the front sidewall rolled way more than it did on my R888s, although in hindsight that was on the stock 8" wide rim which looked much too narrow and is not even within the approved range for the 245F Trofeo R). They were also almost double the price of the R888s, but then again I get the R888s at a huge discount so I am not sure what the comparable street cost would be.

I have two Enkei RPF1 18x9.0 ET35 rims on order with my wheel & tire supplier that I want to run on the front for track use, and will try the 245/40ZR18 Trofeo Rs again and see how well they hold up. Dry grip was great - the only issue was that the L/F rolled over way too much, but mounted on a rim that was 1" too narrow so I do want to give them another shot.


P.S. My very first set of R888s for the C63s were the 235 width, 91Y fronts. They didn't blow up on me, but I have to admit that I was somewhat uncomfortable and after one trackday gave them to a friend who ran them on his 996 GT3 in the same run group.

zcct04

Looks like the retailers agree. I just checked tire recommendations for C63 at Tire Rack & Discount Tire. Neither offers a recommendation for a competition tire. In 18" street tires, Tire Rack shows 31 and Discount shows 16. With the exception of one runflat option at Discount, every other tire set is XL rated. The fronts are all 95Y (1,521# load rated) and the rears are all 94Y (1,477#).

Interestingly, the Toyo website does offer the R888 when searching for C63 tires. Their recommendations are wider than stock but are XL rated: 255/35 ZR18 (94Y) and 275/35 ZR18 (99Y). Has anyone tried a 275 rear R888 for clearance?

Diabolis

I haven't, but in theory it *could* work with a 9.5" wide, ~ET50 rim. The section width of a 275/35 ZR18 R888 mounted on a 9.5" rim is 11" even, or 280mm. The 275/30ZR19 PSS on a 9.5" rim has a section width of 278mm, and I am sure I can find the required 2 mm somewhere (go to ET51 or ET52 for example). The right wheel offset would be absolutely critical though.

Wobble64

Tirerack lists the tire my car came with (235/35/19 Conti 5P) as 91Y rated specifically for the MO (Mercedes version). I think that is where I got the idea the Conti is 91 rated. Whether that is really true, I do not know.....

Another great advantage of the BS body conversion, btw. I can go way wider in the front. My PSC2 in 255/35/19 has a 96 load rating, for example. My rears (305/30/19) a 102.

jc63amg

[QUOTE=zcct04;6501064]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?[/QUOTE

I have just received an offer for a set of Hankook Ventus Z214 compound C51,
fronts 245/40ZR18 - 1433 Lbs. 44 Psi
Rears 275/35ZR18 - 1521 lbs. 44 psi
The rears are ok but the fronts are short for 88 lbs.
Will that be safe???
It's a really good offer, they are new and for usd800.

Mazspeed

The Toyo R888 is not a good tire for our cars. We have had quite a few people in our track group over the years not have any sucess with the tire on cars over 3200lbs. I would not recommend them for any heavy car. Plus they are loud and don't heat cycle well.
I am running the Trofeo R's 265-19 and 245-19 and yave had no issues were the rolling sidewalls at Laguna Seca. What pressures were you running and what were the temps?

Wobble64

I will be at NCM next weekend with Trofeo Rs (265/30/19 in front and 295/30/19 in rear. I would appreciate if you could share the pressures that work for you - so I have a starting point. I was thinking about starting with about 32 PSI, as in my previous experience I saw the pressure go up 8 to 10 PSI during a session.


Is that what you run or do you run different pressures??

arrowskartax9

Any one tried the Falken RT615K??

zcct04

Falken RT615K looks like it has a high enough rating for us (97W and XL with 1609 max load in 245/40R18 and 265/35R18 sizes). Note that treadwear is 200, vs 60 on the Trofeo R and 100 of the Toyo R888, so its performance on the track will probably not be as good.

Reviews I've found show it to be better than the RT615 (no 'K' suffix) that it replaces (no ****!), but no comparisons yet to anything else.

Diabolis

Killing the Trofeo Rs was almost certainly 100% my fault as I had 245/40-18s mounted on the OEM 8" front rims and the sidewalls kept rolling under way too much (I had to make a decision trackside, without the ability to check approved rim widths or anything of the sort). This year I am getting a set of 19s and am mounting them on my old 8.5" & 9.5" forged wheels, so I expect the sidewall wear to be somewhat different. Will post updates once track season starts.

Mazspeed

No worries, I like to kill tires as well, but may I suggest a 8.5 front and a 9.5 rear rim. The reason being is that the outer lining will be better for the issues you might be having. Also front and rear pressures will need to be adjusted for that time front and rear. Hot tires will expand a little more and in general these tires don't need to be over inflated according to Pirelli. But all tires fold, but if you're scraping the wheel, I would go .5 wider on the rim and that should correct the issue.

Wobble64

Mazspeed, what pressure do you run your Trofeo Rs on the track?

Diabolis

That's exactly the plan, plus I'm moving up to 19s in 245 & 265 on 8.5" & 9.5" F & R respectively.

BLKROKT

I have a bit of a quandary on my hands. Just got my car back from having some suspension and trans work, and I look to have enough clearance now for 285's on my 19x10" rears. Want to go Michelin Pilot Sport Cup 2's, but I only see them in 285/35-19 (103Y), and that's causing the overall diameter to be more than I want. UNLESS I go with the "run flat" ZP version, which comes in 285/30-19 (94Y).

Question for the track tire gurus. Is there any difference in handling between the regular and run-flat versions? Compound and everything else is the same as far as I can tell. My guess is that the sidewalls will be a bit stiffer, which I don't mind. The only thing that has me a little worried is the weight rating for the ZP is lower than I would like.

Wobble64

Jim, 94 weight rating would be fine, but don't the run flats have other stuff in it to help them run without pressure? Aren't they much heavier? Also more expensive I guess.
If you have to go to 35 cross section, your diameter would be way off.

BLKROKT

Yes, 29lbs for the ZP versus 27lbs for the 'regular'. My 275 PSS's are 27lbs.

I'm not that bothered by the weight. The overall diameter is more important at this point. 25.8" vs 26.9"

Wobble64

That weight difference is less than I expected. But if you could fit a 295/30/19.....

BLKROKT

295 is not going to happen. On the 275's I have 0.5" clearance on the inside to the suspension, and about the same on the outside. 285 is where I max out, and even then will have to be creative. May just not be worth it....

Mazspeed

It varies due to outside temps and how many laps I am doing or plan to do. Having said that, on a 78 degree day I run F32 and R34 pressures on cold tires, hot tires F35 R36.5 seems to be the sweet spot for me. This seems to a bunch of us to be the best 19 Inch tire to run on heavier cars. You get a good amount of heat cycles out of them, 30 or so. After that they fall off, but by that time you have no tread left anyways. Let me know what you think of them.
By the way, when you first pick up a tire you will be surprised how light is it.