Petevb

So I scrubbed in a set of Sport Maxx Race yesterday and got to try them cool for the first time today on the street. Basically what I'd expected: at 60 to 65 F ambient and cold they are very slippy on dry pavement. It's a very progressive breakaway, not snappy, so very catch-able. However you must be very aware that you're operating with what feels like ~2/3 the grip of a PSS. By low 70s F ambient and with some heat in the tire from regular freeway driving the grip has already picked up dramatically. At that point they grip almost as well as a Pilot Super Sport under similar conditions.

More to follow, but it seems like the crossover point in regular driving will be in the 80s F unless you're pushing the tires and building up heat. I probably won't get a chance to do that until this weekend.

stevecolletti

Thanks for the update.

Manifold

I've also ordered a set of Sport Maxx Race for the Cayman R and will hopefully be trying them on track soon. The standard size is 235/35 and 265/35, but the 235/35 are on a long back order, so I got 245/35 front instead. Anyone see any issues with that? It's only a 1% increase in overall diameter. Will shift the car a little bit towards oversteer (or less understeer), but it's still short of a square setup, so seems it should be OK.

Petevb

The diameter difference may slightly confuse ABS (and traction control, but I assume you have it off) by triggering them differently than they are programmed for. Should be within normal limits, but if you find ice mode provoked more often the diameter difference would probably be the cause.

markow

interesting thoughts. but after all, by german law porsche has to produce winter wheels for the GT3. if ABS and traction control (i turn it off very rarely) are confused by summer tyres with slightly different diameters than things would go much worse with winter tyres, no?
pretty worrisome your report on the dunlop maxx race, even in the dry. did you check them out in the wet already?

Petevb

You'll note that the recommended winter tires generally have exactly the same difference in diameter as the summer tires (ie .7" OD smaller in the front on the cayman). Obviously there is some leeway built in, tough to know how much. My theory is that the ABS is sometimes confused into ice mode even on the standard tires, so anything that might confuse it more is less than ideal. With such a small difference it'll probably be fine, but ABS works by sensing the difference in rotation speed front to rear, and you're changing that difference by a non-trivial amount, almost 40% less just going from 235 to 245.

No wet yet, but what I expect is that the compound itself will be very good, but temperature will again be the problem. Water on the road cools tires very effectively, and it's rarely hot when it rains (around here, anyway). So while there looks like enough void area and I bet the rubber compound it good, if the tire is cooled to 60 degrees F there is no way it's going to grip well. On a circuit where you can get some heat into the tires despite the rain I bet they will be very good, but I'm purely making an educated guess based on other dunlop compounds (Direzza ZII, etc).

markow

if i understand correctly, the dunlop maxx race on the GT3 are precisely the same dimensions as the PZeros on the C4S, although they sit on rims of slightly different
width,
i.e

front GT3: 245/35 ZR 20 on 9J x 20 ET 55
rear GT3: 305/30 ZR 20 on 12J x 20 ET 47

and

front C4S: 245/35 ZR 20 on 8.5 x 20 ET 51
rear C4S: 305/30 ZR 20 on 11J x 20 ET 52

please explain, this is really important to me.
thanks

Manifold

I'm not understanding how you get the 40% number.

Also, FWIW, I had no issues using R888s (R-comps) on the road in dry or wet conditions, temps as low as 35 F, though I never had occassion to use them in the wet when the tread was worn (past the wear bars).

Petevb

So if the tire sizes are nominally the same you'll be fine, no problem.

As for the 40% number, I was responding to:
OD and revs per mile from tire rack are listed as:

235/35: 25.5" 820
245/35: 25.8" 810
265/35: 26.3" 793

So the software is expecting the front to be turning 820/793= 3.4% faster than the rear with everything normal and no slip. With the 245s the fronts will only be turning 2.1% faster than the rear. 3.4%/ 2.1% = 61% of the difference in wheel RPM the software expects, or 39% less.

Now the tires slip a lot before they let go- max grip might be found with in the range of 6% longitudinal slip depending on the tire, and traction control might be programmed to cut in at for example 4% (I'm pulling this number out of thin air, I don't know what it's actually set to). Let's assume it does end the party at what it thinks is 4% slip. You're tricking it with your different tire diameters, so when it thinks it's at 4% slip it's really only at 2.7% slip. So it ends the party early and cuts in sooner. Same in reverse for ABS.

That's the theory, anyway. Whether you'd even notice or not depends on the actual numbers, the software, and how sensitive you are.

markow

ok, thanks. i was already contemplating to change my GT3 allocation over to a ***** C4S ---)))) or another fiat 458---)))

Manifold

I can't say any of this is wrong, but the difference in OD amounts to about 5/32" extra tire radius, compared to 8/32" normal tread depth or 4/32" shaved tread depth. Since it's within the range of the tread depth, I'm hoping it'll be OK.

Petevb

I think you'll be fine, just something to keep in mind if ABS starts acting screwy.

Manifold

Yup, few things worse than ice pedal at over 130 mph.

stevecolletti

ABS will handle that difference easily... the variance you are talking about is close to the difference in full tread versus wear bar. I know of several people that have run 245s on the front with no issue.

Petevb

I've had the Sport Maxx Race tires on my stock 1M in the stock 19" sizes for nearly a week now, street use and one autocross, I took TTOD at that event, but so far things are decidedly mixed. I'm comparing primarily to the Pilot Super Sport, which I just took off, and the Hankook R-S3 which I have on another set of wheels. Much of this review won't be applicable for GT3s, as I'm sure the car will be set up to match the tires.

Grip vs temperature on the street: The SMRs do need some heat to work, similar to the R-S3s. At 60 degrees in the morning you'll be able to light them up all day long. Breakaway isn't as progressive as the Hankooks in these conditions, but they are catch-able. Simply driving on the highway at the speed limit does get a fair bit of heat into the tire, however (about 25-30 degrees) and grip improves quickly. If it's above ~70 degrees out and you get some heat into the tire grip exceeds the PSS or Hankook, and the difference grows significantly with temperature. When warmed and TC off the the SMRs don't spin up the rear even in 1st gear with significant steering lock dialed in- very impressive for the 1M, which doesn't put power down well.

Street noise, vibration, harshness: I'm generally not sensitive to road noise or ride, but the Maxx Race ride better than I would have expected. They seem slightly harsher over cracks, etc than the PSS, but reasonably close when warm (not so much when they are cold). There is significant road noise transmitted on certain pavement, much more than a PSS, but on some roads they are quite.

So far, so good- all of the above was about as I'd expected. What I didn't expect, however:

The SMRs need much more camber to work than the BMW 1M has (or is capable of) stock. My stock car clearly doesn't have enough camber to work them correctly, and this causes big problems.

At the autocross yesterday things started well- with temperatures in the 90s, first run was enough to bring the tires up to temp, and I was on the pace immediately. Unfortunately the car was under-steering somewhat almost immediately, very different to the PSS or Hankooks which I tend to drive very sideways. With more runs the understeer increased until it was very bad- tire temps showed the outside fronts badly overheating, and towards the end of the run (42 second course) the push was debilitating and costing major time.

In the afternoon I changed strategy- I jacked the tire pressure around and I borrowed some water and sprayed the fronts down between every run. This helped- it wasn't enough to eliminate the understeer, but reduced it to the point that I was able to manage it and take TTOD.

Because the car setup was so compromised I'm not sure I can draw great conclusions yet. The tires seem less progressive than the Hankooks, doesn't like to be drifted as much, but significantly stickier. Soft sidewalls, turn-in is maybe similar to the PSS, so less sharp than a PS2. Narrower operating temperature range than I'd expected, and they get greasy when they overheat. Sticky as hell when temps are correct, but they need camber to work.

Bottom line: it's sticky but a bit finicky. I feel fine driving it on the street during the summer, but you absolutely do need to let the tire warm up before you push. It'd be great if temps are above 70, you let them warm and you're pushing. 60s and wet would be no fun (I assume, haven't seen rain yet). I do wish they liked to slide around more like some R compounds.