froggy47

I need to drive to the event (Chuckwalla) about 200 miles each way so my a6's & 710's stay home & I don't want to hassle with renting a trailer.

Thinking about a set of XS on stock rims (about $900)

285/40 fronts and 315/30 rears

They also have a 275 and a 295 front.

Two questions

tc/ah ok for the trip?

Diameters are 26" f and 25.5" r

275 is 25.7" and 295 is 25.1"

I have read that there is a 5% tolerance in wheel speed for tc/ah. I like it on for street/off for track (unless it's pouring)

These all appear to be within 5%, yes?

2nd, bigger question is the tread depth is 8/32 on all these. I wonder if I will tear them up, never been to this (new) track.

I could get them shaved but hate to throw away good rubber.

I'd like to have them in good enough shape to street drive them after.

Tread wear is 180

Has anyone done a track day on full tread XS tires?

How did they hold up.

My buddy has autox'd on them full depth & they look OK.

Thanks, NO speculation, just if you have been there done that.

Jason

They'll probably get greasy at the end of the session, but that'd be fun to me. I'd do it.

ipuig

I have a set of Kuhmo XS that I use for AX on stock Z06 wheels, 275/40 fronts 315/30 rears. The grip is very good and slip is very gradual and predictable. The differential you speak of to keep from having AH/TC problems is not 5%, it's .5" in tire diameter from front to rear (rear should be taller).
With my set up, the outside diameter on both tires is almost identical, TC will activate at highway speeds so I keep it off.

froggy47

Any way you can check on that? The stock oem F1SC tires were .7 diameter bigger in the back.

From Tire Rack specs:

265x40x17 = 25.4"

295x35x18 = 26.1"

5% gives a bigger differential allowance of course. In the past when I have looked into this formula it was always referenced as a % difference, but I have never seen an actual GM specification on it. I'll check my FSM an see what, if anything is there.

Couldn't find anything in the FSM



Maybe it's because taller in the front will always give the tc/ah a problem?

Then I would have to go with the 295 f, no problem.

ipuig

A minimum .5" difference in diameter is the number I've seen talked about on the forum for several years. I do not know if the system can tolerate less. I know that my set up causes the TC system to activate at highway speeds (65 - 70 MPH) so I turn it off.

Greywolfe

You could also try Nitto 555RII's. 275/305 combo on stock zo6 wheels. You can drive them back and forth to track. That is what I'm going to do next (currently on street tires).

geerookie

No codes will be set as long as the EBTCM doesn't see a wheel speed variation of more than 14 Km/h (9 mph) for 2.5 seconds. You would have to have a very large wheel size difference to create this situation. It doesn't matter if the front is bigger or smaller than the back, just the difference.
Obviously you need to be careful and not get to close to the 9mph limit as when you have normal wheel speed differences in a corner you would set the code falsely.
When the codes are set it disables ABS/TCS/AH.
They will automatically clear after 50 ignition cycles with no more codes set. ABS/TCS/AH will re-enable after the condition clears.

Just as an FYI, ABS/TCS?AH are all handled by the EBTCM. There are many codes from the wheel sensors, steering sensor, yaw sensor, lateral acceleration sensor that will disable TCS/AH but not effect ABS. If your wheel speed sensors are working properly I think there are only 4 codes that will disable everything. C1225, C1226, C1227, C1228. These are more than a 9mph difference for 2.5 secs from any sensor.
This is all for a C5......C6's are a whole different story!

RDnomorecobra

interesting ... I run square 295/35's on the street and 315/30's or 305/35's on the track, all on stock 18x10.5" rears. I've never had this problem. '03 z06.

ipuig

The Kuhmo XS 275/40 is .2" taller than the 315/30, perhaps that has something to do with it. I used the same wheel/tire combo on my coupe and the TC system would activate also at highway speeds.
The TC system never activated on either the coupe or the Z with the OEM size tires unless they was actual wheelspin so I do not think it's a malfuction.

slow ride

I ran the 555r2's last friday. Thay already had 2 sessions on them by the previous owner, but had great tread left and worked very well. Stock Z wheels with 275/40/17's and 305/35/18's. Drove to the track and back which is probably 500 miles total and they still are above the wear bars (only come 5/32 new).

froggy47

Can you (or some engineer) calculate what tire diameter/circumference/revolutions would result in that 9 mph difference?

froggy47

zcobra1

Agree- That is what I do- and they are a good compromise tire...and $100 less a set...

Rob31

Anyone have hard info on this tire . Id like to talk to a rep if I coud find one .
What pressure
What temp do they start to work ? working temps ?
Do they get greasy on a long run . I have only had a chance to do three lap sessions on a two mile road course . (or shorter )
274/40 /17 Kuhmo xs

trapp

I have used them for about 6-8 track days. No problems at all. I was doing hard 7-10 laps per session without any issues...they will eventually get greasy if they get to hot but I rarely got to that point......

68sixspeed

x4 to what the others said, they wear well, are not that expensive and are grip well.

Put a fresh set on my buddy's c5 this year, 4 track days of 100-120 miles on track each event, plus street miles (maybe 2k?) and I'd say he can get 2-3 more days out of them easy, maybe more.

c4cruiser

The Nitto website puts the 555RII in with their competition tires and recommends them for that type of use. I don't think I would want to make a 400 mile round trip on them.

Maybe the NT05 would be a better choice?

For the OP, I have run the earlier Kumho MX for track days and I had no problems with them. These tires took a couple laps to get heat built up in them and they provided great grip for my 87 with an autocross-only alignment. They provided good indication when they reached their limits and only felt greasy when I pushed too hard. I found that track surface temps played a part in grip so if the surface is really hot (130 and above), they will feel greasy.

I'll be getting a set of the XS tires for next season; the MX's I have are wore down to about 50% and from what I have read, the compounds used to make the tire grip are only on the upper 50-60% of the tread.

Dirty Howie

I ran the Kumho MX and the 555RII on my C5. The 555RII was awsome, I just kept those tires on for DD too.

Now on my C6Z I run the NTO5 for street and track. I think they are great for both. I have 6 track days and think I have another 6 to go


DH