I picked up a set of Dunlop's "new" SP Super Sport Race tires in 255/35x18's mounted on SSR Comp 8.5x18 wheels for track day events etc. from TireRack. Awesome service BTW. I procrastinated on my decision; finally called on a Tuesday, hoping to have tires/wheels by the coming Friday, and had tires from either Tirerack's Indian or Delware warehouse at my office in Denver ready to put on the car that Thursday. Great service.

I can't offer any real comparison to other "street/track" tire, since these are the first set I've had or used, but from various instructors comments on the cars handling etc., it sure appears like the tires are doing their job. They are a significant step up from running the stock rubber on the track, and actually weigh in at @ 5lbs less per wheel/tire combo than the stock OEM wheels with the Bridgestone RE040E 225/45x18 tire.

My issues/questions are:

1. Does anyone have any solid guidelines for picking setting tire pressures?

2. After running the set hard at one of our local tracks, which generally is run in a clockwise rotation, I find that I am getting a significant "wear" valley, particularly in/on the front left (drives) side tire, located @ 1 to 1.5" in from the outside edge of the tire. I.e. the outside shoulder is holding up, but the (most heavily loaded) tire is wearing a deep grove in the tread. Any thoughts on what's causing this, or how to cure? FWIW, the car was set up with a standard factory (no special "track" tweaks) alignment.

Informed thoughts are appreciated. Oh, FWIW, the December Issue of Sports Compact Car has a nice "R-Compund Tire" Guide, listing some of the various tire options for any one interested in making a step up to track specific rubber ~ you at least owe yourselfs a comparison ride :-)

Thanks

 

Do a Google for "chalking your tires" On a road course you would be adding air, the trick is how much. I would start out about 4 lbs OVER the street setting and see what the chalk / polish tells you.

 

Does this mean that you took it in to an alignment shop and just said "align it"? The factory tolerances for alignment have huge variances built in - you could have positive camber on one front wheel, and negative camber on the other, and it would still be within the standard factory alignment specs.

In other words - you need to decide exactly what you want to run for front toe, camber, and caster, and rear toe and camber, and have a shop set the exact numbers you want. Those can be within the factory tolerances, but getting an accurate alignment done will make a big difference.

Note, also, that the alignment settings change significantly with weight in the car. You should have the car ballasted with the weight you're typically running with when they do an alignment. If you're alone, then ballast your weight in the drivers seat (or just sit in the car while they do the alignment). I had to argue with an alignment shop about this, as they didn't think drivers weight would make any difference to alignment settings. Finally, I got them to set the car up on the rack, measure it, then I got in and they measured it again - they were amazed that the right side rear camber changed by almost 0.5 degrees!

Regards,
Gordon

 

With regard to your groove wearing into the left front tread, it may not be an alignment issue.

BFG had a similar problem with its BFG R1 track tires, aptly named the "groove of doom." R1's were discontinued about 4 years ago.

I believe the BFG's groove of doom was attributed in the end to tire construction. BFG intentionally mfr'd the R1's outer sidewall significantly stiffer than the inner sidewall, effectively building negative camber into the tire. Under sustained corner loads that caused the tread surface to bow outward and the tire tread would form that deep groove about 1 1/2" in from the shoulder. Low pressures made the problem more pronounced. I may still have some info on this at home and if so will get back to you.

Make sure you're not running too low pressure, which may aggravate the problem, and rotate the rears to the front before it gets too bad. Check with Tire Rack and Dunlop as to recommended track pressures for your specific tire and maybe post up in the track section of this forum to see what the guys there have heard. May also want to try the cornercarvers.com forums and see if anyone there is having the same probs with the new Dunlops.

Good luck. Sounds like you had big fun!

 

I'm familiar with tire "chalking" Sidewall rollover in my opinion, hasn't been an issue. I was / have been running the tires at @ 35 psi front and rear, so @ 3 psi over the factory recomended 32 psi for the stock 225/45x18's.

On my last track session at Heartland Park (kind of wish I'd done it sooner) I did increse the tire pressures in the front only from 35 psi cold to @ 38 & this seemed to firm up steering response quite a bit. Haven't been back since running the 38 psi front / 35 psi rear, but that's where I will start from next time out. What I'd like to find out though, is perhaps a more methodical, if not scientific way of going about determining the best tire pressure setting. I plan on getting a lazer "spot" tyre pyrometer for the next go round to try and chart temperature loads across the tire.

Ned M, thanks for the BFG R1 info. I'll call TireRack to see if they have any info on this vis-s-vis the Dunlop tire &/or a direct Dunlop rep or contact to look at the tire(s). The car has been a lot of fun at the track events, and gets a lot of positive comments from instructors as well as other participants, ... quite a few of which have been surprised by how well the Rx8 in basically stock form is hanging with their BMW, Porsches etc. Its a competative car, especially on tight tracks.

 

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I have done one track day so far with the RE040 tires and noticed the same wear area. The outside edge of the 2nd tread block from the outside is where I noticed the rubber getting vaporized. It looked like it was melting there. The edge of the tread block now looks like I trimmed it at a 45 degree angle. I am not worried about it at all as it is not deep into the tread. It is just noticibly more worn than the other tread blocks.

I had started a thread on alignment settings in the Racing forum to get feedback from people who track their cars. I suspected my issue stems from driving skill (or the lack of it) and alignment settings. I was getting some understeer at the track causing my front tires to heat up (maybe too much). I am sure I can control that more with better corner entry and exit. I came into corners too fast and tended to plow out of them. I also think I can get better rotation via a tweaked alignment.

Did you happen to measure tire pressure after time on the track to see where your pressures ended up? I inflated my tires to about 38psi and when I came off the track I had around 47psi.

 

I guess I should have, but I didn't get any tire pressure reading immediately after coming off the track.

FWIW, I put two track events (3 days) on the OEM Bridgestone RE040's before picking up the Dunlop tires. I did not have, or at least see the kind of inner wear you've mention or that I'm seeing on the Dunlops. The "melting" or "feathering" effect on the tire surfaces however is more pronounced with the softer compound in the Dunlop tire than it was with the 140 UTOG Bridgestones.

So maybe this thread ought to be over the "Racing" forum?

HTH

 

Found the old BFG newsletter regarding the groove of doom effect and the other aggravating factor they mentioned beside underinflation was not having the DOT race tires shaved. Tread depth on new DOT race tires is usually 6 or 7/32" and most mfr's normally recommend shaving new track tires to 4/32" if they're going to be used in dry conditions.

The 'groove' on my set of (unshaved) BFG R1's formed like the one Nabil describes on his RE040's, i.e. the edges of the tread blocks on either side of the outermost molded groove in the tire wore down very fast and widened and deepened the molded groove. BFG said the unshaved tread blocks distorting under load caused this and underinflation aggravated it. They did end up revising the belts under that area of the tire to try to help the problem.

I did not experience the grooving effect with unshaved Toyo RA-1's, FWIW.