I am running Dunlop Direzza ZII tires for autox and I am wondering how much traction I am sacrificing compared to a new tire. I am right at the wear markers or just at 1 or 2mm above the wear markers. In the dry on rough concrete would there be any noticeable difference in grip compared to a new tire? This is old airport concrete.

 

My understanding is you should get better grip from almost worn out tires like that. That is if the tires haven't been heat cycled to death. I'm running ours almost worn out like that.

 

For autocross you need at least some tread left and not corded.

In the dry you will be fine. If the tires are very old the rubber gets hard and are less grippy.

If your tires are about 1-2 years old you are OK.

If it rains you will be in trouble, whether on the street or during competition.

 

We ran our first set of Z2s this year till around 160 runs and got rid of them thinking "surely they've fallen off by now". The new set didn't seem to be a huge difference in grip. So basically they last forever.

What size tire do you run?

 

I am running 205/45/17. I am thinking of going to 215/45/17 next season. They have about 90 runs on them and two tires are just over the wear markers, two tires are a little more tread than that. I rotate them every event and do not drive on them between events. The surface we run on is very coarse old concrete. Very high grip and I am sure it eats the tires.

 

Yeah that surface is more abrasive than the asphalt we normally run on. We'd see close to 200 runs if you ran a tire from full tread to the wear indicators. We also run a 235 though so maybe that makes a difference. We used to run a 215/45/17 and had no issues. We also do the same thing with not driving on them between events.

 

In general I favor using a tire size with less sidewall not more.

215/40-17 over the tall 215/45-17. At least 205/45-17 is not tall (higher gearing).

Dunlop Direzza ZII
215/40-17 $152 each (special at tirerack.com)
Fits rims 7-8.5" wide, 22 lbs, 23.8" tire diameter
Costs less than 205/45-17 and weighs 1 lb more. Wider tread and stiffer sidewall.

What class are you in? Stock? If so what are you doing for tires with the changes in Stock coming?

If you are using Extreme Summer tires you have to look for which tire to use plus the size that will work for you.

Your event surface is extra hard on tires, not much you can do about that.

If you weren't in a Stock class you can upgrade to adjustable camber plates for more front negative camber. This will allow you to make better use of the front tires and reduce understeer.

As for comparing new tire to worn tread race tire, it's been said that the optimal tread depth for performance driving is about 4 to 6/32", new tires come with 8+/32" tread depth which may allow less than optimal traction and more risk of overheating the tread blocks.

see
http://www.tirerack.com/tires/tirete...jsp?techid=67&

Best traction and performance in a DOT street tire is one that is slightly but evenly worn. This reduces tire weight and allows for more grip in the dry.

 

In regards to going with a 215/40/17 Dunlop Z2 vs 205/45 vs 215/45...

The 215/40 have a load rating of 83w
The 215/45 have a load rating of 87w
The 205/45 have a load rating of 84w

Does it matter if I go with the 215/40 that has a lower load rating than what OEM suggests?

 

The general rule is for street use you want a tire that is at or above OEM load rating which is 84 to 87 for the MINI.

83 is lower than OEM but close enough that it should not be a practical problem for you.

If you carry four adults and load up your MINI for long trips regularly you might want tires with a load rating closer to 87.

Of note, if you search for tires in 215/40-17 you will see that some are load rated 87 due to their XL (extra load) construction. The Extreme Summer tires in that size are load rated 83.

 

Wouldn't autocross seem to be better with a higher load rating? In effect they are being loaded majorly with performance driving...

 

Load ratings generally apply to cars for street use.
http://www.tirerack.com/tires/tirete....jsp?techid=35

When you are autocrossing you drive alone so a tire that has less load rating is not a problem. At most there could be one passenger. Still not a problem.

In autocrossing you use tires that can fit the wheels/car without rubbing and often have tire diameters that are smaller than OEM for lowered gearing. The resulting tire will often have a load rating less than OEM.

Load rating is not meant to measure loads as you actively drive on the track or autocross. Autocrossing only requires power similar to what you would do on the street or highway, it's not drag racing.

Load rating has to do with a fully loaded car operating on the street under normal use and it's capability of the tires to handle that load. The higher the tire's load rating the better it can handle more weight and still be safe.