shaving time with tires @ autox with an NC

[NCEC670CS]

I own a 2006 Mx5 Sport, i am looking to shave some time off my autox time while still staying in a stock class, my idea for rims/tires is a 16x8 42mm offset, wrapped in 215/40zr/16 Kumho V710's?? is that the best choice for autox tire for the money???

Here is my current suspension set up:

Front:
1.5 degrees Toe-out
1.5 degrees Negative camber L/R

Rear:
1.5 degrees Toe-In
2.0 degrees Negative camber L/R

I dont think the tire/rim combo will rub at all with the negative camber in the rear, but are those tires really gonna help my times, i have never driven on R compound tires before, so i am unsure of the differences it will make. If anyone can give me a hint on good tire pressures for the v710s with a similar set up that will be very helpful too.

[blizzardmx-5]

First of all... 16x8 is not legal for stock class...
If ur car came with 17x7, that's the only size u can use for stock class.
Second, how did u get ur front camber to -1.5? Max I could get was -0.9 and after I installed the Koni Shock... I can only get -0.7 on one side.

[Brian]

Are we talking stock class SCCA autocross here in the USA or perhaps some other definition of stock class elsewhere? Indeed, SCCA rules for stock class make you stay with stock width. Stock 17 inch wheels are 7 inches wide, stock 16 inch wheels are 6.5 inches wide. Under SCCA Stock class rules you can only move your offset 1/4 inch from factory (6.35mm).

[NCEC670CS]

I am talking about a stock autox class here in the U.S. under SCCA guidelines/rules. If i keep the stock 17x7 wheels, can i still go with a wider tire and stay in the C-Stock class? Such as a 225/45-17?

[Brian]

Yes, you can run any tire you can stuff onto a stock rim width.

[Mark Hirt]

I think the alignment rack is out of whack if your "actually" getting -1.5 camber up front.

Tires...
Kumho VictoRacer 225/45R17 - (kind of well slow)
Kumho V710 245/45R17 - will rub for awhile, but at 25.3" is really way too tall to work
Hoosier A6 225/40R17 - Nice tire, at under 23.9" it's a little small
Hoosier A6 225/45R17 - same diameter as the 245/40 but the 245 is a LOT wider
Hoosier A6 245/40R17 - The best tire for the car

[Brian]

Hey Mark,

What are you seeing in your area regarding fender lips and the Hoosier 245/40R17? What we are seeing here is that competitors are effectively rolling the lips by use of that tire...and just praying that it happens evenly instead of the tires grabbing the lip and yanking it down and messing up the paint. Some folks are getting lucky and it is pushing the lip up reasonably even....others are not so lucky and it is getting yanked down.

[Mark Hirt]

The Kumho 245/45 will shave it's corners for the first couple runs. The 245/40 Hoosier works just fine.

How much rear camber are the cars in question running?

We run -1.6 to -1.8 and 50mm offset Kosei K1 TS wheels

[Brian]

I consistently tell the stock class guys to take whatever camber they can get but there has been a lot of variation in the max camber that folks can get on the NC....some are lucky and some are not (even with the same shock choices, etc).

[Mark Hirt]

On the stock NC the problem is really front camber. A talented alignment tech "should" know how to max it out. (I get -1.3) That said most shops have spent money on equipment that could be run by trained Monkeys, unfortunately they don't hire the Monkey. When people see the shop that has done my cars for years they think... Where the hell did Mark send me? This place is dirty, the rack is over a pit (most have never seen one) and that machine is so old it still uses strings. If they trust me they keep coming back

In the rear.... any NC is capable of well over -2 degrees, mine will hit like -2.2

If your looking for a tire that will never ever rub try the 225/40R17 Hoosier. At 23.8" it's a little small for autocross (lots of 3rd gear time), if your a "track day" driver this IS the tire you want.