The Kumho ECSTA V700 (aka V70A) is Kumho's new DOT-legal autocross and wet road racing tire.  While it is DOT approved this is far from a street friendly tire.  It's extremely light weight which is of course very good for competition tires but it also means that these tires aren't likely to handle your local pot-hole farm very well at all.  Some manufacturers even go so far as including a disclaimer with their tires stating that even though they are DOT approved they aren't intended for use on public roads!

The tires that I used on my 1984 Rx-7 GSL-SE autocross car are 235/45R13 mounted on 13 x 8 Diamond Racing wheels at 34psi at all four corners.  I have the stock transmission ratios with the stock (for an 84 GSL-SE) differential ratio of 4.077.  In the past I've run Kumho Victoracer V700s, BF/Goodrich CompT/A R1 competition tires in 205/60R14 on 14x5.5 Panasport wheels and on the Diamond Racing wheels I've used Hoosier bias ply Street T.D.s in 225/45R13 and Hoosier's radial A3S03 in 225/45R13 and 225/50R13.  The short gearing in the differential and in the transmission mean a LOT of shifting with these really short tires.  The big reason to go with these really wide, really short tires is quite simple and very autocross specific.  For autocross you need two things, lateral acceleration and longitudinal acceleration.  Basically, you need to be able to make up the speed you lost in the last corner as quickly as possible but try not to loose any speed at all.

The first run on a very fast autocross course designed by 2 time H Stock national champion Gerry Terranova was less than thrilling.  A spin on a very dusty corner early in the day left me less than thrilled after some very high G, high speed sweepers at the beginning of the course built confidence fast then took it all away.  I took it quite a bit easier for the rest of that run.  A quick look at the tire temperatures showed slightly higher temps on the inside edges of the fronts, indicating too much negative camber was present.  With middle 50F ambient temperatures, tire temps were in the 95 to 110 range after the 95 second run including the spin.  The rear tires were within 5 degrees F across the treadwidth which indicated to me that the pressures I used were at least close to optimum for my car on those tires on that day.

My second run started relatively conservative with no more than a modest effort at being competetive.  The lack of any competition in C Street Prepared didn't help.  This was quite unfortunate as I was quite looking forward to seeing more of my friends and fellow competetors.  Again, tire temperatures were even across the back and slightly elevated on the inside edge of the front tires due to the camber used for the Hoosiers last year.  It appears that the V70A requires slightly less camber than the Hoosier A3S03 radials I had at the end of last season.

After my third run I pulled the data out of my Edlebrock Qwikdata I actually had quite a surprise.  With the Kumho Victoracer V700s I would get about 1.2g lateral and 0.9g under braking, either of the Hoosiers would give me 1.6g lateral and 1.2g under braking when in their peak.  Straight out of the box these tires gave me only about 1.2g but this is probably due to my slow start after the early spin.  After getting a couple of runs and some heat into the tires they completely changed.  By my third and fourth runs I was getting 1.5g laterally and 1.0g under braking and times had dropped to the hight 79 second range.  Not as fast as I'd like but at least it was faster than my stock companions so I was relatively satisfied with initial results.

Compared to the $148 per corner for the 225/50R13 Hoosier the $100 Kumho ECSTA V700 is quite a bargin.  I don't know how long they will last yet but even if they get toasted as quickly as the ultra-soft Hoosiers the Kumho will still be a bargin.  I do expect the Kumho to last longer simply because the rubber is harder than the Hoosier but compaired to a street tire they'll still feel like freshly chewed bubble gum.  After they've been heat cycled it's easy to deform the rubber by pressing on it laterally with your finger, just like any of the super-soft competition tires they are emulating.  For me to stay relatively competetive I have to go through three sets of tires per season and I'm hoping to get by with only two sets of Kumhos.  For me that will translate into almost an $800 saving per season.  Another couple of events will give a better idea of how these will hold up over the course of the year but for now I'm quite satisfied.

Thanks to Todd Eady at Discount Tire for getting these on short order when literally no other tire distributer could get them if they even had them in stock.