Tires for Track Days

[Yellow95]

I’m driving a daily driver ’95 stock coupe. We like to out to the track to play on HPDE events at Willow Springs and Buttonwillow. Both about 2.5 mile road tracks. ( I turn about 1:50 on street tires at Willow big track) Last time out, my new street tires were no fun. Not enough traction. I decided to get some track tires. My street tires are good for the street, not for the track. Plan is to get 4 Kumho ECSTA V700 315/35-17 W rated tires. I intend to use them to drive to the track, run the track, drive home. I don’t intend to shave or heat treat them. They will be mounted on 9.5 inch wheels. Questions: Is the 315s mounted on 9.5 wheels OK? Previous threads seemed to say it was not optimum but OK. Is there enough added traction over the 275 to make them worth the additional money? Will the 315’s fit under the a C4 with stock wheels without a problem? What’s the difference between the Kumho ECSTA V700 and the Kumho Victoracer V700? Other than the ECSTA is symmetrical and the Victoracer is not. Is the W rating of the ECSTA vs the Z rating of the Victoracer a concern? Any comments before I drop the cash?

[Luke@tirerack]

my comments are in red

Originally Posted by Yellow95

I’m driving a daily driver ’95 stock coupe. We like to out to the track to play on HPDE events at Willow Springs and Buttonwillow. Both about 2.5 mile road tracks. ( I turn about 1:50 on street tires at Willow big track)

Last time out, my new street tires were no fun. Not enough traction. I decided to get some track tires. My street tires are good for the street, not for the track.

Plan is to get 4 Kumho ECSTA V700 315/35-17 W rated tires. I intend to use them to drive to the track, run the track, drive home. I don’t intend to shave or heat treat them. They will be mounted on 9.5 inch wheels.
DOT-legal Competition tires begin with about 6/32" of molded tread depth. While some tires do not require shaving for dry autocross use, all of them will benefit from shaving to about 4/32" tread depths for driver's schools, track days and competitive track use in dry conditions. The Ecsta V700 has been known to exhibit irregular wear when not shaved

Questions:
Is the 315s mounted on 9.5 wheels OK? Previous threads seemed to say it was not optimum but OK. Is there enough added traction over the 275 to make them worth the additional money?
minimum wheel width for that tire is 10.5"

Will the 315’s fit under the a C4 with stock wheels without a problem?
I have seen it done many times

What’s the difference between the Kumho ECSTA V700 and the Kumho Victoracer V700? Other than the ECSTA is symmetrical and the Victoracer is not.
the Ecsta was basically designed to be a rain tire

Is the W rating of the ECSTA vs the Z rating of the Victoracer a concern?
if you are going to go over 170 mph then yes

Any comments before I drop the cash?

One of the reasons radial racing slicks are so effective is because they feature shallow tread depths and their contact patch acts as a single unit. However, any tread design breaks up the contact patch into smaller elements and additional deep tread depth (required to enhance wet traction) allows tread block squirm which will reduce dry performance. This means that tires typically provide their worst wet traction ... and their best dry performance just before they wear out. However, its also important to remember that the heat generated every time a tire is driven activates bonding agents in the rubber. As this process is repeated continually throughout the tire's life, its rubber compounds gradually harden and loose flexibility reducing the tire's grip. Therefore, a shaved "new" tire will provide more traction than a tire worn to the exact same tread depth after being driven for thousands of miles on the road.

Tire shaving is an effective means of permitting more of a tire's performance capability to be realized early in its life. Tire shaving removes tread rubber and reduces tire weight by several pounds. A shaved tire's tread profile will usually result in a slight increase in the width of the tire's contact patch putting a little more rubber on the road. The resulting shallower tread depths reduce the tire's slip angle, increases its responsiveness and help stabilize its cornering power by minimizing tread block squirm. Minimizing tread block squirm also reduces heat buildup and the risk of making the tire go "off" by overheating its tread compound. And in many cases, shaved tires used in competition actually have a longer useful life than tires that begin being run at full tread depth.