315/35/18 V710s are great tires R compound tires. I've run several sets of these. 26.4" and on par with R6s for times. Just like R6s, they fall off after 5 sessions or so and don't have much to offer after 10 sessions. After 10 sessions they are on par with 305/35 NT01s. The only other option is a Pirelli 325/660-18. I think he needs to stick to R compounds though.. Having run both, I won't run the short tires anymore.

 

Nah, I do time trials, Hoosier A6 are a must. I like Nittos, but not for competition. Plus Hoosier has a contingency where you get free tires when you win.

 

315/30's R888

 

V710's are really good tires. I haven't run them on the same setup as A6's but they have some great grip. They were my favorite tire before I stumbled onto Hoosiers (aka purple crack).

 

Another way to approach this is gearing. Without accounting for any tire expansion with the following known parameters: 5th gear - .92, axle ratio - 3.44, 6900 rpm, 25.6 static tire diameter:
MPH = (RPM * Tire Diameter)) / (axle ratio * gear ratio * 336)
=(6900*25.6)/(3.44*.92*336)
=166.1 mph

Computing this for a lower gear that doesn't see much centrifugal expansion or aero load, but does likely have car weight effectively reducing the static tire diameter. Let's pick 3rd gear - 1.41 ratio
=(6900*25.6)/(3.44*1.41*336)
=108.4 mph

Seems to agree with the OP's empirical data pretty good: 3rd @ 108mph, 5th @ 166 (with heavy aero).

So the 171mph without much aero must be caused by some expansion factor rather than any slippage/drag factor. Centrifugal expansion effects can readily be seen on drag cars (though to a different degree). Not too hard to imagine on a tire rotating at >2000rpm at 5th gear speeds.

 

You could run 997 gt2 gears for 4th and 5th.

996t 977gt2
4th 1.12 1.09
5th 0.92 0.89

 

I am actually planning on changing to GT2 RS gears next time I break 3rd. I've broken it 3 times since 2010. Next time I'm switching to GT2 RS main shaft and 1st through 5th gears.

 

Pressurize oiling and a cooler may be need in your case. At least a cooler.

 

What kind of setup do you suggest? I've seen a few and 3rd still broke in high DF sticky tire configurations. I rarely run more than 3-4 laps at speed either. Almost exclusively time trials. From what I've seen from temp sensors, the gearbox is barely up to temps in that period of time unless it's heat of summer.

 

V710 is what I run on my gutted Vette. Has full aero and just amazing grip. Best tire that no one knows about.

 

Hey Heavy, have you ever thrown on some A's for a couple of hot laps?

 

A6? Yeah, that's my primary tire.

 

oh yeah those are super fast for a few laps, I thought you were running the R's for some reason

 

Just for reference, I redlined in 6th at 212mph-

18" Wheels with michelin PS2's 315/35

Redline is 7200 I think... It may just be 7000