Once you get to those power levels, the limiting factor is the axles. At 400 plus WHP the axles can and do fail if you apply too much power too quickly. When Dave returned my car with 440 WHP he said do NOT change the factory tire size because it would start failing the axles.

Do your homework and make your own decision.

I run stock size tires and am very happy with them. But I don't track the car.

RTE

 

And no trouble getting power to the ground on the 245s?

 

No

The choice is driven by your use case. If you are going around corners then more grip is generally better. If you are putting a lot of torque into the rear tires and exceeding the strength of the rear axles, then more grip is not a good thing.

In my case, I have followed Dave's recommendation and stayed with grippy stock size tires. I can get as much grip as I want in curves but do not worry that I will break something.

At 400 hp and up, in my experience, you need to turn off TC or you will be frequently experiencing fuel cut off due to momentary loss of traction. This is not a good thing.

With TC "off" you can enjoy the limits of the car without worrying that you will break something.

I don't track the car but enjoy spirited street driving. It is worry free with stock tires. And I get plenty of grip for my driving needs.

RTE

 

For those of you doing AutoX, HPDE or competitive racing in your Kappas, could you clue me in on what a good tire and wheel size would be?

315 hoosier of course...

 

Whoah. Dat is a lotta tire. What width wheel is that on?

 

275/40/18 on 18x9 +51 all around for me.

I've seen the tire comparison video on YouTube. All of it was done on factory alignment. It's good data, but more variables are needed. There are definitely cases where a narrower tires is just as fast or even a touch faster, but they don't do as well with heat, so it becomes a balance.

 

Tire Rack does some of the sloppiest testing I've ever seen. I appreciate that they tried, but often times bad data is worse than no data.

That said - the "use the widest tire you can smash onto the wheel" mantra began and still applies only to racing slicks. Treaded tires are built different and while I have yet to see any data I trust that proves you'll actually be slower with too wide of a tire for your wheel, there is certainly a point where you stop being faster. Generally speaking, the contact patch doesn't lie, and you can make it wider either by going with a wider tire or a wider wheel, preferably both. The human element also comes into play here, as a pinched tire is much more difficult and unpredictable to drive on.

If you're planning on tracking and streeting the car, I'd use something similar to Yamaha's setup, maybe on a 9.5" wheel if you can find them. Shabby's (the standard issue 315 on a 18x11) for autox only.

As far as axles - yeah, they break, but it's not that common and like anything comes down to how you treat the car. A 245 drag radial will break an axle or diff quicker than a 325 Pilot Sport ever would, so If that's what you're worried about you might as well screw a block of wood under the throttle pedal as well, or just keep the car under a cover in the garage and trailer it to your weekly cars and coffee.