JayG

On my 986S I am doing some suspension upgrades, going to M030 ROW springs/struts with camber plates on the front. For now I will use stock S sway bars. The camber plates will get me to around 2 deg camber Front from < 1 now. Rear camber will be around 2 deg

Other than that, I am bone stock

I am looking at a couple of different tire combinations and wondering what would be the best setup. I have 2 sets of 17" wheels I will be using

Fronts
7 et 55
8 et 50

rears
8.5 et 48
9 et 52

the sets are 7 & 8.5, 8 & 9

I am currently running 225 F & 245 or 255 R
I am looking at 235 F and 245 R as a possibility or 235 F 255 R

The tires diameters are

225/45 25.0 "
235/45 25.4 "

245/45 25.7"
245/40 24.7"
255/40 25.0"

Part of my issue has do do with what class I run in and based on points if I want to change to adjustable sway bars, I can do a 235 / 245 combination. If I stay with fixed sway bars I'm fine with 235 / 255

Am I better off using a smaller or larger diameter rear tire?
I don't have PSM, just regular ABS and in any case the largest difference 25.0 / 25.7 is under 3%

Also, if the new Hankook R-S4 is a good tire choice, they won't be available in 245/45 only 245/40. Short term, I will stay with RE-71R. Later maybe the R-S4s

What is the best combination for track as well as AX?

mark kibort

dont worry about the tire size . it wont be an issue at all. i would go for the largest tire possible.. they will wear better and last longer in the end.

as far as your swaybar, when you say adjustable, does it have adjustable drop links as well as the ability to change torsion (stiffness) ? sometimes you get adjustable swaybars that only go stiffer but are not able to be adjusted to avoid preloading one side or the other. If it is fully adjustable, thats an interesting trade off... might go for the adjustable swaybar to help handling, especially in an autocross, where there is a lot of high g transitions.

JayG

When you say largest tire, you are referring to contact patch/width, not diameter, correct?

If I go with the adj sways, they will have adj drop links as well

mark kibort

yes.... the largest tire you can run, usually works best regardless of diameter. the diameter i would be concerned with , is the amount of sidewall. sometimes folks dont want tall tires due to their spring rates or slip characteristics.
porsche cup cars run a HUGE diameter tire in the rear for example. i would run it, but it would hit my chassis! (27"!!!) so , my limit is 26" and generally run 25 to 25.5". so, the sway bars are totally adjustable .. that might be worth a smaller tire, especially if you are setting up the car well for different tracks.... autoX seems to pay bigger dividends for swaybar effects as i mentioned.