TonyC - yeah, the tires need to be approved to use them on the street over here! So there are not many options for 15" street tires that will last 1-2 seasons, work on rain and are approved! For this I find the 17"'s much better.
I also would maybe like to step up to the Viper braket kit, no way that fits under 15"...
Most guys drive those Radial T/A's, I find them the most terrible tire that exists in the meaning of traction.^

I had here a discussion with 2 guys, one drives races with his Charger. He said, that a 15" setup will handle better than a 17" setup on our old mopars.
He said that the b-body front suspension was made to have soft 15" tires with small sidewall stiffness.
When the tires start to deform on a hard turn the camber starts to get negativ and this helps.
When using 17" that are not supposed to deform on a turn this negativ camber makes it handle worst and that a 17" wheel setup probably can't go as fast into a turn than a 15" setup?!? I never heard of this before?

And also the other story I ALWAYS hear, that you have more traction with a 15" tire than with a 17" tire because it sits wider (ballon) on the street.

By the way, why are the leafsprings of the XV1 so soft? Even if the rear swaybar is huge, with those big Tbars it will probably understeer a lot? I calculated my setup back then with the 1.22" Tbars that I need about 200lbs/inch on the leafsprings if I don't want a strong understeer? You got any more info on that?