"P-Zero System" is a specific package, it's not mandatory. You can have (as I do) P-Zero asymmetrics front and rear, just different widths, which is the standard UK fitment.

 

Finally got my XKR back with the new tires on it. Keep in mind it is still only 36ºF outside or so, so I'll have to wait to get some miles on the tires and for the temperature to warm up before I can really give you guys an idea for how the tire performs.

I have to say, the change is UNBELIEVABLE. The car just feels so much more planted. Perhaps it is slightly firmer, but the tires still absorb bumps very well. Best of all, the steering is so much tighter. No more wandering on the highway like with my Hankook Ventus V12 Evo K110s. In those tires, it was like I was always driving on heavily grooved pavement and having to make steering corrections just to go straight on the highway. Now it goes straight as an arrow!

 

One negative I will say is that the rear tire exhibit a minor roaring sound. It's quiet enough that it doesn't bother me, and most of the time I'm driving this car, I'd probably have the top down anyway. Plus maybe the roaring will go away after the tires are broken in.

 

Alan,
I'm just up the road in Frederick, Maryland and current temps are not ideal for any summer tire. I've been taking my XK out for a spin most weekends in anthying from 25-35*F temps and have been very impressed on how the Sumitomos have behaved. OK I'm taking it easy but they are very compliant. Wait for late this week when temps reach 60*F and I bet that roar goes away. I'll also predict you'll find their performance in the wet to be very good.

Steve.

 

I was surprised how in 35-ish temps, the tires were much more grippy than the Hankook Evos. But we'll see later this week in the 60 degree temps as you say!

 

I have Hankooks still on the front, and they do not wander at all. Is it possible you have a small alignment issue?

We have a particular stretch of grooved highway here that makes the back end on my XKR shimmy like a dancer at the Crazy Horse. I've learned to ignore it and the car tracks straight enough. I guess it's the price we pay for that humungous rubber. On all the other roads it is very good, though not as wind resistant as my '96 Firebird.

 

It could've just been that the Hankooks were completely worn and the sidewalls had gotten really soft.

It could be an alignment issue, but now the Sumis run perfectly straight. I still haven't had a chance to drive them in dry weather, but in damp weather the Sumis seem to have much better grip than the Hankooks and are much more confidence inspiring.

 

So I finally had a warm and dry day. Wow! These tires rock!

So much grippier than the Hankooks ever were. On the Hankooks, if I accelerated from a stop aggressively, one tire would silently lose traction and the traction control would come on cutting back power. However, with the Sumitomos, I can pretty much floor it from a stop and the tires will start to slip a little bit but retain a lot of traction and still allow me to accelerate without the traction control kicking in. I also noticed the tires will be more vocal (chirp chirp chirp chirp) when accelerating than the Hankooks ever were, which is interesting.

The roaring sound I reported earlier is completely gone after about 100 miles of driving--must've just been something on the break-in period.

I can see why this is a very popular HPDE tire. If you're considering getting high end Pirellis or Bridgestones, it's worth giving these a shot at less than half the price.