This may be a little sacrilegious but lets take the performance part out of tire selection. Also lets not consider the stagger in getting tires for all four corners. My days of looking for other then street tires have past so I am looking for comfort and ride. So lets get to the point here. Are there any tires in the tire size range that provide a smooth , quiet ride and will provide 20-25K life. Also if you were to buy the same size tire for all 4 and rotate every 10K mikes would you expect to get better tire life. The primary use of our car is 2-3 hour weekend drives and short trips around town all with the top down of course. Presently I am running the OEM Dunlops on 20"wheels and the rears have 11K miles and will most likely last through the summer so this is just a open discussion to see what options are out there.

 

First off, smooth and quite will not happen on 20" rims. The required stiff sidewalls and higher tire pressures make a 20" a harsh tire regardless of brand or compound. There are certainly 'less noisy' tires out there in any size.
If comfort is your goal, consider dropping to 19s, (or as I wish to do, 18s) and the ride quality (and tire selections) will leap significantly. The XK series is very capable of becoming a quite and luxurious highway cruiser on the right rims...

I have also dropped staggered rims on my last car (Lexus IS350) in favor of a standard size on all four corners. This was also done to maximize life and reduce costs, but has the side effect of altering over-steer/under-steer in the corners, as well as the rear adhesion limits on a skidpad. As the car was already biased nose heavy, it still broke the fronts loose first, which is what you want for safety sake.

 

I haven't tried them on the Jag but I had great results with Michelin Pilot Sports (smooth, quiet, good life and amazing grip) on the previous Porsche's If you want a smooth ride as was already said look at a larger side wall / smaller rim.

 

I put Nitto Motivos on my 20's. Like you I'm not looking for ultimate grip. I'm extremely happy with them and the warranty is hard to beat. Nitto even warranties their tires for the full mileage regardless of a staggered fitment. That's 60,000 miles! I had these on my 19's and there is no way they'll last that long. I'd guess somewhere just beyond 30k. They are very quiet and a great value and a good ride for a 20 inch tire. In Atlanta we have heavy rain and rutted highways. A deep tread with good evacuation is a priority. Like you I didn't want to drop $1400 every 10k miles or so for tires. That's more than once a year for me. All four mounted and balanced with the extra "road hazard" Discount Tire warranty was under a grand. They don't make a 285 for the rear so I went with the 295/30-20. I looked at the 275 but it was too narrow for the rim. They do make the "proper" sized front.

 

I just replaced the Dunlop's that came with my car with Michelin Pilot Sport A/S tires. Like Jagtoes, performance was not my number one priority when selecting a new set of tires. Even though the car is stored winters, I wanted to be able to use the car earlier in the Spring and later in the Fall when the temperatures are still in the 30's early in the morning. I also wanted a quieter tire that gave a relatively smooth ride on the 20" rims.
I have less than 1,000 miles on the Michelins, but so far I am very happy with my purchase. They have meet or exceeded my expectations. Only time will tell how well they last and since I only put on around 4,000 miles per year, that will be a while yet.

 

After 3 sets of Dunlop sport maxx, I had a set of Pirelli Zero's mounted a month ago. So far, more grip, much quieter and more comfortable. The steering is better and the tires don't follow trails in the tarmac as the Dunlops did.
I have 20 " Senta rims.

 

What is a little funny here is as I looked at my tires yesterday looking at the fronts they are not even half worn (OEM Dunlops) . It makes me wonder how the rears will be used up by 15K miles while the fronts will go for maybe twice as much. Also meeting the previous owner I know the rears were not abused as well as myself who have not broken them lose. The next logical question would be how long would the tires last if they were all the same size and the rear rims were replaced with the same as the fronts.

 

When I was looking for XKs, I viewed the optional 20" rims as a negative! It seems there's a bunch of us who actually want ride quality over top performance.

I have 19" wheels and they currently have General G-Max tires on them. I would not recommend them. Noticeably noisy. The tires are in very good shape, so its not an end of life noise issue.

When I go to replace, I'll be installing Continental DWS tires since I've had very good experience with them on my two previous vehicles. They have softer side walls and are fairly quiet riding. Both vehicles quieted done and felt a touch more plush after I installed these. In hard cornering, I noticed more 'squirm', but no big deal for me. Tire life has also been respectable, although I have no idea if that will translate well on the XK.

 

Sumitomo I think has a new performance tire with a good tread warranty and/or excellent price from NTB.