Last year I was looking at all the tire sizes available to replace the 275/40/18 Bridgestone S03s on the rear of my car. I really wanted to go with something wider but couldn't find anything that stayed close to the 26.7" OAD of the factory tires. So I just settled for another 275 width tire in the Michelin Pilot Sport PS2. Looking at the tread I noticed the tread seemed pretty narrow and apon measuring found it to be at or just under 9". So for a 20mm wider tire in the back, the tread is actually .4"narrower than my 255/40/18" front tire. So I started looking at other brands in the 275 size for tread widths.

Potenza RE050A Pole position 9.5" Goodyear Eagle F1 GS-D3 9.4"
BF Goodrich g-force T/A KD 10.9"
Kumo ECSTA MX 9.5"
Falken Azenis RT-615 10"
As you can see there is a lot of variations between brands. I finally found a wider tire with a 26.3" diameter in a Bridgestone Potenza S-02 295/35/18 with a tread width of 11.5". That is a wopping 2.5 inches more tread width for only going up 20mm in section width.
I track my car a few times a year and would love to have a dedicated set of rims and race tires but I just don't have the space to store them so I want the widest & stickiest street tires I can get. The only bad news is that this tire has been discontinued but Tire Rack still has a limited supply so I ordered up a set and if I like them may get a second set just to have when the first set wears out.