Iain, it would be awesome to do the community a favor and pay close attention to your rear tire tread wear... and even your fronts. You would do a huge favor to folks by documenting the run count, tread depth, durometer, feel and visual observations of the tires as they wear.
In 2010, I ran 255/40/17 R1Rs exclusively on an S2000 in STR. I would run them unshaved which is at 8/32" of tread depth. In roughly 40-60 runs depending on surface, the tire would wear down to about 4/32". At this depth the tire was optimal. Around 3/32" the tire would start to go off. At 2/32" a different compound would appear through the tread in a random pattern that would indicate a different injection. At this point the tire's grip would plummet... roughly 3-4 seconds on the clock. It was huge and undeniable.
Also, the tire at full tread on the 2700lb S2000 was quite a handful to drive. It was slow to respond and every dicey move felt like a gamble. I did not enjoy it.
This was not the case at all with the 195. It would run untill the end. It just kept getting better and better until you felt the need to change them out because they looked so damn bad. If this trait is discovered in the 235/40-17, it would mean that an Elise would feel fantastic on street tires. You'd have to take advantage of 2014. Savour it, if you will.
Last edited by glagola1; 06-19-2013 at 07:00 AM.