How much grip do road tyres lose with time?

[Shoestringracer]

I'm seling my hillcimb / sprint car but will keep my hand in with some events in my Boxster. Currently the car has 3 matching high quality tyres and one Chinease one (its a long story!). All the tyres have plenty of tread left but the 3 good ones are at least 2 1/2 years old, probably more (they were on the car when I bought it).

Obviously I'll replace the Chinease one. Will the other 3 have lost performance over 3 years, even though it is only about 5k miles?

Thanks

[RobM77]

Yes. Rubber degrades over time. Also, I'd recommend a matching set of tyres. My elise tyres got to five years old and I changed them purely through age. I wouldn't say it makes a huge difference, but if you want to get the most out of your car on track I'd run with tyres a couple of years old at most and, crucially, matching all round.

[Shoestringracer]

I would have definately have a matched set - I would have replaced the odd one with one that matched the other 3 but maybe I should get a whole new set.