don't rent, buy a set for £100 or borrow someones. I may have a spare set somewhere, if you are local (or doing a day with someone who is like Cookster) you can try them
When I went to Silverstone last year on the DUK track day my rear tyre started showing signs of a cold tear (looked a little worse than yours). Got myself a some tyre warmers also had some help from a couple of guys on here and my tyre wear has improved a lot. I would also recommend getting your suspension set up. I had mine setup at Silverstone this year and in conjunction with keeping my tyres warm and and at the right temperature, my rear tyre looks really good! Not sure how good they are but i've seen UBER tyres warmers for sale for £99. Or if you have a look around on Facebook Groupd e.g. track day addicts, there are always companies promoting offers for stuff. I picked my Biketec ones up for around £120 from a company who was doing an offer.
