Itīs true that motorspray dries the tyre out but tiresauce softens the rubber again. Actually we use brakecleaner for motorspray, same stuff, alot cheaper. Also try out WD40, nice cheap stuff for tireadditive. In Europe we are forced to use non-smelling tireadditives and there is alot choose from like Lrp, Team orion and CS. Which one that works best depends on the trackcondition and needs to be tested beforehand. You apply the stuff about 40 min before and wipe it of when go out and drive. The new generation of tires like Sorex and Take-offs are designed for use with tireadditives and produce more grip and better wear with it.