I was going to purchase Q4s but for the price difference, plus $$ rebate i decided to give these S21 a try. I'm a quick A group rider, GSXR 600, NO Warmers. 200+ miles on 12/15-16/2018, 50-60 degrees. Tires were excellent and wore evenly, good feed back on drive and trail braking corner entry. I"m sure the Q4s are excellent too, but so are these. It never ceases to amaze me the N & I riders who have generators & warmers--ridiculous--I had NO warmers and was up to speed after out lap. Will try the RS10s this summer. Your mileage may differ!