Therein lies the balance problem <| sep |> Yes I change into more cushioned shoes for longer runs that are non technical . Specifically the Hoka speed instinct . Also during some Ultras I will change my shoes halfway through the race . <| sep |> They would not win 70 % of their old hardcourt matches against Rafa , Andy , or Novak . 20 % Tops . Rafa destroyed prime Federer on wimbledon in 2008 back when grass was still faster . Novak has sweeped the indoor hardcourt season how many times and Andy despite being a defensive player is EXTREMELY adept on fast courts with his backhand slice and flat groundstrokes . All 3 of these guys gave federer trouble earlyon back when courts were faster as well . Being in their primes they would demolish and abuse Blake and Gonzalez who hit withhigh unforced errors . The only guy that would give them trouble is maybe Safin because of how complete his game is . Its pretty ridiculous to claim such a thing and I ' m trying to be as neutral as possible . I do like Safin ' s and Fernando ' s aggressiveness but lets be real they wouldnt scratch novak , murray , or rafa .