I have been running my ECO close to box stock for about four months now and have had great luck. Haven't shimed the diffs and have had zero issues. For the first two months I ran exclusively indoor on hard packed medium bite clay. The chassis is unlike another indoor. It drives flat with tons of steering and traction which I could never get both out of any of my old chassis. Then the past two months I've been beating the snot out of this thing outdoor on big low bite American style nitro tracks. Day one outdoor all I did was lighten the suspension raised the ride height and it was good to go!! It is the smoothest most consistent chassis I have ran outdoor. The ECO chassis are built to the highest standard and show on the track! I'd say on the sportsman level this is the chassis to have. It is extremly durable, easy to setup and very forgiving to wheel! I must say thank you to Mugen!!! Truly an epic chassis!!