1.5 fits perfect. No issues. I have only had time to take a short flat lander ride so far. I picked up the Tunnel ectension and rail extensions from tracks USA. I had a 136 X 1.25 before. The rails extensions from Tracks are the best out there I think. For one, the are of the tip up design for better trail performance and they are also a full length hyfax design. The tunnel extension on nothing to exciting, however it works and it also gives you different options for bumpers, and coolers as the are not pre-drilled for anything. My only issue right now is I seem to have some belt slippage I can't get rid of. Under any heavy loads it just smokes the belt new or otherwise. I love this sled, I'll never sell it. She has just over 10,000 miles now and still going strong. I mostly ride my Warrior now, but the SRX will stick around forever.