I don't have a 660, but the Kenda HTR's I just put on in 26x11x12 weigh about 2 pounds less than the Grim reapers in the same size, but a LOT more than the stock 25" Dunlop's. I haven't been able to test them on dry ground yet, but everything Iv'e done so far in the snow and on my sanded driveway seems like that size and weight increase had little effect on my 700. Don't know if this helps you any, I'm sure others will chime in soon.