I've got the graps in 35. only an 18inch rim but I love them. had the same tire on the old gasser and put them on the diesel now. I haven't really had any problems with rough riding on the road or anything. You can feel the tread when going slow (crawling) but its minor. on the highway they are smooth. a little loud but honestly if you're looking for an aggressive look you can't be concerned with a little humming! great traction on road and in wet. Pulled a couple thousand pount trailor up hill through the mud without a problem so I'd have to say off road traction is GREAT!
hope this helps
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Black 05 2500 QC SB 6 speed , Pure Performance 4" lift, 18" xd spy's, 35x12.5 Mud Grapplers, ISSpro boost, FP, and pyro, silencer ring and Cat MIA

, S&B, Plenty more to come!