When I had 33's I got harmonic vibes around 64mph. When I went up to 35's they don't come on till around 70mph. This is another plus to being slightly undergeared. My pinion and caster have been in every conceivable angle and I can't dial them out. The only solution is hubs. Right now they're about $1550. I think I can live without them. Who wants to travel over 70 anyway?! If someone drops a bucket of money on me, I might spring for the hubs.I know the feeling. I am going to tweak the pinion some. Once the RPMs exceeds 2500 , my Jeep is not as smooth running. But under that 2500 rpms around 45 to 50 mph things are smooth.