A few tire questions

[oakiemac]

I just replaced by 2 front tires on my F-350 4x4 dually and the dealer said that I should replace all 6 at same time, something about tire wear. The back ones are ok for now so I was hoping to wait until next year and then replace those. Does it matter or was the dealer just trying to get me to pay for all 6?

I put on BF Goodrich commercial TA's which seem to be good tires but not very agressive tread pattern. When I do replace the back tires I want to go with a much more aggresive tire. Does this make sense since the fronts are not the same? In other words, should all 6 pretty much be the same tread pattern?

Final question- before I replaced the fronts, they were wearing badly mainly on the inside on both front tires. Is there anyting I should have checked to make sure that the new tires dont wear like this? The truck does not pull to the right or left and there was no excessive vibration.