57thekid,
I usually go with the law of averages and that means the tires. A lot depends on what you classify as a vibration and where you feel it.
A vibration in the steering wheel usually points the fickle finger of fate at a front tire...or worn steering components.
A seat of the pants vibration would be a rear tire...or a drivline component on its way out.
Physically inspect the tires for splits, bumps or tumors. Jack the front end up and do a wiggle test.
If you have disposable income, take it to a tire shop and say...spin the suckers please! Good luck.
Stuart
