Tires: Odd handling with new tires, odd vibrations, highway ramp

Question
Barry,
Thanks in advance; I'm an expert in the roofing section and this is my first time using our service.

My Vehicle:
2006 GMC extended cab 4x4 Sierra pickup
4 new Goodyear WranglerHT LT245 75 R16 installed yesterday by a tire shop. Mounted and balanced; balance seems fine as there are no odd  vibrations at any speed.

Since having the new tires installed it feels like the truck wags like a tail while making small steering corrections, it's only noticeable at speeds over 45mph.

While going around highway ramp bow-ties the truck feels very unstable because of the fish tail feel. Pavement is dry and vehicle does not break traction, but there is a distinct wagging feel at the rear that wasn't there before. Leaf springs and bushings are tight and all seems ok.

Today I jacked up the rear end; put the truck in gear and watched the treads as the tire spun. The treads don't follow a straight line, they wave back and forth; I would say the deviation is no more than 3/8" over one rotation.

There are bulges in the sidewalls; not huge, but every tire has at least one. Inflation is perfect 80psi just like the door pillar sticker says.

Questions:
1) What could be causing the fishtail/wagging feel?
2) Is it ok that the treads don't seem straight while watching a spinning tire?
3) Are the slight bulges in the sidewall OK?

I'll head back to the tire shop tomorrow but I wanted to be armed with some decent info.

Thanks,
Tom  

Answer
Tom,

You've obviously found the vehicle sticker, but I can tell you that your vehicle doesn't say 80 psi for the front.  I'm assuming the fronts are different and correct and you were only talking about the pressure in the rear because that's where the problem seems to be.

If that is so, i think you need to take the vehicle back to the tire dealer.  3/8" wobble is pretty excessive and either the tires haven't been completely mounted on the rims, or the tires are way out of round.

The bulges in the sidewall probably aren't contributing to the problem.  Those are where the ply fabric overlaps and at 80 psi, there is plenty of tension and these are easy to see.  Structurally they don't amount to much.