new tires feel mushy

[Raceit]

I had four 31 inch Bridgestone mud tires with about half the tread left on all of them. I had a flat that destroyed the right rear tire. So I bought two new tires of the same exact size and type to put on the rear. (I took the left rear tire and am now using that as a full size spare.)
The weird thing is that now the back end seems to be loose on the streets. For example if I switch from one lane to another (especialy at highway speeds) it feels like the back end wants to continue to keep coming around me. Then I have to correct a little bit, as if I was fishtailing, to track it straight again. It's not as bad as it sounds, but I always have to worry about what it's going to do next. This all started imideatly after the two new tires were put on the back. It feels like something is broken. I checked the anti-sway bars front and back and even everything else feels secure. Comparing the front and back tires the front have about half of their lugs left. So that's how I know that I have half the tread left on my older front tires. The only thing I can think of is that the lugs have some give in them and allow the tire to move slightly from side to side while still being firmly planted on the ground.
I don't know if this is normal when you put new tires on with big lugs or if something is wrong with the tires internaly. I had somebody suggest that the plys are slipping inside each other. Thanks.

[Jim F]

Here's an idea. Rotate the back to the front straight forward and put miles on the new tires now in the front. Having them up front may give you better feel of control of the vehicle while the tires are wearing and aging (harding). Then rotate them front to back and the feel may be reduced enough that the feel will be nominal.

A theory: The tires may feel this way only in the back since they are the drive wheels. If moved them up front they may be less noticable.

[AgExplorer]

Is the air pressure the same in all the tires? The guys at the tire shop may have put less air in the new ones.

[Raceit]

I think I will switch the tires to the front to wear them down a bit faster.

The air pressure in all of them is about 45psi. I run them high. The odd thing is that these are Bridgestone tires. I bought them at a actuall Firestone dealership. The guy who mounted them and aired them up only put 25 psi in each tire. Just by looking at the side wall you can see that 25 psi is not enough air. I drove it for about 10 miles with 25 and it was like my axles where going to slide out from the rear end. It was a nasty feeling.
The low tire pressure reminded me of the whole Firestone issue.

[Raceit]

Unbelievable!!

Just changing the new tires to the front fixed everything. Considering how it was handeling before it feels like it tracks like a sports car now. It feels much safer to say the least.

Thanks Jim!

[Jim F]

Your welcome.

[padmonster]

Also keep in mind that new tires need 200-300 miles to "wear in". The top layer of tires is sometimes coated or baked a little harder for storage. Also residue from the spec sticker will lessen traction. After the wear in, you should be in good shape. You want even wear from all four so you should start the new ones in the front. It will also keep your chances of hydroplaning lower, since the fronts have deeper treads.