I have a '95 SE Eibach progressive springs, tokico struts, and the stillen rear sway bar with the stock 15" rims, tires---Yokohama S306--P215/60 R15 93H. the car sticks to the road like glue at any speed. I bought a set of 97-99 I believe, stock 16" SE rims from someone here on the org. I replaced the old tires that came with the rims with Yokohama YK420 P215/55 R16 91V. Now the car feels loose, realy bouncy and unstable going down the highway.
Any ideas or suggestions as to what might be causing this? Thanks for all the input and responses.

 

I've had an opposite experience... I went from my 15" GXE wheels to 16" SE wheels and my car handles the highway much better now. Everything is much smoother, it's like the car is riding on glass. I made sure to have the wheels aligned and balanced before this though. You should take the car to get an alignment if it hasn't had one since you switched wheels. The old alignment could have been compensating for wear patterns in your old tires that aren't there now. Also get the wheels balanced if you haven't already, it's cheap and could help reduce the bouncy feeling.

 

Think about this for a second. What changed on your car? Wheels and tires.

Wheels - should not make any difference in your cars feel. Going from 15 to 16 inch enables you to go with a more agressive profile tire.

Tires - The single most important factor on how your car grips the road. The suspension just keeps them planted. Of course thats a big part of the picture as well, but nothing changed on your car suspension wise.

So what changed? YOUR RUBBER

 

The bounciness is probably due to the different tires but 16's aren't always more stiff than 15's. It depends on the design of the tire.

The looseness/unstability is probably due to the new tires settling in... Give them a few hundred miles... you'll see...