I can feel the rear end a bit unstable and shifts around quite easily around corners or high speed (around 60 mph)Is this to do with nitrogen air in the tyres?

The 500 does the same.
If you hit a bump mid corner, the rear end can hop a little.
I've noticed my new panda does it too.

It's nothing to worry about. The 1st few times it does it you think 'whoa!'
But it's not a big deal. The car doesn't spin around, you regain grip and carry on.

Unlikely to be the nitrogen. Could be incorrect tyre pressures? Or if yours is a 4x4, what you get driving winter tyres on warmer roads - the tread blocks are softer and more agile - there is less grip and they can feel a bit 'squirmy', if that's the right term! I know that from driving all through last summer on full winters in my old mk3 4x4...

I suspect we're back to Fiat's tendency to under-damp on rebound, especially on the rear - makes the rear lurch particularly if the outer rear wheel hits the bump. A solution on the Mk3 100HP is adjustable Konis.

Mine jumps as described, but I just put it down to the fact that the back end is really light, add a lump of concrete like Richard Hammonds 325i convertible on Top Gear and see how you get on.

All part of the fun!

jbanfie said:

Mine jumps as described, but I just put it down to the fact that the back end is really light, add a lump of concrete like Richard Hammonds 325i convertible on Top Gear and see how you get on.

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Similar solution - damps the rebound on the back.

Any solution to this, gas filled shocks?

javnas said:

I can feel the rear end a bit unstable and shifts around quite easily around corners or high speed (around 60 mph)Is this to do with nitrogen air in the tyres?

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I always fill my car tyres with 80% nitrogen & have no handling problems whatsoever.

jrkitching said:

I always fill my car tyres with 80% nitrogen & have no handling problems whatsoever.

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Does the nitrogen raise the pitch of the road noise?