New van - poor stability

[moncman]

Hi all, a bit of a vague one this but here goes anyway.

We have at late 2010 200hp XC90 which has 80,000 miles on it and full main dealer service history. Solo it feels like it always has with perhaps the exception being the ride is a little more harsh but that might be down to fitting XL tyres last year.

We have pulled a variety of caravans over the last 9 years, all 6 berth and about the same length but different weights from a 1300kg Lunar to 1500kg Elddis. All have had a bike rack on the back carrying about 30kgs (please let's not get into a debate whether that's a good idea as I've never had an issue previously).

This year was our first outing with a brand new Swift Challenger 590 - still 6 berth single axle but now about 1650kgs. In all cases towball load was about 85kgs.

Handling was horrendous to begin with, pitching was particularly bad so I moved some internal weight back a bit which helped but sway and pitch was still not great and on occasions it felt like the front wheels had gone light and were struggling to maintain a planted grip.

I'm really scratching my head as to what is different. Car is level, Nivomats are not leaking and it's just had the 80,000 mile service with a clean bill of health. Strangely as well as moving the weight back a bit thus taking some load of the back the handling improved as fuel burned off to the point that on a near empty tank it was a lot better. Could I have something wrong with the self-levelling suspension or rear shocks which aren't visibly obvious? Could the marginally harsher ride be an indicator for something which only comes to light once the car is loaded up?

Any comments ideas gratefully received.