Rear end wandering

[wild_one]

On my ‘09 1.6 zetec S, I’ve noticed that occasionally on the motorway that the rear of the car can feel as though it’s wandering ever so slightly. More noticeable at 70mph than 50mph. Doesn’t do it all the time. Strange feeling. A bit like when there’s crosswind. The steering feels good. I’ve only noticed this problem in the last month. Before lockdown it was fine. And after last MOT had new struts, top mounts, lower arms, arb bushes and drop links, rear shocks, shock mounts, rear springs, spring insulators. The only thing not changed were the rear axle bushes but I couldn’t find any movement in them? Tyres are good and pressures checked? 

So, any ideas?

[Matt Alsop]

I've had a similar problem before and it was a very strange feeling where the back of the car didn't feel like it was always following the front. In my case it was caused by the fact I had a different brand of tyres on the rear to those on the front. It was a small hatchback with firm sports suspension but not a Fiesta. When I swapped the wheels from front to back it solved the problem completely. I was told it was because my rear tyres had more flexible side walls compared with the front. If you've checked the rear suspension than I can't think what it could be unless it's tyre related. In my case the problem seemed to come and go depending on the temperature / weather would you believe. It would sometimes cause the car to feel a bit unstable under braking too.

[wild_one]

17 minutes ago, Matt Alsop said:

I've had a similar problem before and it was a very strange feeling where the back of the car didn't feel like it was always following the front. In my case it was caused by the fact I had a different brand of tyres on the rear to those on the front. It was a small hatchback with firm sports suspension but not a Fiesta. When I swapped the wheels from front to back it solved the problem completely. I was told it was because my rear tyres had more flexible side walls compared with the front. If you've checked the rear suspension than I can't think what it could be unless it's tyre related. In my case the problem seemed to come and go depending on the temperature / weather would you believe. It would sometimes cause the car to feel a bit unstable under braking too.

Funny because I had noticed the tyre pressures were way over inflated. Bringing them down to ‘factory’ has made this wandering sensation worse. Or at least highlighted the issue. Maybe I’ll put them up to fully loaded and compare?

[Matt Alsop]

I think if you have a different brand or age of tyres on the front and back I'd swap the wheels around from front to back and see if it makes any difference. Due to the problem I had before I always buy tyres as a set of all four (the same) these days. I swap the wheels from front to back to even out the wear so I always need all four replacing at the same time. It should only take half an hour to try and it won't cost you anything except the time it takes to do. If your tyres were way over inflated could that damage the structure ?........I don't know.