Rear stability issues

[Markbilney]

Hi all. Would appreciate some advice on my wife's 2016 2.0 Z4. After some advice, I replaced the back tyres with Rainsport 5s and the car was serviced at the same time. Since these events, the car has gone from handling like a go kart to the back end floating all over and the traction light flicking on and off pretty frequently during a drive on the twisty stuff. My first thought was the tyres that screwed up the handling. I have cranked pressures up and dropped them down too but no change. The traction light is throwing me though and making me wonder if it could be something else post the service. Its really unnerving to drive now so any advice would be appreciated. Thanks in advance.

[RobbiZ4]

Hi all. Would appreciate some advice on my wife's 2016 2.0 Z4. After some advice, I replaced the back tyres with Rainsport 5s and the car was serviced at the same time. Since these events, the car has gone from handling like a go kart to the back end floating all over and the traction light flicking on and off pretty frequently during a drive on the twisty stuff. My first thought was the tyres that screwed up the handling. I have cranked pressures up and dropped them down too but no change. The traction light is throwing me though and making me wonder if it could be something else post the service. Its really unnerving to drive now so any advice would be appreciated. Thanks in advance.

Some additional infos are required:
- size of the wheels (17", 18", 19")?
- size of the tyres, front as well as rear
- runflat (RFT) tyres or not?

What pressure do you currently have on the tyres? In the German ZRoadster.com forum we recommend 2.4 bar as a max. on all 4 wheels.

[Chippie]

How many miles have you driven on the new tyres, they can sometimes take a while to bed in

[Markbilney]

Thanks for the responses. Tyres have done around 250 miles. Rears are 255/30 R19s, same size as the ones they replaced. Can't remember the fronts but it's the standard on the 19 inch rims. I started on the standard pressures for the run flats then went up incrementally to around 42 psi, having originally dropped them down to 34psi.

[Argyll Andy]

Thanks for the responses. Tyres have done around 250 miles. Rears are 255/30 R19s, same size as the ones they replaced. Can't remember the fronts but it's the standard on the 19 inch rims. I started on the standard pressures for the run flats then went up incrementally to around 42 psi, having originally dropped them down to 34psi.

I’m running 34F 36R on 19’ non run flats. Garage changing the tyre put 42 in to start and it was all over the place. Drop back down now you’ve got some miles on the tyres and go up a lb or two until you feel it’s ok.

Some brands of tyres can take up to 1000 miles to bed in, until they do that they can be a bit skittish too

[RobbiZ4]

In the German ZRoadster.com forum we recommend 2.4 bar as a max. on all 4 wheels.

As said, our recommendation is 2.4 bar, 34-35 psi all over.

There are 19" on my Z4 as well, but not anymore RFT and I'm driving GOODYEAR EAGLE F1 (ASYMMETRIC) 5.

[flybobbie]

My 23i on 18inch non rft Goodyears i run 38 f and 40 r. No issues and perfect wear patterns. I think every combination needs experimentation.
Only time i saw traction problem was worn out rear shocks at 50k miles. Bilsteins cured that.
Original shocks are cheap looking not a patch on Bilsteins, well worth changing. Fronts done as well.
Only other thing i don't like the Goodyear asym 3 not as good as the 2 i had fitted.

[enuff_zed]

Is it conceivable that the shocks are a bit tired. Jacking the car up to change the tyres will have let them fully extended for a short while. Maybe this was enough to finally kill them off? If the wheel is not being pushed down firmly onto the road that could cause a traction issue?
This is just a theory, but if the tyres aren't causing it.........................

[Markbilney]

OK thanks for your responses. I will play with the pressures again. The car has only done 20k miles, so I wouldn't have anticipated shocks yet. I will keep playing with the pressures and see what happens.

[enuff_zed]

Fair enough.
I'd assume you have checked all the bolts are tight and that the wheels are fitted flush to the hubs?
250 miles isn't much to tell from, but any sign of abnormal wear on the tyres?

Edit: From your previous posts it's not quite clear. When you say standard on the front, do you mean the original Run Flats?

[Pbondar]

Your post implies that you have fitted a new set of rear tyres to a car with a used set , possibly run flats, tyres on the front of unspecified supplier / version?

If so that could be a possible explanation

[mcbutler]

Your post implies that you have fitted a new set of rear tyres to a car with a used set , possibly run flats, tyres on the front of unspecified supplier / version?

If so that could be a possible explanation

Thats a very good point Pete, mixing RFT with non RFT is a big no no, a reputable tyre dealer will not fit them like that, I was turned away from every fitter in Plymouth.........
Might also be worth checking they are the right way around i.e. rotating the right direction....

[kmorgan]

I had a similar problem, the fix was to also replace the front tyres. The stability system was detecting too much of a rotation difference in the new tyres on the rear to the old tyres on the front, the stability system was trying to correct what it thought was the car out of control. The behaviour was more evident on bends around 50mph.

If I remember correctly turning the traction control off, or even just turning on DTC would stop the car from stepping in.

Hope this helps.