Z4 2.5si unstable on corners

R

Reddy

New member
Hi all,
I have a 2006 2.5si, I had the original 17in rft on and changed to 19 inch narrow wide aftermarket mag. The car has AC Shnitzer springs. The problem with the 19s is when I go around bends the car feels very unstable and the steering is twitchy. The car also seems to dip on the corners.

Can anyone help or suggest solutions. I have balanced wheels and done 4 wheel alignment.
 
Considering you've already had a balance and alignment done. (and assuming the shop did a good job on the alignmnet).

Twitchy steering is more common with staggered setups (assuming this is what you mean by 'narrow wide'). Also having a wider contact patch will cause some tramlining / twitchy / light steering on sandy or wet roads. Brand of tire also plays a role here. I found very twitchy steering running Yokohama summer tires staggered on my e36 m3. Hated that rubber. If I let go of the steering wheel it would twitch wildly back and forth following the grooves on the road.

If you have access to some other 19" wheels the same size as your front wheels, I would try putting them on your rears for a 'square' setup and see how the car drives. I'll bet it would be much better than what you're experiencing now.

The car dipping when cornering could be blown shocks.. Does the car also have a little more bounce after driving over potholes or speed bumps?
 
What tyre pressures are you running? I'm asking as mine was quite twitchy after changing fron 18" RFT's to 19" non RFT's. Dropping pressure to 31f 33r made a big improvement and mine is staggered with 235/35 f & 265/30 rear.
 
I assume your front anti rollbar bushes are complete and fit for purpose? Certainly fits the symptoms if they are shagged. :?
 
Gents,
Thank u for responding...
I have 235/35/19 fr & 265/30/19 rear.
Tyre pressure was 3bar all round. I changed it to 2.5bar front and 2.8bar rear as a trial today. Will test it tomorrow on the way to work.
I am going to check bushes and shocks on the weekend and I am going to test my mags for any buckling.
Also, rear tyres are new and fronts are slightly worn on the inside. They are uni-directional tyres. The fronts are falkens and the rears are Achilles. I am considering changing the fronts to Achilles as well.
 
Maybe a combination of too much negative camber, a sidewall too thin to absorb anything, high pressures, and stiffer/lower springs - all make it too much for the unevenness of a normal road?

I'm not sure about Achilles tyres either - I'd stick to a known brand :o


NB: before anyone claims Achilles are the same as/good as, for example PS2s and made by Michelin so must be good, let me point out that my mother and father made both me and my sister, and she's nowhere near as clever/fit/successful as me :P
 
Gents,

Changed the front tyres and what a difference. Smoother ride, no twitching, etc.....so I guess it was the front worn tyres. I wil monitor it this week and let you guys know how things are going.
Are any of you guys filling your tyres with NItrogen? I was told to fill up with regular air cause it is better for handling???
 
Reddy said:
Are any of you guys filling your tyres with NItrogen? I was told to fill up with regular air cause it is better for handling???
Click to expand...
If it's free, then there's no harm in using it, but if they want you to pay extra for it remind them that the air you breathe is composed of almost 80% nitrogen anyway.

There is a scientific reason why it's 'better', but unless you are a race driver with a race team behind you, who needs to measure tyre pressures to 0.1psi, then you'll never see/feel/notice the difference 100% nitrogen will make compared to 80% nitrogen.

You'll also be topping it up with air anyway, so any negligible benefit it had provided will be negated quite quickly.
 
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