Sorting out high speed instability

I can say for mine at least that it's the road, I took mine on track last month and even hard braking From just over 100 mph the car behaves.
 
RX-78 said:
Mr Whippy said:
Try 0.5 less rear camber, if the settings are as per 3.0i

Lots of lateral thrusting comes from that, along with lots more neg camber under bump. All in that is what makes the back end move around on bumpy roads. Evo were just wrong, as is often the case. The kinematics are just very safe and setup isn't ideal for lots of uk roads.

Rft> fk452 made me happy with mine, but only with 31/33psi f/r, so maybe look at pressures?

I'm not sure why your car is unstable, have you driven any other Si's to get a feel? The Si I drove seemed very good to be honest. The z4 is lively, it feels quite unstable, but they DO track solid without rft despite not feeling like it... Hmmmm


Anywhere with Hunter alignment are worth looking at. Tyre pressures worth considering, and make sure car is set up with dummy load. Try get rear camber at least u can within oe spec if u don't fancy a big change. -2.3 ish iirc

Cheers

Dave
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Sorry Dave, I've tried to understand - but completely lost me :oops:

Any chance of simpler explanation for an amature :P ?
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I'm far from an expert, I'm just making observations :)

Basically check alignment, and get the rear camber as low as possible (oe spec is something like -3.1 > -2.3, with the target camber being -2.8 ish), so try get it to the -2.3 end of the scale to remove as much of the rear-end lateral movement weirdness as much as possible.
The alignment check/setup should be done with the 75kg load, 7kg luggage and 67kg on drivers seat iirc!?

If not running RFT, I'd also consider choosing good tyre pressures. Mine are 31psi front, 33psi rear, and my car feels wonderful for stability. It's lively, but stable. Lets not mix up the RFT lateral jumping that is not intuitive and is genuinely scary at speed on rough roads, with the fidget but straight tracking of just a stiff car on rough roads :)

Dave
 
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