Quote:
Originally Posted by The HACK
Seriously? All that careful corner weighting helps DYNAMIC weight transfer. When the car is either accelerating or decelerating, the "rake" of the vehicle will change accordingly. What happens to your carefully measured "rake" of the chassis when the car is entering a corner or exiting a corner? How often do you drive an entire course while doing exactly 200km/h?
Rake is irrelevant. It is FAR more important that the cross weight is as close to neutral as possible and the car is as low as the roll-center allows while still maintaining a reasonable front/rear weight balance. IF lift or aerodynamic grip is your concern, find ways to add or subtract downforce while minimizing the impact on drag, rather than fix the "rake." If your chassis is set-up right, "rake" will fix itself.
Rake is for "stance" crowd poseurs. You might as well lower the car PAST its roll center with massive negative camber in order to tuck your 10.5" F, 12" rear wheels shod with 205f/225r tires into your fenders.
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Yes, I agree that the DYNAMIC load shifting that occurs with acceleration and braking also simultaneously affects the rake angle. IMO the Z4MC's OEM suspension is totally unbalanced and far from neutral.
I've recently written in another thread on the forum:
"The Z4MC's suspension is too soft at the front which allows pitching on braking and lifting on acceleration, which makes the steering floaty and imprecise, and at the rear it's too stiff, which makes the ride very uncomfortable. The 3 centre coils of the rear springs are 19mm thick whereas the front springs are just 11mm thick: obviously there's a huge mismatch between front and rear spring rates, yet BMW cars supposedly have a weigh balance F:R of 50:50.
I've fitted AC Schnitzer Racing suspension (basically Bilstein PSS9 made to ACS's specification), which has rear springs of 16mm and front springs of 14mm, which redresses the mismatch of F:R spring rates. Instantly, this helps to overcome the inherent ride and handling problems of the Z4MC with OEM suspension."
With my ACS Racing suspension the car is considerably more balanced with considerably reduced tendency to pitching and lifting, which, of course, will simultaneously reduce the dynamic rake change that previously occurred.
You ask:
"How often do you drive an entire course while doing exactly 200km/h?" As you know, aerodynamic effects are working at ALL speeds and not just 125mph (200km/hr), and have greater effect at higher speeds. At The Nurburgring I will be doing a lap time averaging in the order of 90mph and reach speeds above 125mph several times and touch above 140mph. As the figures for lift of the Z4 3.0CSi show, the lift is unequal F:R so again any corner weighting done at 0mph goes completely out of the window in the dynamic situation, especially at higher speeds.
As always, it's "horses for courses"; maybe for your purposes you can ignore rake, but for my purpose I consider that it is an important consideration, which I have adressed. I couldn't give a toss about "stance", and I'm not interested in lowering for the sake of it, it's only the performance and handling that concerns me.
This is a photo of me in my M Coupe (S54) at the Nurburgring. It looks to me like my car is very well balanced with minimal lateral bodyroll and a preserved rake angle due to the lack of pitching/squatting. I have also heavily modified that car and it's handling is now superb.
