1994-2002 [Subscribe to Daily Digest] |
drs_VRK < search key word
The only known remedy is the VRK which costs a bit over $800 and will probably cost at least $300 to install.
Hard accelleration causes the fron to lift. This reduces traction and can lead to wheel spin. The lifting of the body also causes the toe-in to change towards the negative which makes steering bogus by itself. Stiffer springs reduce the front end lift caused by theis weight transfer and will also reduce the weight transfer dynamics. Better shocks can also help with control over the weight transfer dynamics, but this is not as good as what springs can do. The Viggen springs were adjusted to address this issue.
The Viggen suspension components (linages) are not really any differenct and the Viggen does get lots of steering artifacts when you get on boost. Hence the Viggen Rescue Kit.
So body lift makes the steering unstable. The steering linkages are much less than rigid. The VRK allows for greater control over whats going on. It allows you to control the struggle.
The center of the tires traction contact patch is not cenered on the the point where the strut turning axis intersects the pavement. Greater wheel offset as provided by wheel spacers makes this worse. The amount of camber effects this too. Lowering springs do reduce the Camber I believe. I am not sure what the overall effect of this is, but I think that it helps. This separation of the effective contact patch center from the steering axis makes the vehicle hung on eneven or rutted pavement. Again the VRK allows for greater control of these dynamics.
If the contact patch was centered on the steering axis, the vehicle will have terrible steering feedback. (MB tried this in the early 1970's.)
The tires and wheels do make a difference, even if the wheel offset is not changed. Stiffer sidewalls make things worse as far as snakey steering goes. So just changine tires can have a great effect. And as a tire ages and the rubber stiffens, this can get worse. Going to larger wheels gives you shorter sidewall sections and things can get worse.
The VRK removes some of the rubbery bits and allows you to control the steering by a firm grip on the wheel. You sort of feel the same forces, but you can resist them. With stock, or stock with aged componets, you can hold the stering wheel so that is is not moving, but the steering will be all over the place. Hence the analogy of fighting with a snake. With the stock situation you cannot just hold the wheel straight so you are overcorrecting and no matter what you do the steering is nuts. At stock boost this is a minor issue.
The rear SAS sway bar keeps the vehicle very flat in corners. This probably helps by not allowing body sway to alter the steering geometry. You adjust to a new steering dynamic and it is really much better.
The Viggen rear sway bar is not as stiff as you might think. A really stiff sway bar, a'la SAS, will make lead to inner driver wheel slip in corners while on boost. So the Viggen reduced body sway with stiff springs and the front and rear sway bars are tuned to povide better traction to cope with the engines high torque.
Worn upper mounts allow the tops of the struts to move around with accelerations and cornering forces. Replacing them can make a world of difference if they are going bad.
The 1995.5+ porduction has a smaller steering rack than the original design. The rubber mounts where make thicker to fill the gap, so all of these vehicles, Viggen included, allow for a nasty amount of steering rack deflection in the mounts. The VRK replaces these with solid aluminum clamping blocks, and a brace to reduce firewall deflection. The rack bolts to the middle of the cookie sheet, Oh I mean the firewall. It can deflect under load. The C900's had the steering rack located low, hard bolted to the underframe which also carried the suspension arms. So that was optimal in terms of reducing the relative defections of the rack relative to the control arm mounting points. The current design has some merits, but sucks when you get into high loads where control becomes vital. The incorporations of the thicker rubber rack mounts is the result of corporate indifference. A mount redesign was called for and they did the least effort work to integrate the new racks smaller diameter.
Perfection is not in reach, but vast improvements are. Traction and cornering/steering reponse cannot be optimized as they have some conflicting requirements. Stiffer springs are the best approach for both of these objectives if the resultant ride quality is to your liking and the roads will allow without bending wheels or breaking oil pans.
95SET, MBC, deans<underscore>list basic power mods, stock SE springs, SAS rear sway bar, new KYB upper strut mounts, Koni's, stock 16" wheels, stock IC, MBC tapped to middle of IC integral return tube, VRK.
140000 miles
posted by 209.172.2...
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