11-16-2018, 04:26 PM
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Senior Club Cobra Member
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Join Date: Jun 1999
Location: Fallbrook, CA USA,
CA
Cobra Make, Engine: Porsche 928 S4
Posts: 739
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Not Ranked
Quote:
Originally Posted by xlr8tr
very interesting Richard! Adding 2" to backspacing would not mess up scrub radius?
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Good catch. If done the way I stated it would indeed alter the scrub radii and wheel rotation would be difficult due to the wheel/upright interference drag induced by the clamping force of the lug nuts. 
What I should have stated is that one would add 1" to both the backspacing and the offset on the front (split the increase) and one would add 2" to the backspacing on the rear.
The front with the standard offsets currently has 2.75" positive scrub radius with 11 degree SAI on a tyre dia. of 24.5".
Therefore the increase in backspacing would change the SR to 1.75" which should still give the desired steering feel and centering effect. Note: the design calls for 2 degrees castor or less as the camber gain required is in the geometry and jacking effects are therein minimized as they are extremely detrimental dynamically.
This would necessitate a toe (static) change to offset the reduced torque on the contact patch under braking. Probably would change from .040 to .070 out but once again tyre construction is the biggest factor here. |
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