Track car suspension evolution
12-21-2011, 12:27 PM
#17
Race Car
Join Date: Sep 2005
Location: TEXAS
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I'm resurrecting this thread as it stops with the question I have on my newly acquired 87 951: Coilover Spring Rates for a track car....
Bilstein coilovers front and rear, stock sway/torsion bars, 245/18 275/18 RA1's....all suspension points are new....very little turbo 'squat', but the car feels 'twitchy' as it gets north of 100mph. It could possibly be my lack of experience with power steering in a track car but I believe it's the lighter front footprint at high speed. Have the GT Racing front splitter/spoiler also.....
Thanks
Bilstein coilovers front and rear, stock sway/torsion bars, 245/18 275/18 RA1's....all suspension points are new....very little turbo 'squat', but the car feels 'twitchy' as it gets north of 100mph. It could possibly be my lack of experience with power steering in a track car but I believe it's the lighter front footprint at high speed. Have the GT Racing front splitter/spoiler also.....
Thanks
) - As droops83 describes below, I have stronger bushings. - And love my zero toe.
Last edited by 95ONE; 12-26-2011 at 12:04 AM.
12-25-2011, 07:55 PM
#19
Three Wheelin'
Do you still have stock rubber suspension bushings in the rear? If so, you need to run some toe-in in the rear. The semi-trailing arm suspension that the 951 has in the rear will deflect and cause the outside rear wheel to toe out during hard braking and cornering due to the deflection of the rubber bushings. This is what gives this type of rear suspension its tail-happy reputation (think E30 BMW). This is the reason that Porsche developed the "Weissach" rear suspension for the 928 that toes the outer rear wheel in during hard braking. The 993 also used a version of this, when you hear the term "kinematic toe" in reference to a 993, this is what is being referred to. The 928 and 993 both have sophisticated multi-link rear suspension and are able to achieve this (you would not want this system on a race car since you would want to install solid suspension bushings that would eliminate the compliance in the rear that causes the deflection issue in the first place).
On our relatively crude rear ends, we need to run more rear toe-in than otherwise would be needed to compensate for toe-out/bushing deflection. On my otherwise stock suspension I run close to 0.2 degrees of rear toe-in, which is a bit more toe-in than the factory settings call for, and my rear end has ben much more stable since setting it this way; slides are a lot easier to control.
In the front I would run zero toe on a track car, mine is plenty stable on fast tracks like Willow Springs and the roval at Cal Speedway, yet still turns in well. I run a bit of toe-out for autoX and tight tracks like Streets of Willow.
On our relatively crude rear ends, we need to run more rear toe-in than otherwise would be needed to compensate for toe-out/bushing deflection. On my otherwise stock suspension I run close to 0.2 degrees of rear toe-in, which is a bit more toe-in than the factory settings call for, and my rear end has ben much more stable since setting it this way; slides are a lot easier to control.
In the front I would run zero toe on a track car, mine is plenty stable on fast tracks like Willow Springs and the roval at Cal Speedway, yet still turns in well. I run a bit of toe-out for autoX and tight tracks like Streets of Willow.
