,
As well as 20 degrees to the right. The difference in degrees on the bubble gauge are noted and the extremes of both right and left. This gives you the overall caster.
With camber and caster roughed out, the toe is now roughed out. Camber caster and toe all have some affect on each other that’s why the car’s settings are roughed out and then redone to zero in on the correct settings. This can be a time consuming process.
Darren adjusts the toe at the tie rods.
Daren adjusts the camber at the spindle. We use the camber plates to set the king pin inclination angle. This affects the scrub radius, straight line stability and counteracts the wheel tilt caused by caster. We prefer to run minimal scrub and lead the caster with king pin angle by a few degrees. This gives good steering feel, excellent straight line stability and great turn in. We set the camber to 3.5 degrees negative, 1/8″ toe out, caster at 8 degrees positive and kingpin angle to 11 degrees..With the new additions to the front of the car, our car now turns in very nicely with very little body roll and no understeer at all. This is one of the best McPherson strut cars we have yet to drive! Stay tuned, we will continue to work over the rear suspension and do some track testing of our car so far vs a stock FR-S. Good stuff is coming!
Sources
Want more Project FR-S? MotoIQ Project Scion FR-S
2 comments
Mike,
Appreciate all your suspension articles on motoiq.
If I understand correctly the stock alignment spec is:
Camber: 0, Caster: 5°54′, Steering Axis Inclination: 15°31′ , Toe: 0mm
and the modified is:
Camber: 3.5 deg neg, Caster: 8°, Steering Axis Inclination: 11° , Toe: 3mm toe out
The camber, castor and toe all seem pretty conventional (and good) mods for getting good turn in, good mid corner front end grip and a car that is responsive to the wheel without getting to spookiness and instability. I am intrigued, and have to admit my ability to think about the geometry without a model is at its limit.
Is the effort of reducing the steering axis inclination about minimising scrub radius? Or is it something more.
In short, could you explain a little more what your aims and ideas are around “We prefer to run minimal scrub and lead the caster with king pin angle by a few degrees.”?
Tuning JDM and British cars I never found an extra degree of castor I didn’t like, but can admit to never being up for exploring KPI. Though with an adjustable strut top and camber pins on a mcpherson strut its very very doable.
Thanks!
David
Actually reducing KPI increases scrub but it also makes for more wheel tilt in the wrong direction that is countered by the caster.