[Bill Verburg]

Originally Posted by phunt

Maintaining suspense geometry is what’s important.

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Originally Posted by phunt

When you raise the spindle you in essence lower the ball joint.

true

Originally Posted by phunt

The distance between them is greater by the amount you raised the spindle.

This confuses me, the distance between what and what

Originally Posted by phunt

Since measurement a can not be changed.

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Originally Posted by phunt

My tire is 205/55-16 so I think it was 303mm on your chart. So a will always be 303.

Range of 205/55 x16 is 303mm to 309mm, 306 mm is avg for the tires I have records for

I’d prefer the average , not the min, unless discussing a particular tire, but ok, lets use the tires where a is 303mm

Originally Posted by phunt

If you use your metrics of 197 for b that would give you a “c” of 106 in that 108 +/- 5.

Since a - b = c or the factory spec of c being 108 +/- 5mm
Then b = a - c
b = 303 – 108 = 195mm

Originally Posted by phunt

However the angle of the control arm from the horizontal will have increased,

true, but again, this was the goal.

The above is for stock ride height per RoW spec of 108mm, I didn’t measure the a arm angle, it is what it is.

The a-arm angle changes via 2 possible mechanisms
1) Use the screw adjusters to raise or lower the chassis
2) Raise the spindle, if the spindle is raised then, to maintain stock chassis height, the screw adjusters would need to be used to raise the chassis
Obviously if you wanted to lower the car by the amount the spindles were raised then no screw adjustment is necessary. so there are 2 cases to consider

Case 1: assume raise spindle 20mm and want to keep stock chassis height, c =108mm or b= 195mm,

Here the ball joint is lowered by 20mm by raising the spindles which increases the a-arm angle and at the same time the steering arm knuckle was raised by the 20mm spindle rise. To compensate and go back to stock geometry both need to be negated.

To negate the a-arm drop, raise the adjuster screws 20mm. This also raises the inner end of the steering arm 20mm which also negates the previous change in steering arm angle

Case 2: assume a 20mm spindle rise and you want the chassis 20mm lower
As above the the ball joint has dropped, This changes the a-arm angle which raises the roll center and increases compression travel. Both are good things which do not need compensation. Once again this was the goal. To restore steering geometry to stock all that is needed is to drop steering knuckle 20mm, because the inner end dropped 20mm when the chassis was lowered due to the raised spindles.

Originally Posted by phunt

However the angle of the control arm from the horizontal will have increased changing the geometry.

true, but is that not the goal of using raised spindles on a lowered car?

What you want to keep constant is the geometric relationship between the spindle, a-arm and steering arm, changing any of these necessitates a change in the others