Front ARB mount relocation

[Roy Kemp]

Hi gents,

Just following on from my blog post about front suspension mods, etc.

Got the car jacked up today and disconnected the front ARB mounts from the chassis. Now, I was expecting the whole lot to move forward to its own "natural" location, and this should mark the point where I refabricate the mounts.

As it happens, they didn't move forward at all, they actually moved back a couple of mm. Is it possibly my mounts have already been modified, or possibly built correctly in the first place?

See attached photos with measurements from the bottom of the chassis box section. Yes, I'm aware my car is filthy and I was using double-width bushes in a single width brackets.

So, bottom stud is about 190-ish from the bottom of the box section.

Can anyone compare/contrast what they have installed? S3 Phaeton with Escort suspension.

Cheers!

[Big Vern]

No caster and camber are different.

Castor angle: the angle of the steering axis when viewed from the side of the car (measured in degrees from vertical, positive is when the axis is forward at the bottom and rearward at the top)

Kingpin angle: the angle of the steering axis when viewed from the front of the car (measured in degrees from vertical, positive is out at the bottom, in at the top)

Trail: the distance between where the castor element of the steering axis meets the ground and the tyre contact patch (positive when the axis meets the ground in front of the tyre)

Scrub radius: the distance between where the kingpin element of the steering axis meets the ground and the tyre contact patch (positive when the axis contacts inside the wheel, negative when outside)

Camber: how upright the wheels are when pointing forwards (negative camber is where the bottom of the wheels are further apart than the tops)

[James Doulton]

I wonder whether the 20 degrees is just a convenient number that all cars can manage in both directions. I assume that there is a table which converts the camber change into castor angle which was calculated by them, based on the +/-20 degree. I would expect that we could probably manage more than 20 degrees, but we'd have to do our own trigonometry - Yikes!

[Roy Kemp]

I was wondering this myself. I have been looking to see if there is any calculation to be done based on the measured camber deflection across the steering range, but I can't find anything. Looks like the measured value IS the caster angle.