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!

[Dave Adams]

i always build my cars for 5 degrees and would be happy with 5+/- 3 degrees. They have both been 5 degrees when checked on a 4 wheel geometry checker. my current car has yet to be checked, to be honest i will be happy with the castor the same side either side!

But as Paul says, as much as 10 degrees on such light cars is fine. they can be left to the owners choice to suit the way they like the car to handle.....if they are able to tell.

my S1's have had different castor on the car at the same time...... one side only had 0.5 degrees on one side, and almost 5 on the other side.

[Steve and Matt Pegrum]

With your S1 like that, did it pull to one side? Also how was steering feel?

Ours is currently set at about 3.5 but reckon it could do with more. I was thinking 8 but we have power steering. 

[Dave Adams]

Steering was .....er.....well it just felt twitchy and uncertain....

Afterwards it felt very positive and sure footed.

[Roy Kemp]

Ok guys, thanks for all the answers so far. What's the advantage of going for a bigger caster angle, other than stability?

I'm thinking I might go for less camber, given what it's used for. Or, alternatively, selectable mounting points for road and Autotest use. Fab guy's going to love me..

Also, the Escort anti-dive kit uses a spacer plate to lower the ARB brackets, bringing the ARB closer to the horizontal. What does this achieve? It would be very easy to space the brackets away from the chassis, and now is the time now that the welder's away to come out!

[Dave Adams]

Increased castor = straight line stability. But heavier steering at slower speed also undesirable camber changes at lock extremes. ....not good for auto trials.

Lower ARB mounts = Lower roll centre 

[Roy Kemp]

Sounds very familiar - I've been noticing I get a lot of positive camber at full lock. Which is about as much good as a kick in the pods. I'll measure the caster angle and see if I'm dealing with anything extreme. 

[James Doulton]

Presumably it is the castor angle that creates the resistance through the steering when cornering, so I would prefer a little less than I have on my Legerra because it was quite a fight at Castle Combe with grippy tyres. I was exhausted after 40 laps and I ached for days after.

[James Doulton]

How do you go about measuring the castor angle? Presumably I need to take the wheel off but then what?

[Steve and Matt Pegrum]

I wish I could say it was easy. The only method I know is to measure the change in camber as you move the steering from 20 degrees left to 20 degrees right. Why 20? I don't really know.

You need both a camber gauge and steering turntables to do that.  Gunsons do a set for this. The turntables are very heavy 

[Dave Adams]

You can use turn tables used for cake making....they are plastic but do the job. About  2.50 - 5  quid each......

[Roy Kemp]

Wow. Ok, this is getting interesting. Much more to it than I thought! So, the change in camber over a range of 40 degrees of steering deflection is your castor angle?

And there I was thinking setting up a spirit level at the vertical and measuring the angle of the front upright in relation would do the trick.

Looks like I have a lot to learn. 

[James Doulton]

Easier on the eye indeed. I watched the whole video but I didn't learn anything. Both of those were on about camber though.