Thanks for all the positive comments!
Just got this back from Centre Gravity after a lengthy geometry setup on both mine and Yoof's Polos. Was an educational trip as well as a productive one. I don't profess to be a chassis expert, so please take the following in that context!
Interestingly, although the damping I'd set on the Gaz coilovers was out by a country mile - and my spring rates are on the hard side, my DIY geometry setup wasn't too ridiculous. String, spirit levels, rulers and measuring tapes can get you to a decent position if you've got a flat surface - though I think some luck and a straight shell also help!
Ride Height
I'd set my ride heights myself, turned out FR and FL were the same to the nearest mm, and RR and RL only 1mm out. Time with a metal rule and coilover C-spanners paid off. The car isn't low, but I'd set the ride height as a compromise between aesthetics and suspension travel - biased towards the latter. Feedback was that suspension travel is good.
Dampers
The car was put on a damper dyno, to check the damper effectiveness. Data from this, coupled with a test drive, enabled CG to significantly alter my randomly-guessed damper settings to something sensible.
Weight
Total car mass, with >3/4 tank of fuel and full washer bottle was 841kg. I have a full interior, no spare wheel, but things like interior rubber mats etc. in the car too. Put it down to half a tank of fuel, and it'd pretty closely match the official G40 weight. Not bad considering massive radiator, intercooler, big heavy exhaust etc. So far so good!
Most places won't touch the rear axle on the Polo, as the computer tells them it's not adjustable. This isn't the opinion of CG thankfully... I'd bolted on a straight-looking G40 rear axle, and aligned the brackets based on the original marks in the underseal. It appears that on a straightish car with a straightish axle that this is a decent place to start.
Rear Axle Before
Camber Left -1°52'
Camber Right -1°29'
Toe Left +0°12'
Toe Right +0°18'
So, it had some negative camber at the back - as most Polos that are straight and have been lowered will have. It wasn't even both sides (remember 60 minutes in a degree, not 100 - so 52' is nearly 1°) but not horrific either.
Toe out is, I believe, desirable to a certain extent on the rear of a FWD track car, as it helps the rear to grip mid-turn and aids turn-in. However, for a road car you don't want the rear to be too lively.
So therefore there was scope to improve...
Rear Axle After
Camber Left -1°29'
Camber Right -1°30'
Toe Left -0°01'
Toe Right +0°07'
As my axle and chassis seemed to be straight, no tweaking on the axle mounts was required - just Eibach shims behind the stub axles.
Rear cambers are now very even, and toe much more appropriate for a road car.
As most geometry setups reference the rear in one way or another, it's important to get this right! Then it was on to the front end - really the whole point of the exercise, as with Stage 3 frame and adjustable TCAs there's a lot more to setup than on a stock Polo.
Now here is where things are interesting, as I'd previously set camber and toe using some borrowed gauges, then taken it all apart and fitted Gaz coilovers, but I kept the TCA and compression strut lengths the same. This meant that on rebuild I had a starting point.
All I'd done on the rebuild was leave the TCAs as they were (I no longer had a decent way of measuring camber), measure the wheelbase to set compression struts (a crude way of setting castor) and got out the string and measuring stick to attempt to set the toe roughly parallel. The results were surprising!
Front Axle Before
Castor Left +2°15'
Castor Right +2°17'
Camber Left -1°23'
Camber Right -1°18'
Toe Left +0°16'
Toe Right +0°16'
Positive castor of around 2 degrees is what we're aiming for, so the 'setting wheelbase' method I'd used seemed to be acceptable here!
Camber is presumably a product of the TCAs staying the same length from when I borrowed kit to set it up last time - and a dose of luck. This amount of camber is not bad for a road car either.
Toe was set to toe-in, though I was aiming for parallel. Not bad for the old fashioned 'string method' though. Definitely some luck in getting it equal both sides.
So the aim was for improvements, but bearing in mind changing any one parameter affects the others, this is a highly iterative process - and hence time consuming. The objective was to keep similar camber and castor to what I had, but had a touch of toe-out. Adding this toe-out aids turn-in, but also is supposed to assist traction, as under acceleration the front wheels have a tendency to toe-in on a FWD car - so a bit of static toe-out means your wheels end up closer to parallel when you put your foot down.
Front Axle After
Castor Left +2°15'
Castor Right +2°06'
Camber Left -1°22'
Camber Right -1°25'
Toe Left -0°09'
Toe Right -0°09'
These might not seem like drastic changes, but they involved cutting down one of the TCAs to get the right amount of adjustment, so weren't done in 5 minutes - and required adjusting all aspects of the front end, not just the steering arm!
So, nice numbers - but ultimately this is all bollocks if it doesn't drive very well. The test drive was an eye opener.
Conclusions
I need to do some miles to decide whether spring rates need softening up, but the work done to arrive at the current damper settings took the car from utter shite to tolerable. Now this is a toy car, so tolerable ride comfort might be acceptable if the handling benefits are there...
Now, I've gone from a soggy FK kit with no ARB to 325lb/200lb front/rear springs with no ARB - so it's no shock that body roll is massively improved. Damper settings were critical to making the car driveable with these spring rates though. If I can live with the ride quality, then I won't be bothering with an ARB - roll is much much much better now.
Conveying how the car now feels to drive is difficult, as this is more subjective and less science. Turn-in is improved - but was okay before from what I remember - better now though. Mid-corner stability and traction are greatly improved, and the rear end likes to follow you round a bend now instead of staying put. This is a big improvement for a FWD car.
I'm going to see how I get on with the front toe-out, as I've always had it set parallel before - so need to get some miles on to review this. I like the turn-in improvement it brings, and certainly traction is better, but I still need to get used to the slightly more active steering you get as a result. No bother though, CG will happily tweak if required in the future.
Before the setup I could throw the car around, but not with the confidence that the chassis balance now inspires. This surprised me, as I've owned this Polo for 13 years, so know it pretty well. It's still no sportscar, but it's an awful lot better than a 20+ year old shopping trolley ought to be! I now need to put miles on the car, and contemplate further tweaks to optimise.
Three words probably sum up what I think this exercise achieved - confidence, balance and control.
Review will follow in due course from Yoof once he's had his car back out on track. His setup was more involved due to track orientated nature of the car, additional adjustability, and what's presumed to be consequences of his Oulton crash on the rear of the car.