Front suspension

strut tops - 405 s2

Use Series 2 405 top mounts, they work very well on the 205s. Note that you will have a metal component leftover if you use these. 405 S2 bits are way better.¹ I bought a 205 which had a much better ride than usual, no clunking. Found out later that it had the 405 tops and have used them ever since.²

The first two pics are the regular 205 parts (one metal cup, one rubber donut) and the third one is the single overmoulded 405 part that replaces them³

anti-roll bar

The diameter of the 205 Si front sway bar is 23mm (the GTi is 18mm).⁴ Get Powerflex ARB bushes [23mm]; this makes a big difference. Don't use SASIC bushes, way too soft.⁵

shocks

XSi or GTi6 (think they are the same) front shocks are also a cheap upgrade. Use the shock, put a 205 gti spring in, new bearing, later series 405 solid rubber and your 205 top hat.⁶
As long as these aren't leaking they will work better than anything you can buy.⁷

205 Si v 205 GTi front suspension

Worldwide, there's a tonne of different 205 versions. And all of them come with one or other of two different front end suspension setups. Only TWO came with the wishbone control arms and droplinks: the GTi 1.9l petrol and the variously badged Turbo Diesels. Everything else, including the Australian 205 Si, came with the standard single lower control arm with the anti-roll bar passing thru it.⁸

Further details of the differences

Is the front GTI lower suspension setup with a proper wishbone better than the Si control arm?

The SI has the "floppy" set up. Not really a problem, they still handle very well and don't crash over every bump as the GTI does.⁹

As long as you use [uprated] plastic bushes [...], I haven't noticed any difference in torque steer etc. The standard aftermarket bushes [SASIC] are far too soft and the originals worn out by now. The Si suspension "suspends" better, and the the car is more precise in the steering than the GTi. The difference, of course, is that GTi will corner harder on the limit, but where are you going to need to corner harder than an Si except for on the racetrack?¹⁰

Rear suspension

rear beam

The GTI beam has go fast yellow paint on the main tube and the Si is black. The main tube is a different diameter.¹¹ The diameter of rear beam main tubes in the widest middle section (approx only): GTI beams are 64mm, Si beam is 59-60mm.¹²

rear beam rebuild advice

See bearing fitting tool/mandrel. The inner bearing is 210mm from the outside of the tube; the outer is recessed by 5mm, for the seal. That’s fitted with a different tool.¹³

torsion bars

Torsion bars are 18.5mm diameter on the Si. ¹⁴ 205 bars are 992mm long with 23mm dia at one end (30 splines) & 25mm at the other (32 splines); splines are 25mm & 27mm wide making the effective bar length 940mm¹⁵

If you're committed to making it handle, you need to move up to 21mm torsion bars as your first move. Sure, it's relatively expensive compared to other mods but it's definitely the starting point.¹⁶

All this talk of bar diameters is a bit irrelevant if you have a cage, as it has a major effect on rigidity. A quality cage with 21mm bars is a great setup, and better than 23mm and no cage.¹⁷

torsion bar lengths

car	length	diameter
106/Saxo	966mm18	19mm
205 Si	992mm19	18.5mm
309	1028mm20
306	1068mm21

rear anti-roll bar

Si ARB is 16mm¹⁴
GTi ARB is 19mm¹⁶

shocks

You can just throw in some 306 XSi or GTi6 rear shocks. They bolt right in and are cheap.²²