hmmmmmmmm. Top bloke for trying perhaps, but all the info is wrong.....
The S3 bar is not the same as the R32 bar at all.
The R32 has a heavy V6, and comes with a 23mm front bar, the S3 with the 1.8T comes with a 19mm front bar.
the efficiency of these bars, and thus how you calculate sizes, varies hugely depending on how you fit them.
If you fit the 19mm S3 bar using std mk4 drop links to the wishbones, it'll be much less effective than the stock 21mm mk4 bar
If you fit the 19mm S3 bar properly using S3 struts and drop links, it'll be more effective than the 21mm mk4 bar, due to the S3 bar acting directly on the strut, and not half way along the lever arm of the wishbone, which reduces it's effect.
S174 says that the choice of front bar won't matter, but it does, hugely.
If you fitted a 23mm R32 front bar, and mounted it in stock mk4 wishbone style, it would be a slight upgrade from stock, and would make the car understeer more.
If you then mounted it properly to the strut R32/S3 style, it would be more effective again, and make the car understeer even more.
You need to think about what size rear bar you want to add, or indeed what you might already have fitted, and how you want to change or retain the balance (oversteer/understeer) of the car.
Fitting a larger front bar will mean you need a proportionally larger rear bar again to experience the gains of a rear ARB that are so often talked about. Fitting a larger front bar then an average sized rear bar will just bring terrible handling back to average.
