There's a GLI suspension on the Jetta cup edition. The sportwagen does not. The Golf sport suspension is actually only very slightly stiffer than the 2.5 suspension. There's a thread somewhere about it but the difference is mostly due to balance and the engine weight, not to make it much sportier than the 2.5.
This comes from Germany. Keep in mind the suspension is designed as a whole system (springs, shocks, control arms, roll bars, wheels, etc., etc.) and the individual settings you see here are just part of the answer:
front anti-roll bar 2.5L = 21mm
rear anti roll bar 2.5L = 19mm (18.5 specifically)
front anti-roll bar TDI = 21mm
rear anti roll bar TDI = 19mm (18.5 specifically)
front anti-roll bar GTI = 23mm
rear anti roll bar GTI = 19mm (19.6 specifically)
Also: Front subframe and control arms are lighter so the spring rates have changed
Front Spring rates
GTI: 33 N/mm
TDI: 25 N/mm
2,5l: 23 N/mm
Dampers are adjusted accordingly based on the spring rates
I'm sure they would work but I wouldn't want to lower my car. IMHO, the cars are low enough due to the aluminum oil pan sticking out under the car. If this wasn't the case I'd say go for it but at least for me, better handling can be found with different shocks and anti rollbars/sway bars and tires/wheels. GTI springs will lower the ride height and I want more clearance, not less.
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