Hey @Pudding what makes the b12 sportlines horrible? Is it a poor choice for performance/track work or comfort? Or both? Sorry for hijacking matey @PKGTI haha
OK, hope your sitting comfortably as the Bilstein stuff gets confusing. I hope this summarised break down helps clear it up!
B3 Springs and mountings - OEM spec.
B4 twin tube dampers - designed for OEM springs. OEM spec damping. OEM droop length.
B6 monotube dampers - designed for OEM springs. Slightly stiffer damping. OEM droop length.
B8 monotube Sprint dampers - designed for lowering springs. Shorter than OEM droop.
B12 - Tailored springs with B8 dampers - kits put together by Bilstein themselves. Springs are made by Eibach.
B14 - Non damping adjustable coilovers.
B16 - Adjustable damping coilovers.
B16 clubsport - Adjustable damping coilovers with camber adjustable top mounts.
So looking at that list, you can see where each Bxx rating sits in the OEM vs sporting hierarchy, with B4 being the softest, to B16 being the stiffest.
Where the B12 kits get confusing is Pro vs Sportline.
Pro is only available for non-gti cars and the lowering is usually -20 to -30mm, and that's compared to a non GTI. As the GTI is approx 10-15mm lower than a non-GTI from the factory, a Pro spring therefore lowers a GTI approx 10-15mm. I hope that makes sense! Which imo, is the perfect lowering amount for a road car.
The Sportline is designed for the cooking models (i.e GTI, R32, R), and is -40mm lower than a non-GTI, so it drops pretty low, too low imo. And when you drop that much, you have to stiffen the spring significantly to stop the struts bottoming out over every bump, which destroys ride comfort.
Why Bilstein don't offer a Pro spring for the GTI is a mystery to me. Marketing probably, because the GTI is the sporting model and they assume no one would want the more forgiving Pro spring.
So in summary, for a mild drop with a spring/damping upgrade over stock for a MK5 GTI, you need a B12 Pro kit for a MK6 TDI - kit no. 46-1879576.
I know that sounds completely arse about face, but it's just how it is!!
Of course, if you do actually want the lower stance and stiffer ride, then the a B12 Sportline may suit some people.....but for me, the B12 Pro is the daily usable option.
Bilstein base their B12 kits on axle weights, and the 2.0 TDI MK6 is very close to a MK5 GTI, so it works out well. And the MK6 dampers aren't as aggressively valved as the MK5's.
Sorry that wasn't a quick answer, but Bilstein have made it a less than straight forward themselves unfortunately.