That's a mouthful but I do understand there is variance in OEM swaybars between PDK v MT, possibly PASM v SPASM, and possibly GTS4 v C4S. What are OEM diameter specs and does the H&R (or Tarrett) C4S kit actually improve on stock GTS units? Are GT3 oriented kits an option? I have my rear camber maxed out (-2* area) but need more stiffness to even out track (DOT-R) tire wear across the profile. Thanks

 

All GTS sways are the same... PDK vs MT, AWD vs 2, PASM vs SPASM.. all the same. The front sway on GTS is stiffer than the C2S/C4S equivalent. Their is a different rear subframe brace on PDK cars that requires a spacer if installing OEM GT3/GT2 rear sways. Not necessary for manual cars IIRC.... not sure can't remember.

Best upgrades are to go to GT3/2 OEM sways (what I have) or Tarett. larger diameter, stiffer and most importantly, adjustable.

 

Thanks nwGTS. Do you know OEM GTS and OEM GT3 diameters? The H&R kit is 26/24mm front/rear.

I believe all of those are solid cross-sections whereas the Tarett kit is hollow, correct? So some maths to do to compare relative stiffness. Both the Tarret and the OEM GT3 are much more $$ than the H&R so would be useful to know the value add.

 

So I measured and the stock 997 GTS sway bars are 24mm front and 20mm rear. That means the 26/24mm H&R bars are 38% stiffer in front and a whopping 107% stiffer in the rear (assuming torsional stiffness varies with diameter to the power of 4). Interesting that the incremental stiffness is so asymmetric between F and R. My guess is the lawyer-prescribed understeer ubiquitously prevalent in most OEM suspension designs (Porsche included) drives a need for a directionally looser rear end for track use, which is achieved by stiffening the rear more than the front.