The 345mm rotors with the 18z kit do not require centering rings, only the 17z kit rotors. I know you said you were getting the 17z to retain your 17" wheels though, just want to provide that info here for anyone else reading.I have already ordered the Apikol 65-68mm rotor centering rings for $50 and Bosch Pads (2004 Touareg V6) for $65.
I just picked up part# 8V1611021B from the dealer (for GTI-R). It measures 25.4mm bore and pushrod of ~44mm which matches the TT-RS info unless I'm measuring the rod length incorrectly.the Golf Bore size is 23mm with a pushrod length of 1.64", front caliper piston is 54mm
The GTI Bore size is 25mm with a pushrod length of 2.05" (both 312mm and 340mm brakes), front caliper piston is 57mm (312mm) and 60mm (340mm)
For reference, a TT-RS is 25.4mm with pushrod length of 1.75" (that's with the Brembo 4-piston calipers with 57mm pistons x4)
Update on my Rotorlabs kit after attempted install today. Your theory was right on the money....The offset IS different (78mm vs 80mm), but it sounds like they take off enough for the widest offset and if you have less, you just use a spacer or two to get the caliper centered over the rotor...
That's probably more to do with having fresh brake fluid, bleed, and thicker pads. I was down in Ft. Myers with my uncle last week- we rented a brand new Infiniti QX30 to drive around, and the brand new brakes were really tight. It took my uncle quite awhile to adjust.It is currently raining in Los Angeles (so people have forgotten how to drive) but I hit the brakes pretty hard today as someone abruptly cut into my lane to avoid some "deep" water. Keeping in mind that I was only going somewhere between 15 and 20, the amount of pedal I gave it would have slowed me down before and I engaged the seat belt safety catch today .
Yes, I understand more caliper piston volume will require more fluid transfer. I am surprised your brake pedal travel feels the same and you don't have a lower pedal? I don't know the volume of the stock TDI caliper single pistons, so I can't use that comparison. You've probably upset the OEM "calibration" with brake fluid vol. needed when the brakes are applied, but agreed you'll get that back when you match your new calipers up with the proper master cyl that has the correct fluid displacement ratios. Your pedal travel really shouldn't change notably with pad/rotor wear as the pad generally retains the same pad/rotor clearance through it's life span.The following quoted from user v8a6 over on audizine: 18z piston size are 30/34/38mm... 17z piston size are 34/36/38mm... So, the 17z have a larger overall piston area and will take more brake travel to push (although in reality you probably wouldnt notice a difference between the two)