157dB

Maybe I dont understand your answer but here goes nothing...
GTs came with 17s OEM and the 12.4" rotors will fit under OEM 17s.
18s are only needed for the 13.2" brake conversion.
The 12.4" 2005-2010 GT caliper brackets are here when you need them....

tx_zstang

I used one of the conversion kits with the stock GT rotors. Yeah, not the best choice if you want different (slotted) rotors. But everything worked out fine otherwise.

Rickoshay

I just completed a conversion on my 06 GT, using the Roush 13.2 in. rotors & bracket take off parts. My choice was the OEM Bullitt/GT500 Carbon Metallic pads to go with this setup.

This combination really worked for me, my driving is a daily driver & also mountain roads on the weekends.

IMO, This combination works like gangbusters for me!!

Mustangarrett

Where did you buy the takeoff parts? I'm interested in the same conversion, but have had a hard time finding anything not too expensive. Thanks

Rickoshay

You can buy the take off parts from either the Roush on line store, or there Roush Ebay store.
The OEM 08-09 Bullitt/ 07, 08 & 09 GT500 (Non Brembo) carbon Metallic front & rear pads I bought from my Ford dealer. I can look up the pad numbers if you need them.

Hope this helps

Rickoshay

Added Note For Post Above:

Ford OEM Carbon Metallic pad part numbers.

Front Carbon Metallic pad set 8R3Z-2001-A (Part interchanges with Motorcraft #BRF1081B)

Rear pad set 7R3Z-2200-A (Part interchanges with CR3Z-2200-A)

SteveDwsn

What he said. I would also add, unless it has been done recently, take an extra hour, flush all the old brake fluid out, and replace it with new. You are already there, so why not? Honestly, new fluid made more of a difference in my braking than the upgrade did.