Securing a GSW subwoofer in a full size spare
For a GSW: To allow the Fender subwoofer to be secured within a full size 205/55-16, 225/45-17, or 225/40-18 spare tire:
The Problem: A full size spare tire will fit in the GSW spare well nicely, but the OE Fender subwoofer can't be held-down with the stock stud & nut because the sub sits quite a bit higher from the well floor.
The Solution: Increase stud length (insert joke here).
Get a 2nd stud/nut set (p/n 5Q0803899). Pull the end caps off both studs and connect the two studs back-to-back with 1" PVC pipe. The pipe is a perfect press fit in the stud bores and can be secured either with epoxy/adhesive or 7/16" threaded rod w/ lock nuts on each end. I chose threaded rod since I wanted to be able to use the stud for both temporary and full size spares and this method allows quick conversion from short to long stud. Also I didn't want to risk possible iffy bonding between PVC and POM parts (and so I can't vouch for this method).
If using threaded rod, drill out the end hole in each stud to 7/16". Mock up the full size spare w/ the "double" stud and sub in place in the spare well in order to determine the correct length of pipe. I won't specify a pipe length since wheel backside inner diameters and tire widths will vary and hence sub mounting height relative to well floor will vary with each application. If using threaded rod, you want minimal projection of the ends of the threaded rod past the "T" on the studs; just enough for the lock nuts to fully engage rod threads.
Hopefully its obvious from the photos that the wheel and sub are held-down separately with their own nuts. You don't want to use only a single nut to hold down both because only the 18" temp. spare wheel (and possibly an 18" full-size spare) allows the sub to fit flush in the wheel, which distributes a stable clamping force to sub & wheel. Smaller wheels force the sub to sit wedged into and above the wheel which makes sub mounting somewhat unstable and subject to possible rocking and loosening of the nut over time. The two-nut method assures secure hold-down of the spare regardless of what's going on with the sub hold-down.
The sub clears the underside of the cargo floor only w/ floor in upper mounting position. This is why I use the full size spare only on long trips and the temp. spare for routine local driving; I want to have the option to lower the cargo floor when driving locally while having the safety and no speed limitation of a full- size spare on a trip.
The higher sub mounting position will stretch the sub wiring harness and it may no longer reach the sub connector. If so, cut a second harness exit slit in the spare well soft trim several inches directly to the rear of the existing slit and relocate the harness through the new slit.
A 195/65-15 spare is somewhat iffy because the sub sits precariously high in the backside of the wheel and is more subject to rocking than when mounted in larger wheels.