Towing with a G8:
In the US, you can only get a class 1 hitch (aka RECEIVER, aka TOWBAR in Australia) unless you get something custom made. Class 1 is rated to 1,500lbs which is ok for a small utility ot tire trailer or a bike rack. They all go UNDER the bumper (you will see a bar coming out from under the bumper and a raised receiver for the tongue). The class 1 receiver hole is 1 1/4 inches. They cost about $125 (ebay) to $200.
In Australia, where SUVs and gas are expensive and they're not afraid to tow with a car, you can get a Class 3 (3,500lbs) or Class 4 hitch (4,500 lbs) that bolts right onto the car, from the dealer as an option. They're 2 inch receivers. You can also order an optional trans cooler. The class 4 is exactly the same as the class 3, but they come with a frame balancing harness (aka equalizer) and you have an option for "pump up" rear shocks. They have air bladders to keep the rear of the car from squatting under a heavy tongue load. You can get the class 3 hitch in Australia new for $350 to $400. The hitch wiring kit is about $150, but we dont need it in the US (more on that later). The big problem is getting it shipped to the US. I see hitches on Australia Ebay all the time for $100 picked up. Nobody will ship it across Aust much less to the US. Its a 90 pound steel bar almost 4 feet long, its NOT cheap to package and ship, especially overseas.
Here is how it installs:
The painted bumper you see on the back of your car is actually called a bumper cover. The bumper itself is an aluminum bar designed to be lightweight and deform in an accident and transfer force into the frame rails. There are two bumper mounts that bolt to the bumper and go into each frame rail and are bolted in. When you install the hitch, you discard the bumper mounts and the hitch itself goes into the ends of the frame rails and is bolted in, and the aluminum bumper is then bolted to the hitch. Benefits: tow weight goes right into the frame, you now have two bumpers to absorb energy in an accident, the frame rails are now better tied together to brace the frame. The hitch goes through the precut hole in the bumper diffuser and integrates into the back of car instead of a bar hanging under the bumper like a US class 1 hitch. Whats bad: you added 90lbs of weight to the tail of your car, hitch pin is covered by GT diffuser (but clears on GXP diffuser).
The class 1 hitches made and sold in the US dont go into the frame rail. They have a bracket that sits on top of the frame and is then bolted into the existing holes. Thats why they have such a limited tow rating. And also why a custom shop would have so much trouble making a heavy duty hitch for this car. Holden and Reese have the exact shape and bolt holes for their hitch to go inside the frame rail and have the bumper bolt to it. That would be a nightmare for anyone designing and welding it from scratch.
What you need:
-The hitch itself: $800 to $1500 from Australia with all bolts and brackets, see below how I got it.
-A wiring kit: Since the Australia wiring kit is for a 7 flat trailer plug (we use 4 flat or round) and $120, I got a powered (takes power from car battery and not tailight wiring) kit for $30. Since our battery is right there in the trunk, install is a synch.
-Tongue (aka BALL MOUNT aka DRAWBAR) and ball: Everything in Australia is metric, so I was afraid to get a ball from Holden since I knew it would be slightly off from 2 inches. I did get the holden tongue since I couldnt find one that didnt stick out as little as the Holden one did. The problem I had was a 1inch ball shank (what goes through the tongue hole and holds ball on with a nut) was too large to go through the hole since it was metric. I had to have a machine shop drill out the hole to 1.05 inches. Since a US tongue fits fine in the hitch, you can skip this and use any US tongue/ball combo you want that fits in a 2" receiver.
-optional GXP diffuser: Since the US bumper sticks out 3 to 4 inches farther than Australian bumpers to meet more stick US bumper requirements, the pin hole in the hitch that is used to hold the tongue onto the hitch will be covered when you put your diffuser back on. This is because the lip that sticks out between the mesh area and the bottom of the diffuser is lined up right with the hole. Ways around it: remove diffuser every time you tow, when you put the diffuser on reach under and get the pin in then so your tongue and ball will be permanently installed until you take the diffuser off again to get to the pin, make a huge ugly hole around your hitch so you can get to the pin with everything installed, or just put on a GXP diffuser which clears fine.
-optional escutchion: in Australia once you cut the hole in the diffuser, there is a plastic trim piece that pops into the hole. I never figured out what part number goes on the GT diffuser, but when I did my GXP diffuser I cut the hole very very tight to the hitch and I dont need or want any trim around it. Looks tight and factory.
How I got mine:
I called a few guys who deal with selling Australian products in the US. With shipping and customs fees every quote I got was over a grand. I called a Holden dealer, $1,500 shipped. I called some custom tow shops that make their own hitch for the G8 but its basically a copy of the Reese/Holden part; over a grand. Also would take 2+ weeks to get to me. Then I called JHP. They could get it to me via DHL in 3-4 days for $820 with a tongue. They could also get me the escutcheon (trim that goes in the hole in the diffuser) from Holden. Sweet. Turns our I didnt need it. Less sweet.
-Remove diffuser (see http://forum.***********/showthread.php?t=4965
-Remove bumper cover (see http://forum.***********/showthread.php?t=24062
-This is what you get from Australia:
-The bumper has a foam impact bar clipped onto it, it pops off. Remove it:
-There are four holes in the aluminum bumper bar for the four nuts holding it onto the bumper mounts, remove the four nuts:
-Now you have the two bumper mounts sticking out of the frame rails. Pics:
You need to remove the four bolts inside the trunk that go through the frame into the bumper mounts. When you open the trunk and lift the spare tire cover tray, you'll see two on the right side of the spare well. Pic:
The left (drivers side) bolts are under the trim that blocks your view to the battery. I was going to remove the whole trim piece, but I found if you remove the two screw in hooks for the cargo net, you can move it enough to get a socket on them:
Without any bolts holding them in, the brackets slide right out. Now you can slide the hitch into the frame, and use the same bolts to attach it. Dont forget to put the bolts through the braces that came with your hitch (in pic above) , to strengthen the bolt holes. Here is a pic of a removed bumper bracket next to the part of the hitch that will slide in its place:
-Now you need to bolt your bumper onto the hitch. Here is the ONE thing different between a Holden VE and your G8: the bottom stud on the hitch is a quarter inch lower than on your bumper bracket. So you need to drill a new hole for the stud to go through just below the existing hole. Luckily the bumper is aluminum and you can drill through it like butter. Excuse the ugly drill hole, I did it by eye and with a hand drill:
-Clip foam crash bar back onto aluminum bumper
-Reinstall bumper cover
-Your diffuser has a precut hole in it for the hitch, but I found its WAY too large and will leave a huge ugly gap around the hitch. Since I couldnt find an escutcheon to fit my GXP diffuser, I cut a very small hole in the middle and kept test fitting the diffuser over the hitch until I had almost no gap at all.