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For those that only want to tow a minimal load, this design is probably visble, but in my opinion far from ideal. One of the major limitations of this design is that you are towing through the rear bumper shocks, which are not designed or intended for this type of load.
Good point. I wasn't planning on towing a boat, probably just a teardrop trailer for Camp 928.
Here are a couple more pictures of what little progress I am making on this Hitch. I have spend the morning making another prototype of the main rear cross member in quarter inch plywood. I have located the holes a bit better and have put the shock strut holes in each end. I have also narrowed it just a tiny bit. There are going to be three holes along the top to bolt it to the middle of the top of the rear crossmember.
Last edited by Jerry Feather; 03-31-2024 at 11:45 AM.
Thanks for posting these. I'd forgotten that the GTS hitch was a completely different design that the earlier Porsche hitch.
@hwyengr Which style do you have available to you?
The pic you posted of the Porsche hitch is from the sellers ad in Norway from whom I bought that very hitch and fitted it to the -89 GT I owned at the time. I then used the GT to haul my trackcar (964 RS) to the tracks back then.
I sold the car in 2010 and the buyer still has it. Me and the car/hitch reside in Sweden.
The next major member of my hitch design will entail another piece of steel that reaches from nearly end to end of this first one and will be made out of half inch steel plate and will be about 2 inches wide from front to back. I am working up the shape of the opening in it that will need to clear around the exhaust hanger just left of center and another opening in it that will allow for what appears to be the fuel tank vent. I may put a series of lightening holes in it also just to reduce its weight some. It will have wider kind of arms at each end and to them will be welded some angle iron that will have two holes in each one for bolting it to the bottom of the rear ends of the frame rails just under the bumper struts. This member will be welded to the bottom front of the member that I am now making out of thin plywood. I'll make my mock-up out of half inch plywood also.
Another aspect of this hitch design that needs some thought is how and where to design and place some loops for hooking the safety chains from the trailer to the car. I think that they are probably required in just about every State.
And finally, I hope, is the design of a method to fold the license plate out of its recess so that it is still visible and probably still lighted. I find that that too is required in just about every state. This will be required since my hitch receiver will be accessed through the license plate recess in the bumper cover.
Jerry, the tow hook threaded into it's receiver makes a great place to hook the safety chain. Its threads are accessible without the fold down license plate.
I am doing some preliminary measurements for this hitch application. I find that the top of the rear bumper cover is about 31 inches from the ground up. The bottom of my hitch design is about 13 1/2 inches below the top of the bumper cover. With the receiver welded at the bottom on the hitch members that will put the top of the hitch receiver right near the top of the license plate recess. So, guess what? With the hitch ball mounted level with the top of the receiver opening that will put the top of the ball just about right at Jeremy's desired 21 inches. For any others that will require a ball mount to have some drop in it for the ball to be bolted to. I guess that I had better double check my measurements.
…I have abandoned the idea of incorporating the 2 inch hitch receiver in favor of the 1 1/4 inch one. My reason is that on simply looking at some of my own 2 inch hitch tongues they simply look too hefty for the 928. I also went to look for a hitch tongue in 1 1/4 inch and could find only one in three stores look at. Then I also noticed that many of the 2 inch ones looked at were rated for about 35000 pounds of pull weight. The 1 1/4 inch one that I bought is rated at 3500 pull weight and I think that should be just about maximum for the 928 in any case. I think that putting a 2 inch receiver on my hitch will simply send the wrong message about what ought to be pulled with it. This is in spite of the advantage of putting things like a bicycle rack or luggage rack of some sort on the back of the 928 in the 2 inch hitch receiver.
I am extremely interested in this thread as it has been my intention to do something similar.
I would however require a 2" receiver since I have a bike carrier that fits a 2" receiver.
As someone else mentioned, my idea was also to mount the receiver in front of the licence plate mount with a suitable hole under the plate. Make the plate removable and insert the hitch and electrical plug through holes in the plastic. When not towing, put the licence plate back and everything is completely hidden. I did this very successfully with a Toyota Supra many years ago.
My actual desire is to be able to tow a trailer with a 928 on it. I think it's doable with the correct design of towbar and for that reason, I have my doubts about the lack of any torque stabiliser. All that weight (up, down, forward, back, depending on what the tow car is doing) solely on the main chassis beams, but over a relatively small area might not be enough. The long stabiliser arm reduces those forces so its attachment at the front doesn't need to be massively strong, but contributes enormously to the overall strength of the bar.
The 1 1/4 inch ball mount that I bought to work from is rated at only 3500 pounds of pull weight. To pull a trailer with a 928 on it is probably about 4500 or 5000 pounds, depending on the trailer. There are about two suggestions in this thread about pulling a 928; so I am rethinking my decision about the size of the receiver. But rather than going back to a 2 inch receiver, I am going to go hybrid and design and fabricate one that is 1 1/2 inch inside. I'll use 2 inch box tubing with a quarter inch wall and then a fairly heavy 1 1/2 inch square tube for the ball mount/tongue to fit inside of it.
But rather than going back to a 2 inch receiver, I am going to go hybrid and design and fabricate one that is 1 1/2 inch inside. I'll use 2 inch box tubing with a quarter inch wall and then a fairly heavy 1 1/2 inch square tube for the ball mount/tongue to fit inside of it.
going with 1-1/2" seems like an od choice since the standards are 2" and 1-1/4" if you use 1-1/2 every tounge for any rise/drop would need to be custom, and it wouldn't fit any standard accessories (bike racks, cargo platforms ...) just seems using a current standard would make sense.
going with 1-1/2" seems like an od choice since the standards are 2" and 1-1/4" if you use 1-1/2 every tounge for any rise/drop would need to be custom, and it wouldn't fit any standard accessories (bike racks, cargo platforms ...) just seems using a current standard would make sense.
However, what I am designing here, as the title of this thread suggests, is a TOW hitch and not a HAUL hitch. For my design I think that the TOW weight is going to be limited to about 5000 pounds and the tongue weight is going to be limited to about 50 pounds. It is not going to be designed for any kind of contraption hung onto or into the receiver that might weight over 50 pounds. That is probably part of the reason that neither of the factory hitches have any provision for any kind of haul platform or other haul rig. With an inch and a half receiver and a custom ball mount made for the particular trailer to be pulled there will be very much resistance to adapting something like a baggage platform to haul something like an engine or even a 928 transmission out to Greg B for overhaul.
However, what I am designing here, as the title of this thread suggests, is a TOW hitch and not a HAUL hitch. For my design I think that the TOW weight is going to be limited to about 5000 pounds and the tongue weight is going to be limited to about 50 pounds. It is not going to be designed for any kind of contraption hung onto or into the receiver that might weight over 50 pounds. That is probably part of the reason that neither of the factory hitches have any provision for any kind of haul platform or other haul rig. With an inch and a half receiver and a custom ball mount made for the particular trailer to be pulled there will be very much resistance to adapting something like a baggage platform to haul something like an engine or even a 928 transmission out to Greg B for overhaul.
5000 lbs gross and 50 lbs tounge. That's a 1٪ tongue weight. I believe the typical suggested tounge weight for safe towing is 10% 50 lbs would be scary light.
The original wasn't designed with a US standard 1-1/4" or 2" receiver because it wasn't the standard for Europe. As a matter of fact it still isn't the standard in Europe.
For instance, if you look at the US Cayenne, you will see it delivers from the factory with a 2" receiver. If you look at a Euro Cayenne it is a totally different configuration. Not because it isn't capable of supporting the weight of a bike rack, but because it needs to meet Euro hitch design specs.
It just seems ludicrous to me to go through the effort to design and build a hitch system the eliminates or at least complicates the attachment style the most of the customers desire. There are likely a lot that will likely never tow a trailer, but would enjoy the ability to install a hitch bike rack.
I made a bike rack using a 1/2" steel plate held by 4 3/8" allen bolts to the alum bumper. should be strong due to the towing hook being used in the same location to pull the car for some reason.
And the license plate can move up and down when not is use.
Wow. That is a revelation. In fact, everything I now find on the internet says 10 to 15%. I just don't think that the 928 is built to handle 500 to 750 pounds of weight hung just outside the rear bumper, no matter how it is fastened to the car.
03-30-2024, 12:44 PM
