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Discussion Starter · #1 · (Edited)
here's the v2 post link

I have an adventure style SUV with an aftermarket steel bumper / spare tire on a swing arm. This, combined with the liftgate/hatch made for a tough fit for almost all typical retail racks. The only options were a few spare tire type mounts which had only two or three bike capacity, and aren't compatible with modern full suspension frames.

There are of course hitch based designs, which tank ground clearance at a minimum, but also with the spare tire in the way, mean a long extender / receiver which puts a lot of mass out far behind. Add to that that a four to six bike version like the Lolo or Velocirax is around $1000k, and that I couldn't get into my truck with the rack mounted to the hitch (due to the tire swingarm), and it looked like homebrew was the only way.

I studied the designs and decided I could adapt the lug studs on my spare tire carrier as the central point. There are adapter plates made for some off the shelf spare tire racks from Yakima, Thule, etc, but my truck has an uncommon bolt circle, and the adapter plates all terminated in a 'hitch like' square size that were proprietary (of course), which I thought might be tough to adapt to. The single point was also a single point, and I wanted something with some triangles in it for stiffness and control.

It isn't clear yet if my swing arm can handle the spare (110lb) and 5 bikes (150lb) and rack (40 lb) = 300lb, but I'm pretty certain I can carry the bikes/rack safely and maybe put the spare back underneath the truck for bicycle adventures.

The final consideration was material. I chose Aluminum as it is just easier to manage post build (no finish required). i'm not a super great welder, but for the number of joints that needed welding (one) it seemed I could do some reinforced AL stuff and not worry about it. The aluminum tube weighs a little less, but not dramatic as the wall thickness is double that of steel. Cost was about for the same for either material from my local metal supply.

So the wheel studs on the tire carrier are three, two above and one below. I decided to create an X shape using the studs, and then have horizontal crossbars for the handlebars and tire contact points. If necessary additional vertical bars can be added to other parts of the tire carrier, but I'm starting with the basic rack. If that works - there will be no need to engineer additional points.

General dimensions:
60" horizontals
42" handlebar to tires

Parts:
Handlebar horizontal 1 1/2" 0.25" AL Angle.
Tire Horizontal 1 1/2" 0.25" AL Angle
X bars 1" 0.125 AL Square tube - these will be roughly 50" long. I bought 72" to make sure they were long enough
X bar reinforcer 3/4" 0.125" AL Square tube - 1 ft
Some number of handlebar hangers. I'm using the Lolo rack product which are really nice. $45 each. Lolo specifies 10.5" minimum center/center spacing, and uses 60" bars for four, five, or six bikes.
Lots of bolts to suit your stuff. Mine is all 3/8" stainless and m14 for the studs.
 

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Discussion Starter · #10 ·
Don't put any bikes on that thing that would make you sad when they go bouncing down the road...
I can stand on it. Deflection at the end of the horizontals is less than 1/8". Color me not worried. Just because it doesn't come from a factory doesn't make it crap.
You might want to look into how much mass three m14 bolts can handle before you get worked up.
 

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No doubt the bolts can handle it, but can the aluminum spars (the X ) handle the deflection? The weak points would be holes drilled into the aluminum.
Test it by facing the truck, standing on the bottom horizontal, and grab the top horizontal (kind of like Jesus on the cross), and tug backwards on the top horizontal as if you're trying to rip it off.
Let us know what happens.
But I'm not an engineer and I did not stay at a Holiday Inn (it was a Hilton).
 

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Discussion Starter · #12 ·
Yeah I get it looks spare, scale is tough on pictures. Those are thick wall 1” square tubes.
It’s also not done. Because the tire is in the way of the saddles, I’ve had to make a spacer on the bottom.
I also have another set of vertical braces that are going in on the edges. More triangles is better. And now that the bottom will step out, they’ll be across the twist too.

However, in this form, I can do a pull-up on one side.
I weigh more than five bikes.
 

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I can stand on it. Deflection at the end of the horizontals is less than 1/8". Color me not worried. Just because it doesn't come from a factory doesn't make it crap.
You might want to look into how much mass three m14 bolts can handle before you get worked up.
I wasn't worried about the bolts, but you created some stress risers around them- but hey it's not my bikes.
 
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