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Do you feel uncomfortable without a spare? Do mini-spares count? Or, does your registration jurisdiction demand protection for the rear of your Locost, so that a spare tire serves the purpose of keeping the safety inspector happy? Nova Scotia’s designated engineer inspector looks for protection for the gas tank, and accepts a spare tire to that end. Nova Scotia’s Registry of Motor Vehicles goes one step farther and looks for a bumper (ugh). I decided to have both a spare tire carrier and ‘bumperettes,’ to keep the regulator happy. And I’m old enough to want a spare anyways ….

Following is a photo of the completed work, complete with paper bodywork ... more details to follow in the next two posts.

[Edit, 8 October 2012: It only seems fair to add a photo of the finished fabrication all by itself, so here is a photo during painting: I thought I'd paint before I stored the assembly.]

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Warren
Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601

And now for the spare tire carrier ...

My spare tire carrier is in the Birkin style. It is outwardly like Uncle Ron’s, but relies on mechanical fasteners rather than a bayonet-like mounting. The mock-up photo shows extensions of the ‘horizontal’ loop, but only for first fitting, and to allow me to do the bends manually (see the second photo). The ratchet mechanism of my conduit bender failed, so I just popped the bender’s ¾ inch die in the vice and pulled on the free end of the tube. The overly long ends of the horizontal loop gave me extra leverage for the bend.

In the third photo I have welded the horizontal and vertical bits together and added two horizontals to the vertical piece. The upper horizontal (nearer to the camera) is 2 x 1/8 flat bar and the other one is a piece of ¾ inch square tube, which is not used on the Birkin tire carrier. I will show what these bits will do later. The 1 inch square tube is simply a jig clamped in place to ensure that the lower mounting brackets are attached (welded) in proper alignment.

In the next photo I am fitting up the bracket made from flat-bar that will carry the mounting stud for the spare tire. This is followed by the fit up for the diagonal braces for the flat bar. In the Birkin, these braces go out to the vertical hoop, rather than to my 1x1 square tube. Welding the diagonal braces was an exercise in contortion. I have cut off the ends of the horizontal tube, but not yet ground the stubs flat.

Finally I show the nearly completed carrier. The wheel stud still needs to be installed here, but the concept is clear. What isn’t clear (intentionally) in the photo is that the vertical loop is not symmetrical, but there will be a spare tire in the way, so who will know?

_________________
Warren
Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601

I quite easily decided that I would not have a continuous bumper, but rather bumperettes on each side of the spare tire carrier. What did cause me considerable thought was choice of material. I did have some 1 1/2x0.095 DOM around, but that might well transfer impact loads directly into the frame which is largely ¾ inch tubing in the rear. Since I’d sooner replace a bumper after a minor bump than repair the chassis I decided to use exhaust tubing left over from a roll-bar mock-up for the bumperettes.

I wanted the bumperettes to provide at least some parking lot protection, so I located them 15 inches above ground, something like the minimum in the construction codes. Regardless, my Britax tail-lights will probably bear the brunt of any parking by Braille. There is not a lot of structure at this level, so I decided to mount the mid-span of the bumperette to the roll-bar brace and turned down the inner ends so that they could share the lower mounting point for the spare tire carrier. In the end I decided to forgo this shared mount approach as looking rather busy; instead I would weld the bumperettes to the spare tire carrier.

The brackets on the roll-bar braces were made out of 2x2 inch square tube. Bolt holes were elongated vertically, which together with horizontal slots on the bumper supports will allow bumper alignment. You can also see the single wheel stud on the spare tire carrier in the first of the two following photos.

To bend up the bumperettes I had the good fortune to still have my friend’s Pro-tools bender on hand …

After trimming the ends of the tube I mocked up the bumperette ….

The ‘end-on’ photo shows how I approximated a curve in the bumperette with some discrete 6 degree bends, so it would conform to the fender shape. The open end of the bumperette will probably be filled with a side-marker light to keep the Registry of Motor Vehicles inspectors happy.

The inboard ends of the bumperettes were slotted to accept 1/8 inch brackets that would be welded to the spare tire carrier, here shown in mock-up, and below that as completed bumperettes.

_________________
Warren
Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601