Radio Shack Red Arrow Buggy wheel set

Overview

I made this model when restoring my Radio Shack Red Arrow Buggy. All parts are hard to acquire for this old buggy. Tires wear out and replacements aren't available. Some people switch out the wheels for other more-common wheel sizes. I prefer to stick to the original aesthetics as much as possible. This wheel is based on the original Red Arrow wheel along with some changes in order to fit a Tamiya Hornet tire. Front tire: Tamiya 58016 9805033, Rear tire: Tamiya 58034 9805034.

The Tamiya Hornet tire is the only tire I could find with the massive spikes like the original Red Arrow tires. There are some other spiked tires but they don't have spikes on the side or have a different grip pattern. The Hornet tire's inner diameter is way too small to fit on the Red Arrow wheel without modification. So the tire will have to be trimmed and the wheel dimensions altered to make everything fit property.

I've done a lot of trial and error in order to get the hornet tire to work properly. I've included a modified wheel as well as a clamp used for trimming the tire. In my initial attempts, I had issues with the tire shifting side to side as well as wobble when rotating. These parts and this guide should reduce the likelihood of running into these problems.

My modified wheel is a good amount wider than the original Red Arrow's wheel. This is necessary to fit the tire properly. With the way the original Red Arrow tire bulges out, all together they end up having about the same amount of ground contact. I made sure that it still fits on the shaft the same way.

Printing the Wheel

The model is printed in two parts. There are screw holes and slots for threaded inserts for screwing the parts together. I ended up acetone welding instead but I kept them in the model.

I didn't include wheel vents. The hornet tire already has a hole built into it. Should you want vents in the wheel itself, I suggest drilling them instead of trying to print the tiny holes.

Print the parts in the orientation I have them in the STL file. The cover should print facing up. Also the part of the wheel that interfaces with the hub adapter needs to be facing up. 

I printed this in Inland White ASA just because that is what I had on hand in white that could be smoothed. I had initial plans to do the wheel body in nylon but ended up going all ASA. The key is to use a filament that can be vapor smoothed so the wheels will be shiny and match. So ABS is fine and I'd expect PolySmooth to work well too. 

While plastic can yellow with age, I think the original wheel color wasn't as bright of white as my 3d print came out. So maybe an off-white would be a better match.

For the wheel cover, I printed with a 0.25 nozzle 100% infill and very slow speed. This will need supports underneath. I put that in an acetone vapor bath to smooth it.

For the wheel body, I printed with a 0.4 nozzle 100% infill and at a normal speed. This too requires supports. I didn't vapor smooth this as it could impact the dimensions.

Then join the two parts with threaded inserts, glue, or solvent weld.

Tire Trimming

Now for the hard part, trimming the inner diameter of tire. You need the tire's inner diameter to be increased to around 45.5mm. It is challenging to cut a perfectly round circle that is centered in the middle of the tire. I tried to carefully free-hand cut it with a hobby knife but it didn't turn out well.

I switched to using my drill press with a 1.75 in (44mm) hole saw. A 44mm hole is close enough to fit. This is difficult but the results are fantastic. Should you take this approach, I included a wheel hub that you can use. This keeps the tire centered and provides a center hole for the hole saw's guiding bit to grab. An original Tamiya Hornet wheel would likely work for this as well. Getting the hub into the Hornet tire can be quite difficult. You have to roll it in sideways as you stretch the tire hole.

I didn't get injured doing this, but you might! Be careful! Here are my tips on how I got it to work.

1. Go very slow!!! Not just slow speed on the drill press but also lots of breaks for the hole saw to cool. Cutting soft rubber causes a lot of friction and it tries to grip the cutter. I used cutting oil but I don't think it helped much.
2. Keep flipping between both wheel sides and drill evenly. We are cutting the tire off the hub. So once one side breaks free, it really isn't possible to start drilling on the other side.
3. Provide support underneath the hub. The hub won't sit flat due to the tire bulging out. You'll need something small to support the center of the hub.
4. Once the tire starts breaking free from the hub, you might have to stop. The tire will grip the cutter much more strongly due to being loose. Use a hobby knife to cut the thin rubber that remains.