Downhill soapbox racers are great. It (usually) occurs when a parent gets a bit nostalgic about an experience they had as a child, gunning it down a hill of some sort, possibly in gumboots, probably too fast, and possibly with a sibling or friend atop the beer crate seat (somewhat dangerously).
The types of cart (kart?) I had a experience like this on was a 'rope-steering' jobby. I think I was in bare-feet, as it was summer at the bach, and the hill wasn't too big, but as with most things on wheels, its often about how close to the ground you get that makes it exhilerating.
Each year at the most amazing festival that happens in our suburb of Island Bay, there are the Ribble Street Races. These are located on a steep back street, and the road gets closed off for the action. There are Lego races for the smaller kids, and cart races for the more adventurous.
As I see it, there are only two categories of carts:
- the throw-togethers
- the elite-attention-to-detail-I-want-to-win types
Research and development
Theres lots of ideas on the net, and the approach is varied. I didn't want to spend ages making pushrods, stub axles, and my welding skills are a C+ rating, so I didn't even attempt to go down that approach. I did spend a bit of time looking for a pedal car that I could work from, but in the end I found a video of a off-road racer based on bike parts and this approach looked achieveable.
I was on the lookout for a bike with rigid front forks, and a good (working) brake. I ended up buying a second-hand kids bike with 24" wheels for $10. I didn't feel too good attacking a working bike with a angle grinder.
I found two good condition 24" thin profile wheels at the dump shop, the bearings were still good in them and the spindle was intact. I couldn't find any road or mountain bike rigid forks either, and I was against buying more bikes to decapitate...
Building the frame
I bought some new 32mm box section mild steel, its medium thickness wall, from this I did some quick maths and sketches to figure out dimensions. I welded it up and got it pretty square, which I was stoked at, and was more than strong enough. I added some other box section steel I had so I could mount some brackets on to brace the downtube of the bike. I initially tried welding the downtube to the base frame, but the downtube was very thin and not good quality steel, resulting in some big burnouts from the welder.
I feel that costumes are required if the trolley is not adorned. Also according to the laws of science, we all know red is faster, even its meant to be a red octopus.
The (professional) competition - a bathtub racer built by a panelbeater. Image credit: Keith Johnson