So you want to build your own box bike?
At Rodford we applaud innovation, those creative “men in sheds” and we like to support people who wish to do their own thing. So here’s a few things to consider when designing your own box bike. Some information to help you avoid some of the common pitfalls.
Box bikes are usually either single spar or twin spar.
The single spar is the simplest build but overly long bikes of this type can waggle. Side rails or front and rear deck hoops can help reduce this.
If you want to create a very long load area then consider a twin spar design. This also has the advantage that front wheel can be tucked into the frame, creating better use of the wheel base length.
Which ever design you choose, when you are working to reduce flex in either the horizontal or vertical plane, then always remember how the shape of the tube and how the position of reinforcements can help. Here is some text on the engineering subject of “moments” which may help.
The box bike has more weight over the front wheel when it is fully loaded, but when empty the front can become light.
Steering can become heavy and a problem known as “wheel flop” can be too large when a bike is loaded but this can be reduced by having less trail.
However too little trail and the bike may start to shimmy when empty. There is a fine balance to be struck here and the actual value of trail you end up with depends on many factors, but you could try building some forks with several wheel positions to find what works best for you. For the most part a box bike will have a steeper headstock angle than a normal bike to help reduce wheel flop and also have less trail.
Check these two articles to learn more about steering and geometry.
A lot of the steering geometry is governed by the Fork. If you are making your own then you can get creative and try different amounts of trail and rake, but if you are using a standard fork then the rake might be fixed so you will have to adjust the headstock angle to get the trail you would like. For 20″ wheels a BMX fork is nice and strong, but this will typically be designed for rim brakes which maybe OK for your design or not. If you are fitting hub brakes then roller or drum are an easy retro fit, whereas disc will require a mounting tab on the fork correctly orientated and spaced from the axle.
Load bay length.
It is temping to make this large to get the most for your hard work but it is worth noting that even a short load bay is super useful. Just 400mm of load space will allow you to put several large bags on, or a stack of Euro-crates or a child seat. We find our short box bike incredibly useful and convenient to use.
Some people need a small bike for storage reasons. As mentioned above, a short load area will help and still provide a useful bike. Smaller wheels is another variable, but be aware how this affects your gearing options. A small back wheel will make all the gears seem low. Of course a larger chain ring will give a small wheel some higher gears but then you might not get a chain guard to fit (if you want one). Small wheels produce a more harsh ride too, but don’t let that stop you experimenting with this idea, it does have benefits.
For a first build, steel is your best friend. It is easily joined and not likely to fatigue. Aluminium is lighter, but difficult to weld and the weight benefits can be lost if you end up adding too much bracing. A steel donor bike frame is a good way to start and it will give you most of what you need rewards of the handlebars, leaving you to fabricate just the front section.
Box bikes usually either have a single bend or “S-bend” steering rod. The single bend types can be attached to the bottom of one fork leg and they stick out sideways to allow the rod to clear the tyre at full lock. S-bend types usually attach to the fork crown and go behind the wheel as it turns. There are other options too, like cables, chains, hydraulics and rope; but most people use rods. The single bend rods allow the front wheel to be closer to the cargo box so will help if you are trying to produce a compact design, whereas the S-bend design usually needs some clearance to avoid a clash with the box/tyre. Also note that the S-bend design can use conventional ball joints at both ends leaving the bar free to swing about, whereas the single bend type must be held out to the side for it to work properly.
If using a steering bar you can change the length of the arm at the bottom of the steering tube to make the steering quicker or slower.
Always remember that responsive steering is critical to the balance and control of the bike. Ensuring that the steering is smooth and that the link bar does not clash with any of features on the underside of the bike is essential to make it safe to ride.
This is a big deal and one of the hardest things to get right. There are some box bikes on the market that ride really well but are let down by a centre stand that is either difficult to deploy or difficult to retract. The stand must not fall down when riding and not fold away when children climb aboard. Bikes can wobble if the stand legs are too short and if they are too long it makes the bike heavy to lift onto the stand.
Trial and error is probably the best way forward and adding some adjust-ability to your design will make tuning it easier. Consider how different tyre sizes might affect the stand.
There are also two, three and four leg designs you can use. The 4 legged ones are the most stable, they are self centring and require no spring action. Twin leg stands need a spring to hold their position or if you prefer, a damped gas spring.
Wood is easy and for non-complex shapes some plywood sheet and Gorilla glue is all you need.
Aluminium is light and durable but can “boom” when empty and the edges can be too sharp for passengers.
Simplest of all is probably a wooden deck with some soft luggage. Very versatile and durable. If you are concerned about efficiencies, then this arrangement will be the lightest and the most aerodynamic.
For child carrying, avoid handlebar clash with their heads by seating them low down in the box.
Hopefully this text helps and gives you some ideas.
If you have any questions then please get in touch or come and try one of our box bikes to see how it’s done !