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The common 'butterfly' steering used on most trolleys may need some modifications to be safe on the road. A book could be written on the various ways ropes, cables, steel bars, wooden rods, car rack and pinions etc. have been put together to make the best (and the worst) trolley steering ever devised. Keep it simple, keep it strong, keep it self centering.

Castor Castor is the angle of the king bolt or king pins.  The top of the bolt can be angled towards the front or rear of the trolley.  The greater the angle, the greater the self centering effect.   Drawing is 7 degrees. A simple way to do this is to cut a piece of timber into two wedges, attach them to the chassis, then drill the hole for the king bolt. Mounting the axle on the top of the king bolt will lower the chassis, mounting it below will raise the chassis.  Use whichever suits your hill.

This is all very fine if the chassis doesn't roll and/or you don't corner hard enough to lift a rear wheel off the road.

Even if you have no castor, you will have if a rear wheel lifts, as the chassis then tips the king bolt forward.  Try lifting a rear wheel and see what your steering does.  Ideally it should still point straight ahead.  It probably won't.  It will either steer away or towards the lifted side depending on the angle of the king bolt.

Have a look at a skateboard.  If you tilt the board to the left, the front truck steers left.  What does the rear truck do?  In theory, you could steer your trolley by shifting your weight from side to side, like riding a skateboard.  How well this would work would depend on the combination of the castor angle, the flexibility of the rear suspension and the skill of the driver.
 

Top of the king bolt angled to the rear: If steering to the left causes the chassis to roll to the right it will cause the steering to pull left, exaggerating the turn. This could contribute to 'speed wobbles' (see Supporting the shoulders).

Top of the king bolt angled to the front:
If steering to the left causes the chassis to roll to the right it will cause the steering to pull right, resisting the turn.
This does two things.  Firstly, it tends to balance the driver on the trolley.  Secondly, it can make it difficult to turn a hard corner.

With all four wheels on the road it is doing just fine.	A rear wheel just raised, the front wheels are still pointing into the corner.
The rear wheel is higher now and the steering is now nearly straight ahead instead of around the corner.	A front wheel is raised now and the steering has turned towards the hay bales.
It looks like he may have been able to point the steering more towards the corner now, but......	...it is too late and his race is over.

Experiment, test, practise.
Design to suit the course and style of the derby.

Attach a piece of inner tube to each side of the butterfly, pull it taut, set the steering straight and nail/screw the centre of the tube to the chassis.

Very simple and can be very effective.

Once again.........Experiment, test, practise, design to suit the course and style of the derby.

A rope can easily be replaced by two metal or wooden rods, running from the butterfly to two levers beside the driver. The further the rods are from the king bolt the more leverage you will have. The closer the rods are to the pivot points of the steering levers the more leverage you will have. Note:  This will probably decrease the turning circle of your trolley.

Important Note:  I have seen a trolley with the steering working the opposite way (right hand forward to turn right) to what the driver would expect.  The driver crashed and broke his shoulder blade on his first run.
 

Steering wheels ideas A car rack and pinion can be mounted lengthwise on the chassis with one end attached to one side of the butterfly. The rope can be run through a couple of pulleys and wrapped around the steering column. A badly designed steering wheel system will still get you into trouble as seen in these photos from a Billy Cart derby in Bundeena, NSW The further your hands have to move to change your direction, the more control you will have over your trolley.

Increasing the distance between the front and rear wheels increases the turning circle.  This can help to minimise 'speed wobbles'

Supporting the shoulders (rope or tiller steering) When a trolley is steered to the right the shoulders swing to the left hand side of the trolley causing the driver to over-steer.  When the driver tries to correct his shoulders will swing to the right hand side of the trolley, causing an over-correction.  This is the dreaded 'speed wobbles' that loses many races. Designing the seat to support the shoulders will help to minimise the problem.

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