Wallaby Wheels

• Price: Price on application

The importance of Wallaby Wheels design will only be evident to those who have attempted to design the same. Even plastic wheels typically have a metal bead around their tyres. This bead acts as an inductive loop coupling with the transmitter and receiver loops such that ground response is overwhelmed by this inductive response.

 We have used Kevlar bead tyres on glass fibre filled nylon wheels with side force bracing hubs designed for trotting carts. Unlike other plastic wheels, these have been able to take the rough cross-country treatment we apply to them. Their metal axles and bearings are found to be inductively manageable.

 As Wallaby is designed to match towing vehicles of weight from 500kg to 3000kg it itself weighs 220kg and this creates considerable forces on the wheels. Most tyre options fail quickly. Simple air inflation is useless over thorny vegetation and severe side-forces can tear low pressure air inflated tyres off rims. Moving to high pressure of 50 psi we find the tyre becomes hard and unable to absorb cross-country impacts well. For this reason, Wallaby suspension is principally within the undercarriage rather than reliant on soft tyres.

 Sealing ‘goo’ can be poured into tyres to repair thorn puncture holes – we find this problematic and inadequate under the stresses we apply although in country without thorns it is suitable.

 We have tried using solid urethane infill on tyres and found that in most country this is fine but on jagged rocks the tyre tread will get cut off in less than an hour.

 Our final solution involves encasing a solid tyre core with a cured urethane foam sheath within a Kevar bead tyre with extra width.

Finally let me emphasise the importance of wheel diameter for cross-country travel – the larger the diameter the flatter the incidence angle on every impact. We use 24” diameter wheels rather than smaller options that are more readily available. Sleds and tracks can improve incidence angle and thus ride smoothness but we have found that sleds grind away quickly on rocks and gravel.