Wheel Number

• Two - A bicycle works for much of the race but will not be stable when in the mud bog. Advantages: low cost and low friction.
• Three - Simple and stable.
• Four - With four wheels you need a suspension. Otherwise the stresses will tend to destroy your frame.

Tire Size

Diameter

• Road - Size not very important.
• Mud - Large diameter helps reach below the gunk.
• Sand - Large diameter helps keep friction down. And reduces the climbing effect.

Width

• Road - Narrow, high pressure tires provide lower friction.
• Sand - Very wide, very low pressure tires allow permit floating above the sand. This gives lowest friction.
• Mud - Unclear.

Stress on the Wheel

Dynamic Load - Bumps increase effective weight of vehicle. On a conventional bike you can absorb most of the bump with your legs. On recumbent the wheels take the full force.

Side Load - Turns and Hills. On a bike you lean during turns, virtually eliminating side force. On three or four wheel vehicle wheels have more side force. Solution: wider hub for spoked wheels. Cost: increased stress on the spokes. Note: Almost every year a bike wheel potato-chips.

Stiffness Loosening spokes weakens the wheel. A strong wheel is a stiff wheel. If you need a soft ride, use a suspension, either on the axles or on the seats.

Drive System

Live Axle - Advantages

• Easier to interchange wheel types.
• Easier to install brakes.
• Easier to get all the parts to work together.
• One set of sprockets works for all wheels.

Direct Drive - Advantages

• Less weight.
• Fewer parts.
• Lower friction in bearings.
• Changing wheel can cause gear range change.

Rear Wheel Drive

• Puts weight on rear wheel when climbing hills.
• When exiting the river the rear wheels must be lowered enough to contact hard ground below the water.

Front Wheel Drive

• Takes weight off the driven wheels when climbing hills.
• No problem contacting the ground when exiting water.

Kinds of wheels and tires.

Bicycle. + Low friction. - Not good for side loads.

Motorcycle. Compromise between bike strength and auto weight.

Automotive. - Heavy.

ATV. + Excellent off-road. - Terrible on-road.

Full custom.

Tips

Local bike shops will often give second hand parts to Kinetic Konstructors. This includes wheels, tires, frames.

Reference

The Bicycle Wheel - Jobst Brandt - Avocet - ISBN 0-9607236-6-8