Make a solid tire first: compression-mould rubber into a solid ring, which is heavy but cannot puncture and suits carts and wheelbarrows. A pneumatic tire needs a carcass of several plies of rubberised fabric, a rubber tread and a separate inner tube built up by dipping on a ring-shaped form, and it is far harder to make reliably. With a rolling-resistance coefficient of 0.025 for solid rubber, a 300 kg cart at 1.5 m/s needs about 110 W to move, roughly five times the 22 W an air tire at 0.005 would take.
Part of Rubber Processing
Solid and pneumatic tires for village vehicles, with the power cost of each.
The Solid Tire Is Simple And Costs Power; The Air Tire Is Hard And Saves It
The carrier’s two kinds:
| Kind | Construction | Use |
|---|---|---|
| Solid | Compression-moulded rubber ring; heavy, puncture-proof | Carts, wheelbarrows |
| Pneumatic | Carcass of multiple rubberised-fabric plies, rubber tread, separate dip-moulded inner tube | Vehicles where comfort and low drag matter |
The inner tube is the critical part of a pneumatic tire, because a leak anywhere in it flattens the tyre. The carrier builds it by dip-moulding on a toroidal (ring-shaped) form. Using the carrier’s 0.1-0.2 mm per dip, a tube wall of 2 mm (an illustrative thickness) takes 2 ÷ 0.2 = 10 to 2 ÷ 0.1 = 20 dips; see Dip Molding (Latex).
What You Need
- A ring mould and a press for solid tires; see Compression Molding.
- A fabric carcass and tread rubber for pneumatic tires.
- A toroidal former for the inner tube.
- A tested compound, since a tire flexes millions of times; see Quality Testing.
- For stopgaps: Tire Alternatives covers split garden hose and tarred rope.
Method: A Solid Tire
Step 1: Size the ring to the rim.
Step 2: Mould it from compound in a ring mould; press and cure.
Step 3: Fit it to the rim, bonding or retaining it so it cannot creep.
Worked Example
Weight of a solid tire. A ring of outer diameter 600 mm, inner diameter 400 mm and width 50 mm (illustrative): volume = π ÷ 4 × (60² − 40²) cm² × 5 cm = 0.7854 × 2,000 × 5 = 7,854 cm³. At a compound density of about 1.1 g/cm³ (recalled, not from the corpus) the tire weighs about 8.6 kg. A cart with four such tires carries 34 kg in tires alone.
Rolling power. The Tire Alternatives article uses an assumed solid-tire coefficient of 0.025 and gets 17.7 W for air tires at 4 m/s for a 90 kg rider. Working back: 17.7 ÷ (90 × 9.81 × 4) = 17.7 ÷ 3,531.6 = 0.005 for air. For a 300 kg cart (illustrative) at 1.5 m/s, force is coefficient × mass × 9.81. Solid: 0.025 × 300 × 9.81 = 73.6 N, and power is 73.6 × 1.5 = 110 W. Air: 0.005 × 300 × 9.81 = 14.7 N, so 14.7 × 1.5 = 22 W. The solid tire costs 110 ÷ 22 = 5 times the power of the air tire, in work done by a person, a draught animal or a motor. These coefficients describe a hard smooth surface; soft ground is worse.
Common Mistakes
- Starting with pneumatic. Seal and hose first, as in Essential Rubber Products.
- A thin or pinholed tube. The dips must overlap with no gaps.
- Using force in kilograms. 73.6 N is about 7.5 kgf, not 73.6 kg.
Safety
A burst tire throws shrapnel and a pressure wave
A tire or tube holds compressed air, and the energy stored is roughly pressure times volume. For an assumed 2 bar of gauge pressure in 20 litres, that is about 200,000 Pa × 0.02 m³ = 4,000 J, similar to a 1 kg object thrown at 90 m/s (½ × 1 × 90² = 4,050 J). Inflate a new tire slowly, from a distance, with the wheel inside a cage or held down, and never stand in front of the tread. Do not exceed the pressure a tested sample has held.
What’s Next
- Learn next: Reclaimed Rubber — old tires as feedstock
- Combine with: Tire Alternatives — stopgaps while you build