Tracks vs wheels: which is better, and when?

Neither is better everywhere. Tracks win on soft ground, loose sand and steps, because they spread the weight over a long strip and hook over edges. Wheels win on smooth floors and long runs, because they roll with less waste and turn more easily. The fun part is finding where each one stops working, and you can test that on the floor with a few Technic-style builds.

This guide compares the two with real builds and a lab you can run first. If your question is about cars that won't go up ramps, see why a Technic-style car won't climb, which covers gearing, grip and balance on slopes.

Before you start

The tracked builds here use two motors and a remote, so they suit builders who have finished a first motor build. The RC Tank (level 4, about 60 minutes) lists the Motor Buggy as the build to do first. The Tracks vs Wheels page is a one-minute primer.

How a tracked vehicle steers

The RC Tank has no steering wheel. Each track has its own motor, so both forwards drives straight, and one forwards with one backwards spins it round on the spot. That is called skid steering, because the tracks have to skid sideways over the ground as the tank twists.

Wheels can skid steer too. The Skid-Steer Loader (level 4, about 65 minutes) has no steering at all: one motor drives the left wheels and another the right, and a row of three gears on each side links the front and back wheels so they turn together. Spin it on the spot and you can hear the tyres scrub.

Test 1: can it spin on the spot?

When a skid-steer vehicle turns, the two sides push in opposite directions to twist it. Meanwhile the ground resists the ends of each track being dragged sideways. The longer the track is compared with the gap between the tracks, the more the ground resists. Engineers compare the length (L) of the track on the ground with the gauge (B), the distance between the tracks.

The RC Tank's sprockets are 8 studs apart and its tracks are 11 studs apart, so it is short and wide: L/B is under 1, and it spins easily. Try the lab: then stretch the tracks and see when it gives up.

On the real build: spin the tank on carpet, then on a smooth floor. On which surface does it turn more easily, and does the motor sound strained? Then spin the Skid-Steer Loader on the same two surfaces and compare.

Test 2: can it climb a step?

A wheel climbs a step only if it can grip the edge well enough to lift itself. When the step is low, the wheel touches the edge near its bottom and pushes almost straight into it, so it can't get on top. In the lab, one driven 56 mm wheel with nothing pushing it gets over only about 6 mm. A track wraps round its front wheel, so it can roll up over an edge almost as high as that wheel's centre: about 21 mm on the RC Tank.

On the real build: stack thin books or flat plates into a step, starting low. Drive the RC Tank at it, then a wheeled car such as the Motor Buggy, and add a layer each time until each one gets stuck. Write down the highest step each climbed. A car with all four wheels driven, like the Skid-Steer Loader, should do better than the lab's single wheel, because the back wheels push the front ones up.

So which should you build?

• Driving on carpet, sand, gravel or over obstacles: tracks. The Twin-Motor Dozer (level 5, about 100 minutes) has wide pads that spread its weight so it does not sink into sand, one motor per track, and a worm-geared blade that holds itself up. Its build page lists the RC Tank and the Skid-Steer Loader as builds to do first.
• Driving fast on a smooth floor: wheels. Tracks waste effort as every link bends round the wheels, so wheeled builds usually go faster and further on the same batteries.
• Spinning in tight spaces: either, as long as it is short and wide. Long, narrow vehicles of either kind fight the turn.

Common problems and fixes

• A track keeps falling off. It is too loose, or the front and back wheels are not lined up. Check both sprockets sit square on their axles, held by bushes, and that the track runs straight between them.
• The tank won't spin on carpet. The sideways scrub is high on carpet. Turn in gentle arcs instead, with one track slower than the other, or try a smoother surface.
• One side drives the wrong way. Each motor's direction depends on which way the electricity flows through it (see switching direction). Check which receiver socket each motor is plugged into against the build steps, then test each lever on its own.

Check yourself