Mugen Seiki MRX7

The kind of vehicle the maker sells it as. It sets what the car is built to do and which cars it is fair to compare it with.

• Street covers on-road bashers: speed-run, muscle and drag cars built for straight-line speed rather than racing.

All four wheels are driven, which puts power down more evenly and keeps the car steadier accelerating out of corners.

• The cost is more parts to maintain.

A small two-stroke engine running glow fuel (methanol, nitromethane and oil).

• It needs fuel, a glow igniter and some tuning.
• It has no motor KV or battery rating.

A kit you build yourself from parts.

• Most kits come without motor, ESC, servo, radio and battery, and many without tires or a painted body.
• The manual lists what to add.

The maker's nominal size compared with a full-size vehicle. It works more as a class label than a measurement.

• A 1/10 monster truck is far bigger than a 1/10 touring car, so compare length and weight for real size.

The maker's product number for this exact version.

• A V2, a new color, or a kit instead of an RTR usually has a different number, and parts can differ between them.
• Check it against your box or receipt before ordering parts.

On a nitro car the gear on the engine is the clutch bell.

• Its teeth work like a pinion's: more teeth gear the car taller, for more top speed and slower acceleration.

The large gear the pinion drives. A bigger spur with the same pinion gears the car shorter.

• Pinion and spur must have the same pitch, or tooth size, to mesh.
• On a nitro car the clutch bell drives it.

Every reduction after the spur, multiplied together: transmission, differentials and axle gears.

• It is fixed by the design; the gearing you change is the pinion and spur.

How many times the motor turns for one turn of the wheels. A higher number is shorter gearing: more acceleration and pulling power, less top speed.

The outside diameter of the mounted tire, tread to tread. A taller tire covers more ground each turn, which gears the car taller.

• At high speed tires can balloon and grow, so the real gearing gets taller as the car goes faster.

An engine has no KV rating.

• Nitro engines are sized by displacement in cubic inches, such as .21.

An engine car has no drive battery.

• A small receiver pack or a BEC powers the radio and servos.

An engine has no KV, so a theoretical top speed cannot be worked out from the gearing alone.