HPI Racing nano-TTR BMW 2002 Turbo - White

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.

• Touring cars are 4WD on-road cars for asphalt and carpet tracks, often raced in classes with fixed motor and battery rules.

Only one axle is driven, the rear on almost every 2WD RC car.

• It is lighter and simpler, and it takes more throttle control out of corners.

Ready to run: built at the factory with the electronics installed.

• Some come without a battery or charger; the maker's box contents say which.

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.
• This one is 73 mm long.

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.

The small gear on the motor shaft. Fewer teeth gear the car shorter: quicker acceleration, lower top speed and a cooler motor. More teeth do the opposite.

• It depends on the motor you fit, so the maker does not list one.

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.

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.

• On-road racers often compare gearing by rollout instead, because tire sizes differ between cars.

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

• Race tires wear down over a day, and a smaller tire gears the car shorter.

Motor KV is the RPM a motor turns per volt with no load.

• The maker does not publish it.

The highest LiPo cell count the maker rates the electronics for.

• The maker does not publish it.

A transmitter comes in the box, already bound to the car's receiver.

A drive battery comes in the box.

Other items the maker lists in the box.

Theoretical top speed is unavailable because motor KV, rated battery cell count, stock tire outside diameter and complete final drive ratio are missing.

• Enter the missing inputs in the calculator to work out a theoretical speed.

The vehicle's weight as the maker states it.

• The maker does not say whether it includes a battery.
• Lighter cars accelerate and stop faster; many race classes set a minimum weight.

Overall length as the maker states it, usually with the body fitted.

• Useful for comparing real size, since scale labels are loose.

Overall width as the maker states it, usually with the body fitted.

• A wider car is more stable in corners and harder to roll over.

Overall height as the maker states it, usually with the body fitted.

• Useful when checking it fits a shelf, a bag or a car trunk.

The distance between the front and rear axle centers. A longer wheelbase is steadier at speed and over bumps; a shorter one turns more tightly.