Arrma Kraton 8S EXB Roller

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.

• Monster trucks have tall tires and long suspension travel, built for jumping and rough ground rather than a race track.

All four wheels are driven. That gives more grip under power, especially on loose ground.

• The cost is more parts to maintain.

Sold without a motor, so you choose the motor, ESC and battery yourself.

• Rows that depend on the motor say so.

Almost ready to run: built at the factory but missing some electronics, usually the radio and sometimes the motor, ESC or servo.

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 771 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.
• The Gearing parts table below shows this car's pitch and part numbers.

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.

The hex on the axle that the wheel locks onto and is driven by. A wheel must match the hex size to fit.

• 24 mm is used on the largest trucks.
• The wheel nut is a separate size, so check its thread too before buying nuts.

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

• This vehicle comes without a motor, so there is no stock KV; it depends on the one you fit.

The diameter of the motor's output shaft, which a pinion's bore must match.

• This vehicle comes without a motor, so it depends on the one you fit.

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

• This vehicle comes without electronics, so it depends on the ESC and motor you fit.

The biggest pack that fits the tray, as the maker states it: length and width, and height where given.

• Compare it with the pack's case size, not its capacity.
• Allow room for the leads.

It needs a motor KV, and this vehicle comes without a motor. Fit one and the calculator works it out from the motor's KV and the gearing.

The vehicle's weight as the maker states it.

• The maker does not say whether it includes a battery.
• More weight takes more power to accelerate and lands harder on the parts; it changes top speed very little.

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.