Rlaarlo AK-917 Metal Brushless RTR

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 brushless motor has no brushes to wear, so it makes more power and runs more efficiently than a brushed one.

• It needs a brushless ESC.

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 460 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.

• On this car one tooth changes the gearing by about 3.3%.
• A bigger pinion loads the motor and ESC harder, so check the maker's gearing chart and feel the motor temperature after a run.

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.
• This one is worked out from the tooth counts the maker publishes.

Spur teeth divided by pinion teeth: the part of the gearing that a pinion or spur swap changes.

• Here it is 2.600:1.

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.

• Among 1/10 street cars in the catalog, the middle half run between 6.0:1 and 9.6:1 on stock gearing; this one is 7.8:1.

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

• This figure is not from the maker's documents, so treat it as close rather than exact.
• At high speed tires can balloon and grow, so the real gearing gets taller as the car goes faster.

How far the car moves for one turn of the motor: tire circumference divided by final drive.

• It lets you compare gearing across different tire sizes; more rollout is taller gearing.
• Here it is 26.2 mm.

RPM per volt with no load on the motor. Higher KV spins faster on the same pack; lower KV on more cells can reach the same RPM with less current.

• On 4S (14.8 V nominal) this motor spins about 63,640 rpm with no load.
• Under load the real RPM is lower.

The highest LiPo cell count the maker rates the electronics for. Each cell is 3.7 V nominal and 4.2 V fully charged.

• 4S is 14.8 V nominal and 16.8 V off the charger.
• Running more cells than this risks the ESC and motor.
• Many cars also run on fewer cells, only slower.

The motor fitted at the factory, as the maker names it.

• In a name like 3650, the digits usually give the can size: 36 mm across and 50 mm long. A bigger can makes more torque and sheds heat better.

The electronic speed control. It feeds power from the battery to the motor as you work the throttle, and usually powers the receiver and servo too.

• An amp figure in its name is normally the maker's continuous rating.
• Set its low-voltage cutoff for LiPo, so a pack is not run flat.

Motor RPM times rollout, worked out on 4S at nominal voltage with stock gearing.

• It assumes no load, no battery sag, no wheel slip and no drag, so read it as a ceiling for comparing setups.
• A GPS usually reads below it; the gap is load, battery sag, tire slip and drag.

The motor's RPM with no load: KV times pack voltage.

• Under load it drops, which is one reason real speed is lower than the theoretical figure.

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.