HPI Racing VectR4 Ford Escort RS Cosworth Rally Sanremo

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.

• Rally cars are 4WD cars with more suspension travel and treaded tires, for dirt, gravel and broken pavement.

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

• The cost is more parts to maintain.

A brushed motor carries current through carbon brushes that rub on the commutator.

• It is cheaper and smooth at low speed.
• The brushes wear and the motor loses power over time.

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 285 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 4.8%.
• 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.
• 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.
• 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 2.667:1.

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.

The type of each differential, as the maker states it.

• A gear or ball diff lets the wheels on one axle turn at different speeds in a corner; a spool or locked diff turns them together for straight-line drive and climbing, at the cost of steering.

The pinion sizes the maker lists for the stock setup.

• Going larger than the maker's limit gears the car taller than the motor and ESC are meant to run, which risks overheating them.
• The Target pinion calculator shows what each size does to speed.

The nominal size of the hole that mates with the motor shaft.

• Match the pinion mounting method as well as its size. A press-fit hole cannot be inferred from motor shaft diameter.

The tooth spacing of the fitted gear, stated as metric module or diametral pitch.

• The meshing pinion and spur need matching pitch. A missing pitch can be inferred from the other fitted gear; module and diametral pitch are not silently converted.

The tooth spacing of the fitted gear, stated as metric module or diametral pitch.

• The meshing pinion and spur need matching pitch. A missing pitch can be inferred from the other fitted gear; module and diametral pitch are not silently converted.

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.

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 16.0 mm.

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

• 12 mm is the common size on 1/10 cars, so most 1/10 wheels fit; offset and width still vary.
• The wheel nut is a separate size, so check its thread too before buying nuts.

Stock wheel diameter: A documented stock wheel, tire, or axle measurement. Stock dimensions alone do not establish the largest size that will clear the body and suspension.

Stock wheel width: A documented stock wheel, tire, or axle measurement. Stock dimensions alone do not establish the largest size that will clear the body and suspension.

Stock tire width: A documented stock wheel, tire, or axle measurement. Stock dimensions alone do not establish the largest size that will clear the body and suspension.

What the main chassis is made of and how it is built, as stated for this car. Braces, stiffeners and skid plates are not counted.

• Composite is the makers' word for molded plastic, usually nylon with glass or other fibers: it flexes and shrugs off hits, and it is light and cheap to replace.
• A tub is one molded piece with raised sides that hold the parts and keep dirt out.

What the shocks are and how they are built, as the maker describes them.

• Oil-filled shocks damp with silicone oil; friction shocks, found on some entry-level cars, damp with a sprung plunger and cannot be tuned with oil.

The oil in the shocks slows how fast the suspension moves. Thicker oil settles the car more slowly and resists bottoming out; thinner oil lets the wheels follow bumps.

• Front and rear run the same oil on this car, so both ends respond alike. Changing one end at a time is the usual way to shift the balance.
• It is graded in cSt (centistokes), a measure of thickness that is the same across brands.

Brushed motors are commonly described by can size and turns. No motor KV is published for this vehicle; turns alone cannot supply an exact value.

A nominal motor-shaft fit inferred from the identified fitted pinion.

• This is an inferred mating size, not a measured shaft diameter. Check for adapters and confirm the mounting method before ordering.

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

• The maker does not publish it.

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

• Brushed motors are often named by can size, such as 540 or 550, and by turns: fewer turns is faster.

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.
• A brushed ESC cannot run a brushless motor.
• Set its low-voltage cutoff for LiPo, so a pack is not run flat.

The size of the stock motor's can, as the maker names it.

Battery retention: A documented battery, motor, or ESC installation detail. Electrical ratings and physical fit are separate checks.

The stock servo that steers the car.

• Plastic gears are light and cheap but strip more easily from hard knocks to the front wheels.

How hard the servo can turn, at the voltage the maker rates it.

• More torque steers heavier cars and bigger tires more precisely and holds the wheels straight over rough ground.
• Kilogram-centimetres and ounce-inches measure the same thing; the other unit is converted for comparison.

How long the servo takes to turn 60 degrees, at the voltage the maker rates it.

• A smaller number is a quicker servo, which feels sharper when changing direction.

The stock transmitter, the radio you hold.

• Two channels are steering and throttle; more channels work extras such as a two-speed, lights or a winch.

The stock receiver in the car, which takes the transmitter's signal to the servo and ESC.

• Another transmitter works with it only if it speaks the same protocol.

Stock servo spline: A documented servo or steering interface for this model. Matching torque alone does not establish mounting or horn fit.

Stock servo dimensions: A documented servo or steering interface for this model. Matching torque alone does not establish mounting or horn fit.

Body mounting: A documented body mounting or clearance detail. Check the stated body and chassis configuration before assuming another shell fits.

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

A drive battery comes in the box.

A charger comes in the box.

Theoretical top speed is unavailable because motor KV and rated battery cell count are missing.

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

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.