Traxxas Ford Fiesta ST Rally VXL

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 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 535 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 7.7%.
• 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.

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.

A taller pinion (and on some vehicles a spur) that the maker puts in the box for top-speed runs.

• It is stock but not fitted at the factory. The headline top speed and the calculators use it, since it is the fastest gearing the vehicle ships with.
• Follow the maker's notes on surface and motor temperature before using it.

The final drive with the in-box speed pinion fitted.

• The top speed rows below show what it is worth, in theory.

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.
• A limited-slip diff sits between the two: it lets the wheels differ, but only so far.

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.

• 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.

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.

• At the front it mostly shapes the steering: thicker oil makes the car turn in more calmly and dive less under braking; thinner oil turns in sharper and keeps the front tires on the ground over bumps.
• Racers go thicker for big, smooth jumps and thinner for rough, choppy tracks.
• It is graded in wt here. A wt number is the oil maker's own grade and differs between brands, so match the brand, or use the oil maker's chart to convert.

The rear shocks mostly shape grip under power and how the car lands.

• Thicker oil at the rear holds the back up on landings and keeps it steadier on the throttle; thinner oil lets it squat and follow rough or loose ground for more grip.
• This car runs thicker oil at the front (60 wt) than the rear (40 wt). The front reacts more slowly, which steadies the steering, while the rear follows the ground more freely for grip under power.

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 3S (11.1 V nominal) this motor spins about 38,850 rpm with no load.
• Under load the real RPM is lower.

The diameter of the motor's output shaft. A pinion's bore, the hole in its middle, must match it.

• 3 mm is slightly smaller than the 1/8 inch (3.175 mm) shaft on many motors, so choose pinions made for 3 mm.

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

• 3S is 11.1 V nominal and 12.6 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.

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.

The plug on the battery lead. Your battery needs the same plug.

• An adapter works, but it adds resistance and another joint that can work loose.
• Traxxas's plug is its own. Packs from other makers need the same plug fitted or an adapter.

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.

The stock servo that steers the car.

A gyro in the receiver that corrects steering and throttle to keep the car straight.

• It helps on slippery ground and high-speed runs; most can be turned down or off for racing or tricks.

It needs a motor KV, which this vehicle does not have on record, so no theoretical top speed is worked out.

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.