Traxxas 4-Tec 2.0 BL-2s Chassis

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.

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 379 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 3.4%.
• 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.

• 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 6.9:1.

Silicone oil sealed inside the differential. A diff lets the wheels on one axle turn at different speeds in a corner; thicker oil makes it act more like a solid axle.

• At the front, thicker oil keeps both front wheels pulling out of a corner but makes the car turn in less willingly; thinner oil steers more easily.
• It is graded in cSt (centistokes), a measure of thickness that means the same across brands. K means thousands, so 30K is 30,000 cSt.

The rear diff mostly shapes drive out of corners.

• Thicker oil there puts power down more evenly on loose or slippery ground; thinner oil lets the car rotate more easily through a corner.
• This car runs thicker oil in the front diff (30K) than the rear (10K): steadier on turn-in, with a rear that lets the car rotate.

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 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 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.

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 2S (7.4 V nominal) this motor spins about 24,420 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.

• 2S is 7.4 V nominal and 8.4 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.

What the maker says about water, in its own words.

• Waterproof electronics survive splashes, puddles and wet grass; they are not meant to be submerged.
• After a wet run, dry the car and check the bearings, which rust.

The stock servo that steers the car.

• A digital servo holds its position more firmly and reacts sooner.

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

The top speed the maker claims.

• Makers often quote it with optional gearing, a bigger battery or a fully charged pack, so read their wording before comparing it with another car's claim or with the calculated figure.

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.