HPI Racing Bullet MT 3.0

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.

A small two-stroke engine running glow fuel (methanol, nitromethane and oil).

• It needs fuel, a glow igniter and some tuning.
• It has no motor KV or battery rating.

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 417 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.

On a nitro car the gear on the engine is the clutch bell.

• Its teeth work like a pinion's: more teeth gear the car taller, for more top speed and slower acceleration.

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.
• On a nitro car the clutch bell drives it.

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.

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 monster trucks in the catalog, the middle half run between 11.3:1 and 15.1:1 on stock gearing; this one is 12.8:1.

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 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.

• 14 mm is used on some larger 1/10 trucks; 12 mm wheels will not fit it without adapters.
• 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.

• This working size comes from a replacement advertised for the identified OEM part. Confirm the fitted part before ordering; a replacement's size may differ.

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.

• Aluminum is stiffer than composite, which keeps the handling consistent; it can bend in a hard crash, and a bent chassis is usually replaced rather than straightened.

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 shaft size matters when buying seals, ends and rebuild kits.

An engine has no KV rating.

• Nitro engines are sized by displacement in cubic inches, such as .21.

An engine car has no drive battery.

• A small receiver pack or a BEC powers the radio and servos.

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.

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

• This working size comes from a replacement advertised for the identified OEM part. Confirm the fitted part before ordering; a replacement's size may differ.

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

• This working size comes from a replacement advertised for the identified OEM part. Confirm the fitted part before ordering; a replacement's size may differ.

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

• This working size comes from a replacement advertised for the identified OEM part. Confirm the fitted part before ordering; a replacement's size may differ.

An engine has no KV, so a theoretical top speed cannot be worked out from the gearing alone.

The vehicle's weight as the maker states it, without the battery.

• Add your pack's weight for running weight.
• 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.