The Rock Rey RTR (LOS03009) is Losi's 1/10 four-wheel-drive rock racer, sold ready to run with a Dynamite Fuze 2800Kv brushless motor and a Fuze 130A waterproof speed control.
A 12T pinion turns tires of 146 mm, and Losi claims 40 mph or more on a 3S pack, but the printed final drive does not match that claim and is left out. The truck is 527 mm long on a 381 mm wheelbase and weighs 2.97 kg, so fit a 3S pack and check the pinion mesh after any gear swap.
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.
Desert and trophy trucks copy full-size off-road racers: long travel, and bodies that leave the rear wheels open.
The maker does not name a class for this one, so this is the site's judgment from its design.
Drive
All four wheels are driven. That gives more grip under power, especially on loose ground.
The cost is more parts to maintain.
Power
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.
Build
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.
Scale
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 527 mm long.
Part number
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.
Class
Desert truckour call
Drive
4WD
Power
Brushless
Build
Ready to run
Scale
1/10
Part number
LOS03009
Drivetrain
Pinion
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 8.3%.
A bigger pinion loads the motor and ESC harder, so check the maker's gearing chart and feel the motor temperature after a run.
Spur
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.
Transmission & axle
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.
Final drive
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.
Pinion
12TStock
Stock
Spur
Not published
Transmission & axle
Not published
Final drive
Not published
Wheels & tires
Tire diameter
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.
Tire diameter
146mmStock
Stock
Power
Motor
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 31,080 rpm with no load.
Under load the real RPM is lower.
Battery
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.
Stock motor
The motor fitted at the factory, as the maker names it.
Stock ESC
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
2800KVStock
Stock
Battery
Up to 3SLiPoStock
Stock
Stock motor
Dynamite Fuze 550 Brushless Motor 2800Kv 6-PoleStock
It needs a motor KV, which this vehicle does not have on record, so no theoretical top speed is worked out.
Advertised top speed
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.
Theoretical top speed
Not published
Advertised top speed
40mphMaker's claim
Maker's claim
Size & weight
Weight
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.
Length
Overall length as the maker states it, usually with the body fitted.
Useful for comparing real size, since scale labels are loose.
Width
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.
Height
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.
Wheelbase
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.
Weight
2.97 kg (6.5 lb)Stock
Stock
Length
527 mm20.7 inStock
Stock
Width
324 mm12.8 inStock
Stock
Height
222 mm8.7 inStock
Stock
Wheelbase
381 mm15 inStock
Stock
How to read these figures
Stock is as the vehicle ships.
Calculated is worked from the stock figures on this page rather than stored beside them, so the two cannot drift apart.
Not published means it exists but no source we could find prints it.
Gearing dimensions
Pinion and spur dimensions for the Losi Rock Rey RTR (LOS03009): fitted, and optional gearing supplied in the box
Component
Teeth
Pitch
Bore
Fitted at the factory
Pinion
12T
Mod 1
Not published
Spur
Not published
Not recorded
Not applicable
About teeth, pitch and bore
Tooth counts are the ones in the specifications above.
Pitch is given as metric module (Mod 1, Mod 0.8) or diametral pitch (32P, 48P). They are different standards and are not interchangeable, even where the numbers look close.
Bore is the pinion’s hole, listed separately from the motor shaft.
Losi sells the Rock Rey as a rock racer, and it is listed here with the desert trucks.
Losi's page prints a 12T pinion, a 5.75 in (146 mm) outer diameter and a 2800Kv Dynamite Fuze motor, and the manual's parts list names the 12T pinion as LOSA3572.
The page also prints a 32.30:1 final drive, but that cannot be right for this truck: with the 12T pinion on 3S it would give about 16 mph, far under Losi's claim of 40+ mph, so the final drive is left blank along with the spur and the transmission and axle ratio.
The page says the power system handles 2S or 3S LiPo packs, so the cell count is 3.
The separate Rock Rey BND listing carries the same 32.30:1 figure with a 113 mm tire.
Sources
Every figure on this page traces to one of these; where they disagreed, the note above says which was used and why. Links open in a new tab.
