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RC Glossary


New to the RC Hobbies? What does buggy, bulkhead, nitro mean in radio control car hobbies? Check out the glossary for remote control cars below.


  • O-Ring --
  • A donut-shaped circle of rubber or silicone that seals rotating or sliding shafts, used in areas like shock absorbers and differentials.

  • Off Camber (Corner) --
  • This is the opposite of a bank on a track - the grade angles down to the outside lane, which causes the model to push towards the outside during the entrance and apex of the corner.

  • Off Power íV Off Time --
  • Refers to the time that no throttle or brake is applied to the model - such as while the model is coasting or at idle. For nitro and gas models, this is commonly referred to as off power, while may be referred to as off time for electric models

  • Off-Road --
  • Any type of running surface that is not on a paved surface. Off-Road can mean gravel, loose or hard-packed dirt, grass, etc. Racing classes that run on off-road surfaces include buggies, trucks and usually rally cars.

  • Offset (Wheel) --
  • Offset refers to the distance between the centerline of the rim and face of the hub. Negative (-) offset is the most common, with the centerline of the rim closer to the hub. Positive offset (+) results in more of a 'deep dish' rim, which adds stability at the expense of cornering.

  • Offset --
  • see Wheel Offset

  • Oil % (Percent) --
  • Refers to the total percent of oil in nitro fuel. This oil may be castor oil or synthetic oil. This oil provides vital lubrication for the engine. In general, more oil means better protection for the engine at the expense of power.

  • Oil (Reference) --
  • After Run Oil, Air Filter Oil, DIFF Oil, Shock Oil.

  • Oil (Retention) Groove --
  • Refers to the grooves around the outer diameter of a nitro engine's piston. These grooves help to retain the oils of nitro fuel for lubrication between the piston and sleeve.

  • Oiling Hole --
  • A small passage drilled into the connecting rod of a nitro engine that allows the oil in nitromethane fuels to lubricate the wrist pin and / or rod journal.

  • On Power - On Time --
  • Refers to the point when a model is under acceleration or when the throttle is applied. For nitro or gas models, this is commonly referred to as 'on power', for electric models, it is commonly referred to as 'on time'.

  • On Road --
  • Usually refers to running cars on a paved asphalt or tarmac surface. The term could also refer to a class of cars, such as touring cars, pan cars, etc.

  • On the Pipe --
  • Refers to an engine that is tuned to perfection, resulting in a nice steady sound from the exhaust pipe.

  • One Way --
  • A term that refers to either one-way diffs or one-way pulleys.

  • One Way Bearing --
  • A special and expensive type of bearing that will only allow a shaft to turn in one direction. Commonly used in one way diffs or pulleys. One way bearings may also be referred to as roller clutches.

  • One Way DIFF (Differential) --
  • "At some points on a race track, the inside wheels can lift up because of high cornering forces. This causes a normal ball diff or gear diff to """"unload"""". A ball diff prevents diff unloading because it does not allow the tire to spin less than the speed of the belt that turns the pulley. One-way diffs do take getting used to, because you must use very light braking power or none at all. When brakes are applied to a car using one-way diffs only the rear wheels will stop, making the car spin out very easily. Most drivers will need practice to get used to one-ways, but for racers on high-grip surfaces they can be a valuable tuning aid."

  • One Way Pulley --
  • One-way pulleys operate in the same manner as one-way diffs, except the one-way action takes place on a gear shaft instead of the front axle of the car. One-way diffs and pulleys do take getting used to, because you must use very light braking power or none at all. When brakes are applied to a car using one-way pulleys only the rear wheels will stop, making the car spin out very easily. Most drivers will need practice to get used to one-ways, but for racers on high-grip surfaces they can be a valuable tuning aid.

  • Open Cell Foam --
  • The less expensive type of inner foam that some tires come with in the package. For general use these are fine, however for racing purposes a molded inner foam works much better.

  • Open Endbell (Motor) --
  • Refers to a brushed motor's Endbell that allows the brushes and springs to be serviced or replaced.

  • Outdrive --
  • The part of the differential that outputs power to dogbones or universal dogbones.

  • Outdrive Shaft --
  • The shaft that transfers power from the gears in the tranny or diff to the axle. For diffs, it is almost always integrated into the output gear and is what the drive cup attaches to.

  • Outlaw --
  • Refers to a motor or engine that isn't legal for sanctioned racing due to size or tune-ability. The 'open' or 'modified' classes at some tracks may be referred to as the outlaw class.

  • Output Gear --
  • The gear rotated by the spider or planetary gears in a gear diff. The output gear is almost always integrated into the outdrive shaft.

  • Output Shaft --
  • The 'gear-like', splined shaft that pokes out of the top of a servo. The splines on the shaft align with the splines on a servo horn, holding it in place. The threaded hole in the center of the shaft is for the screw that holds the servo horn down.

  • Outrunner --
  • A brushless motor with the inside remaining stationary (as the mount) and the outside of the motor spinning. This typically produces more torque and less top speed than equivalent inrunners (the typical brushless motor). Outrunners are commonly used for RC plane applications, but may be found in some crawlers.

  • Oval --
  • The American-style stock car type of racing, where cars compete on oval tracks of different shapes (true oval, square oval, tri-oval, etc.) and are tuned to only go straight or left. Other types of vehicles not covered in this glossary also compete on ovals, including sprint cars, midgets, motorcycles, snowmobiles, etc. In RC terms, most oval race cars are pan cars, with all the weight (batteries, electronics, etc.) on the left side so the car is the most stable when turning left.

  • Overdrive --
  • When a set of wheels (front or rear) on a 4WD model are either smaller (or driven by a smaller pulley) than the other set, they are overdriven. Overdrive is rarely used, but overdriven front wheels can produce a more aggressive feel for steering.

  • Overgeared --
  • Refers to running a pinion or clutchbell that is too big or a spur gear that is too small for the powerplant, such as when gearing for top speed. Overgearing causes excessive stress and heat on the engine or motor / electronics. For electrics, if your ESC is shutting down or the electronics and battery are too hot to touch after a run, you are probably overgeared. Try dropping a few teeth on the pinion or bumping up a tooth or two on the spur.

  • Overspray Film --
  • A thin, saran wrap-like covering that coats most clear, aftermarket bodies. This film protects the outside of the body from overspray while painting, and also provides a surface to layout the intended paint design. Overspray film is removed once the body is painted.

  • Oversprung --
  • Refers to a shock set up that is bouncy (A.K.A. pogo shocks). This may be most evident in off road, where the model may bounce back into the air after landing a jump. To cure oversprung shocks, try the following (in order of importance): use softer shock springs, use thicker shock oil, change to a shock piston with fewer or smaller holes, try a more horizontal shock position, or any combination of these.

  • Oversteer íV Loose --
  • "This happens when the rear tires lose traction before the front tires, resulting in the model wanting to turn in towards the inside of the corner. Oversteer causes a """"loose"""" feeling, as if the model is about to swap ends. The rear tires will lose traction before the front wheels, wasting power as the tires slip, looking for something to grip to. Oversteer may be reduced by decreasing rear toe, using softer shocks on the rear, or replacing with a stickier/ newer tires, or simply letting off the throttle a bit while cornering (of course, no one wants to do that)"""

  • A rating that shows how much torque a servo has. Basically, this is how many ounces a servo can lift if the weight is attached to an arm 1 inch from the center of the output shaft (pivot point). Thus, a servo with 120 oz. / in. can lift 120 ounces (10 cans of soda)?if it was?1 inch from the pivot point. Alternately, the same servo could?lift 60 ounces if it was 2 inches from the pivot point. This rating is also usually listed with the speed, degree of movement, and voltage used, such as - 120 oz. / in. @ 0.08 sec. / 60* @ 6.0V. This shows that the servo will lift 120 ounces a full 60 degrees of rotation in 0.08 seconds when using a 6 volt battery pack. Increasing or decreasing the voltage will likewise increase or decrease the speed, however, the maximum oz. / in. will remain the same.

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