Technically, it’s possible to install an oval chainring on a dirt jumper, but this choice comes with downsides such as uneven chain tension, and makes little sense when it comes to pedaling feel and performance.
Dirt jumpers fall in the single-speed bike category and do not have a dynamic chain tensioning mechanism such as a rear derailleur or a dedicated tensioner.
On a dirt jumper, the chain is pre-tensioned by pulling the rear wheel back and tightening the axle. Dirt jumpers have horizontal dropouts making the procedure easier.
Oval chainrings create a small issue, however, because their radius changes slightly at two distinct points. The different radiuses result in small alterations of the chain’s tension.
As a result, it’s technically not ideal to install an oval chainring on a dirt jumper. That said, if the oval chainring is machined and engineered well, the number of teeth that remain in contact with the chain is constant. This design reduces the chain tension variations to a minimum and improves chain retention too.
Lack of Logic
The main goal of oval chainrings is to make pedaling more efficient by playing with the leverage that the rider has before pressing down.
Dirt jumpers are not built for efficient pedaling to begin with. Their size, geometry, and gearing reflect their main functions – jumps and stunts.
When a dirt jumper is used as intended, the pedaling is kept to a minimum and thus it doesn’t matter how efficient it is.
Of course, some people commute on their dirt jumpers, but that practice is an exception rather than the rule.
Even in that case, an oval chainring is no good because the dirt jumper size and geometry create pedaling and aerodynamic inefficiencies that completely cancel whatever benefits an oval chainring might bring.
What Is The Recommended Chainring For a Dirt Jump Bike?
Any single-speed chainring that fits the gear combination that you want is acceptable.
That said, most dirt jumpers rely on the so-called narrow-wide chainrings. As the name suggests, the teeth of those chainrings vary in width. One tooth is narrow, the next is wide.
The goal of a narrow-wide chainring is increased chain retention on 1x drivetrains.
Bicycle chains have inner and outer links resulting in two widths (inner and outer). The teeth profile of a narrow-wide chain mimics that pattern so that there is little to no side movement of the chain once it engages a certain part of the chainring. The result is increased chain retention.
FAQ: When is an oval chainring appropriate?
An oval chainring gives the rider more leverage at the top via a longer radius. As a result, the rider saves power and can cover a longer distance.
Oval chainrings are primarily seen on mountain bikes with a 1x drivetrain, although they can also be found on road bikes with a 2x drivetrain. In all cases, they work best on bicycles designed for fairly long distances and equipped with a dynamic chain tensioner such as a standard rear derailleur.