The Best Choice for Your Fleet – Direct Drive or Gear Reduction Starters?

There are two methods that a starter can use to drive the ring gear of a flex plate or flywheel.

  • Direct drive
  • Gear reduction

Direct drive is the original. It involves a large, low speed motor rotating a pinion gear in a 1:1 ratio.

Gear reduction was first introduced by Chrysler in the 1960s, but only entered mainstream use about two decades ago.

Gear reduction starters use smaller, faster motors to rotate pinion gears in a roughly 4:1 ratio, resulting in low power consumption and high torque.

  • Direct drive starters are typically more affordable.
  • Gear reduction starters are smaller, lighter and more efficient.

Differences Between Gear Reduction and Direct Drive

The armature shaft of the starter motor is attached directly to the drive mechanism in a direct drive starter. Although “gear reduction” technically happens between the starter’s pinion gear and the ring gear on the flywheel or flex plate, the pinion gear itself and armature shaft rotate in a 1:1 ratio.

True gear reduction can be achieved with either spur or planetary gears. Starters using spur gears require an offset armature, so the starter drive is placed in a separate gear housing. In starters using planetary gears, the gears can be contained in an in line drive-end housing. In either case, the armature shaft will typically rotate about four times for each rotation of the pinion gear.

Gear reduction facilitates significantly smaller starter designs which produce torque equal to or greater than much larger direct drive starters. The more technical design means they cost more too.

Why Replace Direct Drive With Gear Reduction?

Since the late 1980s, OEMs have steadily migrated from direct drive starters toward gear reduction starters. Gear reduction starters are more complex, and more expensive, but the size and efficiency benefits are too enticing to ignore. Since The gear reduction ratio of 4:1 allows smaller, faster motors drawing less amperage. That means they are more efficient than direct drive starters, but it also makes them particularly well suited for cold weather when the available cranking amperage from a battery drops.

Of course, a 4:1 gear reduction ratio also means that a gear reduction starter can often produce more torque than a much larger, heavier direct drive starter. In some cases, a direct drive starter can weigh as much as two times more than a comparable gear reduction unit. That represents a significant power/torque to weight ratio benefit, but it also means they are physically smaller and often easier to install.

Why Would Anybody Continue Using Direct Drive?

Although gear reduction starters are superior to direct drive in most cases, some managers still stick with direct drive. The most obvious benefit of direct drive is price, but direct drive starters are also preferred in heavy duty diesel applications. In some diesel applications, a gear reduction starter can cost 30% more than a direct drive unit.

Direct Drive or Gear Reduction?

Direct drive and gear reduction starters have continued to exist side by side for years, and we don’t expect that to change. To determine which one is the best choice for any given situation, think about cost, torque to weight ratio, efficiency, and cranking ability in cold weather.

Have a look at our selection of starters here to get started.