What are straight-cut gears?

What are straight-cut gears?

Straight-cut gears

A car’s gearbox is a sensitive component, but used correctly, it will give you everything you require, from power to torque.

However, there are some who need more from their transmission, and it might be that they look into what are called: straight-cut gears.

How do straight-cut gears work?

Straight-cut gears are actually very commonly used across many different capacities – however, in your typical road car, you will not find such a setup – they will be helical gears.

Cars that look to make use of straight-cut gears will be, most of the time, those that hit the track on a regular basis – or are just a flat-out race car in general.

The ‘straight-cut’ element of the equation refers to the nature of the gear teeth themselves, which are – as you might have guessed – cut straight instead of the helical or spiral shape you’ll see on a typical vehicle’s transmission.

What are the pros of straight-cut gears?

The core reason you would want straight-cut gears is that they allow for no axial load, or in other words, there is no restriction applied in regards to torque.

This is why you’ll find race cars making use of straight-cut gears due to this benefit, allowing them to utilise much larger powertrains without them being restricted or at risk of damage.

Additionally, straight-cut gears are actually more efficient than its helical-geared counterpart, with the latter creating much more friction, resulting in energy loss through heat.

The simple structure of straight-cut gears is also something race teams are attracted to, as any failures will tend to be much less catastrophic as a result of their straightforward construction. 

This also helps in terms of weight saving, something race teams are always chasing.

Any disadvantages to straight-cut gears?

Like anything that is good for motorsport, it tends not to translate well to the road.

Firstly, straight-cut gears make a hell of a lot of noise – this is due to the fact that they are always in contact with each other fully, and for a longer period of time. That whine you can hear as a race car blazes past on the track? Yup; straight-cut gears.

Fun fact: the reverse gear in your road car is actually a straight-cut gear, and is notably smaller than the helical forward gears – this is why your car has a similar whine when reversing.

Another aspect that you might have witnessed when it comes to race cars is that, when they change gear, it can be a brutal affair, with the gears very aggressively cracking into place.

You may have also noticed that race cars are pretty terrible at getting away from stationary, which is another drawback of straight-cut gears.

Straight-cut gears vs helical

Straight-cut gears

  • Great for race cars/track cars
  • Allow for much more torque
  • Very efficient
  • More affordable and easier to repair
  • Incredibly noisy
  • Brutal gear changes
  • Hard to set off with
  • Not good for heavier cars

Helical gears

  • Perfect for typical road users
  • Much smoother gear changes
  • A lot less noise and vibration
  • Can be used for heavier vehicles
  • Higher cost to make/repair
  • More energy loss
  • Heavier