RPMs and Redlining Demystified

You might have heard “RPMs” references a lot, but perhaps you’re embarrassed to admit that you don’t know what “RPMs” are? On a related note, you might have noticed that one of your dashboard gauges has this red area or a “redline,” if you will. But why does this redline even exist? And what happens if your gauge reaches this area? In this blog post, you’ll discover:

• What “RPMs” actually mean
• Why the “redline” is – and why it’s an absolute no-go area
• What a “rev limiter” is – and how it works

RPMs or “Revolutions Per Minute” refers to how many times the crankshaft in your engine rotates each minute.  Essentially, RPMs refer to how fast your engine is running. The more you turn the throttle, the faster the engine runs (especially if you’re in low gear). But even if you’re standing completely still, the engine still runs a little bit. For this reason, your motorcycle or scooter has a gauge called a “tachometer” to monitor your RPMs. The tachometer is sometimes a separate gauge from the speedometer, like the bike below (the tachometer is the one on the right):

Image by Manfred Richter from Pixabay

If you look closely at your tachometer, you’ll notice that there’s an area in the far right end of the gauge that has a red zone in it.

Image by OpenClipart-Vectors from Pixabay

This is the “redline” – and the important thing to keep in mind is that the reading on the tachometer gauge should stay away to from this region. But why? If the engine starts to reach the RPMs at or even near the redline, the engine will run too fast – so fast that you might damage it severely.  The redline depends on the bike – but the same rule of thumb applies – don’t go enter this area. For a more in-depth explanation about the redline check out this video from the RevZilla YouTube channel:

So how do you avoid reaching the redline? The best way is to be in the highest possible gear – but to give you an extra safety margin against overrevving the engine, most modern motorcycles have what’s known as a “rev limiter.”

A rev limiter does just what the name suggests at an absolute basic level – it limits the revs to avoid causing unnecessary wear and tear on your engine. But how does it all work? At a very simple level, if you overrev the engine (either accidentally or deliberately), the rev limiter shuts off one of the parks that control the combustion process, such as:  

• Ignition timing
• Spark plugs
• Fuel injectors (for fuel injected motorcycles)