Most dashboards have two big dials. One tells you how fast you're going. The other, the rev counter or tachometer, tells you how fast the engine is spinning. That second number is RPM: revolutions per minute. At 3,000 RPM, the engine's crankshaft is turning 3,000 times every minute, or 50 times a second.
Speed and RPM are linked, but not directly. Between the engine and the wheels sits the gearbox, and the gear you're in decides how much road speed you get from each turn of the engine.
Gears are the translator
Think of a bicycle. In a low gear you pedal quickly but move slowly, with lots of pushing power for hills. In a high gear you pedal slowly and move fast. A car works the same way. The engine is your legs; RPM is how fast you pedal.
"Low" and "high" describe the speed a gear gives you, not the number on the lever. On a car or a bike with 6 gears, it breaks down like this:
| Low gears | Middle gears | High gears | |
|---|---|---|---|
| Car (6-speed) | 1st, 2nd | 3rd, 4th | 5th, 6th |
| Bicycle (6-speed) | Gear 1: biggest rear sprocket | Gears 3–4 | Gear 6: smallest rear sprocket |
| How it feels | Easy to push, engine or legs spin fast, slow road speed | Everyday town speeds | Hard to push from a standstill, engine or legs spin slowly, fast road speed |
| Use it for | Pulling away, steep hills, crawling in traffic | Accelerating through town | Cruising on open roads and highways |
So 1st is the lowest gear and 6th is the highest. On a bike, the low gears are the big sprockets at the back, the ones that make pedalling uphill easy. Some bike shifters number the gears the other way round, so go by feel: if pedalling gets easier, you've shifted to a lower gear.
You don't need to memorise this. The key idea is simple: in any one gear, RPM and speed rise and fall together. Change gear and the relationship changes. That's why the same 60 km/h can mean 4,000 RPM in 2nd gear and under 2,000 RPM in 5th.
If you drive a manual
In a manual, you pick the gear, so the rev counter is your main guide for when to change. Choose a speed and a gear below and see where the needle lands. The chart underneath shows what every other gear would give you at the same speed.
Gear finder
Rules of thumb for manual drivers
- Relaxed driving: change up at about 2,000 to 2,500 RPM in a petrol car, or 1,700 to 2,000 in a diesel. You'll save fuel and the engine stays quiet.
- Before you overtake or climb: change down first, so the needle sits in the pulling range. That's roughly 3,000 to 5,000 RPM for petrol and 2,000 to 3,500 for diesel.
- Shudder when you press the accelerator? The revs are too low for that gear. The engine is "lugging". Change down.
- Smoother downshifts: the gear finder shows the RPM the lower gear needs at your speed. Give the accelerator a quick blip as you change down so the engine is already there. The clutch then engages without a jolt.
- Clutch health check: if you press the accelerator in a higher gear and the revs climb but the car barely speeds up, the clutch is slipping. Get it looked at.
If you drive an automatic
An automatic changes gear for you. But "automatic" covers four quite different gearboxes, and each one moves the needle in its own way. Knowing which one you have tells you what's normal and what isn't.
Pick your gearbox and a driving style, then press play to watch a run from standstill to 80 km/h.
Choose your gearbox
What to use the rev counter for in an automatic
- Check the idle. Once warm, most petrol engines idle at 600 to 900 RPM. A little higher with the AC on is normal. A needle that sits well above 1,000, or bobs up and down, is worth a check.
- Spot slipping early. If the revs jump and the car doesn't pick up speed to match, the gearbox may be slipping. In a CVT, high steady revs are normal; revs that surge with no extra pull are not.
- Drive lighter, save fuel. With a gentle foot, a stepped automatic changes up by about 2,000 to 2,500 RPM. If yours keeps reaching 3,500 in town, ease off.
- Use manual or L mode on long descents. Select a lower gear (or L, 2, or the minus paddle) and let the engine hold the car back. Higher revs here are fine and they save your brakes. Keep clear of the red zone.
- Read the load. Higher RPM than usual at a familiar speed means the car is working harder: a hill, a full car, towing, or the AC running flat out.
Is this normal?
Tap a symptom to see what it usually means. The filter follows the gearbox you picked above, and you can switch to any other.
Learn your car's numbers
Every engine is a little different. Next time you drive, note three numbers. Once you know them, anything unusual stands out straight away.
The checks update as you type. Your numbers stay in this browser only.