I’ve seen websites that say “Lower Gears in Cars means more power”, Which is what I’m guessing, means more rpm, but then I see other people say that if you increase the gear, then it makes the rpm higher… Which one is it?
In: Engineering
Your rpm rises as you apply gas. But it doesn’t translate directly to power or vehicle speed.
E.g. let’s say you have a gas car with an engine that goes up to 5000 rpm. The thing is, it provides the most power at about, say 2500 rpm. So you want to keep the engine somewhere around those rpms.
Now the transmission comes in and it serves 2 main purposes:
1) to provide the most power onto the wheels. E.g. if you want to go uphil you may need more power even for low speed, just like on a bike. Even if your rpm goes outside the good zone.
2) so you (on manual trans) or the automatic can keep the engine near its most effective rpms. E.g. if you’re cruising at 70 kph (~50 mph I think?), you’re most likely in 4th gear on most cars. You can technically be in 3rd, where you’ll get higher rpm, but you won’t get anything extra out of it. In fact if you keep the engine in high rpm unnecessarily, you can blow the engine. Or on the other hand you can be in 5th or 6th, but you better downshift again if you need to accelerate or go uphill.
So, you upshift in these cases:
A) you’re accelerating to a speed where lower gear is no longer effective
B) you don’t need the power, e.g. going downhill
When you upshift, the rpm drops momentarily, and then it depends what you’re doing. When you apply gas, rpm goes back up. How fast depends on the load. If your rpm is low and the load is high, the engine dies.
You downshift when:
A) need to go slower (e.g. entering a lower speed zone) while also applying brakes
B) going uphill, and your current gear isn’t effective, i.e. either rpm is too low or you’re losing speed
C) you’re already cruising and want to accelerate rapidly: this will increase rpm and thus power, but not in an effective manner because the engine will be out of its comfort zone. Note you’ll need to upshift again to keep up the acceleration.
When you downshift, rpm goes up momentarily. Then it depends on what you’re doing. If you keep rpm too high, you may blow the engine, especially with low load.
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