As the title says, I know that different shifts mean different gear sizes bein used, but I don’t understand why it makes you unable to start moving the car. I have been able to start a couple of cars on the 2nd shift as an experiment and I understand that I could damage the car and I do it just once for testing purposes but I don’t understand why I cannot do so on other shifts. To clarify, I mean start as in start moving the car and not just turning the car on. Thanks
In: Engineering
It’s because of transmission ratios. When your car is stopped, you want the lowest transmission ratio to go from 0 -> moving so you can have the highest load-pulling capacity. Going from 0 -> moving is actually the hardest thing for your car to do. Once you are already moving, you have inertia helping you out, so you can use the higher transmission ratios (and need less torque to keep things spinning). Moving cars in 2nd, like you’ve tried out, only really works for lighter cars. If you tried to move a bus in 2nd it probably wouldn’t budge haha.
Some cars actually recommend skipping gears for better fuel economy, some are just fine to start in 2nd on flat pavement. Many can do a 2-4 shift (skipping three) when the car is light and on flat or downslopes. Fortunately you can easily detect if you are in too high a gear because the car immediately starts ‘lugging.’
Many tractor trailers have something called a ‘crawler’ gear that is so low that it is inconvenient to use on a regular basis, but needed if you are heavy and need to move up a hill from a dead stop. In that engineering, the higher gear is normally used and the lower one is only used for specific situations a driver might encounter.
The damage comes from the possibility of the friction plate / clutch wearing faster and the cylinders overheating, but that is something that happens with *consistent* engine lugging.
There’s a video of Jeremy Clarkson launching a C6 corvette in 5th gear.
Standstill to 170mph in 1 gear
[https://www.youtube.com/watch?v=Ko9kzyqW-l8](https://www.youtube.com/watch?v=Ko9kzyqW-l8)
Put your bicycle on an uphill and put it in a high gear (like 10th). How come you can’t move the pedals? Your legs don’t have the torque (pushing power). Same thing for the car.
You can, acceleration just suffers. Top Gear did this with a Corvette; started it in 5th gear and went from a stop. It can be done, but most engines do not have enough low end torque to do it.
Imagine you have three balls on a flat surface. One weighs 10 lbs, one weighs 100 lbs, and one weighs 1000 lbs. Now, imagine trying to roll them. The first one would be very easy to get rolling, the second would be harder, but still possible, and the third one you can’t even budge because the amount of power or “torque” required to start the ball rolling is greater than the amount of power you can provide. Now imagine you could take the energy of the already rolling 10 lb ball, and use it to help you get the 100 lb ball rolling, and then you could take the energy from the 100 lb ball and use it to help you get the 1000 ball rolling. Well, now, you have enough energy, and once the 1000 ball is rolling, you can keep it rolling with less energy than you needed to get it rolling in the first place.
You’re also risking a stall the higher gear you go. Since on manual cars the pistons are essentially directly linked with the wheels, if you start at low speed, that means not enough RPM for the engine to sustain
Manual cars cannot start in higher gears primarily due to the relationship between torque and speed in the drivetrain.
* **Torque:** This is the rotational force that gets your car moving from a standstill. Lower gears provide higher torque, which is necessary to overcome inertia and get the car rolling.
* **Speed:** Higher gears are designed for maintaining speed once the car is already in motion. They sacrifice torque for the ability to reach and sustain higher speeds.
Trying to start in a higher gear is like trying to move a heavy object with a weak force. The engine simply doesn’t generate enough torque in higher gears to get the car moving from a stop. If you attempt to do so, you’ll likely stall the engine or put excessive strain on the clutch.
the car engine has a range of rpms it’s happy with which the gears transfer through a ratio to the wheels. In high gear at low speed the engine would have to go too slow and would probably stall.
The gears give an output of low speed, high torque in low gear and high speed, low torque in high gear. This is why switching down a gear increases acceleration. Starting off takes a lot of torque at low speed so a low gear is better; normally: on ice you might be better up a gear or two because torque will make the wheels slip. Normally high gear at low speed will require slipping the clutch if you don’t stall.
Imagine a standard flight of stairs in a two story house. You want to climb up those stairs. Picture trying to climb up those stairs in two strides (covering 7 stairs per stride). Now picture climbing up those stairs in 14 strides (covering 1 stair per stride). One stair per stride is the equivalent of starting to drive in 1st gear, while 7 stairs in one stride is the equivalent of starting to drive in a much higher gear.
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