Eli5: Why do cars have four wheels instead of three?
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It’s mostly a stability thing. With only a single wheel at the front, vehicles are more inclined to roll when turned at high speeds. This is to do with how the centre of mass “shifts” under the effect of inertia, but you can think of it as trying to balance a marble on a plate in a moving vehicle, having three wheels reduces the wheel base and that’s like using a smaller plate
To see how poorly something like this handles, top gear did a segment on it.
Historically, the first cars were built by carriage builders (horse drawn carriage builders) and 4 wheels were sort of the standard.
3 wheels are reasonably feasible only when the roads are fairly level and good. Otherwise the vehicle is rather unstable. When cars were first invented, roads were pretty badly built as they were primarily used for horse drawn vehicles.
The manufacturing techniques of the time were crude by modern standards. Engines tended to be huge and vehicles were very heavy – things like aluminium and plastic were expensive or not even invented yet. So pretty much everything structural was iron or iron based or sometimes wood. 4 wheels were needed just to have the strength and stability needed to support the vehicle.
As vehicles developed the focus was on speed and comfort. 3 wheeled vehicles are simply not very safe when driven fast.
There have been three wheel cars. They are terrible.
Imagine you have four limbs on the ground on all fours as someone is trying to push you over. You can change your weight to different limbs and it makes it hard to push you over. Now your two hands together and you will fall over with hardy a push.
My dad used to drive us around in a three wheeled car: a robin reliant.
it wasn’t great, but it got us places. and we never had any issues with it rolling off to the side, most of those videos are weighted down and done deliberately for comic effect.
there was no particular benefit to having a three wheeler except legal. my dad didn’t have a full driving licence, and at the time could drive the three wheeler with just his motorbike license.
Imagine you have a toy car. If it had only three wheels, it might wobble and tip over easily, just like a three-legged chair can be wobbly. But with four wheels, the car can balance better and go smoothly without tipping over.
Having four wheels helps the car stay stable and safe when you drive, just like how you feel balanced when you have both feet on the ground. So, cars have four wheels to make sure they can move around safely and without wobbling!
What would the advantage to having three tires be? Yes I know motor trikes exist, but there is a reason they are so small.
With four tires, assuming 2wd:
–The weight of the vehicle is distributed over more points, so less ground pressure at each point and more contact area (also why today’s tires are short and wide compared to early car tires, I mean just [look at this thing!](https://www.britannica.com/technology/Model-T) )
–Your tracks are in two sets of two, with a gap in the middle. Useful for dodging obstacles, a low obstacle such as a pothole or small animal can be lined up on the centerline of the car and you’ll pass over it.
–simplification, as you can have four identical tires and assuming your suspension is fine, they should wear down symmetrically. As opposed to three, where that solo tire will wear down out of sync with the other two.
and of course
–tradition, as mentioned. The car was originally called the horseless carriage for a reason, and carriages have four wheels for the reasons above (especially as a horse drawn carriage tends to create its own centerlined obstacles, namely fresh horse poop piles)
I take it you haven’t watched Mr Bean?
That three wheeled vehicle tipped over every episode it was in.
There were attempts. [They didn’t go very well](https://www.youtube.com/watch?v=QQh56geU0X8) (note: this is an exaggerated comedy skit but they *were* quite unstable), because as it happens, in turns most of the weight of the car is on the corners of the hull where a four wheel car has a wheel and a three wheel car has an air.
3 wheels is not stable, can tip over easily. Also there is no benefit to 3 vs. 4, make design/layout more difficult and less practical.
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