The question is in the title. I’m aware that this may depend on the driver and how sudden the acceleration/retardation is, but certain luxury buses are for instance way smoother and softer than other. Obviously, this depends on the cost and quality of the engine. But what exactly makes it smooth?
In: Engineering
A bus has a huge mass. This means it takes a larger force to accelerate or bump it. Given a pothole of a certain size, a bus has a lot more mass to dampen the bump you feel than your compact car has.
It comes down to its suspension and tires. I remember back in the day Mercedes was one of the first with the air suspension trend which resulted in more comfortable rides
The smoothness of a vehicle largely comes down to its suspension. If you go look under a car, you’ll see that there are some very big springs that are part of how the axel attaches to the car. Those springs help absorb shocks to smooth out the ride.
The better the suspension (ie, using more than just a basic spring, like a hydraulic system) the more the car can “float”. Basically, you want the wheels to be able to move up and down as much as possible without the rest of the bus moving up and down. Of course, the wheels still need to hold up the bus, so they still need to push upwards against the bus, but if you can take a 1 millisecond spike when the wheel hits a bump and spread that out over 10 seconds the rider will barely feel it. A cheaply made bus is going to have as basic a suspension as it can get away with, while a luxury bus is probably going to have a pretty fancy one.
Four factors help vehicles drive “smoother” than others:
1) wheelbase, the longer the distance between the front and back wheels, the less that riders will feel bumps hit by the wheels furthest from them
2) wheel size and tires, the bigger the wheel, the more you will feel each bump in the road. The more of the wheel that is tire vs wheel, the softer the ride is.
3) mass, the heavier something is, the less it will be impacted by lighter things
4) most importantly, the suspension. Suspensions are made up of two things — shocks and springs. Shocks stop bouncing, springs absorb bumps. Ride comfort comes at the expense of handling (how much control and precision you have when driving). The more precise you want your control, the stiffer your springs have to be. The more comfort you want, the less precise your steering will be. Buses have incredibly soft suspensions for passenger ride comfort.
Difference between two busses or between a bus and a car? Between busses it all depends on what kind of suspension the bus has and what engine transmission.
The smoother bus might have pneumatic suspension versus regular gas piston/springs for the shittier bus. Might also have better gearbox with dual clutches or it might even be an electric hybrid.
Many good answers here. All of them are pretty much right. It’s a combination of all of them.
Wheelbase. The rear wheels on a bus are far enough away from the front that when the front hits a bump, the rear passengers don’t really feel it because the angle of the bus changes only slightly. Those sitting in the middle feel the bump but less than the people over the front wheels. When the rear passes over the bump, the front passengers don’t really feel it and those in the middle again feel it less than those in the rear. In a short vehicle, the front moves when it hits the bump, the rear is close enough to feel the change in angle of the car as it goes over so both front and rear passengers feel both bumps almost equally.
Tyre depth. Bus tyres have a deep profile. Loads of tyre to soak up the bump.
Weight of the vehicle versus weight of the wheels. This is a bit hard to grasp. It’s known as unsprung weight. The bus weighs a lot, in comparison it’s wheels weigh very little. The wheels are bouncing up and down as the bus drives along. The suspension has to control the movement of the wheels by damping the movement of the springs. To damp the movement the suspension uses the mass of the bus as an anchor. Because the bus is heavy, the suspension does not move the bus much when it controls the wheels. It’s a bit like a small child trying to control a rabbit in their hands, the rabbit weighs a decent proportion of the weight of the child so the struggling of the rabbit has a great impact on the child. Give the rabbit to an adult and the effect is lessened.
Soft suspension. Busses have long travel, soft suspension which allows the wheels to move a lot over bumps. This is why busses handle the corners, er, like busses. They’re all soft and squidgy because they’re designed to isolate the passengers from bumps but the downside of that is that they leans violently if you drive them like a race car.
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