# Tag Info

### Why do cars have mirrors for rear view rather than cameras?

This is another case of fancy new (SHINY!!!) technology being A Bad Idea(TM) . When you're driving, your eyes are focussed roughly at infinity, i.e. looking at objects more than 5 m away. When you ...
• 4,043
Accepted

### How was Volkswagen able to trick the lab pollution test?

After the 2014 ICCT report revealed that these light-duty passenger diesel vehicles were emitting too much NOx and US regulators confronted VW about the results, VW did some testing and proposed a ...
• 3,211

### Why do cars have mirrors for rear view rather than cameras?

We still use mirrors because: A mirror is cheap, simple, passive technology that works. Pretty much the only failure mode is it breaking on impact. (Though I have had a center rearview mirror fall ...
Accepted

### Why are engine blocks so robust apart from containing high pressure?

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few ...
• 22.6k
Accepted

### Why do heavy trucks use air brakes?

Biggest advantage is that when connecting to trailers, there are no bleeding issues. Imagine having to connect hydraulic pipes and remove the air bubbles... As for the amount of air - the compressor ...
• 13.9k

### Why do cars have mirrors for rear view rather than cameras?

The industry is already going down that path for the exact reasons you mentioned. There is an article that provides information about that. In summary the main reasons why we don't have it yet are ...
• 1,704
Accepted

### Why are rear wheels not placed at the extreme rear of a bus?

Some ideas: Wheel Load Distribution: The load is greater on the rear wheels providing the power; more force on the front ones bring no benefit and would provide less traction. Better manoeuvrability ...
• 940
Accepted

### Which is Worse: Car vs. Car or Car vs. Wall?

From the point of view of the driver of a car, impacting another car is about as bad as crashing against an ideal wall (a wall with zero deformation whatsoever). If there were a plane reflection ...
Accepted

### Why do car wheels have holes?

Car wheels have holes mostly due to weight and cost considerations. Each hole is a chunk of material that you aren't wasting and weighing down the wheel with. As another bonus, the holes help with ...
• 5,666

### Why do cars have mirrors for rear view rather than cameras?

Digital camera systems with LCD screens impose latency of at least a frame on the images. Fine for slow moving parking cameras, maybe a problem at speed. An object moving at 60mph shown through a ...
• 329

### Why do car wheels have holes?

Many of the answers so far have mentioned that part of the purpose of the holes is weight reduction, but most of them don't express why weight reduction in the wheels is important. There are two ...
• 6,306
Accepted

### Why do cars turn by turning the front wheel?

If you were going to turn left 90 degrees, without turning the wheels, then you wind up dragging the wheels sideways while you turn. 16 seconds into this video shows exactly what I'm talking about. ...
• 3,525

### How can "mpg" be high under low engine load?

Thermodynamic efficiency vs. fuel economy When you cite an efficiency of 25-30% for an internal combustion energy, you're talking about the thermodynamic efficiency of the engine. This is, at the ...
• 3,211

### Why do car wheels have holes?

Mainly to reduce weight. A car's handling characteristics are improved by keeping the 'unsprung weight' (the weight of the car not isolated from the ground by springs i.e. the wheels, axles, hubs, ...
• 281

### Copper is more conductive, so why use lead battery terminals?

Yes, copper is more conductive than lead, but that is not necessarily the primary criterion for selecting the connector material. For car batteries, making sure there's a good connection between the ...
• 6,749

### Why are rear wheels not placed at the extreme rear of a bus?

I think one of the reasons is structural. The bottom on the bus is like a bridge with long steel beam running the length, and if the supports are at the ends the stresses and deflections would be too ...
• 688

### Is there a reason (in terms of the physics involved) why it is better to push start a car in 2nd gear rather than 1st?

It depends on the car. If it's a big displacement high performance engine, then you may not be able to get the rear wheels to turn unless you're in the highest gear. If it's got an itty bitty engine,...
• 2,218

### Why are engine blocks so robust apart from containing high pressure?

You need to consider that the complete engine block has to withstand the reciprocating forces generated by each of the pistons and con rods moving as well as the rotational forces from the rotating ...
• 13.9k

### Are pneumatic tires obsolete?

A pneumatic tire provides the mechanical "decoupling" of the tiniest variations in a road surface (the highest freqeuncies), involving a small "unsprung mass" (the rubber of the tread) and a spring (...
• 6,749

### Can the Sabatier reaction power a vehicle?

According to Wikipedia: It [Sabatier reaction ] involves the reaction of hydrogen with carbon dioxide at elevated temperatures (optimally 300–400 °C) and pressures in the presence of a nickel ...
• 2,149

### Why do heavy trucks use air brakes?

Several characteristics led to the adoption of air brakes. The primary one is reliability. A leak on a hydraulic brake system means the brakes don't work. A leak on air brake system means the ...
• 4,668

### What happens when you put the wrong type of fuel in an internal combustion engine?

To understand how these fuels behave in internal combustion (IC) engines, you need to first understand the properties of the fuels and how they differ. Fuel Properties Both petrol (gasoline) and ...
• 3,211
Accepted

### Why wont Petrol engine run on Acetylene?

There are certainly a few reasons why acetylene is not a very practical fuel for an IC engine. Perhaps the most important is that it is inherently unstable and tends to explode under pressure, this ...
• 15k

### What is the purpose of grid-like details on engine blocks?

This pattern is to provide sufficient strength while minimising the mass of the block. These "webs" are designed to prevent any vibration, if the block wall was made thin and the full length and ...
• 13.9k

### Why are engine blocks so robust apart from containing high pressure?

The vibration, loading, and fatigue aspects have already been addressed, but a wide range of operating temperatures is another factor. A typical consumer engine can be deployed in anything from say -...
• 221

### Are pneumatic tires obsolete?

While I don't see them going obsolete any time soon, you make some great points that really made me think. I thought of some upsides to pneumatic tyres that overcome some edge-cases, but actually they ...
• 5,930

### Which is Worse: Car vs. Car or Car vs. Wall?

In the limit of the cars being identical and the wall being immutable, I would argue that the two situations are the same based on symmetry. Consider the collision of the two cars with no wall. ...
• 6,306
Accepted

### How much clearance does a car need when turning a corner?

To slightly generalize I'll reform the question slightly. A ridged 2-D body (car) has a line $l$ that moves with it. The car can be linearly transformed as long as the instantaneous center of ...
• 1,295

### Why are rear wheels not placed at the extreme rear of a bus?

Front axle load is an important consideration. It's hard to carry a lot of weight on an axle that steers, as you are effectively limited to single wheels, and you want to minimise the power ...
• 269

### Why do cars have mirrors for rear view rather than cameras?

Cameras are used as rear-view mirrors, simply not in mainstream passenger cars. For example, here's how rear-view is done in tramways: Aside from improved wind resistance which you mentioned, cameras ...

Only top scored, non community-wiki answers of a minimum length are eligible