# Tag Info

110

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 look at a rear view mirror, you are still looking at distant objects. But when you look at a camera display, you're focussing on the image screen, which is ...

61

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 voluntary software recall to recalibrate the various emissions control devices on the affected vehicles. From the California Air Resources Board's (CARB's) in-use ...

58

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 once because the adhesive that held it to the windshield failed.) Camera and screens are more expensive, more complex, active devices. There are many more ...

44

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 thousand rpm (Revolution Per Minute), so there are dynamic considerations here. Fatigue When materials are subjected to cyclic loading they exhibit a reduction in ...

32

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 State laws require mirrors and would have to change first Conventional mirrors are basically fail safe, imagine the camera system turning off on the motor way. ...

31

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 from having a shorter wheelbase. Better Ground Clearance in some conditions, especially for bumps and or up a increasing slope for instance. Better Driving: The ...

29

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 between the two cars, then vs. Car would be exactly equal to vs. Wall (the contact points between both cars would all be on the same plane, due to reflection, so ...

27

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 cooling the brakes by allowing airflow between the inside and outside. The shape and size of the holes are calculated to have a minimal impact on the structural ...

21

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 30fps camera with a latency of 1 frame is 1m away from where it appears to be. (CRT screens with analog TV cameras that have no digital in the signal path are ...

19

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 major reasons; the first (also mentioned by Steve Ives) is that the suspension systems in vehicles operate better if the 'unsprung' mass is kept as low as possible, ...

19

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. So every time you try to back out of your driveway, or a parking spot, or turn into a parking spot, or turn anywhere for any reason, you're going to lay down ...

18

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 theoretical level, based on a temperature differential. It has nothing directly to do with the fuel. When you cite a fuel economy of 34 miles per gallon, you're now ...

17

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, brake disks, calipers, etc.) as low as possible. Holes in the wheels reduce this weight. The lower weight helps the unsprung portions of the car to follow the ...

16

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 crankshaft. The 1 litre 4 cylinder engine used in the Hillman imp was known for twisting under load especially once it was tuned as it was an aluminium block. One ...

15

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 high. By moving the wheels more towards the center of gravity in reduces the flexure of the center of the bus. In addition the driveshaft can be shorter which ...

15

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, then push-starting in 1st may work best. While I don't have personal experience, because weight transfers to the front on deceleration a front wheel drive ...

14

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 catalyst to produce methane and water. $$CO_2 + 4H_2 \rightarrow CH_4 + H_2O + \text{Energy}$$ as you can see from the previous chemical reaction, to obtain 1 ...

13

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 diesel are lighter-than-water organic liquids, most commonly produced from petroleum. Diesel requires much less effort to produce—you can make it yourself from ...

13

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 (the air pressure) working against the "sprung mass" of the wheel and the axle. The vehicle's suspension (springs, shock absorbers, etc.), working between the ...

13

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 two pieces of metal (the stud on the battery and the connector on the wire) is more important, and lead wins out here because it is so much more malleable (soft)...

12

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 makes it much more difficulty to store as it must be dissolved in acetone in an inert matrix, unlike say propane which can just be liquefied. This means that ...

12

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 -50F to 120F (-45C to 50C), and some blocks will crack when operated or even stored at those extremes. An engine operating at those extremes will experience ...

11

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 all boil down to the same thing: Any protrusion will cause a focus point for the weight which is usually spread over the entire contact surface of the tyre. ...

11

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. Conservation of momentum implies that the end result is both cars at a stand-still. If they hit each other perfectly head on, the vehicles will buckle and absorb ...

11

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 rotation lies along $l$ at least distance $R$ away from a point $c$ that also moves with the car. In this case point $c$ lies in the center of the rear axle and $l$ ...

10

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 assistance needed to actually turn the steering wheel.

10

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 allow to cut maintenance costs. Vehicles without external mirrors can be easily washed by automated washing stations. On older tramways with mirrors, the cabin ...

10

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 width it would buckle or fail under the loads / stresses applied. This design allows the wall to be thin in-between the webs so reducing the mass and helping to ...

9

The concept of what you're doing is sound, and as Russell McMahon notes the efficiency gains could be significant enough to justify the change. I'd strongly suggest that you consider adding a ramp to the back edge as well. Drag force is very sensitive to the downstream (rear) end of a body as well You get some positive pressure at the front of the vehicle, ...

9

The simple answer is yes. In Australia they have freight trucks that they call road trains. They have a second engine in the middle primary to start up which they switch off when they reach a certain speed limit. They use this type of topology when transporting freight across the outback. I thing most of them use a 400 hp Cummins diesel engine in the middle. ...

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