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27 votes
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What limits the speed of a car?

There are a few simple reasons why the speed of a vehicle (road conditions notwithstanding) may be limited: Gearing -- Production vehicles with conventional transmissions have a limited number of ...
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11 votes

What limits the speed of a car?

So, what limits the speed is a combination of two things : the power from the engine with the gearing and the rolling and air resistance. Up to approx 40mph the rolling resistance is the largest ...
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9 votes

What limits the speed of a car?

Physics stops you. Ever ride a bicycle? 25 mph is easy, 30 is hard, 40 requres special gear or a very pumped up body, and 50 is nigh impossible. Why does the effort get so steep for such small ...
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9 votes

Is it true that four-wheel drive is less efficient and if so, why?

Simply put, power transmission is not free. Every time you have some energy over here, and you want to move it to over there, you are going to lose some of it in the process. In this case, if your ...
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  • 2,511
9 votes

When a car with an open differential turns, why does the inner wheel slow down and the outer wheel speed up?

TL;DR: The kinematic constraint imposes the redistribution of forces on the four wheels. This redistribution is permitted due to the car differential. IMHO it is easier understand this if you first ...
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8 votes

Why do electric cars claim "instant torque?"

ICEs (internal combustion engines) take some time to ramp up their output torque. Various mechanical systems have to react before more mixture is injected into cylinders, and that then makes more ...
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7 votes
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Why does "Google self-driving car"'s roof camera rotate?

It isn't an ordinary video camera. It's a high-resolution LIDAR that uses laser beams to measure the distance to thousands of points on every rotation. I believe the one used by the car in that video ...
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  • 6,759
7 votes

What are those large cylinder "tanks" attached to the outside of trucks for?

They are external air filters for the engine.
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  • 9,517
7 votes

Does lowering the ride height of a car 50 mm exactly lower the height of C.G by 50 mm?

No. All the wheels, axles, brakes and parts of the suspension would remain in the same position relative to the ground so their contribution to the centre of gravity doesn't change. The overall CoG ...
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  • 8,449
7 votes

On a car with all-wheel drive, how does the engine provide the angled front wheels with power?

You could also include front-wheel drive in your question. It would be enlightening for you to look at what radio control rock crawlers do. It has much of the excess of a full-sized car stripped away. ...
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6 votes

When a car with an open differential turns, why does the inner wheel slow down and the outer wheel speed up?

This is a simple explanation/observation. A two-wheel dolly rotates along a circular path by a constant torque (T). The position of the wheels changed from point 1 to point 2 in one second (t = 1s), ...
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  • 7,624
5 votes

How do hybrid cars achieve greater fuel efficiency?

Paparazzo pretty much nailed it, but I'd like to add a few things. Regenerative braking is certainly a large part of it, but there are other synergies when utilizing multiple engines in an ...
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5 votes
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How do hybrid cars achieve greater fuel efficiency?

The difference is the regenerative braking. It take as much work to decelerate a car as to accelerate. I don't know the actual efficiency but even 50% recovers a lot of the energy that would have ...
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5 votes
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Why do electric cars claim "instant torque?"

I think the instant torque claim mostly applies to "off the line" acceleration. That is from a standstill and electric motor has 100% of its available torque available at 0 rpm (mostly). The tradeoff ...
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5 votes
Accepted

When a car with an open differential turns, why does the inner wheel slow down and the outer wheel speed up?

In order to change the speed of the inner and outer wheels, there must be additional torque(s), which must be different for the two wheels. What is this torque, and where does it come from? If the ...
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4 votes

Why does "Google self-driving car"'s roof camera rotate?

That's a lidar sensor, which is making a continuous 360 degree sweep, rather than a camera which has a field of view as such. Rotating mirrors are a fundamental part of how the system works. Note ...
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4 votes
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Equal power transmission in 4x4 vehicles?

It depends on what type of differential it has. The nature of an open differential (as found on normal road cars) is that the spinning wheel(s) will get all of the torque. Proper off-road vehicles ...
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4 votes

Does the speed of Heavy Vehicles make more potholes

Vertical loading does (almost) nothing to a properly designed and constructed bitumen road surface, it is horizontal loading that causes deterioration. Horizontal loading comes from acceleration, ...
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4 votes
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Passing by a semi truck on a highway

A truck speeding down a highway creates an envelope stream of high pressure air surrounding it. This is basically a wake, composed of layers of high pressure shockwaves, created when the front of the ...
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  • 21k
4 votes
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Proccess of a 4-wheeled vehicle taking turn

It depends. The driven wheels need to be connected by a differential whcih allows power to be transferred to both wheels but still allowing them to turn at different speeds. It's not that easy to ...
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4 votes
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Why does a tractor not do wheelie with a lot of weight on the trolley?

Because the rear wheels are larger so the hitch connection point is below the centre line of the rear axle. However, if there is enough power then the tractor can do a wheelie anyway, have a look a ...
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4 votes
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Is the effect of weight-to-horsepower ratio linear?

If we ignore friction and drag we can revert back to, One horsepower is equal to 745.7 watts. one watt is 1kg force moving 1-meter per second. a car with N times power is being pushed by N times force,...
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  • 21k
3 votes
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Why do I need to place car cabin filter according Air flow label

Usually because the strengthening in the filter is optimised for one direction and the layers may also be optimised so the oncoming air is met with a coarse layer first, followed by successively finer ...
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  • 14.1k
3 votes

Friction clutch and the force required

Clutches do indeed carry quite lot of force but when you pull away from stationary the correct technique is to use fairly low revs and blend the clutch in quickly but smoothly. In this case the clutch ...
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3 votes

Why do electric cars claim "instant torque?"

No, it's a characteristic that electric motors produce most, if not all, of their torque from zero rpm - which is why the electric cars are so good at getting off the line and how electric motors don'...
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  • 14.1k
3 votes

Does the speed of Heavy Vehicles make more potholes

If you have a 20 ton truck sitting stationary on the road, it's exerting 20 tons of force on the roadway. If that truck is traveling at 100km/hr, it is still exerting 20 tons of force on the road. I'...
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  • 133
3 votes

What should be the material and thickness of front pillars to stop car (~1,847kg and ~262 km/h) without killing the driver?

In high speed collisions essentially the human body fails under high g negative acceleration even if the structure of the car or cabin or test vehicle is strong enough to survive the collision. ...
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3 votes

Does the shape of a car really matter for how much gasoline it drinks?

The difference is in the drag coefficient. Typical drag coefficient of the 50's cars have been in the range of 0.38 to 0.42 or so. typical drag coefficient of modern cars even the ones not renowned ...
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  • 21k
3 votes

What is pitch stability in cars?

According to the wiki regarding pitch stability in aircraft, the terminology generally refers to the tendency of an aircraft to not diverge along the lateral axis when the stable configuration is ...
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