As of May 31, 2023, we have updated our Code of Conduct.

Questions tagged [theory]

Use this tag when the question is **primarily** about the underlying ideas behind how something works. This tag should be used in conjunction with another tag for the area of interest, for example [electrical] or [suspension]. It should not be used "stand alone." Please use the [engine-theory] tag for those questions.

Filter by
Sorted by
Tagged with
1 vote
1 answer
73 views

What are the benefits of lowering a vehicle for racing

Lowering a vehicle affects many aspects related to suspension geometry and aerodynamics. I am trying to understand these phenomena better. Note that although my question sounds like an opinion, it's ...
Emile Papillon-Corbeil's user avatar
0 votes
0 answers
54 views

Why did old cars have really long throw shifters?

What was the reason that old cars had very long throw shifters and that modern cars now have much shorter throw shifters? For example even old sports cars like the urmodell generation of 911 had very ...
Timothy Scherer's user avatar
3 votes
2 answers
43 views

Oxygen sensor "clean air source"?

('07 Cobalt, Ecotec 2.2L) I came on the text below in the AllData (paywalled) service manual. It seems like they're saying that ambient air comes into the exhaust 'oxygen' sensor (pic below) ... ...
George's user avatar
  • 1,103
5 votes
1 answer
352 views

Why does the impeller of a torque converter sit behind the turbine?

i saw this picture of a Chrysler A-727 TorqueFlite and it shows that the impeller actually comes after the turbine. Why is it done like this? Doesn't it make more sense to put the impeller before the ...
Timothy Scherer's user avatar
1 vote
2 answers
29 views

A sprocket, sprocket-wheel or chainwheel is a "profiled wheel" with teeth that mesh with a chain, track or other perforated or indented material

What does "profiled wheel" mean in "a sprocket, sprocket-wheel or chainwheel is a profiled wheel with teeth that mesh with a chain, track or other perforated or indented material"? ...
Maurice's user avatar
  • 243
7 votes
1 answer
1k views

Purpose of small forward-facing deflectors in front of rear wheels

On many new vehicles there are small, forward-facing deflectors in front of the rear wheels that look like small splash guards. What is the purpose of these? I assume they are for aerodynamic (fuel-...
masospaghetti's user avatar
0 votes
0 answers
45 views

How does an epicyclic differential split torque?

How does an epicyclic differential split torque even when rotating as a single locked unit with no relative motion between its parts? Should it not have 50/50 torque split because its all rotating as ...
Timothy Scherer's user avatar
0 votes
1 answer
89 views

Why do most cars have positive offset wheels from the factory?

Most cars come with stock wheels that have very high positive offset. Why was this design choice taken? Does it improve fuel economy or make it cheaper to manufacture?
Ruslan's user avatar
  • 302
5 votes
2 answers
686 views

Does electric fuel pumps run at constant or variable speed?

In websites I have seen that fuel pumps have a pressure range of say 30-95 psi. Why do they give a range of pressure? I had read that these pressure values refer to the unobstructed flow pressure ...
Abhishek P G's user avatar
5 votes
2 answers
3k views

Why does brake pedal ever move

I don't think my question has any connection to vehicle maintenance or repair but I think this is the closest site to my question topic. My question may be arising from misunderstanding. For that I'm ...
John greg's user avatar
3 votes
1 answer
598 views

Why does the wheel size affect the cars gearing?

Using online gearing top speed calculators I realized that the bigger the diameter of the wheels, the higher the theoretical gearing top speed is. Why is that? Why does bigger wheel act as increasing ...
Timothy Scherer's user avatar
2 votes
1 answer
89 views

Does increasing final drive ratio actually improve overall acceleration?

Hopefully, this is the correct forum to ask this. There's lots of stuff online about final drive ratios, but not much with respect to actual acceleration times, and usually it's just anecdotal, butt-...
bertmoog's user avatar
  • 123
2 votes
2 answers
82 views

Why does a car push start?

A lot of people've been there. I also have done this (unfortunately). But why does this happen? Procedure is very simple: turn the ignition on, engage 2nd gear, push the clutch in, get up to speed, ...
J. Doe's user avatar
  • 63
2 votes
1 answer
56 views

Theoretical AWD question

Don't know if this is a right place to ask this. So I know there's a difference between 4WD and AWD, and the difference being AWD has equal power distribution between front and rear axles right while ...
J. Doe's user avatar
  • 63
0 votes
4 answers
74 views

Could all cars ride four times faster? [Transmission / Differential mechanism]

In a book "How a car works" I have read such sentence: The crown wheel usually has about four times as many teeth as the pinion gear, causing the wheels to turn at a quarter the propeller-...
bridgemnc's user avatar
2 votes
2 answers
67 views

To ground or not To ground

Sure most cars have neg earth chassis return .Boats have single point ground so there are no hull currents to cause electrolytic corrosion .My question is about busses .They have been known to have ...
Autistic's user avatar
  • 2,063
0 votes
1 answer
135 views

Can inline plunger mechanical injection pumps pull through the fuel?

I know that they have lift pumps that bring the fuel towards the plungers so that the plungers can push and pressurize the fuel towards the injectors but i was wondering if lets say we removed the ...
Timothy Scherer's user avatar
0 votes
2 answers
89 views

Bolt torque estimation based on angle and material

Is there a valid generic formula to roughly estimate a bolt's tightening torque similar to the "tighten by hand until seated, tighten XXX degrees more with your wrench"? I have used for many ...
kokobill's user avatar
  • 1,015
0 votes
1 answer
444 views

Does a diameter of a brake line affect braking pressure

I am currently building a brake system for a vehicle ground up and I know that the diameter of the master cylinder would affect the braking force proportionally to the area of the master cylinder. But ...
John Rawls's user avatar
1 vote
2 answers
691 views

Dual brake calipers with one brake line?

A comment at the end of this ChrisFix video (at about 14:42): https://youtu.be/gjqeFEyaUxc?t=882 raised my eyebrows a tiny bit. Chris says that you can run two brake calipers (two calipers on each of ...
Goulash's user avatar
  • 63
26 votes
2 answers
5k views

Why do the brakes "freeze" the suspension?

Last week I was driving a motorcycle. When I stopped at a traffic light I noticed the rear suspension dropped a little when I released the rear brake. Later I noticed my car did the same thing. When ...
user60481's user avatar
  • 1,344
1 vote
2 answers
126 views

Questions about the clutch pilot bearing

I understand how the clutch system works in a manual transmission, but I'm struggling to get a proper image of what the pilot bearing does into my head. Does the input shaft always rest inside it, ...
george7378's user avatar
1 vote
1 answer
370 views

How can a DCT be so fast and smooth during hard acceleration and high rpm shifting?

I know how a DCT works and what parts it has, but I've always wondered how it manages to shift very fast and still be smooth, while having little torque drop during shifts.In a manual transmission, ...
ALPINA's user avatar
  • 11
1 vote
1 answer
434 views

Can car alternator be used to save fuel by using it as a regenerative system at the same time?

Car alternators are 3 phase DC excited synchronous electric machines. They can be used as a motor by a proper 3 phase motor driver. Let's think that we connected a 200Ah Lithium based (eg. LiFePO4) ...
ceremcem's user avatar
  • 113
2 votes
1 answer
129 views

Why doesn't polarity matter for fuel injectors?

Why doesn't polarity matter for fuel injectors? If they are essentially a solenoid, then it seems it would matter; swapping polarity would change the direction the electromagnet pulls or pushes.
Geremia's user avatar
  • 187
0 votes
1 answer
296 views

Idling a cold engine before driving away: contradictory advice

With modern combustion engines it is common advice that idling before driving away for more than a few seconds (to build up oil pressure) does more harm than good, even in "arctic" winter conditions (...
Christoph Groth's user avatar
0 votes
2 answers
465 views

Dry motorcycle clutch vs Wet motorcycle clutch discs material

I was wondering if the wet clutch discs on a motorcycle would be made out of the same friction material to the dry clutch discs. I understand this is probably not true, but does anyone know the exact ...
kokobill's user avatar
  • 1,015
3 votes
1 answer
259 views

How is automatic gliding realized with an automatic transmission?

It is generally accepted wisdom that it is a bad idea to coast or glide a car equipped with a conventional hydraulic automatic transmission. Coasting (running with an idling engine that is ...
Christoph Groth's user avatar
0 votes
1 answer
1k views

What are Wheel ticks and Wheel impulses?

I have some Odometry data taken from a Volkswagen Passat which gives the position. This is calculated using wheel ticks and in addition, I also have data which gives me the number of wheel impulses at ...
surajr's user avatar
  • 1
0 votes
3 answers
667 views

What are diamond cut alloy wheels?

I'm thinking of buying a new car, and one of the options it has is diamond cut alloy wheels. What's the difference between normal and diamond cut alloys?
George's user avatar
  • 6,515
0 votes
0 answers
283 views

Why ambient temperature used to measure pressure for car ac system

Since the ac system is located mostly inside a car engine and the car is warmed up prior to adding freon, and the temp/humidity in engine bay is different from ambient temperature//humidity, and all ...
StackUser's user avatar
0 votes
0 answers
131 views

Do all cars rust eventually even with repeated proper rustproofing methods?

My understanding is that rustproofing works and lasts when done properly, but once the coating used to rustproof wears off I'm guessing the process to rustproof needs to be done all over again. With ...
Narcotixs's user avatar
  • 775
3 votes
2 answers
4k views

How do automatic cars rev match so quickly when up shifting?

In a manual car, when you up shift, you need to wait for the engine RPM to drop to a certain value so that the engine speed matches with the speed of the gears you want to shift into. On my manual car,...
user1969903's user avatar
4 votes
4 answers
150 views

Work over time; humans versus automobiles

I've been doing some research lately on torque and horsepower to understand how they are connected to one another. Take my car, a 2.0 TDI, outputs 390 Nm torque. 390 Nm alone without considering an ...
Erik's user avatar
  • 293
3 votes
1 answer
101 views

How is fuel pressure maintained when the pump isn't running?

Pretty simple question, if liquids are incompressible then how is fuel pressure "stored" when the fuel pump isn't running, i.e. after turning to run and waiting a few seconds, but not turning to start?...
Ceshion's user avatar
  • 1,708
4 votes
4 answers
315 views

What does the hybrid engine do with surplus energy?

This question is based on Toyota Hybrid flyers / experience but I suppose it's meant to be general for hybrids? The concept is to use electric motor for braking (therefore often the power of electric ...
Danubian Sailor's user avatar
2 votes
1 answer
453 views

Does a dual-clutch transmission require synchronizer cones?

When you shift in a traditional manual transmission, the clutch is disengaged and a sleeve is shifted from one gear to another. The teeth of the sleeve must align with the teeth of the target gear. ...
Woodrow Barlow's user avatar
6 votes
1 answer
29k views

What is surface charge and how does it affect battery testing?

I've read in numerous places that "surface charge" can give false positives when testing a battery, and you need to remove the said surface charge to get an accurate result. I've also read various ...
Robert S. Barnes's user avatar
3 votes
1 answer
954 views

Triangular/Parallel four-link suspension system, how it works

I've been really interested at car suspensions lately and this particular system confuses me the most... Are they simple hinges or do they also move other ways than that the angle they're placed ...
TweakBox's user avatar
6 votes
5 answers
130k views

How to convert Amp Hours to CCA?

Is there a formula for converting a battery amp hour rating, which is used in much of Europe and Asia, to an Cold Cranking Amps (CCA) rating?
Robert S. Barnes's user avatar
4 votes
0 answers
161 views

Can a Battery Conductance Test tell the difference between damaged plates and sulfation?

I'm just going to lay out my assumptions, or what I think I know, so that there's a better context for the question. I understand that there are basically four main situations in which a standard ...
Robert S. Barnes's user avatar
3 votes
3 answers
714 views

How would a car handle differently if it had independent brake controls, like a pedal bike?

Facts - Cars have one brake pedal. Bikes have two brake levers. So a cyclist can brake fully with the front or the rear, or some combination of both, or alternate between the brakes. If a car had ...
Criggie's user avatar
  • 2,693
8 votes
2 answers
683 views

What is torque steer?

I saw an old Top Gear episode, and I think it was Jeremy who said something along the lines of The torque steer is terrible What is torque steer though? Is it a bad thing? Why does it happen? ...
George's user avatar
  • 6,515
6 votes
3 answers
149 views

Multiple Batteries Charging

I have multiple batteries off from motorcycles, and each of them has it's own charge level (12-13 Volt measured at rest). Assuming I have only one 12 Volt charger, can I charge them in parallel until ...
oryades's user avatar
  • 346
3 votes
3 answers
4k views

How does a timing light detect the electricity in the plug wire?

I assume that a timing light functions by some kind of inductive pickup and the signal is amplified by power from the battery and turned into a flash at the bulb. But I was wondering, is it picking ...
Robert S. Barnes's user avatar
3 votes
1 answer
1k views

Why do hybrids have the aesthetic wheel cover on the body?

I've noticed that the manufacturers tend to cover the rear and/or front wheels on the hybrid models more often than the regular vehicles. Are there practical or functional reasons for the covers? Is ...
UndeadBob's user avatar
  • 133
4 votes
1 answer
5k views

Can a lightning strike cause your car to not run?

If lightning strikes a tree in your yard and your car is close by, can this cause your car to not work properly? I had an employee call in stating that lightning struck a tree beside their mobile ...
user avatar
15 votes
6 answers
7k views

Turbo equivalent on electric motors

Is there anything functionally equivalent to a turbo for electric motors? Obviously, I am not asking for something that reuses exhaust gases to force in more air, because there are no exhaust gases ...
sergiol's user avatar
  • 686
9 votes
3 answers
2k views

Why do electric motors produce peak torque instantly vs gasoline engines

On a separate forum, someone had asked why electric cars do not have transmissions. The simple answer was that electric cars produce peak torque at any RPM but the gasoline engine needs to rev up to ...
Shobin P's user avatar
  • 8,946
5 votes
1 answer
20k views

How do electric car transmission systems work?

How do electric car transmission systems work? Does it have an auto or manual gear concept like gasoline vehicles? As an electric motor can run in any speed (slow), is it necessary to have a clutch?
sugunan's user avatar
  • 153