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Old 10th March 2016, 10:38   #1
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Default Automotive misconceptions demystified

Most automotive enthusiasts (and many young automotive journalists) gather information about cars and technology from the internet. Which is not to say that the internet is a bad thing. But there are plenty of technological concepts that are stood on their head by half-informed / mis-informed enthusiasts, and these concepts continue to be propounded as Gospel over time.

The information that is available by casually browsing the internet is sometimes vastly different from the knowledge of the automobile engineer, or even the practical experience of the old mechanic.

This thread will hope to bring out the truth about some of those misconceptions, from the OP as well as through contributions from other knowledgeable members of the forum.

Last edited by SS-Traveller : 10th March 2016 at 11:20.
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Old 10th March 2016, 11:12   #2
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Default Re: Automotive misconceptions demystified

Wheels and tyres

Perhaps one of the most sought after items on a new car buyer's list is a switch to better wheels and tyres. The more the wheels jut out of the bodywork, and the fatter the tyres, the better. Or is it?



Misconception: Fatter tyres, knobbier treads and negative offset wheels make for better performance & road-holding. Low profile tyres mean a better handling car.

The truth:
  • Wider tyres, upto a limit, do improve road-holding, traction in a straight line and around corners.
  • Tyre treads are designed for specific purposes, such as use on the track, on the highway, on rough roads, in mud, or on snow. On surfaces which a given type of tyres are not designed for, performance would naturally suffer. Thus, it is imperative to understand where the car would run through the majority of its life, and choose tyres accordingly. MT (mud terrain) tyres have extremely poor grip and lateral stability when used on highways, and wear out at much higher rates at high speeds.
  • Wider rims may be useful to accommodate wider tyres, but check what is the maximum size of tyre that your existing rim can accommodate.
  • Negative offset rims increase track width and may contribute to a little more stability, but the suspension system and bearings suffer immensely more stress.
  • Beyond a limit, wider tyres sap engine power and return poorer performance & FE.
  • Low profile tyres (i.e. lower than what the manufacturer recommends) will cause a harsher ride as well as damage rims and suspension components, but handling will not necessarily improve.
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Last edited by SS-Traveller : 11th March 2016 at 21:26.
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Old 10th March 2016, 11:48   #3
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Default Re: Automotive misconceptions demystified

I agree, I upsized my Swift wheels. The ride is crashy, suspension has worn, fuel consumption 10% below normal. Not worth it at all
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Old 10th March 2016, 16:55   #4
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Default Re: Automotive misconceptions demystified

Engine oils

Automotive enthusiasts love their engines. And engines, like humans, supposedly deserve the best nourishment, aka engine oil. All-natural and organic stuff is the best choice for humans, while all-synthetic lubricating oils are supposed to be best for engines. Or are they?

Much debate has taken place about which is the best engine oil for one's car, what should be the right drain interval, and how synthetic oils are more effective, protective and longer lasting than mineral oils or semi-synthetics.

Misconception: The more expensive and higher the numbers of the oil, the better it is for your car. 0W-60 is better than 15W-50, CI4 rated oils are better than CF4 oils, and synthetic oils are better than semi-synthetic oils.

The truth:
  • Oils are designed for specific purposes, specific applications, and specific build tolerances of engines. If the engine manufacturer recommends 20W-40, the engine is not going to run better with a 0W-30 or 10W-60 oil - in fact, lubrication might suffer because of the mismatched viscosity.
  • Synthetic oils do tolerate higher temperatures and more merciless use, but tend to degrade quickly under certain circumstances, such as usage of adulterated fuel (sulphur in fuels due to adulteration with kerosene / naphtha ruins the effectiveness of synthetic oils quicker than of semi-synth or mineral oils).
  • A higher grade oil such as CI4 is not necessarily designed to lubricate better, but to not damage pollution control equipment such as catalytic converters and diesel particulate filters. However, such oils are extremely sensitive to bad fuel quality, and themselves degrade much quicker when poor quality fuels are used. Euro 6 engines require different specifications & grades of oil only to protect pollution control devices from deterioration, but themselves deteriorate rapidly when bad quality / adulterated fuels are used. The sulphur levels in Euro 6 diesel need to be at 10-15 ppm only to prevent the engine oil and pollution control devices from self-destructing.
  • Stop-start driving, not allowing the engine to reach full operating temperature, low-rpm driving, extremely high-rpm driving, all degrade the engine oil rapidly.
  • The oil change interval published by manufacturers is not sacrosanct, but is an advisory for maximum interval when driving under ideal conditions - which is impossible to achieve in real life.
  • The best way to test whether an engine oil still has service life left or not, is to use an oil analysis kit, or to send it for UOA (used oil analysis) to a laboratory. However, this is a technical test that not many can do or understand. If you cannot figure out what is TAN / TBN in an engine oil, just remember to change the engine oil sooner than your car's manufacturer recommends. And stick to the recommended grade, viscosity and specification of oil as mentioned in the owner's handbook.
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Old 10th March 2016, 23:33   #5
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Default Re: Automotive misconceptions demystified

Brakes

The design of hydraulic brakes of automobiles has not changed drastically over the last few decades. What has changed, is how these brakes are made to operate and behave electronically under certain circumstances, to make for a safer driving experience. The essential mechanism of stopping the car remains much the same, i.e. friction between discs and pads, or between drums and shoes.

Misconception 1: Disc brakes stop the car better than drum brakes.

The truth:
  • Disc brakes are a lot less efficient at stopping a car - hence, to multiply the force applied by the driver's foot as well as the mechanical advantage that hydraulics offer, an invisible force in the form of a vacuum booster has to be added to make them work optimally.
  • The biggest advantages of disc brakes are (a) their ability to run cooler, thus reducing brake fade under extreme use; and (b) weight savings.
  • For extremely heavy-duty applications, drum brakes are the system of choice - look under trucks and buses, and you will find there are rarely, if ever, any disc brakes being used.
Misconception 2: Electronic add-ons such as ABS & EBD always stop a car within a shorter distance.

The truth:
  • ABS allows the driver to retain control over the car and steer away from danger, and improves safety in certain situations
  • ABS increases the braking distance on loose surfaces like sand and gravel
  • ABS does not compensate for late braking or driver inattention
  • A trained driver who can perform threshold braking on a non-ABS vehicle, can produce lower braking distances than a less trained driver in an ABS-equipped vehicle.
Misconception 3: The brake fluid lasts for many years, and does not need replacement. Different types of brake fluids cannot be mixed.

The truth:
  • Current brake oils are glycol-based and hygroscopic (i.e. they attract moisture), which corrodes the components in contact with it. The recommended replacement interval is usually about 2 years.
  • DOT 5 fluids are silicone-based, non-hygroscopic, and do not need replacement at frequent intervals.
  • DOT 3, DOT 4 and DOT 5.1 brake fluids are glycol based fluids, and systems using a lower grade can be upgraded to a higher grade of brake oil (i.e. DOT 3 can be replaced with DOT 4, and DOT 4 can be replaced with DOT 5.1). DOT 5 fluids are silicone based, and cannot be replaced / interchanged with other types.

Last edited by SS-Traveller : 11th March 2016 at 21:56.
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Old 11th March 2016, 13:44   #6
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Default Re: Automotive misconceptions demystified

Driving for fuel efficiency

The Petroleum Conservation Research Association under the Ministry of Petroleum & Natural Gas, Government of India, states that driving at 45 to 55 kmph produces the best fuel efficiency, and that driving above 60 kmph wastes fuel. Switching off the engine at stops longer than 15-20 seconds also saves fuel. Or does it?

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Misconception:
Driving slowly in a higher gear returns better fuel efficiency. So does switching off at stops longer than 15-20 seconds.

The truth:
  • 45-55 kmph for best fuel efficiency applied to vehicles which were in production 20-30 years ago. Today's vehicles have better fuel efficiency at higher speeds. In fact, many cars are unable to engage top gear at these speeds.
  • Moving up the gears at the lowest possible RPM without lugging the engine is not the best practice for returning the best fuel efficiency. Driving at an optimum RPM (~1800 - 2500 RPM for most vehicles) for any given gear is more fuel efficient than, say, driving at 1300 RPM in top gear.
  • An interesting article about how to shift gears for maximum acceleration also gives a lot of insights about what RPM is best to drive in.
  • Switching off the engine at short stops actually consumes more fuel to fire up the engine again, than if it was allowed to idle.
  • Repeatedly starting and stopping engines (especially turbo-charged engines) causes more expensive harm than a paltry saving in fuel consumption can compensate for.

Last edited by SS-Traveller : 11th March 2016 at 18:49.
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Old 11th March 2016, 20:55   #7
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Default Re: Automotive misconceptions demystified

Bull-bars / nudge guards

In the chaotic traffic that rules this country, impact on bumpers (now overwhelmingly made of plastic, and technically known as the bumper cover) are a common occurrence. How we all hate that ugly scratch on those body-coloured plastic bits, and how we seek to protect them from the vagaries of traffic. Enter the bull-bar, in the form of chrome-plated steel pipes attached to the front and rear ends of the spanking new car. But do they really protect?

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Misconception: Installing a bull-bar in front is safer than not having one.

Truth:
  • In a minor accident, the bull-bar would quite likely protect the paintwork from being scratched, but repairing a bent or cracked chrome-plated pipe is tougher (and looks uglier) than repairing a scratched bumper cover.
  • In a more severe crash, the force of the impact would not be absorbed by the original bumper which is designed to do that. Instead, the force would be transmitted to the mounting point of the bull-bar and then on, to critical sections of the chassis, resulting in permanent and irreparable structural damage.
  • Bull-bars distort the front of the car in the wrong places in case of major crashes, increasing the likelihood of non-deployment of airbags - a major safety issue in airbag-equipped cars.
  • Pedestrian injury is higher, with greater chances of death, if hit by an upright bull-bar, rather than an energy-absorbing plastic bumper cover and a sloping bonnet.
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Old 11th March 2016, 21:19   #8
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Default Re: Automotive misconceptions demystified

Premium fuels

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Premium fuels with brands such as XtraMile, XtraPremium, Speed and Power were available for a few extra rupees per litre till a couple of years ago, and many motorists swore by their better fuel efficiency and smoother running. But did they work better?

Misconception:
Premium fuels return better fuel economy and cause the engine to run more smoothly.

The truth:
  • Premium fuels contain additives which are essentially detergents. In the days before fuel injected petrol / common rail diesel engines, th combustion process was less efficient, and carbon built up in the engine more quickly. The detergent helped to clear up the deposits, whereas regular fuels did not contain such additives.
  • Newer fuels compatible with BS-III/IV vehicles already have such additives added, and premium fuels do not improve matters in any way.
  • Premium fuels never reduce friction, and are not a replacement for a good engine oil, despite misleading advertisements.
  • Thankfully, premium branded fuels have disappeared from pumps in India. Unfortunately, adulterated fuel still hasn't.

Last edited by SS-Traveller : 11th March 2016 at 21:28.
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Old 12th March 2016, 10:47   #9
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Default Re: Automotive misconceptions demystified

Thread moved from the Assembly Line (The "Assembly Line" Forum section) to the Technical Section. Thanks for sharing!
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Old 12th March 2016, 11:09   #10
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Default Re: Automotive misconceptions demystified

Awesome and timely thread!!!

One from my side (but I am not sure that this belongs to this thread or not) that A/Ts are boring to drive while in reality they are not that bad as made out to be.
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Old 12th March 2016, 12:34   #11
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Excellent thread there. The information about various brake fluids is new to me.

I had devised a 75% rule for my the then Indigo. According to that, I used to change the necessary lubricants / parts after completing / utilizing 75% of the recommended distance / time.

A query - Is extensive use of engine braking harmful for the engine? A majority part of my braking happens by engine braking and downshifting.
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Old 12th March 2016, 13:18   #12
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Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by SS-Traveller View Post
  • A higher grade oil such as CI4 is not necessarily designed to lubricate better, but to not damage pollution control equipment such as catalytic converters and diesel particulate filters. However, such oils are extremely sensitive to bad fuel quality, and themselves degrade much quicker when poor quality fuels are used.

I am confused. I thought the engine oil does not circulate through the cat-con or the DPF or any other part of the fuel injection / combustion system. How is engine oil sensitive to fuel quality? Cat con / DPF / emission control equipment sensitive to fuel quality - yes, but I can't see the link for the engine oil at all. Please explain in more detail.
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Old 12th March 2016, 13:52   #13
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Quote:
Originally Posted by phamilyman View Post
I am confused. I thought the engine oil does not circulate through the cat-con or the DPF or any other part of the fuel injection / combustion system. How is engine oil sensitive to fuel quality? Cat con / DPF / emission control equipment sensitive to fuel quality - yes, but I can't see the link for the engine oil at all. Please explain in more detail.
Excellent question.

Engine oil and fuel always mix in every internal combustion engine, though in small quantities.

1) Engine oil vapours are recirculated through PCV (positive crankcase ventilation) system into the combustion chamber, where the vapour is ignited and combustion products (of both diesel and engine oil) pass out through the exhaust (where this meets the cat-con, DPF etc.)

2) All engines, even new, have a minuscule quantity of the fuel blowing by past the piston rings into the engine oil chamber, where it comes in contact and mixes with the engine oil, contaminating it.
Quote:
Originally Posted by Swapnil4585 View Post
A query - Is extensive use of engine braking harmful for the engine? A majority part of my braking happens by engine braking and downshifting.
No harm done whatsoever. One can use engine braking to retain control over the car over an infinite distance. Much more sense doing this, than using brakes!
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Old 12th March 2016, 14:32   #14
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Quote:
Originally Posted by SS-Traveller View Post
Brakes

The design of hydraulic brakes of automobiles has not changed drastically over the last few decades. What has changed, is how these brakes are made to operate and behave electronically under certain circumstances, to make for a safer driving experience. The essential mechanism of stopping the car remains much the same, i.e. friction between discs and pads, or between drums and shoes.

Misconception 1: Disc brakes stop the car better than drum brakes.

The truth:
  • Disc brakes are a lot less efficient at stopping a car - hence, to multiply the force applied by the driver's foot as well as the mechanical advantage that hydraulics offer, an invisible force in the form of a vacuum booster has to be added to make them work optimally.
  • The biggest advantages of disc brakes are (a) their ability to run cooler, thus reducing brake fade under extreme use; and (b) weight savings.
  • For extremely heavy-duty applications, drum brakes are the system of choice - look under trucks and buses, and you will find there are rarely, if ever, any disc brakes being used.
Dear Sir,

I would like to disagree here. From what I have studied, seen and felt, The disc brakes in my opinion are actually better than drum brakes on all counts, including efficiency at stopping a vehicle.

1. Compare two bikes, one with disc brakes and another one with drum brakes. I've seen drum brakes offer bad feedback, longer stopping distance and over all bad braking performance when compared to bikes with disc brakes. and I've driven enough bikes (100CC-220CC) to say this. Disc brakes offer superior feedback, better braking.

2. All high end cars, run discs all around. All reviews here in TBHP point out that, also the fact that its better to have discs all around in cars. Some cars like i20 (if I remember correctly) lost the rear discs and Hyundai was criticized for the same move on this forum.

3. Volvo buses (B7R, information from company website) offer disc brakes. and these buses are the epitome of modern technology.

4. You say heavier vehicles do not run Disc Brakes. Sir, would you consider trains heavy enough? To your surprise, you may find that the new LHB Coaches the Indian Railways uses are equipped with disc brakes. These coaches offer superior braking and better safety. The WAP5 loco (rated for high speed operations in India), which is used for Bhopal Shatabdi (The fastest train in India, running at 150KMPH Max Speed for a specified stretch) uses disc brakes. Now I'm sure the reason cant be that disc brakes run cooler.

5. You talked about vacuum booster. What is that? I'm sure the bikes with disc brakes dont have this. But still bikes with disc brakes offer better performance, isn't it?

6. Weight savings: For a supercar, every gram may actually matter. But for a bike, or a hatchback/sedan, or a Volvo bus, how much additional weight would a drum brake contribute? Would it hamper the performance? Would it bring down the cost? In fact I've seen the exact opposite- bikes with disc brakes have higher cost, compared to bikes with drum brakes.

All these points are said with humility and an intention to learn. I hope my points are considered for your original post.
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Old 12th March 2016, 17:35   #15
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Thank you, Lord, for a detailed reply.
Quote:
Originally Posted by LordSharan View Post
I would like to disagree here. From what I have studied, seen and felt, The disc brakes in my opinion are actually better than drum brakes on all counts, including efficiency at stopping a vehicle.
Of course there are big advantages in disc brakes. No denying that.
Quote:
1. Compare two bikes, one with disc brakes and another one with drum brakes. I've seen drum brakes offer bad feedback, longer stopping distance and over all bad braking performance when compared to bikes with disc brakes. and I've driven enough bikes (100CC-220CC) to say this. Disc brakes offer superior feedback, better braking.
One of the disadvantages of drums is that the weight goes up in relation to stopping power. On a bike, where weight matters, a powerful disc brake is lighter than an equivalent drum - and also more expensive.
Quote:
2. All high end cars, run discs all around. All reviews here in TBHP point out that, also the fact that its better to have discs all around in cars. Some cars like i20 (if I remember correctly) lost the rear discs and Hyundai was criticized for the same move on this forum.
Indeed, we want our cars to be cheaper, but the technology to be cutting-edge. Manufacturers take into account the cost of manufacturing too. It isn't as if the drum brakes on a car are any less effective in stopping the car than discs.
Quote:
3. Volvo buses (B7R, information from company website) offer disc brakes. and these buses are the epitome of modern technology.
True. And Tata's racing trucks (Driven: The Tata Prima Race Truck!) run drum brakes.
Quote:
4. You say heavier vehicles do not run Disc Brakes. Sir, would you consider trains heavy enough? To your surprise, you may find that the new LHB Coaches the Indian Railways uses are equipped with disc brakes.
I am afraid I have no idea about how train brakes work, or for that matter, aircraft brakes. But I wouldn't want to take that into consideration in the discussion.
Quote:
5. You talked about vacuum booster. What is that?
I am certain you can find out.
Quote:
I'm sure the bikes with disc brakes dont have this. But still bikes with disc brakes offer better performance, isn't it?
Bikes with drums often have cable-operated mechanical systems, while disc brake equipped bikes have hydraulic systems. Cable-operated discs are rare, if at all present, on motorcycles. Bicycle discs also come with hydraulic actuation in the high-end versions (though low-end disc-equipped bicycles make do with cable operation).
Quote:
6. Weight savings: For a supercar, every gram may actually matter. But for a bike, or a hatchback/sedan, or a Volvo bus, how much additional weight would a drum brake contribute? Would it hamper the performance? Would it bring down the cost?
Quite a bit, actually.
Quote:
In fact I've seen the exact opposite- bikes with disc brakes have higher cost, compared to bikes with drum brakes.
You are right, and you are repeating what has been already mentioned. Let me reiterate on the disc vs. drum debate:

Pros of disc brakes:
  • Lighter
  • Less chance of fading
  • Dry out quicker after water immersion
Cons of disc brakes:
  • Disc brake systems are quite a bit more expensive than drum brakes
  • Need more mechanical advantage (multiplication of force applied) to produce equal stopping power
  • Bigger discs interfere with suspension and other clearances
Hope this explains things in a better manner.
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