Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 12th March 2016, 18:05   #16
Distinguished - BHPian
 
dhanushs's Avatar
 
Join Date: Oct 2009
Location: Bathery/BLR
Posts: 3,445
Thanked: 4,054 Times
Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by SS-Traveller View Post
Misconception 1: Disc brakes stop the car better than drum brakes.

The truth:
Excellent thread SST. And thank you for bringing up the above topic.

To practically experience how disc brakes work vs drum brakes, one can try out a double cylinder type front drum brakes fitted Mahindra 540 (which was in production) against a front OE disc type Army Mahindra 540s. Both without Vacuum assist.

End Result: Disc Brakes Suck in front of Drum Brakes.

However
: Apart from stopping power, the practical applications of disc brakes are much higher than that of drum brakes and hence the latter is more common. Eg: Drum brakes(design) lose braking power by a huge margin (~90%) when immersed in water.
Quote:
Originally Posted by SS-Traveller View Post
  • 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.
I'm wondering how the newer MicroHybrids think in this regard?

Last edited by dhanushs : 12th March 2016 at 18:07.
dhanushs is offline   (9) Thanks Reply With Quote
Old 12th March 2016, 20:28   #17
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Kolkata
Posts: 3,506
Thanked: 2,066 Times
Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by SS-Traveller View Post
I am afraid I have no idea about how train brakes work
Latest (actually has been for quite some time on high speed rakes abroad) is eddy current braking. No mechanical contact. Heat dissipated in the rail.

Regards
Sutripta
Sutripta is offline   (7) Thanks Reply With Quote
Old 13th March 2016, 09:13   #18
BHPian
 
d_himan's Avatar
 
Join Date: Nov 2006
Location: Bombay
Posts: 728
Thanked: 589 Times
Default

Quote:
Originally Posted by SS-Traveller View Post
[u][b]Premium fuels
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
Great thread! However, I notice a massive difference in smoothness a clean revving using speed 97 with my 1.2 TSI. There is a bit of engine lugging with normal petrol in the D mode of the DSG in some situations which also disappears with 97. Given the occasional stock outs of 97, I keep switching. The difference is very noticeable.
d_himan is offline   (2) Thanks Reply With Quote
Old 13th March 2016, 09:36   #19
Distinguished - BHPian
 
Join Date: Oct 2012
Location: Delhi
Posts: 3,056
Thanked: 6,169 Times
Default

Quote:
Originally Posted by Sutripta View Post
Latest (actually has been for quite some time on high speed rakes abroad) is eddy current braking. No mechanical contact. Heat dissipated in the rail.



Regards

Sutripta

Eddy current braking explained:

http://www.explainthatstuff.com/eddy...nt-brakes.html

Quote:
Originally Posted by SS-Traveller View Post
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. [b]Or are they?
A dirty oil filter does more harm to your engine than another 1000 km on the same oil. Always change the oil filter at the manufacturer specified intervals. Get the best filter money can buy.

Last edited by Gannu_1 : 13th March 2016 at 12:42. Reason: Back to back posts merged. Quoted post trimmed = inconveniences mobile users. Thanks!
Jeroen is online now   (5) Thanks Reply With Quote
Old 13th March 2016, 09:41   #20
BHPian
 
samaspire's Avatar
 
Join Date: Sep 2015
Location: Manipal / Udupi
Posts: 952
Thanked: 2,256 Times
Default Re: Automotive misconceptions demystified

Excellent thread Ss-traveller.
Very informative and thought provoking.

Quote:
Originally Posted by SS-Traveller View Post
Thankfully, premium branded fuels have disappeared from pumps in India.
Sadly, you are wrong here. IndianOil have started selling Xtra Premium again. At least here in my hometown.
samaspire is offline   (1) Thanks Reply With Quote
Old 13th March 2016, 10:16   #21
BHPian
 
WorkingGuru's Avatar
 
Join Date: Sep 2013
Location: Bangalore
Posts: 198
Thanked: 237 Times
Default Re: Automotive misconceptions demystified

Nice thread, summarises alot for us newbies.

Btw, n00B question alert!

What is the difference between 'Variant' & 'Trim' ?
WorkingGuru is offline   (1) Thanks Reply With Quote
Old 13th March 2016, 10:20   #22
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 6,617
Thanked: 10,775 Times
Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by d_himan View Post
...using speed 97 with my 1.2 TSI.
Speed97 is a higher octane fuel (RON 97) than Speed (the usual RON 91, which unbranded fuels are as well). Higher octane fuels have their advantages over regular fuels, no denying that.
Quote:
Originally Posted by Jeroen View Post
Always change the oil filter at the manufacturer specified intervals. Get the best filter money can buy.
I would have thought there's no misconception about changing (or not changing) oil filter at the time of changing engine oil. It's pretty much mandatory to change oil filter at the same time as changing oil, isn't it?
Quote:
Originally Posted by samaspire View Post
Sadly, you are wrong here. IndianOil have started selling Xtra Premium again. At least here in my hometown.
Nothing to be sad about. There were talks about reviving branded fuels a year or two ago, and the government cut excise duties on them, but I haven't noticed any on sale in Delhi pumps recently. However, the marketing spiel pushing these fuels does give rise to the misconception that they are better for the engine.
SS-Traveller is offline   (1) Thanks Reply With Quote
Old 13th March 2016, 10:46   #23
BHPian
 
timuseravan's Avatar
 
Join Date: Feb 2016
Location: Pune
Posts: 285
Thanked: 317 Times
Default Re: Automotive misconceptions demystified

Fantastic thread!
However I have to partially disagree with:

Quote:
Originally Posted by SS-Traveller View Post
Premium fuels
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.
I use Shell VPower for my Duke390 and the engine runs noticeably smoother with VPower than regular shell. I have experimented with alternate cycles and combinations of regular and Vpower shell and Vpower is definitely better for D390. It might have something to do with the high 12.6:1 compression ratio of the engine.
I did similar experiments with VPower for my Swift and there was no difference. For normal cars it does not make sense to pay more for premium fuel. But what I do is fill VPower every 4-5 fills for the cleaning effect.

Last edited by timuseravan : 13th March 2016 at 10:48.
timuseravan is offline   (2) Thanks Reply With Quote
Old 13th March 2016, 11:18   #24
BANNED
 
Join Date: Aug 2009
Location: Coimbatore / MENA
Posts: 673
Thanked: 973 Times
Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by SS-Traveller View Post
Brakes

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.
Even though drum brakes are used in certain heavy duty applications where chances of disc warping are high, the general consensus is that disc brakes are better.

Some of the critical factors in braking efficiency are friction area, cooling of said area, and amount of clamping force that can be applied. Disc brakes are superior in all criteria, plus the added benefit of freedom to locate the calipers, like behind the disc in front and ahead of the disc in rear further aid in braking dynamics.

So, I would say, unless extraordinary circumstances, disc brakes are better.

Quote:
Originally Posted by SS-Traveller View Post
Premium fuels

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.
I assumed premium fuels in India like regular Speed had higher RON rating as well.

Higher RON rating fuel will make an improvement on some of the newer gen high compression ratio vehicles that are actually rated for 95 RON but running retarded EFI maps for lower rating fuel.

Cheers.

Last edited by gthang : 13th March 2016 at 11:23. Reason: To Edit
gthang is offline   (5) Thanks Reply With Quote
Old 13th March 2016, 12:23   #25
Senior - BHPian
 
comfortablynumb's Avatar
 
Join Date: Jul 2007
Location: Pune
Posts: 1,295
Thanked: 896 Times
Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by SS-Traveller View Post
Engine oil
What is your opinion on people changing engine oil after the car has run just a 1000 kms, even though it's not recommended in the manual? Apparently, this is to get rid of the metallic debris from a new engine. I can understand the rationale being valid 15 years ago, but is this valid even now? Or is it something people do to be safe than sorry?

Quote:
Originally Posted by gthang View Post
I assumed premium fuels in India like regular Speed had higher RON rating as well. Higher RON rating fuel will make an improvement on some of the newer gen high compression ratio vehicles that are actually rated for 95 RON but running retarded EFI maps for lower rating fuel.
I think at least IOC premium Petrol (XtraPower) has a higher RON rating, according to the doc attached below (taken from https://www.iocl.com/Products/Gasoline.aspx)

MS_BS_IV_Specification _Current_.pdf

Couldn't find anything similar about BP (normal Speed, not Speed 97) and HP premium fuels, though.

Cheers,
Vikram

Last edited by comfortablynumb : 13th March 2016 at 12:38.
comfortablynumb is offline   (1) Thanks Reply With Quote
Old 13th March 2016, 12:48   #26
Senior - BHPian
 
Join Date: Aug 2010
Location: Delhi
Posts: 2,131
Thanked: 1,001 Times
Default Re: Automotive misconceptions demystified

A)
On high compression engines higher RON rating will result in better combustion control in the engine, hence it will run smoother. If a "Premium" fuel has the same RON as the normal fuel, then it is only additives that give it the "Premium" tag, and some cases the additives may result in poorer combustion. That is why you may notice some improvement in the fuel injected (and turbo) petrol engines used by VAG and Mercedes here. They are usually higher compression and will benefit with RON of 95/97 rating.

At times additives are beneficial. I remember that both Cielo and Opel cars had injector problems due to gumming. An additive with fuel solved it. Now a days most fuels come with the additives anyway.

B)
Drum brakes need less effort for a given braking efficiency, simply because the friction area is much larger. That is one of the reasons that the "hand brake" mechanism still relies on drum brakes. There is simply no way a hand operated brake will match a hydraulic brake in mechanical advantage. In case all wheels have disk brakes, the hand brake is either "boosted" or as in case of a few SUV's a small drum ;for hand brake only; is attached to the disks

Disk brakes require much more effort, hence the braking system has to incorporate additional components to "boost" the hydraulic effort. For larger braking area in disk brakes you need larger diameter disks, where as in case of a drum you use a longer shoe. That is the reason for large diameter rims in performance cars, but that comes at the cost of ride comfort and higher possibility of rim damage.

The major advantage of disk brakes is that cool faster, hence under heavy use, especially in hot weather they will remain cooler than drum brakes and fade less. With modern electronics backed by efficient 'boosters' disk brakes are the way to go, but as with every thing in modern car, they are more complicated with more points of failure than simple hydraulic drum brakes.
Aroy is offline   (3) Thanks Reply With Quote
Old 13th March 2016, 13:11   #27
BHPian
 
bivin's Avatar
 
Join Date: Aug 2009
Location: MAA/DXB/CDG
Posts: 932
Thanked: 113 Times
Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by SS-Traveller View Post
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?

Attachment 1484696
Attachment 1484697
Source

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.




So what about engines with start stop systems. Would turbo wear be higher in such cars? and also, in a way fuel consumption? In most metros traffic creeps along at really slow speeds, the engine turns on and off repeatedly during this time, which im sure isnt helping the fuel economy, also repeated cranking of the engine is extremely annoying after a point.

Last edited by bivin : 13th March 2016 at 13:16.
bivin is offline   (1) Thanks Reply With Quote
Old 13th March 2016, 13:39   #28
Senior - BHPian
 
Join Date: Aug 2010
Location: Delhi
Posts: 2,131
Thanked: 1,001 Times
Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by bivin View Post
[/b]

So what about engines with start stop systems. Would turbo wear be higher in such cars? and also, in a way fuel consumption? In most metros traffic creeps along at really slow speeds, the engine turns on and off repeatedly during this time, which im sure isnt helping the fuel economy, also repeated cranking of the engine is extremely annoying after a point.
Each start of the IC engine consumes some fuel. How much is that in equivalent minutes of idling is debated, but the general consensus is that stops more than a minute benefit from engine stop.

In case of hybrids the situation is different. At low speeds most hybrids run on battery and there is no extra energy spent in starting the electric motor. So even 5 sec stop benefits electric traction. Here some manufacturers have incorporated the start/stop of a hybrid without any electric traction, which is wasteful if stops are short. Further the turbo charger suffers from abrupt start/stop. Hence on the whole in my opinion switching the engine for short stops is counter production for normally aspirated engines, and may be harmful for turbocharge engines.

OT. In a start stop, slow moving urban traffic an electric traction is most efficient form of transportation.
Aroy is offline   (1) Thanks Reply With Quote
Old 13th March 2016, 14:29   #29
BHPian
 
prakhar1998's Avatar
 
Join Date: Aug 2013
Location: Berkeley, CA
Posts: 288
Thanked: 494 Times
Default Re: Automotive misconceptions demystified

1.Wearing the seatbelt is not important when you have front Airbags

This misconception is fairly prevalent and people believe that Airbags have god like abilities and can save you from any crash. I'm sure all of us have seen the letters SRS written alongside airbags. This stands for "Secondary Restraint System" and hence implies that airbags are a secondary safety apparatus. On the other hand, a seatbelt is a PRS "Primary Restraint System" which may have a greater role during crashes than Airbags. Both these safety apparatus work in tandem to provide the maximum safety, but an Airbag might be more detrimental without a seatbelt, but its usually not vice-versa.

Hence, always wear your seatbelt, even if your car has 10 airbags.

2. Rear passengers don't need seatbelts. No structures pose threat to them in the rear.
This misconception is probably the biggest one in India. Almost no one in India wears a rear seatbelt. In fact, people almost ridicule you for doing it. Almost all taxis have their rear seat belt as well as buckle hidden behind the seat. Its a disaster.

One needs to wear their seatbelt in the rear not only to increase their own safety, but to ensure that they don't cause harm to the passengers in the front seats. I can't emphasise this enough but the decelerations experienced during an accident are immense. This means that an unbelted passenger can act as a projectile with such a high velocity that he might even crush the front passenger. I hope this video clarifies my idea.


Belting up all around is essential. I don't know why the Delhi government removed the law that required rear passengers to belt up.

Last edited by prakhar1998 : 13th March 2016 at 14:36.
prakhar1998 is offline   (8) Thanks Reply With Quote
Old 13th March 2016, 20:59   #30
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Kolkata
Posts: 3,506
Thanked: 2,066 Times
Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by Aroy View Post
Drum brakes need less effort for a given braking efficiency, simply because the friction area is much larger.
Would increasing the pad dimensions (not disc diameter) increase braking 'efficiency' in a disc brake system?

Regards
Sutripta
Sutripta is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Engine Decarbonising - Demystified SS-Traveller Technical Stuff 94 10th July 2016 19:50
Women's Automotive Satisfaction Awards 2002 amit The International Automotive Scene 2 19th July 2013 12:46
GPS Solutions Demystified vishnugs Modifications & Accessories 234 7th June 2010 19:10
The Most Powerful Automotive People in the world GTO The International Automotive Scene 5 27th January 2005 01:12


All times are GMT +5.5. The time now is 23:26.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks