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Old 14th March 2016, 15:37   #46
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Default Re: Automotive misconceptions demystified

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Originally Posted by Sutripta View Post
Would increasing the pad dimensions (not disc diameter) increase braking 'efficiency' in a disc brake system?

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Sutripta
Quote:
Originally Posted by Ricci View Post
Yes, and that's what's done often, but I guesstimate there is a loss of pressure (keeping the same net force, increasing the pad-disk contact area). Pads are often in light contact with the disc anyhow, so it takes a bit of pressure to generate enough friction force. When stronger braking is required, the number of pistons may be increased rather than make the pistons larger - such as 6 piston callipers on 1200cc+ bikes whereas 600-1000cc bikes have typically 4 piston callipers. Piston size , to my knowledge, doesn't vary much between 250cc and 1200-1400cc bikes , with 32-34mm being the usual range. Some modern callipers may employ separate pads per piston than a single conjoined pad over 2 or 3 pistons per side.
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Originally Posted by Sutripta View Post
^^^
Was talking of pad contact area, not pistons.

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Sutripta
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Originally Posted by Jeroen View Post
I'm not so sure that increasing the size of the pads will increase braking. I'm pretty sure it doesn't actually. With disk brakes it is all about clamping force. As the clamping force remains the same the braking action will remain roughly the same.

To your earlier point, you need to increase the calliper dimension pistons or find a way to increase the pressure (in a hydraulic brake system) e.g. booster, multi piston or just push the brake pedal harder.

If you increase the diameter of the rotor and keep the same pads, that would certainly increase braking effectiveness.

http://stoptech.com/technical-suppor...rade-selection

Jeroen
Quote:
Originally Posted by purohitanuj View Post
Sure. Braking force is a function of friction and friction is proportional to the cross sectional area between two surfaces.

This is the reason behind the pad's curved design to capture as much disc as possible. Also you can notice massive pad size used in high performance cars; however there is a relation of cooling disc as well which restricts complete coverage.
Quote:
Originally Posted by Aroy View Post
The braking efficiency;in terms of force for a given braking effort; is dependent on the friction area. So yes increasing the area will increase braking, but then the pressure (force/area) on the pads decreases, hence you will have to increase the hydraulic mechanical advantage to achieve better breaking with larger pad area. This is done in a number of ways for performance cars
. Have longer pads, but that requires better designed calipers otherwise excessive length will cause flexing at the ends negating the longer pads.
. Having broader pad. This requires larger diameter disks.
. Having two sets of calipers. This is most efficient as you need not change the disk diameter or any other thing.

That said, you can also boost breaking power by having more force act on the pads - increase the number of calipers. That will also ensure that the longer pads do not flex.
Having gone through the posts on braking I realised that there were many misconceptions even in this thread so I hope that my contribution below will help clear up some of them.

Consider a disc brake system only - we're not comparing with a drum brake system.
Braking is simply reducing speed of a moving object by converting the kinetic energy of the moving object into heat by frictional force.

So more frictional force = more braking effect.
Braking (frictional) force = force applied to the moving object by the friction material (we'll call it clamping force) x coefficient of friction ().
You can't change as the friction material is fixed. You could increase the of the material but only up to a point above which the brake response becomes grabby.

So to increase braking force you can only increase the clamping force.

In a hydraulic system the pressure is same throughout the system. This means that the pressure at the master cylinder piston is the same as the pressure at the caliper piston.
Pressure = Force/area

So Force = pressure x area
So if you want to increase the braking force you increase the caliper piston diameter. Now this is limited by the disc size so instead of increasing the diameter you increase the number of pistons.

Notice that area has not come up anywhere in the equations. This means that frictional area does not contribute to frictional force.

So what does contact area have to do with braking? Every friction material's life is sensitive to contact pressure and rubbing speed. The higher either or both are, the shorter the friction material life.

So in theory, it's possible to have a bigger caliper with smaller pads but this would cause the pad to wear out unreasonably (depending on application, etc.) fast.

So why do fast cars have big brake discs? The larger the brake disc diameter, the greater the mechanical advantage. This means that since the brake is on a rotating wheel, the farther from the axis of the wheel a given braking force is applied, the greater the braking effect (braking torque).

The converse of this is to increase caliper size for the same size brake disc to increase braking force.
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Old 14th March 2016, 19:25   #47
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Default Re: Automotive misconceptions demystified

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Follow the service manual / warranty conditions of Honda. Oil grades and oil change intervals should be as per manufacturer conditions ONLY if you want to save warranty partly. In any case the blame of part failure will again be on you and you have to prove your innocence similar to IPC 498A or dowry harassment cases.

If you are planning to go synthetic, it is recommended to for 7500 Km drain period. I drain the oil poured by Maruti during my service within 2 - 3 weeks and pour in synthetic of my choice. This way I save my warranty and limit to minimal blame.
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Originally Posted by Jeroen View Post
Is the guy going to pay for the repair of your engine if it falls to bit?

When it comes to oil, stick to the original Manufacturers specification.
The brand of oil is of no importance, really, the compliance to the specification is!
- Only switch to to synthethic if you have it in writing from the manufacturer. E.g. the owners manual mentions it, or there is an official service bulleting.
Don't believe to much when it comes to oil advise on the internet. Very few of us have the insight or access to real data to make a meaningful contribution.

Did you stick to changing the oil filter at the original 5000 km or are you changing that at 10.000 km a swell. If you do, that is likely to be your biggest 'exposure' on wear and tear long term.


Jeroen
I totally agree with all the above mentioned points, 100%.
My car is outside warranty now, so no worries of claim.
All I care is how engine life is affected (good/bad) if we deviate from OEM recommendations (are they always right? considering they try to rip customers at some point in some way)?

3rd and 4th gen City i-vtec engine's are almost identical and I believe service internal for the later is at 10k with synthetic oil?
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Old 14th March 2016, 20:07   #48
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Originally Posted by skyliner34 View Post
I totally agree with all the above mentioned points, 100%.
My car is outside warranty now, so no worries of claim.


3rd and 4th gen City i-vtec engine's are almost identical and I believe service internal for the later is at 10k with synthetic oil?
In that case you are free as a bird in jungle. No worries in shifting to reputed synth.
BTW whats the oil grade as per manual ?
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Old 14th March 2016, 20:12   #49
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Default Re: Automotive misconceptions demystified

MB, thanks for saving me from a lot of typing.
The fact that frictional force depends only on the normal force and mu, and is independent of the area of contact, and so
Quote:
Originally Posted by Motard_Blr View Post
Notice that area has not come up anywhere in the equations. This means that frictional area does not contribute to frictional force.
is high school Physics, but forgotten by most.

So now the next part of the question: why do drums require less effort (actuating force) than discs for equivalent stopping power. (Or is this premise false!)

Regards
Sutripta
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Old 14th March 2016, 21:01   #50
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Default Re: Automotive misconceptions demystified

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Originally Posted by Sutripta View Post

So now the next part of the question: why do drums require less effort (actuating force) than discs for equivalent stopping power. (Or is this premise false!)

Regards
Sutripta
Because drum brakes have a self energising effect, the liner wedges against the drum in the direction of rotation multiplying the braking force. This however is applicable only to the leading shoe and not the trailing shoe, hence twin leading shoe brakes were designed. Unfortunately a downside to this design is the missing servo effect while braking in reverse.
Regards

Last edited by boeuff : 14th March 2016 at 21:07.
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Old 14th March 2016, 21:15   #51
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Originally Posted by skyliner34 View Post
All I care is how engine life is affected (good/bad) if we deviate from OEM recommendations (are they always right? considering they try to rip customers at some point in some way)?
Well if anything Manufacturers, contrary to all us car enthusiast, have access to tonnes of actual data. So they are in the best position to make a call what is the most appropiate oil recommendation/specification.

People on this forum or anywhere else on the net, typically don’t. They will throw in how much experience they have, but it’s just never significant enough. Very few of us have the experience of actually measuring wear and tear on an engine and be able to do so for different kind of oils and come to a statistical significant conclusion. So run a mile from anybody on the net that claims put this or that oil in your engine. Unless, they have similar data as your typical car and or engine manufacturer it is just gibberish.

Now on the upside, as long as whatever oil you put in your engine is in compliance with the specifications, or near enough, it is unlikely to do any harm to your engine quickly. Very unlikely anything will show up during the first 100-150.000 km or so.

So as long as you use the appropriate oil, specification wise, and change it at the appropiate times, you are good to go. So if you got the correct oil what else causes wear and tear. Actually, two very important parts. Oil filter and engine temperature. If your oil filter doesn’t get changed out on the specified intervals with a filter with the correct specification you could end up with undue wear and tear in as little as 10.000km. I have been involved in some of the empirical testing of engines and their oils. I wrote about it somewhere else.

As a rule of thumb, we found we could easily double up on the engine oil change intervals. Modern oils are very good, very stable. But the filter would not last that long.

The other thing is engine temperature. Running your engine on less then it normal operating temperature is hard on it. So go easy on the throttle when the engine is cold. If you have a stuck thermostat and your engine cooling liquid doesn’t reach the normal operating temperature get it fixed. In general, again, its really not a big problem to push the oil change out by 1-2000 km. But driving your car for 2000km with a stuck thermostat will cause noticeable wear and tear.

And again, don’t believe anything on the Internet, especially when it comes to lub oils and engine. Easily the most frequented topic on any car forum anywhere in the world or the net, with least actual factual content. Lots of well meant opinions, rarely beyond that. Very little statistically significant data to back up any claims.

So be safe, stick to the manufacturers recommendations. Oil and filters are cheap compared to an engine overhaul.

Jeroen

PS: I absolutely love the oil guru’s on the car forums that keep putting all these expensive oils in their engines and then sell their cars at 100-150.000 kilometers. That’s the point where you might begin to see some small benefits on a well maintained car. That’s one of the reasons I buy cars with that sort of mileage, if well maintained, not a problem at all! And I will always put it the cheapest oil I can find that complies with the specifications and the best filter money can buy!

Last edited by Jeroen : 14th March 2016 at 21:19.
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Old 15th March 2016, 01:17   #52
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Default Re: Automotive misconceptions demystified

Excellent compilation of common misconceptions in one place You may also consider adding Nitrogen filling of tyres, Teflon Coating of paint etc to name a few.
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Old 15th March 2016, 06:07   #53
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Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by Sutripta View Post
So now the next part of the question: why do drums require less effort (actuating force) than discs for equivalent stopping power. (Or is this premise false!)
That is an interesting question. I never gave it much thought before. MB brings up some relevant points, but I think the total equation is a bit more complex.

Whereas nearly all drum brakes (at least on ordinary cars) tend to have mechanical linkage between brake pedal and the drum, on most discs it’s mostly a hydraulic actuation all the way from the pedal (brake cilinder) to the calipper.

So on the drums with mechanical linkage its all about moment (force times distance) against disk with hydraulics (pressure on a give surface). That is even before we start debating how to size drum versus disc to have an apple to apple comparison on the drum assembly versus the disc assembly to start with!

The short answer is I have no idea whether it is true or not perse. I can’t even remember my last car that did not have a brake boost, even if it had drum brakes so very difficult to compare even going by experience. There are still a surprising number of cars out there that would sport discs up front and drums at the back.

Our previous Ford Focus springs to mind (not sure about the current models). Typical set up for a car braking system is to have it balanced towards more braking force generated by the front wheels.

Quote:
Originally Posted by Samfromindia View Post
Excellent compilation of common misconceptions in one place You may also consider adding Nitrogen filling of tyres, Teflon Coating of paint etc to name a few.
What do you believe the misconception about Nitrogen and Teflon Coating to be? I have some experience with the first and lots with the second.

Jeroen
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Old 15th March 2016, 09:23   #54
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Default Re: Automotive misconceptions demystified

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Originally Posted by Jeroen View Post
Whereas nearly all drum brakes (at least on ordinary cars) tend to have mechanical linkage between brake pedal and the drum, on most discs its mostly a hydraulic actuation all the way from the pedal (brake cilinder) to the calipper.
Not really. I have not seen any car (at least in India) which has a mechanical linkage between brake pedal and drum brake - it is always hydraulic. The fluid from the tandem master cylinder is distributed to all four wheel brakes - whether disc or drums - and it pushes the respective pistons in the calipers / wheel cylinders.

The mechanical linkage is applicable for drum brakes in motorcycles, and also for rear parking brake mechanisms.

The primary reason why many budget cars still have drum brakes at the rear is that drum brakes are much cheaper than disc brakes. Most of the braking is done by the front brakes, and hence OEMs settle for rear drums to save money.
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Old 15th March 2016, 10:22   #55
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Default Re: Automotive misconceptions demystified

One thing that I have read and also experienced is that engine oil change interval is dictated by
1. Loss of viscosity - oil thinning
2. Accumulation of combustion residue
3. Depletion of detergents and other additives

If a vehicle is normally driven for
1. short distances and that too in a B2B traffic, then all the above factors come into force earlier.
2. mostly on highways at reasonable speeds the above factors come much later.

In general the oil change interval recommended by manufacturer is based on what the decide is "average" user's cycle. So if you are mostly case 1), then the oil change interval has to be advanced, and if case 2) it can be delayed.

That said, manufacturers also recommend change after a certain interval even if the mileage is not achieved. That is to ensure that any time dependent degradation (as well as accumulation of combustion residues due to short distance traveled) do not harm the engine.

OT.

There is a very interesting method used for recycling mineral engine oil by some large fleet owners. They collect the spent oil, filter it to to get rid of small solids, and add the relevant additives. This oil is tested and viscosity modifiers added if necessary and the processed oil used. Of course this can be done by owners who have a very large fleet, but it is done.
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Old 15th March 2016, 11:15   #56
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Originally Posted by Aroy View Post

In general the oil change interval recommended by manufacturer is based on what the decide is "average" user's cycle. So if you are mostly case 1), then the oil change interval has to be advanced, and if case 2) it can be delayed.

That said, manufacturers also recommend change after a certain interval even if the mileage is not achieved. That is to ensure that any time dependent degradation (as well as accumulation of combustion residues due to short distance traveled) do not harm the engine.

OT.

There is a very interesting method used for recycling mineral engine oil by some large fleet owners. They collect the spent oil, filter it to to get rid of small solids, and add the relevant additives. This oil is tested and viscosity modifiers added if necessary and the processed oil used. Of course this can be done by owners who have a very large fleet, but it is done.
So on what data/facts can you advance or delay an oil change (and more importantly oil filter)

You can't get an oil back to its original specifications by just adding additives. A lub oil gets its properties through means of a pretty sophisticated process, not just by mixing a couple of ingredients together.

I know this gets done, but I doubt very much it would get you anywhere near the original oil specifications. Mind you, it would be hugely interesting to understand the wear and tear of engines running on these recyled oils, compared to wear and tear of engines running on regular/normal oil.

Jeroen
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Old 15th March 2016, 13:31   #57
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Originally Posted by Jeroen View Post
So on what data/facts can you advance or delay an oil change (and more importantly oil filter)

You can't get an oil back to its original specifications by just adding additives. A lub oil gets its properties through means of a pretty sophisticated process, not just by mixing a couple of ingredients together.

I know this gets done, but I doubt very much it would get you anywhere near the original oil specifications. Mind you, it would be hugely interesting to understand the wear and tear of engines running on these recyled oils, compared to wear and tear of engines running on regular/normal oil.

Jeroen
From what I had read, the base mineral oil dose not degrade significantly unless it has been subjected to extremely high temperatures. So all recovery systems try to recover the base oil after filtering out the solid contaminants, water and acids. Then they add detergent, viscosity modifiers and additives.

This works for large fleets since they can afford technical expertise to analyse and recycle huge quantities of engine oil.

For a layman the factors that affect engine oil are
1. Number of starts/stops.
2. Length of journey, especially significant if the engine does not achieve operating temperature most of the time.
3. High percentage of time spent on idling.

In case of short journeys with a lot of time spent idling, the engine does hot heat up enough to evaporate the gasses and acids which invariably leak from the combustion chamber. So with time the oil thins and collects gum.related

In case of long journeys the engine attains operating temperature and most of the acids and carbon are expelled with the exhaust gasses, so very little percolates to the engine oil.

The oil change time comes when the oil has thinned, additives have either been used up or degraded with time and combustion related solids have increased.

Here are some interesting links
http://www.scientificamerican.com/ar...l-be-recycled/
Can motor oil be recycled—and how?
Franceschi: Yes, oil can be recycled.
In general, you take crude oil and refine it to make a lubricant. This is called base lube stock. Then you have to take that base lube stock and blend it with additives in order to put it into a passenger car. That's what gives it color actually. You're adding an anti-foaming additive, a dispersant and a detergent.
When you put the oil into the engine, it is essentially degraded by heating it, and is also oxidized. As all these additives start to break down, the engine starts to wear more. That puts some heavy metals into the oil. The anti-foaming additive breaks down and you start to get water mixing with the oil and making sludge. The same breakdown happens with the dispersant and the detergent. That's the reason they recommend to change it every X number of miles because of the thermal degradation and oxidation. Oil only has a certain life span.

http://recyclenation.com/2014/04/recycle-motor-oil

http://www.earth911.com/inspire/diy/...or-oil-how-to/

http://www.ecoultraoil.com/our_process.php?

Last edited by Aroy : 15th March 2016 at 13:34.
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Old 15th March 2016, 14:11   #58
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Originally Posted by Aroy View Post
Here are some interesting links
http://www.scientificamerican.com/ar...l-be-recycled/
[l]

For a layman like me these are some interesting links. Based on your earlier mail I was under the assumption you were referring to a very simple way of recycling. And there are plenty of places around where they simply filter the oil, chuck some additives in, if you're lucky leave the oil for a few days to settle so maybe some water can be drained off etc. Very basic way of recycling.

The first link describes essentially a real refinery process which gets pretty close to the original production process. Although, getting the exact specification is likely to be very difficult as all oil companies keep their oil recipes a very closely guarded secret.

Still, I still don't know how to advance or delay my oil change. Other then sending an oil sample of for analysis. In the USA I could do that, although just changing the oil and filter might cost just about as much.

Jeroen
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Old 15th March 2016, 14:11   #59
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Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by Sutripta View Post
...

So now the next part of the question: why do drums require less effort (actuating force) than discs for equivalent stopping power. (Or is this premise false!)

Regards
Sutripta
Quote:
Originally Posted by boeuff View Post
Because drum brakes have a self energising effect, the liner wedges against the drum in the direction of rotation multiplying the braking force. This however is applicable only to the leading shoe and not the trailing shoe, hence twin leading shoe brakes were designed. Unfortunately a downside to this design is the missing servo effect while braking in reverse.
Regards
boeuff,
thanks for answering Sutripta's question so succinctly.

Quote:
Originally Posted by Jeroen View Post
That is an interesting question. I never gave it much thought before. MB brings up some relevant points, but I think the total equation is a bit more complex.

Whereas nearly all drum brakes (at least on ordinary cars) tend to have mechanical linkage between brake pedal and the drum, on most discs it’s mostly a hydraulic actuation all the way from the pedal (brake cilinder) to the calipper.

So on the drums with mechanical linkage its all about moment (force times distance) against disk with hydraulics (pressure on a give surface). That is even before we start debating how to size drum versus disc to have an apple to apple comparison on the drum assembly versus the disc assembly to start with!

The short answer is I have no idea whether it is true or not perse. I can’t even remember my last car that did not have a brake boost, even if it had drum brakes so very difficult to compare even going by experience. There are still a surprising number of cars out there that would sport discs up front and drums at the back.

Our previous Ford Focus springs to mind (not sure about the current models). Typical set up for a car braking system is to have it balanced towards more braking force generated by the front wheels.
...
Jeroen
Quote:
Originally Posted by Viju View Post
Not really. I have not seen any car (at least in India) which has a mechanical linkage between brake pedal and drum brake - it is always hydraulic. The fluid from the tandem master cylinder is distributed to all four wheel brakes - whether disc or drums - and it pushes the respective pistons in the calipers / wheel cylinders.

The mechanical linkage is applicable for drum brakes in motorcycles, and also for rear parking brake mechanisms.

The primary reason why many budget cars still have drum brakes at the rear is that drum brakes are much cheaper than disc brakes. Most of the braking is done by the front brakes, and hence OEMs settle for rear drums to save money.
Some more info on discs and drum brakes:

Disc brakes have less braking capacity than a drum brake of similar diameter for the same hydraulic pressure. The reason is the self-energising effect that (boeuff has mentioned this above) drum brakes have.

So if disc brakes are worse than drum brakes, how come some motorcycles that have optional disc brakes are much better at stopping than the model with drum brakes? There are 2 reasons:

1) The diameter of the disc is much larger than that of the drum. This allows a much higher braking torque for the same brake lever force.

2) The steel cable stretches when pulled hard. So some of the force applied at the lever is wasted on stretching the cable. Hydraulic hoses also expand due to pressure and that's why some high performance bikes come with steel reinforced hoses that provide much better control and lever feel.

So we have just established that drum brakes have better braking capacity than disc brakes but what's the big advantage of disc brakes? In 2 words: heat dissipation. Disc brakes are able to dissipate heat much faster than drum brakes to keep temperatures much lower than in drum brakes. This happens because of the much larger surface area of a brake disc compared to a drum. This improves the fade resistance significantly and makes the brakes more dependable.

To increase the braking capacity of a disc brake, a brake booster boosts the pedal force and increases the braking force at the caliper. The trouble with brake boosters is that they don't work when the engine is shut off. So in cars with all disc brakes, the parking brakes are actually drum brakes on the rear wheel. The drum is hat shaped and combines the drum and disc in one piece.

Last edited by Motard_Blr : 15th March 2016 at 14:12.
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Old 15th March 2016, 14:17   #60
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Originally Posted by Motard_Blr View Post

So we have just established that drum brakes have better braking capacity than disc brakes but what's the big advantage of disc brakes? In 2 words: heat dissipation. Disc brakes are able to dissipate heat much faster than drum brakes to keep temperatures much lower than in drum brakes. This happens because of the much larger surface area of a brake disc compared to a drum. This improves the fade resistance significantly and makes the brakes more dependable.

So in cars with all disc brakes, the parking brakes are actually drum brakes on the rear wheel. The drum is hat shaped and combines the drum and disc in one piece.
The other big advantage or disc over drum brakes is the weight advantage which is very relevant for the unsprung weight/mass of a vehicle. Which is particularly relevant for handling characteristics:

https://en.wikipedia.org/wiki/Unsprung_mass

There are a few parking brakes out there that actually work on the caliper! So no drum, let me see if I can find some pictures

Jeroen
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