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Old 25th June 2017, 04:44   #1
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Default Brake Caliper Location - How do engineers decide on its placement?

I have been wondering as how do manufacturers decide where to place the brake calipers in a round disk brake?

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Below is a crude diagram which I have drawn using Microsoft paint, for better understanding:
P.S: Consider this as the front passenger side wheel in RHD vehicles, other images are also taken in the same scenario

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From what I have gathered in the Fron wheel: front portion is commonly used in the passenger cars, the rear side of the disc is used in most of the sports cars. There are few exceptions though.

Passenger Cars:
Brake Caliper Location - How do engineers decide on its placement?-img_1370-copy.jpg
Our Mi10's S Cross 1.6 having
Front Disc: Front
Rear Disc: Top

Brake Caliper Location - How do engineers decide on its placement?-vw-jetta_graaja.jpg
Our graaja's VW Jetta
Front Disc: Front
Rear Disc: Front

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Lamborghini Aventador
Front Disc: Rear
Rear Disc: Front

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Aston Martin Vantage
Front Disc: Rear
Rear Disc: Front

Conclusion from Images:
Front Wheels:
1. Normal Cars: Front
2. Sports/Super Cars: Rear
Rear Wheels
1. Normal Cars: Front
2. Sports/Super Cars: Front




This video has quite a few reasons listed but I do not agree on all the facts proposed by them, Few points are reasonably acceptable.

Upon researching quite a bit I found the below reasons,

1. Accessibility during maintenance/Ease of bleeding - Accepted
2.
Load Applied on the caliper- Accepted
3. Weight Distribution- Naah
4. Aerodynamics- Naah
5. Suspension packaging- Accepted
6. Vehicle Purpose- Naah

Few reasons I found was,

1. Accessibility during maintenance/Ease of bleeding
Mounting at 6 ‘o’clock position would help in lowering of Center of Gravity but do not provide ease of bleeding, too vulnerable to debris so imparts no particular advantage. 12 ‘o’ clock position leads to difficulty in bleeding and increases height of Center of Gravity.
Hence, the 3 ‘o’ clock and 9 ‘o’ clock positions are the most common in front of or behind the rotor as this provides good protection, allows the caliper to be mounted with the bleed screw up for ease of bleeding, lowers height of Center of Gravity, lower polar moment of inertia and provides better ground clearance.

2. Load Applied on the caliper
Loads applied on the caliper mounts when the vehicle in motion. When brakes are applied in a car a part of the kinetic energy of the wheels is dissipated as heat, however much of the energy is transmitted onto the brake assembly itself(this explains their sturdy construction). Now the brake assembly is a highly stiff unit and would not dissipate the energy the way a spring or a gas-pot would do.
Thus the point at which the brakes are anchored to the chassis would be subjected to a large load in turn. Therefore it implies that the chassis location where the brake assembly is fixed to must be a hard point(just like the cables of a suspension bridge is anchored at two towers buried deep in bedrock on either side of the bridge)

3. Weight Distribution
As you know already for a body to be stable it primarily depends on the center of gravity. "COG is the point at which the entire weight of the body acts upon". In cars the COG is near the drivers seat for best stability under various conditions.

Following are the conditions for stability based upon COG:
  1. It should be low as possible.
  2. COG should fall within the base of the body.
  3. COG should be centered as possible.
Taking these factors into account, the manufacturers position the calipers (front and rear) in a position that provides maximum stability, especially in the performance oriented cars.
So the caliper positions are more centered and low as possible in sports cars.

5. Suspension packaging:
The position of the brake calipers should not interfere with the suspension elements (control arm, dampers,..) of an automobile.Not much to it, the calipers are positioned, giving way to the suspension components which takes first place over the caliper positioning.

6. Vehicle Purpose:
SUV built for off road purposes, then you are going to be positioning the calipers in a way, that the elements of off road conditions like mud,dust and water don't affect your calipers in any way.

Finally the theory which made sense was:
Quote:
Largest correlation to brake caliper position on the front wheel is the opposite side of the steering tie rod attachment to the steering arm on the knuckle. All cars with steering rack in front of wheel center have calipers behind wheel center. and vice versa.
  1. front calipers
    1. The case for the longitudinal engine configuration: Steering rack tends to be in front of the engine, or just underneath the front of the lowest part of the engine (oil sump). Some cases where steering rack is behind the engine force the engine and transmission up, raising CG height and hood height (which in turn can raise the roof height and driver seating reference point SgRP up to maintain forward down-vision). Steering rack in front of wheel center also allows for better ackermann during turning…thus most longitudinal front engine rear wheel drive (F/R) cars will have calipers rear of wheel center.
    2. The case for transverse engine configuration. Most cars with engine mounted transverse have the engine and transmission in front of wheel center, for packaging and for engine roll characteristics.Thus most transverse mounted (FWD/AWD) cars will have the steering rack in the rear because that is the best place to put the steering rack… and thus the calipers have to be front of wheel center.
  2. rear calipers
    1. Rear caliper placement will tend to arranged to allow the best package for all suspension arms going to the knuckle. Usually damper position, and compatibility with park brake systems (if integrated into the caliper instead of the hub). Most manufacturers will try to attach the rear damper to the knuckle to achieve the best damper motion ratio for ride quality, package permitting.
Note to Mods: The above contents both pictures and information have been taken from various sites in google, with an intent to have a healthy discussion and provide maximum insight on the placement of the calipers. Please remove/reject this thread if you find this information in violation of any rules.
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Old 26th June 2017, 22:05   #2
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Default Re: Brake Caliper Location - How do engineers decide on its placement?

Quote:
Originally Posted by Thanga_RS View Post
I have been wondering as how do manufacturers decide where to place the brake calipers in a round disk brake?
Even I have wondered on this, even with two wheelers there are different placements. As far as I have figured out, your last quote is the actual reason.

Quote:
Finally the theory which made sense was:
Do share more since you seem to have gathered some info from the web on this. Really would love to read up more on this.
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Old 26th June 2017, 23:49   #3
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Default Re: Brake Caliper Location - How do engineers decide on its placement?

Very good observation.

Observed this different positioning of brake calipers, but never tried to find out. I used to think something to do with cars engine location (FWD vs RWD), engine power, and smoothness of brake application

Just now goggled it and found this informative link below to start with our topic:-

https://www.quora.com/How-do-manufac...brake-calipers
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Old 27th June 2017, 10:13   #4
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Default Re: Brake Caliper Location - How do engineers decide on its placement?

Quote:
Originally Posted by Jaggu View Post
Even I have wondered on this, even with two wheelers there are different placements. As far as I have figured out, your last quote is the actual reason.
Yes, even my curiosity kicked in while noticing quite a few custom bikes which had their calipers placed in different locations.

Quote:
Do share more since you seem to have gathered some info from the web on this. Really would love to read up more on this.
Sure, will try to share more information on this.

Quote:
Originally Posted by Sail View Post
Very good observation.

Observed this different positioning of brake calipers, but never tried to find out. I used to think something to do with cars engine location (FWD vs RWD), engine power, and smoothness of brake application
Thank you Sir. Even I was searching for the same but couldn't find any concrete reason as to why the particular location was selected. Once we start searching there are quite a few reasons but each and every reason does not tick the box.

Even quite a few observations found in this thread are from the URL which you have provided. Will try to provide more information as I am trying to search through the web.
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Old 27th June 2017, 17:53   #5
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Default Re: Brake Caliper Location - How do engineers decide on its placement?

The foremost reason is the performance. This depends on primarily the radial distance of the calliper- further the calliper, better is the performance (considering the same pad area). You also get a bigger disc and an added contact area.

The second aspect is the which truly affects the positioning is the strength of the mounting point.

As we know the brake calliper is mounted on the knuckle using bolts. When the brakes are applied, the reaction force is borne by the knuckle. The knuckle (IMHO- the best part of any car- integrating steering, suspension, wheels brakes and transmission together) is a highly complicated part handling multiple stresses. traditionally it is a heavy part and any additional weight that can be shaved off is better. When modelling the knuckle on CAE, the point where the stresses are optimal are chosen. There are 100s of iterations done in order to optimise the position.

Once the base design is finalized, the forging/casting simulations are done. If there is a complexity in the die/any additional residual stress due to the process are checked and iterations happen to reduce these residual stresses. High importance is given to stresses as this is one of the highest strength component facing a lot of abuse.

Beyond this, factors of serviceability, cooling, boise(another very important parameter- resonance is a nasty factor in brakes), come into play to decide the final position of the caliper.
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