A rather trivial question but one that sparked my curiousity;
Why is it that when a vehicle is fitted with disc brakes all-round the front calipers are usually located at the "3 o'clock" position and the rear calipers at the "9 o'clock" position?
Chad.
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depends which side of the car you are looking at surely :-)
(Glass-Tech)
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yup, he's right!(just been out to check),
on the left side of the car my front one is at 3, rear at 9,
on the right side, my front is 9, rear at 3. :-)
basically, (i am probably wrong!) it goes back to the shoe and drum days where you had a leading and trailing shoe, the leading shoe was usually the more worn, which indicated that it was more effective than the trailing shoe. by placing the caliper at the front of the disc, you effectively have two leading (shoes)pads. the rear ones are also placed at the front of the disc when you are travelling in a reverse direction, so which ever direction you are going, you have an equally balanced braking system.
technically, it is probably something to do with the various forces involved, torqe, g-force, mass x motion, i don't know!! but there must be a reason for the positioning, so lets have some techies veiws please.
billy.
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an equally balanced braking system
Hmmm. I think I'd rather have a more powerful braking system when travelling forwards. IIRC, my record speed in reverse is somewhat less than when in forward motion.
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Putting them at the rear of the wheel allows air to flow over the disc more smoothly and cool it more effectively.
I've no idea why you might put them at the front.
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One reason for both front and rear wheels is likely to be cost efficient packaging, but given that a front wheel is rarely located directly at the end of the suspension strut, I wonder if this is to do with torque reaction and how it loads the suspension unit.
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It's not always true. Both mine are at the back, 3 o'clock on left hand side.
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Is your's a BMW Cliff?
I remember reading something about this, in the distant past. It said that the optimum position for the front caliper was at the front of the wheel, but that BMW put theirs at the back for soem reason (space I think?)
It used this as an example that their ad slogan of the time (something about no compromises) was untrue.
I'm afraid I can remember no more than that, I can't remember the reason why having the calipers there was better or worse. And I wouldn't like to go into details of the reason why the only part of it I remember is the part having a go at BMW ;)
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It's not always true. Both mine are at the back, 3 o'clock on left hand side.
Cliff,
I did a quick scan while in local superstore car park before I posted the question and all cars fitted the "front-3/rear-9" rule. However as that was a bit of a straw poll, I added "usually" as a get-out clause :-)
SjB,
"I wonder if this is to do with torque reaction and how it loads the suspension unit.
I was thinking along the same lines but can't remember/don't know enough applied maths/physics to work it out!
Chad.
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Two possibilities, as most steering racks are to the rear of the axle it is easier to mount the caliper away from the steering ball joint. and due to the direction of rotation the dust from the pad is thrown down into the free air. The rear capilers are very difficult to fit at the front due to the number of cars with swinging arms and beams in the way so logically they went for the rear of the disk. !! Sound Good to Me. Regards Peter
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Peter D has it.
Doesn't matter if they are positioned at 3 or 9 position - torque reaction is exactly the same. Position is chosen to avoid conflict with other components (eg steering and anti-sway bar at front, trailings arms etc. at back).
There are a number of models that don't fit this rule, but I can't remember them now!
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I have wondered about this one. Other than restrictions due to other components surely the 9'o'clock at the front helps anti-dive, and the 9'o'clock at the rear resists the back of the car rising-so making the car more stable when braking. Cheers.
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"9'o'clock at the front helps anti-dive"
A myth perpetuated by BMW, I'm afraid. They tried to claim that positioning the caliper at the rear of the front wheel (on a motorbike) created anti-dive characteristics, when Mr Newton could have told them that opposing forces cancel this out. It certainly allowed other motorcycle manufacturers a moment of schadenfreude!
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Many years ago I Mot'd a Volvo 245 with one front caliper at 3 and the other at 9. Obviously different suspension legs were fitted to each side of the car. As I recall, brake balance was ok and a road test didn't show any tendency to pull one way or the other. A questioning phone call to the local Volvo dealer was met with a quick "yep, that's ok."
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Many years ago I Mot'd a Volvo 245 with one front caliper at 3 and the other at 9. Obviously different suspension legs were fitted to each side of the car. As I recall, brake balance was ok and a road test didn't show any tendency to pull one way or the other. A questioning phone call to the local Volvo dealer was met with a quick "yep, that's ok."
That's interesting. I had been going to add to my original post and explain my car is a Volvo 240, not a BMW!
I have owned and worked on lots of 240s and all have had all calipers at the rear. It certainly makes access easier at the back, and meets someone's theory about clearing the steering arm at the front.
Aprilia answers what I suspected - it doesn't matter!
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.....with one front caliper at 3 and the other at 9. Obviously different suspension legs were fitted to each side of the car......
Am I alone in thinking that this how they should be! Ie both in front (or behind) the suspension leg?
pmh (was peter)
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Pmh, What I meant was that one caliper was forward of the stub axle, the other behind. Sorry for any confusion. I suppose that it's possible (in this case) that two n/s or two o/s suspension legs had been fitted. (If you follow what I mean)
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I have wondered about this one. Other than restrictions due to other components surely the 9'o'clock at the front helps anti-dive, and the 9'o'clock at the rear resists the back of the car rising-so making the car more stable when braking. Cheers.
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I can't see how you make that claim. The reaction is in the same direction irrespective of where the braking force is applied to the disc.
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Although I said 9'o' clock at the front, what I really meant was 3'o'clock-i.e. at the front at the front and at the rear at the rear. Consider the direction that the disc is travelling in at these locations. Another bonus for the rear is that it makes changing the pads a bit easier.
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I think the mistake comes in seeing the reaction as either 'up' or'down'. In fact it is rotational, in the form of a twisting force on the suspension leg or whatever is used, centred on the axle.
Interesting that no one has reported seeing any at the top (bottom would be silly for pretty obvious reasons). Top might give the pads a more positive seating, instead of the rather vague location that always puzzles me.
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I suspect that top/bottom location of caliper would be a bad idea due to likelihood of small stones dropping onto caliper and working their way between pad and disc.
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Has anyone thought of airflow to callipers pads.as all car`s not built the same.could be positioning due to air flow?.ie cooling
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A rather trivial question but one that sparked my curiousity; Why is it that when a vehicle is fitted with disc brakes all-round the front calipers are usually located at the "3 o'clock" position and the rear calipers at the "9 o'clock" position? If its a new Maserati Quattroporte then at an extra £388 for coloured brake calipers I think they should be at both 3 and 9 all round.
Do the few cars with carbon brake disks have the calipers in the familiar locations?
Do those with inboard disk brakes have them mounted in the same relative positions?
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