Stopped at lights on Sutton bypass/M6 Toll this morning, LHD Jaguar XF on trade plates pulls up beside me followed by a Jaguar coupe also on trade plates (not unusual around here - aabout 2 miles from the factory)
It had a blue assembly in place of the front brake disk about 10" in diameter and did not appear to have a brake disk at all.
Is this what ceramic brakes look like?
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Ceramic = China
JLR=Tata = India
Poor Joke!
Even by my Standards!!
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did it look plastic? if so then this is the covers that go on the cars when they are new are being tranported, but usually on the back of a transporter or low loader.
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Having looked at the bosses XF in the car park the disk is clearly visible and much bigger than the blue thing I saw this morning. Would be very surprised in there was an XF with 10" discs on the front.
It did not look like a protection cover and nothing like a disc and caliper.
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Sounds like a dust cover for the discs to reduce dust on the alloys ?
Ceramic discs still have calipers, and look like drilled discs (usually grey).
Take a peek behind the blue cover from under the front of the car to see if the disc assembly is evident.
Edited by Lygonos on 15/09/2009 at 14:06
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He was stopped for 15-20 seconds at the red light and I was stopped beside him. Not too easy to get out and have a closer look.
Definitely not the usual disc arrangement and too small for a dust cover - am I repeating myself?
It looked more like an F1 style disc pack.
Tried to get a closer look ut he was going round the roundabout and back the way he had come.
must get a phone with a camera in it!
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This is what a carbon ceramic brake looks like:
tinyurl.com/ceramicbrake
(image found on google images, no connection)
Much the same as a normal one, only not shiny but a kind of matt, grainy finish not dissimilar to that of conventional brake pads. If you catch it in the right light you can sometimes see "rainbow" marks like oil on a puddle or heat discolouration on sheet metal.
You will also see petrolheads looking at them with the same slightly dreamy expression as women looking at diamonds, possibly because both items cost thousands of pounds.
Dave TD
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a wheel off view www.autocult.com.au/img/gallery/5BBYD3JR.jpg
As an interesting aside, the piccie shows a six piston caliper - why does this perform better than a four piston caliper, and why does the four piston caliper perform better than a single piston caliper.
[Hint - the obvious answer is the wrong answer!]
These multi-piston calipers do have the weakness of the hydraulic pipe from one side to the other pssing very close to the very hot outer surface of the disc - but at least with an external pipe it will also be exposed to the cooling flow unlike those calipers where the fluid passes through a drilling in the caliper body.
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>>As an interesting aside, the piccie shows a six piston caliper - why does this perform better than a four piston caliper, and why does the four piston caliper perform better than a single piston caliper.
I await the answer with baited breath.
I was mildly surprised to find my daughter's old Estelle had 4-pot front calipers, rear engine as well.
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Could multiple piston calipers be just another fashion thing?
The brakes were better on my 1980 Guzzi, with double pistons than they are on my 2003 Triumph, with four-pot ones but twice the horsepower.
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i was told my ceramic hob was very good for putting heat straight into the pan with minimul loss to cohedisions of global warming
so how can ceramic discs be anygood if all they can do is transfer the heat back to the pads
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Don't they work better when they're nearly white hot bb?
Must be fun in central London (or better still provincial mimseburgs like Manchester or Bristol) getting the brakes in your Porsche GT3 or MacLaren Mercedes up to working temperature so you won't scare anyone. Wish I could afford it.
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OK, I'll dispense with the obvious answer - there's more total piston area in a six pot caliper than in a four.
It's no great problem to provide pistons of equivalent area - as the area goes up with diameter squared. The pistons in a four piston caliper only need to be about 22% larger diameter than those in a six piston caliper to give the same total area.
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I'll bite NC.
More pistons spread the pressure more evenly over the pad backplate, which perhaps can be a bit thinner as a result. And there would be less stress on the piston seals too.
Be gentle with me. I mean well.
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>>I'll bite NC.
Interesting point about the thickness of the backing plates - though that's not what I had in mind as the big performance difference.
If you had two discs;
- with the same outer diameter
- one fitted with a six piston caliper
- the other fitted with a four piston caliper
- with the pistons of each caliper sized to give the same total area
- supply both calipers with the same hydraulic pressure
- fit both calipers with pads with the same coefficient of friction
The brake fitted with the six piston caliper would produce more braking torque.
Each brake pad would be being pushed into the disc with the same force, and would therefore produce the same friction force - BUT, this friction force would be acting at a different average distance from the centre of the disc, and hence the brakes would produce different braking torques.
If you look at the piccie of the brake in the link above, you'll be able to imagine the pad in the 6 piston caliper being long and thin, while taking the opposite extreme, the pad from a single piston caliper is not much longer than it is wide. The pad in the 6 piston caliper runs at a larger "effective" radius.
For a single piston caliper, the inner contact radius is much smaller than for, say, a six piston caliper.
A reasonable estimate of this "effective" radius is simply the average of the outer and inner contact radii of the pad - therefore a thinner, longer pad running near the outer edge of the disc is better.
So, at last!, here's the advantage of a multi piston caliper - for a given packaging volume, it allows the use of a larger "effective" radius.
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As an up to the minute example of this aspect of brake design, look at how closely the front calipers of the Mercedes SLS AMG hug the inside of the wheel rim - there's not much clearance there at all!
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Push bike makers have known this for decades - thats why you can rapidly stop 150kg of bike and fat guy using brake blocks the size of matchbox strikers on the rims.
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I remember watching endurance racing at Le Mans in the eighties. The Honda-engined Elf racer had a single-sided front swing-arm suspension set-up.
This meant they could only have one front disc. I recall that they pioneered ceramic discs.
T'was interesting watching the brakes glowing red in the dark.............
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