Any difference between bells?
20 December 2001, 11:43 AM
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I know theres a difference between AP rotors and cheaper ones but is there also a difference between the bells? Is it a case of if it fits itll do the job of is there a genuine benefit to be had by going with an AP bell?
Bren
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20 December 2001, 11:51 AM
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Dying for an excuse to show this picture 
- AP bells, anodised aluminium, with a cool AP logo just visible. Gotta be the danglies. PS the green stuff on the pads didn't last long!
- AP bells, anodised aluminium, with a cool AP logo just visible. Gotta be the danglies. PS the green stuff on the pads didn't last long!
20 December 2001, 02:07 PM
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Bren, IMHO the bells are key. It is one of the reasons I keep banging on here that the main problem with Scoob brakes is not the calipers, but the discs.
Discs have to absorb huge amounts of heat very quickly, without warping etc. In a full-on 100-0mph stop, the brakes absorb enough heat to boil three kettles of water in about four seconds (thanks to AndyMc for that info
) If one side of the disc has substantially more heat soak than the other, as with an integral cast bell, when the disc expands it's going to expand on one side more than the other. Result warping.
An APR disc has a separate alloy bell, as do some Godspeed discs amongst others. This allows the disc to expand evenly and the mechanical joint between disc and bell allows for tiny movement. In addition, the alloy bell is much lighter and has superior heat conducting properties.
The lightness of the bell also allows APR to put more metal where it matters - into the disc itself. Their official Impreza kit has 48-vane 28mm thick discs (not 24-vane as some other 'APR' kits). Just as a disc has to absorb heat quickly, it's got to lose it quickly before the next big stop. More vanes gives much greater surface area for cooling and the vanes act as a pump, sucking air in at the centre and forcing it through the disc, and all the heat with it.
APR discs are the best you can get because they are cast from the highest friction metal available, the design offers maximum heat absorbsion and cooling performance, and the construction with a separate alloy bell prevents warping. The only down-side is cost, but as you can re-use the bell again and again, over the life of a car they might even work out cheaper.
Having said all that (phew!) on a road car you probably don't need all that braking potential, but it's sure nice to have. When you've used them in anger a few times, and recovered from the awsome, gut-wrenching, almost vomit-inducing power of the things, they will transform your driving such is the confidence they inspire. And you just know that they'll do it again and again and again, which is what you need at Donington, for example. The main problem at Donington is not the number of hard-braking corners, but the lack of long cooling straights between them.
Okay. Rant mode off. Now then, what was the question?
Happy stopping,
Richard.
(APR 6-pots, 100-0mph in 3.3 secs as many times as you can stand it.)
[Edited by Hoppy - 12/20/2001 2:08:39 PM]
Discs have to absorb huge amounts of heat very quickly, without warping etc. In a full-on 100-0mph stop, the brakes absorb enough heat to boil three kettles of water in about four seconds (thanks to AndyMc for that info
) If one side of the disc has substantially more heat soak than the other, as with an integral cast bell, when the disc expands it's going to expand on one side more than the other. Result warping.An APR disc has a separate alloy bell, as do some Godspeed discs amongst others. This allows the disc to expand evenly and the mechanical joint between disc and bell allows for tiny movement. In addition, the alloy bell is much lighter and has superior heat conducting properties.
The lightness of the bell also allows APR to put more metal where it matters - into the disc itself. Their official Impreza kit has 48-vane 28mm thick discs (not 24-vane as some other 'APR' kits). Just as a disc has to absorb heat quickly, it's got to lose it quickly before the next big stop. More vanes gives much greater surface area for cooling and the vanes act as a pump, sucking air in at the centre and forcing it through the disc, and all the heat with it.
APR discs are the best you can get because they are cast from the highest friction metal available, the design offers maximum heat absorbsion and cooling performance, and the construction with a separate alloy bell prevents warping. The only down-side is cost, but as you can re-use the bell again and again, over the life of a car they might even work out cheaper.
Having said all that (phew!) on a road car you probably don't need all that braking potential, but it's sure nice to have. When you've used them in anger a few times, and recovered from the awsome, gut-wrenching, almost vomit-inducing power of the things, they will transform your driving such is the confidence they inspire. And you just know that they'll do it again and again and again, which is what you need at Donington, for example. The main problem at Donington is not the number of hard-braking corners, but the lack of long cooling straights between them.
Okay. Rant mode off. Now then, what was the question?
Happy stopping,
Richard.
(APR 6-pots, 100-0mph in 3.3 secs as many times as you can stand it.)
[Edited by Hoppy - 12/20/2001 2:08:39 PM]
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