Alfa Romeo Forum - View Single Post - Front disc replacement...drilled, slots or std
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johnlear
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Join Date: Mar 2016
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Quote:
Originally Posted by Dave Brand View Post
Good post, John!

Just a couple of comments.

The differentiation between "hard" & "soft" pads is much less marked with modern friction materials. A lot of work has gone into, & continues, in developing pads which have acceptably high friction levels over a very wide temperature range.

Friction level is dependent on rubbing speed; again, modern pads have reduced this effect to almost insignificant levels.

Developing friction materials isn't easy - it's still as much a black art as it is a science!
Yes, but even so I think there is still a significant difference between 'performance' pads and 'commuter' pads (as fitted to most cars). Of course any pad material must generate reasonable friction when dead cold. A racing car doesn't need pads that work all that well when cold, but for any pad intended to be used on a road car the pads do need to work at least acceptably from cold (even if this means the pedal pressure might be a bit high).

Modern pads may well be better than less modern pads, but I'm still not convinced that they are as good as they were when asbestos was a major ingredient of the material. Modern pads are certainly much harder on the discs than when asbestos was used, with discs now being a routinely consumable item, when years ago (in the mists...) disc wear was much less and discs only rarely needing replacement. To be clear, I'm not advocating a return to asbestos based pad compounds...

A little story; Some years ago I was driving a taxi (for my sins) and was carrying a passenger who turned out to be a dangerous psychopath (possibly under the influence of meth...). This person threatened to physically assault me if I did not drive him to a destination at increasingly high speed. This journey was on a rural motorway late at night with minimal other traffic, and the speeds reached became frighteningly high, maxxing at 220kmh (while being continually threatened with violence...). This is the maximum speed that a 2.4 litre Camry can reach, pedal to the floor (and the handling becomes very 'indeterminate' as the air lifts the front end...).

Anyway, approaching an open service centre at about 200kmh, I slammed on the brakes as hard as possible (both feet), entered the service centre and exited the vehicle (while actually being attacked). Taking refuge in the shop, the attendant locked the doors and called the police, while the mad person trashed the car on the forecourt.

The point of this story is what happened when I hit the brakes so hard from such a high speed. The brakes would have had standard pads fitted, which would have been cold at initial application, for about two seconds, being about as long as it took to cook the pads. From there the braking effect almost instantly became very poor. I only barely managed to slow the vehicle enough to enter the service centre, at a substantially higher speed than I had intended. I could smell the strong aroma of well cooked pads. I'm fairly sure that 'high performance' pads would have worked somewhat better in this scenario...

On the other hand, when I was racing karts I'd use discarded 'standard' road car pads (fairly 'soft' compound) cut down to fit the kart caliper (single brake on the rear axle), rather than the expensive 'racing' pads that everyone else used (fairly 'hard' compound). I'd have very good braking from the first application at the first corner, and from there never suffered from the pads 'fading' during the race (because they never did).

Regards,
John.

Last edited by johnlear; 15-06-19 at 00:38.
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