How hard is it to find a good mechanic??
in [Aussie Drivers]
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From: jonz on 27 May 2010 19:57 On 5/27/2010 9:44 PM, Clocky wrote: > John_H wrote: >> Clocky wrote: >>> John_H wrote: >>>> Clocky wrote: >>>>> John_H wrote: >>>>>> Clocky wrote: >>>>>>> >>>>>>> In theory braking performance should increase with grooves >>>>>>> because you are effectively increasing the surface area of the >>>>>>> disc. >>>>>> >>>>>> In theory, the braking performance should be exactly the same, >>>>>> with or without being bedded in, unless heat transfer is an issue >>>>>> (which would be improved by the scoring). >>>>> >>>>> Braking performance is reduced if the pads are not bedded into a >>>>> scored disc as the pads are only in contact with the upper ridges >>>>> which reduced the effective surface area of cotact between the pad >>>>> and the disc surface. >>>> >>>> No it isn't. The frictional force between the pad and the rotor is >>>> proportional to the pressure acting between the surfaces. Under >>>> normal design pressures and equal working temperatures the >>>> coefficient of friction is a constant and the total friction >>>> (braking force) is the coefficient of friction multiplied by the >>>> contact pressure. Double the contact surface and you halve the >>>> pressure (or vice versa) but the overall braking force remains the >>>> same. >>>> >>>> The exception is at very high pressure, which will increase the >>>> coefficient of friction as the materials approach the point of >>>> seizure. If brakes operated under those conditions (which they >>>> don't) decreasing the pad area would *increase* the braking force >>>> applied to the rotor... the exact opposite of what you're claiming. >>>> >>>>>> >>>> <snip> >>>>>> >>>>>> Force applied to the pad multiplied by the coefficient of friction >>>>>> is the braking force applied to the rotor, irrespective of the >>>>>> contact area. >>>> >>>> My previous statement is incorrect... I should've written *Force >>>> per unit area* (ie pressure) multiplied by the coefficient of >>>> friction is the braking force applied to the rotor.... >>>> >>>>> >>>>> Sure, the force may be the same but the amount of friction is >>>>> reduced by having less contact between the disc and the pad which >>>>> results in poorer brake performance, until the pads are bedded in >>>>> that is. >>>> >>>> Nope. Exactly the same principle applies between tyres and road. If >>>> what you're claiming is correct you'd increase the grip by reducing >>>> the tyre pressures (which increases the area of the contact while >>>> weight of the car remains the same). >>>> >>>> In fact the opposite applies, same as it would for brake materials >>>> operating above their design pressures. >>> >>> That's a great theory. All I know is that bedding (or wearing as you >>> put it) the pads to the rotor results in more friction material >>> being in contact with the rotor surface and braking performance >>> increasing as a result. >> >> Go back to to your original post... the one that says "In theory >> braking performance should increase with grooves because >> you are effectively increasing the surface area of the disc." >> >> The theory, according to the physics textbook, doesn't support your >> claim. >> >> What happens in practice *might* be something else again, since >> factors other than the surface area of the disc apply. Perhaps you >> forgot to mention them! :) > > Throwing physics textbooks under the wheels of the car may improve braking > performance also. ~~~~~~~~~~~~~~~~~~~~~~~ if you can`t dazzle `em with brilliance.......baffle `em with bullshit.............. > > -- jonz "Usenet is like a herd of performing elephants with diarrhea - massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind - boggling amounts of excrement when you least expect it." - Gene Spafford,1992
From: jonz on 27 May 2010 20:13 On 5/27/2010 10:36 PM, Noddy wrote: > "Clocky"<notgonn(a)happen.com> wrote in message > news:4bfe5af3$0$27823$c3e8da3(a)news.astraweb.com... > >> Agree with who? > > You and John. > > It may look like you're disagreeing, but as I read it you're essentially > saying the same thing. ~~~~~~~~~~~~~~ ???????....... > > -- > Regards, > Noddy. > > -- jonz "Usenet is like a herd of performing elephants with diarrhea - massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind - boggling amounts of excrement when you least expect it." - Gene Spafford,1992
From: Noddy on 27 May 2010 20:20 "Milton" <millame23(a)yahoo.com> wrote in message news:4bfef274$0$8847$c3e8da3(a)news.astraweb.com... .. > Come on Noddy, let's see you get out of this one. Explain yourself, > please! Woger, perhaps if you had the comprehension ability of a postage stamp (which you currently don't) you'd be able to understand what's being discussed and realise that the differences of opinion are on minor points. -- Regards, Noddy.
From: Noddy on 27 May 2010 20:23 "John_H" <john4721(a)inbox.com> wrote in message news:hbqtv59khu67vhiioh1iqd8ijm0ereje90(a)4ax.com... > Almost, but not quite... and I _never_ have brake rotors machined. > Either reuse them or replace them. Agreed. > I agree that grooved discs don't matter (as do most car > manufacturers). I neither agree nor disagree that they work better > than ungrooved rotors after the pads are worn in to conform with the > grooves (some might, some might not). > > What I'm disputing is the existence of any credible theory that says > the increased surface area due to scoring affects the performance in > any way. I also tend to agree, however the theory that increased contact via larger surface area seems to make sense. > Throw away the crappy OEM pads and replace them with something decent, > preferably Bendix Ultimates. Using a suitable location do three > consecutive crash stops from 150kph or so, don't lock 'em up and don't > brake to a complete stop. The rotors will be glowing and the pads > will be smoking! > > They're now bedded in and the brake performance will *probably* be as > good as it's ever likely to get. That's exactly how I used to bed in metal kings when they were the pad of choice. > After they're cooled down inspect the rotors. It's highly unlikely > the pads will be sufficiently worn to fill the grooves at that point > in time, nor is the brake performance likely to improve once they > have. If perchance it does I'd be looking for other explanation than > surface area... brake dust collecting in the grooves perhaps. Could be. -- Regards, Noddy.
From: Noddy on 27 May 2010 20:23
"jonz" <fj40(a)deisel.com> wrote in message news:4bff06f4$1(a)dnews.tpgi.com.au... > if you can`t dazzle `em with brilliance.......baffle `em with > bullshit.............. Which is the credo you live your life by, huh? -- Regards, Noddy. |