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From: Sylvia Else on 28 May 2010 04:31 On 26/05/2010 10:54 PM, Clocky wrote: > 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. It is hugely counterintuitive that friction should not be a function of area in contact (for non-adhesive surfaces). But it's true nevertheless, and if you think you know otherwise, you know wrongly. Sylvia.
From: Jason James on 28 May 2010 04:58 "Sylvia Else" <sylvia(a)not.at.this.address> wrote in message news:4bff7f68$0$2122$c3e8da3(a)news.astraweb.com... > On 26/05/2010 10:54 PM, Clocky wrote: > >> 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. > > It is hugely counterintuitive that friction should not be a function of > area in contact (for non-adhesive surfaces). But it's true nevertheless, > and if you think you know otherwise, you know wrongly. M'dear,..scoring by nature does not present the pad with more parallel wearing surface. The sides of the scores are angular. God knows what extra friction that produces,...but it aint a function of the additional area. Jason
From: atec7 7 ""atec77" on 28 May 2010 05:10 John_H wrote: > Noddy wrote: >> "John_H" <john4721(a)inbox.com> wrote in message >> news:hbqtv59khu67vhiioh1iqd8ijm0ereje90(a)4ax.com... >>> 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. > > But it doesn't make any sense at all. The basic theory of friction > found in any physics textbook (attributed to Coulomb) states that the > force of friction equals the coefficient of friction multiplied by the > force pushing the two objects together (Ff = COF x Fn) . No mention > of surface area. > > Imagine a 3m diameter brake disc with a 1m diameter brake pad. You > operate it by pushing on the centre of the pad with your finger. > > Now change the 1m pad for one 10cm in diameter, of the same material, > located at the same centre position. Operate it with the same finger. > > Which setup do think will provide the greatest braking force? > > The answer is neither. Assuming you apply the same force with your > finger, the braking force (due to friction) will be exactly the same > even though the second disc only has a thousandth of the contact area > of the first. the rule is the coefficient of friction of a known area and a known applied force hence if you increase the swept are without modification of the other two braking force as in resistance to travel increases so it brakes better ,same applied to any friction situation > > What possible difference could a few score marks in the disc make? not much but it may be measurable > > IIRC Coulomb made his observations back in sixteen hundred and > something using blocks of wood. It's not hard to come up with far > more complex situations but provided the coefficient of friction > remains a constant (as it will for the same materials under the same > conditions) the equation still holds for both static and kinetic > friction. see above >
From: jonz on 28 May 2010 05:17 On 5/28/2010 4:51 PM, John_H wrote: > D Walford wrote: >> On 27/05/2010 6:06 PM, John_H wrote: >>> D Walford wrote: >>>> >>>> Clubman racers use 16-18psi in their tyres because the lower pressure >>>> improves grip, any higher and you can't keep the car on the road. >>>> The most popular tyre on racing Clubmans at club level is Avon ACB's >>>> which are Formula Ford tyres. >>> >>> They also use entirely different technology to road tyres (it's not >>> comparing apples with apples). >> >> I knew that was the case but I threw it in just to confuse the issue:-) > > You also provide the clue to the difference further down. Unlike a > conventional car tyre they don't work by friction! > >> They get so sticky with heat that you often have to clean the rubbish >> that's stuck to the tyres before the next run. > > Racing slicks work the same way as adhesive tape does (the penny > should've dropped earlier). > > And for the trivia department... that stuff they used to call friction > tape wasn't. :) ~~~~~~~~~~~~~~~~~~ DOH............. > -- 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 28 May 2010 05:21
On 5/28/2010 6:58 PM, Jason James wrote: > "Sylvia Else"<sylvia(a)not.at.this.address> wrote in message > news:4bff7f68$0$2122$c3e8da3(a)news.astraweb.com... >> On 26/05/2010 10:54 PM, Clocky wrote: >> >>> 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. >> >> It is hugely counterintuitive that friction should not be a function of >> area in contact (for non-adhesive surfaces). But it's true nevertheless, >> and if you think you know otherwise, you know wrongly. > > M'dear,..scoring by nature does not present the pad with more parallel > wearing surface. The sides of the scores are angular. ~~~~~~~~~~~~~~~~ sure about are you?.... God knows what extra > friction that produces,...but it aint a function of the additional area. > > Jason > > -- 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 |