stock is as stock does

[aboyandhisdawg]

yup, yer missing something. its a matter of the mechanical advantage gained or lost by the length of the "lever arm". the road has a "lever arm" equal to the radius of the tire and wheel, the brakes have a "lever arm" equal to the radius of the rotor. in "playground physics" you have the equivalent of a fat kid on a see-saw (in this case, the motorcycle, rider and any gear), if the fat kid is siting at the end of the see-saw (AKA: teeter-totter) you'll need two skinny kids on the end, or three in the middle of the opposite side to overcome the mechanical advantage. another way to look at it is, if you are trying to stop a heavy door from slamming, is it easier to stop by blocking it at the inside edge, middle or outside edge? front end dive serves as a simple measure of how quickly the brakes are able to stop the bike. if the weight transfer is over a longer time, the front will dive less, over a shorter time, it will dive more. the larger rotor does have more thermal mass, but that's minor compared to the mechanical advantage offered over the stock rotor. fixer KLR A1 Lost Wages, NV --- In DSN_klr650@yahoogroups.com, "Eric L. Green" wrote:

> Well, my front brake gave a little metal-to-metal squeal yesterday. I > looked down when I got home, and sure enough, it's time for new brake > pads. And, for that matter, possibly a new brake rotor, because this guy > is looking a bit tired and worn -- the previous owner put sintered > metallic pads on the thing. We'll see what happens when I clean it up. The > good news is that the cycle accessories place down the street is a Galfer > dealer. The even better news is that his Galfer distributor is about 1 > mile away from his shop, so that even though he'll have to order pads, > they shouldn't take long to arrive. > > I looked at the "big rotor" kit. I'm not convinced. Braking efficiency is > detirmined by three things: > > 1) Temperature of the rotor and brake pads. This is reduced by the big > rotor, but modern brake pads aren't as sensitive to temperature. However, > the big rotor does allow more heat dispersal. > > 2) Area of brake pad in contact with the rotor. This is identical between > the two. > > 3) Amount of force exerted against the rotor by the brake pads. This, > along with the coefficient of friction, detirmines how much directional > energy will be transformed into heat energy. The calipers continue to > exert the same amount of force against the rotor, and steel continues to > have the same coefficient of friction that it's always had. > > Now, there seem to be people absolutely convinced that the big rotors

make

> their brakes stop better. They point to the amount of suspension dive. > However, suspension dive is not only a matter of weight transfer, it is > also a matter of moment arm. The relocated brake pads, being further out > on the fork, will transfer additional torque to the fork. This is not > causing additional braking by any means -- amount of braking is detirmined > by how much forward energy is converted into heat energy. This has > absolutely nothing to do with fork dive. > > The other thing they point to is how much easier it is to do a "stoppie". > But again, this is a matter of moment arm, not of braking efficiency. > > Another confounding issue is the fact that most people also upgrade to the > Galfer stainless steel lines at the same time. The Galfer lines will cause > greater braking power with less lever motion, because they have a slightly > smaller inside diameter, meaning less buffering by the fluid column in the > brake line. More of the force instead goes against the calipers. So people > may be confusing the better feel from the Galfer lines with the effects of > the rotor. People also often update to the Galfer green brake pads at the > same time, which will increase the coefficient of friction between brake > pad and rotor, and thus stopping power. > > It appears to me that the temperature issue is the only one where the > larger rotor will produce better results. If I were intending to go down a > 4% slope using my brakes rather than my engine to slow me down, I might > think it's worth it. But at the moment, looking at the simple physics > involved, it seems to me that it'd make more sense to just put another > OEM-style rotor by EBC or etc. on there (for half the price or less of the > big rotor kit) and go with the Galfer Green pads and stainless steel brake > line. > > From what I can tell, the only way that the bigger rotor would result in > more braking power would be if there were bigger pads and more powerful > calipers to go with it. Without that, it seems like a vanity project to > me, not to mention that it puts forces onto the fork that the fork wasn't > designed for. Am I overlooking something? Is physics lying to me? Did I > overlook a coefficient of friction somewhere that is improved by the > bigger rotor? Do the big rotor kits include something that isn't shown on > the web sites (which show a rotor, and a bracket for moving the calipers > upwards)? Scientific minds want to know! > > -E

[Doug Pippin]

Eric Since you're a person that would let their brake pads wear until there was metal to metal contact it's kind of a paradox that you know so much about brakes. Do you think that the surface swept area from one rotation of the wheel might have something to do with the amount of braking force exerted. Since the size of the rotor (in your opinion) doesn't make any difference I suggest you buy a smaller rotor (should be cheaper) to replace your damaged one. For the rest of the world the larger rotor does give you better braking. Recently I rode my KLR with SS brake line and 320mm rotor to Helen Georgia with a friend who also has a KLR. His bike has a SS brake line with the stock rotor. After riding 30 miles we switched bikes to see what the difference was. The first thing he said was wow you really have front brakes. The other big thing that was apparent was the stability that the fork brace gives to the wimpy forks on the KLR. Doug in NC At 05:14 AM 5/28/04, you wrote: Date: Fri, 28 May 2004 00:16:43 -0700 (PDT) From: "Eric L. Green" Subject: Brakes Well, my front brake gave a little metal-to-metal squeal yesterday. I looked down when I got home, and sure enough, it's time for new brake pads. And, for that matter, possibly a new brake rotor, because this guy is looking a bit tired and worn -- the previous owner put sintered metallic pads on the thing. We'll see what happens when I clean it up. The good news is that the cycle accessories place down the street is a Galfer dealer. The even better news is that his Galfer distributor is about 1 mile away from his shop, so that even though he'll have to order pads, they shouldn't take long to arrive. I looked at the "big rotor" kit. I'm not convinced. Braking efficiency is detirmined by three things: 1) Temperature of the rotor and brake pads. This is reduced by the big rotor, but modern brake pads aren't as sensitive to temperature. However, the big rotor does allow more heat dispersal. 2) Area of brake pad in contact with the rotor. This is identical between the two. 3) Amount of force exerted against the rotor by the brake pads. This, along with the coefficient of friction, detirmines how much directional energy will be transformed into heat energy. The calipers continue to exert the same amount of force against the rotor, and steel continues to have the same coefficient of friction that it's always had. Now, there seem to be people absolutely convinced that the big rotors make their brakes stop better. They point to the amount of suspension dive. However, suspension dive is not only a matter of weight transfer, it is also a matter of moment arm. The relocated brake pads, being further out on the fork, will transfer additional torque to the fork. This is not causing additional braking by any means -- amount of braking is detirmined by how much forward energy is converted into heat energy. This has absolutely nothing to do with fork dive. The other thing they point to is how much easier it is to do a "stoppie". But again, this is a matter of moment arm, not of braking efficiency. Another confounding issue is the fact that most people also upgrade to the Galfer stainless steel lines at the same time. The Galfer lines will cause greater braking power with less lever motion, because they have a slightly smaller inside diameter, meaning less buffering by the fluid column in the brake line. More of the force instead goes against the calipers. So people may be confusing the better feel from the Galfer lines with the effects of the rotor. People also often update to the Galfer green brake pads at the same time, which will increase the coefficient of friction between brake pad and rotor, and thus stopping power. It appears to me that the temperature issue is the only one where the larger rotor will produce better results. If I were intending to go down a 4% slope using my brakes rather than my engine to slow me down, I might think it's worth it. But at the moment, looking at the simple physics involved, it seems to me that it'd make more sense to just put another OEM-style rotor by EBC or etc. on there (for half the price or less of the big rotor kit) and go with the Galfer Green pads and stainless steel brake line. From what I can tell, the only way that the bigger rotor would result in more braking power would be if there were bigger pads and more powerful calipers to go with it. Without that, it seems like a vanity project to me, not to mention that it puts forces onto the fork that the fork wasn't designed for. Am I overlooking something? Is physics lying to me? Did I overlook a coefficient of friction somewhere that is improved by the bigger rotor? Do the big rotor kits include something that isn't shown on the web sites (which show a rotor, and a bracket for moving the calipers upwards)? Scientific minds want to know! -E ---------- Doug Pippin 828-684-8488 dpippin5@... ---------- [Non-text portions of this message have been removed]

[Tengai Mark Van Horn]

At 12:16 AM -0700 5/28/04, Eric L. Green wrote:

>Now, there seem to be people absolutely convinced that the big rotors make >their brakes stop better.

They do without a doubt, but not $315.00 better. I think SS lines and good pads are all ya need. People who need more need to start squeezing tennis balls and/or learn how to bleed their brakes. I was happy with my SBS pads, but I'm trying DP Brakes for my current set. Mark http://www.reelrider.com

[rsanders30117]

Boy did you miss the mark! The biggest benefit of larger brake rotor is the increase in the brake pads moment arm (lever length) & a heat dissipation improvement due to increased rotor surface area. I've done both. 1st was installation of the larger rotor for a dramatic improvement. 2nd I added SS brake line for negligible braking improvement but much esthetic improvement. --- In DSN_klr650@yahoogroups.com, "Eric L. Green" wrote:

> Well, my front brake gave a little metal-to-metal squeal yesterday.

I

> looked down when I got home, and sure enough, it's time for new

brake

> pads. And, for that matter, possibly a new brake rotor, because

this guy

> is looking a bit tired and worn -- the previous owner put sintered > metallic pads on the thing. We'll see what happens when I clean it

up. The

> good news is that the cycle accessories place down the street is a

Galfer

> dealer. The even better news is that his Galfer distributor is

about 1

> mile away from his shop, so that even though he'll have to order

pads,

> they shouldn't take long to arrive. > > I looked at the "big rotor" kit. I'm not convinced. Braking

efficiency is

> detirmined by three things: > > 1) Temperature of the rotor and brake pads. This is reduced by the

big

> rotor, but modern brake pads aren't as sensitive to temperature.

However,

> the big rotor does allow more heat dispersal. > > 2) Area of brake pad in contact with the rotor. This is identical

between

> the two. > > 3) Amount of force exerted against the rotor by the brake pads.

This,

> along with the coefficient of friction, detirmines how much

directional

> energy will be transformed into heat energy. The calipers continue

to

> exert the same amount of force against the rotor, and steel

continues to

> have the same coefficient of friction that it's always had. > > Now, there seem to be people absolutely convinced that the big

rotors make

> their brakes stop better. They point to the amount of suspension

dive.

> However, suspension dive is not only a matter of weight transfer,

it is

> also a matter of moment arm. The relocated brake pads, being

further out

> on the fork, will transfer additional torque to the fork. This is

not

> causing additional braking by any means -- amount of braking is

detirmined

> by how much forward energy is converted into heat energy. This has > absolutely nothing to do with fork dive. > > The other thing they point to is how much easier it is to do

a "stoppie".

> But again, this is a matter of moment arm, not of braking

efficiency.

> > Another confounding issue is the fact that most people also upgrade

to the

> Galfer stainless steel lines at the same time. The Galfer lines

will cause

> greater braking power with less lever motion, because they have a

slightly

> smaller inside diameter, meaning less buffering by the fluid column

in the

> brake line. More of the force instead goes against the calipers. So

people

> may be confusing the better feel from the Galfer lines with the

effects of

> the rotor. People also often update to the Galfer green brake pads

at the

> same time, which will increase the coefficient of friction between

brake

> pad and rotor, and thus stopping power. > > It appears to me that the temperature issue is the only one where

the

> larger rotor will produce better results. If I were intending to go

down a

> 4% slope using my brakes rather than my engine to slow me down, I

might

> think it's worth it. But at the moment, looking at the simple

physics

> involved, it seems to me that it'd make more sense to just put

another

> OEM-style rotor by EBC or etc. on there (for half the price or less

of the

> big rotor kit) and go with the Galfer Green pads and stainless

steel brake

> line. > > From what I can tell, the only way that the bigger rotor would

result in

> more braking power would be if there were bigger pads and more

powerful

> calipers to go with it. Without that, it seems like a vanity

project to

> me, not to mention that it puts forces onto the fork that the fork

wasn't

> designed for. Am I overlooking something? Is physics lying to me?

Did I

> overlook a coefficient of friction somewhere that is improved by the > bigger rotor? Do the big rotor kits include something that isn't

shown on

> the web sites (which show a rotor, and a bracket for moving the

calipers

> upwards)? Scientific minds want to know! > > -E

[klrdon@aol.com]

> From what I can tell, the only way that the bigger rotor would result in > more braking power would be if there were bigger pads and more powerful > calipers to go with it. Am I overlooking something?

Why does a cheater handle make a stuck nut easier to remove? More leverage - same as you get with a larger diameter disk and caliper moved away from the axel. The big disk kits are usually taylored to take max advantage of the disk alloy and friction material relationship. Get a big enough disk on that bugger and you should be able to do stoppies. Don M Atlanta, GA A16 [Non-text portions of this message have been removed]

[kdxkawboy@aol.com]

In a message dated 2004-05-28 5:40:25 AM Pacific Daylight Time, Tengai650@... writes:

> > They do without a doubt, but not $315.00 better. I think SS lines and > good pads are all ya need. People who need more need to start > squeezing tennis balls and/or learn how to bleed their brakes. I was > happy with my SBS pads, but I'm trying DP Brakes for my current set. > >

With the stock brake lines I could squeeze the brake lever all the way into the handgrip without much additional braking power. With metal brake lines it only takes two fingers to get the same amount of braking power and the lever is still easily clearing the knuckles on my other two fingers. By using my whole hand to grab the brake lever I can generate enough force to cause my Race Tech valved, PS springs, 15W fork oil, forks to completely bottom out. For any sort of brake mod to have value for me, it would have to give me that type of braking power with no more than two fingers - on MX bikes and Super Sports this has become the standard by which brakes are measured, how little effort to takes to get max braking. Without replacing the master cylinder and caliper I don't see how a bigger rotor will give me what I want in a brake mod. Pat G'ville, Nv [Non-text portions of this message have been removed]

[Eric L. Green]

On Fri, 28 May 2004, Doug Pippin wrote:

> Since you're a person that would let their brake pads wear until there was > metal to metal contact it's kind of a paradox that you know so much about

Uhm, nope, no metal to metal contact. Not yet.

> Do you think that the surface swept area from one rotation of the wheel > might have something to do with the amount of braking force exerted.

Ah. Okay. Now you have an explanation that makes sense. The friction is greater per rotation of the wheel because the brake pads are travelling a greater distance per rotation of the wheel, even though the absolute friction per unit of travel remains the same.

> For the rest of the world the larger rotor does give you better braking. > Recently I rode my KLR with SS brake line and 320mm rotor to Helen Georgia > with a friend who also has a KLR. His bike has a SS brake line with the > stock rotor.

Same pads? -E

[Eric L. Green]

On Fri, 28 May 2004 klrdon@... wrote:

> > From what I can tell, the only way that the bigger rotor would result in > > more braking power would be if there were bigger pads and more powerful > > calipers to go with it. Am I overlooking something? > > Why does a cheater handle make a stuck nut easier to remove? More leverage -

The amount of power applied to the nut, however, remains identical (power being force applied over a distance). The per-rotation swept area is what makes the bigger rotor shed more energy, as another person correctly pointed out, because while the brake pads and rotor convert the same amount of energy per inch of travel into heat, they are travelling more inches per rotation. BTW, do brake pads normally last more than 500 miles? I checked my brake pads 500 miles ago and they were fine, plenty of material, etc. Now it's clearly time to change them. That's an indication that my rotor's pretty badly beat up, right? -E

[Eric L. Green]

On Fri, 28 May 2004, aboyandhisdawg wrote:

> yup, yer missing something. > > its a matter of the mechanical advantage gained or lost by the length of the > "lever arm".

Err, no. As explained by someone else, it's a matter of the friction per inch of sweep of the brake pads over the rotor being the same -- i.e., the same amount of momentum energy is converted into heat energy per inch of sweep -- but the brake pads sweeping over more inches of rotor in the course of one revolution of the rotor. Thus converting more momentum energy to heat energy over the course of one revolution of the front wheel. Mechanical advantage does not convert energy from one form to another. All it does is adjust the work equation (work = force applied over a distance) to increase the distance part of that equation while reducing the force part of that equation. High school Physics. -E

[rm@richardmay.net]

On Fri, 28 May 2004, Eric L. Green wrote:

>And, for that matter, possibly a new brake rotor, because this guy is >looking a bit tired and worn -- the previous owner put sintered metallic >pads on the thing.

The OEM pads are sintered metallic. They're the only pads that will survive muddy conditions for any length of time.

>I looked at the "big rotor" kit. I'm not convinced. Braking efficiency is >detirmined by three things: >1) Temperature of the rotor and brake pads.

[snip]

>2) Area of brake pad in contact with the rotor. This is identical between >the two.

[snip]

>3) Amount of force exerted against the rotor by the brake pads.

[snip] You forgot 4) Moment Arm. "The magnitude of the torque acting on a body is equal to the product of the force acting on the body and the distance from its point of application to the axis around which the body is free to rotate." The larger rotor increases the force-application distance from the axis (or axle). But I agree with you in that bigger rotors are what you install when you've exhausted other, more affordable options. RM