Doppelgänger

iTrader: (12)

lol@ both posts above this one.

I dunno why I always expect the answer to some things to be more in depth, esp. when the first thing I think of ends up being correct..I have a hard time believing it

j_man

Larger pad won't change anything clamping force related. It could help with overheating, it will make the pads come up to temperature slower (which for autocross he doesn't want) but it won't change the balance.

These are the only things which will change the balance:

- rotor radius

- messing with the F/R hudralic pressure (prop valve or dual cylinders with prop bar)

- caliper piston diameter

- pads with different friction coef. (you won't see mixing different pads front/rear recommended often, because such pads usually behave different at different temperatures thus brake heat can change the balance )

gospeed81

iTrader: (51)

There is a reason the unit for torque is ft-lbs. 1ft-lb is one pound of force applied one foot from the center.

If you increase the force but not the distance you get more torque. If you increase the distance but not the force you also get more torque.

The latter is what happens when we use our same piddly calipers but put on bigger brackets and rotors.

Torque makes car go...torque makes car stop.

ScottFW

iTrader: (4)

A partially relevant analogy would be to think of a lever. The longer the lever, the more force it exerts on the opposite end given an equal input force. An equal clamping force at a radius farther out from the hub center will have greater effect in slowing rotation. It's related to the "moment of inertia" discussions pertaining to wheel weight & construction, clutches, and flywheels. I'm sure the physicists in the audience will have all kinds of problems with the lever analogy, but whatever. My recollection is that pretty much every equation pertaining to a rotating mass has some r^2 component, so the radius has a huge effect on everything else.

y8s

iTrader: (8)

remember the golden rule: friction is independent of surace area

everything else being equal, the brake rotor with the highest average radius (outside+inside)/2 will have the highest torque.

as an example, imagine a brake disk that used the whole disk face instead of just an outer ring for the brake area. it would have an average radius of .500R and one that only used the outer 1/4 would have an average radius of .875R. almost double the stopping power for the same size rotor.

Stein

iTrader: (46)

MT.net = tech, engineering, learning. Good stuff.
hondatech.com = (literally) 5 page thread trying to get across how an MBC works. I read it this weekend. Some still couldn't understand the concept of how a simple ball/spring MBC does what it does. In page FOUR, after multiple attempts to explain this simple concept, someone still was saying something to the effect of "OK, I think I got it now. So, just add the amount of PSI from the MBC to the PSI of my wastegate, right?" My head hurt.

boileralum

iTrader: (8)

+1

The added mass is a secondary help to keep the system from overheating as well.

hustler

iTrader: (6)

um, I don't understand how a larger pad area doesn't increase the stopping power. The same logic applies to tires. You get more grip with a larger tire, I always assumed a larger pad yielded the same results.

miatauser884

iTrader: (11)

I'm with Hustler. Apply equal pressure to a small pad or the large pad. The large pad will create more friction (which creates more heat) The rotational energy is being converted to heat energy via the friction between the rotor and pad. As long as the pad does not deteriorate. The more heat means the more rotational energy lost. Big pad stops faster than little pad.

The coefficient of friction is independent of surface area. It depends on the two materials in question. However, the larger the surface area of pad touching the rotor, the faster you will stop.

hustler

iTrader: (6)

What you talking about bro? How many ways can you adjust those fancy suspensions? Yeah, I thought so. BC Racing have 30 levels of adjustment. That's right bro: 30! Plus, I can slam the **** out of it, roll my fenders, dial in some 3* of negative camber and run some sick 20 X 10 Giovannis (with 40mm spacers to clear the *huge* Brembos) with 245/10s. No ******* sidewall flex for me and a center of gravity so low that I'll be pulling mad Gs in the twistiez.

M-Tuned

iTrader: (6)

M-Tuned 1.8 Miata Sport Brake Bracket Kit (Rear) M-Tuned

Here is the rear kit!

Savington

iTrader: (31)

100% wrong, but thanks for playing.

y8s

iTrader: (8)

the equation for friction force is F = uN where F is the force of friction, u is the coefficient of friction, and N is the clamping force of the pad against the rotor.

where is area? I dont see area.

lets say you had two pads of some magic material "stoptanium" that does not wear out and has an infinite heat transfer coefficient. lets call its coefficient of friction 1.0 for easy calculations. clamping force is 10 lbs.

for the giant brake pad with surface area of 100, the force is the same as the tiny brake pad with surface area of 10, right? F = 1.0 * 10 lbs. F = 10 lbs.

The reason for this is microstructure of the surface interaction. imagine a bed of nails. a large bed distributes the surface interaction over a larger area and the nails dont push into you much. a smaller area of nails digs into you under your body weight. same thing with friction and brakes.

Tires are different to a degree because of their compliance. Though if you think of a tractor on a freshly tilled field, you get a better idea whats going on. Larger tires float on top and small tires dig in. (ignore that the soil moves on its own)

JasonC SBB

Big difference between tires and pads.

Tires gripping the pavement is pseudo static friction and rubber is like a visco-elastic thing - when a tire slides it "tears" bits of it - larger footprint takes more force to "tear" for a given weight.

Pads are more like classical kinetic friction, area doesn't matter.

What the larger area gets you is a bigger area over which to spread the heat - less pad fade.

gospeed81

iTrader: (51)

y8s has got it....friction is independent of area, and based solely on the normal force.

Area does affect pressure, which is a force over an area. Larger tires give you more traction by reducing the pressure on each unit area of the rubber compound. You can get too large of a tire when you get to the point that there isn't enough pressure to utilize the coefficient of static friction...and you are then operating on kinetic friction, which is always less than your static number. This happens when the force (corner weight of car) over the area (contact patch) is below some certain pressure, which depends on the compound of the tire.

If you were to use the same material found in M+S tires in a 225 on a 6UL you'd actually lose traction earlier. Since most of us use softer compounds when moving to wider tires we avoid this, but increasing contact area reduces the pressure, and means more force is required to achieve the same pressure.

Brakes of course operate on kinetic friction (as Jason noted)...where area doesn't matter in regards to friction. Area does dissipate heat...and a larger area does require less pressure to apply the same force. This is why it takes less pedal effort to do the same stopping work when you upgrade brakes.

mx5tunerchallenge

As far as unsprung weight goes, how must weight does the conversion to the corrado 11'' g60 rotors add?

Braineack

iTrader: (62)

I believe it was 3-4lbs a corner, something like that.



i need a rear kit now...

kotomile

iTrader: (24)

Absolutely.


My analogy - think of two piston engines, all other things equal the one with the longer stroke will make more torque at low RPM, largely due to the additional mechanical advantage of the big end rod being further from the center of the crankshaft and therefore able to apply more torque.

cueball1

iTrader: (13)

Think PSI. You have one brake pad of 5 square inches and another of 10. If you apply 10 lbs of clamping force the 5" pad has 2 lbs of pressure on it per square inch, the 10" pad has 1lb per inch. The additional friction of a larger surface is offset by a reduction in force per square inch.

Obviously I'm no engineer. I am sure there is a tremendous amount of frictional dynamics along with fluid/hydraulic and heat formulas that come into play. My understanding of the advantage of larger brake pad surfaces has always been longer wear and increased heat absorbtion capacity, not additional clamping force.

ak4two

Think about the clutch. Why do higher hp motors require a larger diameter clutch? 1.6=little clutch, 1.8=slightly larger diameter clutch which allows it to handle more torque. The force is being applied the other direction but same difference.