area difference between NA6 and NA8 brake pads

[plohl]

Sooo.... has anyone got any figures on the brake pad area between NA6 and NA8 (and late model NB)?

cheers
plohl

[NitroDann]

You can just go to repco and ask to see a pair and compare them straight back to back, im sure they wont mind.

Dann

[plohl]

it isnt the exact area....

but from bendix site:

NA6 (89-93)
Front: 110x46x14 Front Area: 5060 mm^2
Rear: 102x39x12 Rear Area: 3978 mm^2

NA8 (93-01)
Front: 110x57x13 Front Area: 6270 mm^2
Rear: 102x43x12 Rear Area: 4386 mm^2

NB (01-03)
Front: 123x59x15 Front Area: 7257 mm^2
Rear: 102x43x12 Rear Area: 4386 mm^2

Percentage Difference (NA6 Baseline)
NA6 - NA8 = F: 23.9% increase R: 10.3% increase
NA6 - NB (01+) = F: 43.4% increase R:10.3% increase
NA8 - NB(01+) = F: 15.7% increase

The problem with these dimension is that is assumes the pad is a rectangle, so the above values are fairly rough. Next thing to find out is moment arm, piston area and brake pressure....

[plohl]

You can just go to repco and ask to see a pair and compare them straight back to back, im sure they wont mind.

Dann

Yeah, the bendix site helped a little. Can print out 'life size' images of the pads. Will do this at some point, measure it up and get a much closer approximation.

[NitroDann]

brake pressure is 100% how hard you push the pedal reliant information.

Also piston size is easy to find and torque due to leverage is just the diameter of the disks. why do you want to know all this anyways?

Dann

[plohl]

Your moment arm is to the centre line of the pad. So it will be the disc OD - 1/2 brake pad height (or width, depending reference frame).

There is a maximum brake pressure which would depend on fluid, lines and the calipers - I'm just interested to see if anyone has numbers.

I want to know cause I am bored.... and want to see some numbers to help me make the decision on whether it is worth going from rear NA6 to rear NA8 calipers, when you can increase the moment arm so you can run NA8 discs with NA6 caplipers and pads. but mostly cause im bored.

cheers
plohl

[plohl]

and wtf is with having a limited time to edit posts????

[NitroDann]

All of THOSE above stats only tell you how little pressure will be required, it doesnt tell you the important stuff like heat capacity.

Dann

[plohl]

Most of what I am after is basic dimensions, for basic calculations. But if you assume that your fluid, brake pad compound and disc material are constant (this is even easier with the rear disc as it is solid!) than you don't really need the more complex information to make an educated decision. But hell, if some one wants to post it up i'll be happy to read it

[NitroDann]

Total mass (assuming all materials between different calipers disks etc have the same volumetric thermal capacity) and surface area touching fresh air along with relevant efficiency of pumping ventilation design are the most important things really. So long as the brakes feel good and can lock the tyres when at the right temperature, only keeping them at that temp is important.

Dann

[sailaholic]

But his problem is that they don't feel good and they don't stay in a temperature range.
This is more likley to be the fronts fading then the rears though i would have thought...

[NitroDann]

and wtf is with having a limited time to edit posts????

Im back. Please PM okibi with this question, but word it politely. he is the forum admin and Ive been posing this question for ages. Ive found mentioning it on the forum get syou nowhere as a lot of regular members just suck up his ass as hes the forum owner, and wont give him real feedback.

Dann

[NitroDann]

But his problem is that they don't feel good and they don't stay in a temperature range.
This is more likley to be the fronts fading then the rears though i would have thought...

Ive no idea what he hopes to achieve so ive just posted fairly non specific stuff.

If the rears never fade, and they dont lock up, he needs a bias adjuster and more front cooling first.

Dann

[jerrah]

I believe the rear calipers are more or less the same between NA6-8 but the caliper bracket, disc and pads are different.

I went NA8 brakes all around with my car but the biggest increase in wheel stopping power came from fitting Hawk HPS+ pads. I've never had fade from the NA8 brakes and didn't have the NA6 brakes long enough to find out.

[plohl]

Total mass (assuming all materials between different calipers disks etc have the same volumetric thermal capacity) and surface area touching fresh air along with relevant efficiency of pumping ventilation design are the most important things really. So long as the brakes feel good and can lock the tyres when at the right temperature, only keeping them at that temp is important.

Dann

Dann, what you have said above is not wrong, by any means, but I think it is out of context for a weekend track/hill climb car, even a dedicated track car. I am also yet to see a road registered mx5 with rear brake ducting!

The average person isn't going to be able to influence anything to do with the specific heat capacity of materiel except the brake pads, which will come down to cost and what they are used for.

If you are going to go to all the trouble of looking at heat capacities, wouldn't you need the friction coefficients (which are temperature dependant)? Now if you have all this complicated data, we can plot the equations as a function of speed.... Now as fun as this would be to do, it’s not going to change what is available on the market, might give you a better idea on the brake pad need for different tracks, dependant on entry speed, but now you have to think about wear... Let’s assume you calculate all the data and you know the most appropriate gear to be running and you finally head out to the track.

Do you really think this is going to help? I’m pretty sure you would agree when I say the person driving the car has the most influence on how ‘quick’ a car is. I know for a fact I’m not a world class driver, so it is probably going to make little difference to me except to my wallet. More experience on track would be yield faster times.

The reason I started the thread is I was curious to see what the geometrical differences were between each series of mx5, because some basic analysis would show whether it is worth spending the extra money on rear NA8 brakes. This could mean that your brakes aren’t balanced perfectly but there is only a 10% difference in area assuming they are rectangles, with a 4 mm difference in height. I think the actual difference would be less than this when you look at the pads – go to bendix site. The front upgrade is an easy decision.

Now this analysis would be a little subjective, because I am cheap.

If some basic assumptions are made, we should be able to come up with a comparative approximation for the performance of each set of brakes. A brake performance coefficient you could call it. Now, friction from the pad produces a moment which counteracts the motion of the wheel. The friction is pressure (caliper) and temperature (pad) dependent (fluid will also have some influence). Assume you have the same pads and fluid, this removes the main temperature dependence. Now dann i assume you know most of this, but for the benefit of anyone else following the discussion i’m going to step it out.

Now, we know that Pressure, P=Force, F/Area, A
Therefore F = PA
The moment, M caused by the brakes can be approximated at a distance, d, which equals brake disc Diameter – 0.5*Pad width (centreline of pad).
M = F*d, substitute in Pressure.
M = PAd
Now are known information here is the Area and approximated distance. P is unknown, but we can calculate A and d to give us our brake performance Coefficients it is P is proportional to M.
So, the variables
NA6: Rear Disc Diameter: 231 mm Pad Area = 3978 mm^2 Pad Height = 39 mm
NA8: Rear Disc Diameter: 250.5 mm Pad Area = 4386 mm^2 Pad Height = 43 mm
Now: NA6 Disc and Pad gives;
M(NA6R) = P * (231-(0.5*39)) x 3978
M(NA6R) = 0.841P Nm
M(NA8R disc, NA6 capliper) = 0.919P Nm
M(NA8R) = 1.00P Nm

So, comparing the coefficients, there is a 9% increase in moment switching from NA6 Discs to NA8 discs with NA6 capliers/pads and a 19% increase when going from NA6 disc and calipesr to NA8 disc and calipers. This means there is a 10% difference between the NA8/NA6 combo and the NA8 set. Now this is basic and only a guide! But, basic math and sound reasoning can be much more helpful than the specific heat capacities of each component.

I could have come and asked “should I upgrade my rear brakes from na6 to na8?”, but wear is the fun in that?! Would you prefer to spend the extra money for calipers, or use it for ‘better’ pads?