AP Racing 6 Pots have arrived (pics)

[Branners]

But in the real world outside mathematical calculations would they be any better? Would a 1.18% increase help, or would better/wider tyres or better balanced suspension actually make more difference?

[jevansio]

I am confident in saying that from 180mph+ these will out perform UK brakes easily. That's why I bought them, the UKs just couldn't cut the mustard

[dandan]

But in the real world outside mathematical calculations would they be any better?

 

IMHO I definitely believe so....but it does all depend on what it is you want to be "better".

The mechanical braking force calculations obviously ignore the BBK benefits of unsprung weight reduction, potentially wider pad selection, reduction in pad knock back and the associated improvement in feel, consistency, and predictibility.

 

Would a 1.18% increase help

 

Not at all - the mathematical braking force/torque increase is irrelevant in this case.

 

...would better/wider tyres or better balanced suspension actually make more difference?

 

More difference? Maybe - but when you've changed tyres, suspension components, weight distribution and brakes then conclusions about which components or changes give perceived or measureable improvements is almost impossible.

[Branners]

So you are saying the braking force/torque increase is not the benefit of the brakes?

 

What is the benefit then?

 

A set of UK specs with decent pads, fluid and brake lines will take a massive amount of abuse. The question here is whether the AP 6 pots would actually make any difference in a real world situation.

 

The APs no doubt look great but is the cost vs benefit the same as sticking with UK specs and fast road pads?

[jevansio]

Can someone explain how increasing the diameter of the disc by 1.3 inches does not make a hell of a lot of difference to the braking force?

[bignum]

Probably not the actual braking force(unless pad area is much bigger) but the ability to dissipate heat much better, the ap`s should win hands down on repeated high speed stops, oh and look shit loads better:d

[SupraAyf]

What is the benefit then?

 

A set of UK specs with decent pads, fluid and brake lines will take a massive amount of abuse. The question here is whether the AP 6 pots would actually make any difference in a real world situation.

 

That's a good point you make. I was always led to believe that a UK set-up, as mentioned in the above configuration, had a better braking force than a standard AP 6-Pot kit wit DS2500 pads.

 

In all honesty, my AP's are for show.

[jevansio]

I still don't understand how larger discs aren't a massive improvement.

 

As an example, take a mountain bike wheel with disc brakes.

 

You put the bike upsidedown, spin the front wheel, then grab the tyre to stop it with your index finger & thumb, pretty easy.

 

Next you spin the wheel up & do the same with the disc, no doubt it takes time for the wheel to stop as you don't have as much mechanical advantage.

 

So why doesn't the same argument hold true for brakes?

[johnny g]

Larger discs = more torque/leverage, so you'd need less pressure I think to stop at the same rate.

 

You will be limited by the traction of the tyres in how quickly you can slow down - but, the pedal feel and initial bite will be a lot better, plus the heat dissipation will be better, as we saw on Saturday!!

 

Chris Wilson can explain this a lot better, am sure he's written a whitepaper on this.

[imi]

Larger discs = more torque/leverage, so you'd need less pressure I think to stop at the same rate.

 

You will be limited by the traction of the tyres in how quickly you can slow down - but, the pedal feel and initial bite will be a lot better, plus the heat dissipation will be better, as we saw on Saturday!!

 

Chris Wilson can explain this a lot better, am sure he's written a whitepaper on this.

 

 

CW wrote a good whitepaper on this which is what I was referring to, shame I cant find it though....

[Branners]

THey are much better to disipate the heat and will be better designed for cooling.

 

When you stomp the brakes the nose of the car will dive down. Brakes with greater braking power will make that situation worse and could unsettle the car by throwing more weight on to the front tyres. If the tyres are not up to it then the ABS has to try and compensate and so the braking could be worse.

 

If the car is set to cope with that and the brake balance is sorted for larger brakes at the front then the APs will be better.

 

A lot of it is around the brake pads used. My first import had j-spec brakes, I fitted Chris Wilson race pads (£300 a set...) and it stopped as quick as a UK spec and had no brake fade even on track days. However the extra heat they generated ended up cracking the rear disks which had to be scrapped. It also made the car nose heavy during braking so the rear end was a bit loose.

 

If you can get a balanced setup on the brakes with the best pads you can find then the APs will be almost unbeatable. I would certainly explore the pad options for the APs to see what matches your driving style.

[TLicense]

Well there are 2 primary factors that effect braking force.

 

The first is the lever arm. Which is the distance from the centre of the disc to the centre of pressure of the pad. This is what resists the rotational force of the wheel. Pretty simple.

 

The second is the friction force generated by the pad and disc. This is where it get's a little bit tricky. The problem is that the friction force between the pad and disc depends on two seperate things. The first is the friction coefficient between the materials of the pad and disc. The second is the normal force applied to the pads.

 

The friction coefficient is pretty obvious. The higher the friction coefficient the higher the level of retardation. Most discs in the kits we'd be talking about are steel so can be considered to be the same, but obviously pad materials can be different. If you were doing a fair comparison you would use identical pad materials.

 

The normal force is determined by the pressure applied onto the back face of the caliper pistons, and their area. Increase either and you'll increase the normal force.

 

Now that would be pretty simple in itself, but the 3rd level problem is heat. The problem with heat is that it can effect the friction coefficient of the materials and can also limit the amount of normal force that you can apply. (Either due to the pads out-gassing or the brake fluid that is providing the pressure on the back of the cylinders boiling and resultantly not transferring all of the pressure generated onto the cylinder surface)

 

So bearing all of this in mind the things that effect the braking performance of any disc pad / caliper combination is:-

 

1. Distance between the centre of the disc and centre of the pad surface.

2. The friction coefficient of the pad / disc

3. The pressure generated in the brake lines

4. The surface area of the caliper pistons

5. The rate at which the whole system can dissipate any heat generated.

 

It's fairly easy to measure and calculate 1 for two kits. It's also easy to make sure 2 is the same (just use the same pad material). We'll assume that 3 is going to be the same. 4 again is pretty easy to measure.

5. is the problem. The reason being it depends upon the materials used and the geometry of the components.

 

So until we have all of those, any real comparison is going to purely speculative.

[dandan]

Can someone explain how increasing the diameter of the disc by 1.3 inches does not make a hell of a lot of difference to the braking force?

 

The AP calipers have a piston area that is only 87% of the UK calipers and are therefore less "powerful"....applying less force onto the back of the pad to squeeze the disc.

 

The disc diameter increase is needed to restore the braking torque back up to what it would be with a stock size 323mm UK disc and caliper.

 

(This still ignores changes in friction factor between the pad and disc)

Edited July 20, 2010 by dandan (see edit history)

[dandan]

I still don't understand how larger discs aren't a massive improvement.

 

As an example, take a mountain bike wheel with disc brakes.......................

 

So why doesn't the same argument hold true for brakes?

 

With the AP calipers the "squeezing action" is a little bit weaker (87% of the UK caliper) so even though it is out on a bigger diameter you don't see mega increases.

 

Larger discs = more torque/leverage, so you'd need less pressure I think to stop at the same rate.

 

 

Disc diameter isn't the whole story (and it actually plays less of a part than most people think) there are other factors which Tony listed.

 

You will be limited by the traction of the tyres in how quickly you can slow down - but, the pedal feel and initial bite will be a lot better, plus the heat dissipation will be better, as we saw on Saturday!!

 

Tyres have no effect on the theoretical braking force calculations for one setup vs. another. However, as everyone loves to point out... if you can repeatably reach the tyres' limit of adhesion then further increases in braking torque are pointless.

 

Don't forget that once you improve things with different tyres, more favourable weight distribution and suspension changes you can increase that tyres' "limit" and make use of more braking torque. Not many people with big power motors are still running a 235 45 17 Original Equipment (17 year old design) front tyre so there is plenty of scope nowadays for more powerful brakes as tyre technology has moved on.

Edited July 20, 2010 by dandan
Tyre section change to 45 (see edit history)

[jevansio]

The AP calipers have a piston area that is only 87% of the UK calipers and are therefore less "powerful"....applying less force onto the back of the pad to squeeze the disc.

 

The disc diameter increase is needed to restore the braking torque back up to what it would be with a stock size 323mm UK disc and caliper.

 

(This still ignores changes in friction factor between the pad and disc)

Ah right, what are the UK piston sizes?

[dandan]

Ah right, what are the UK piston sizes?

 

I don't have the numbers on my laptop but if memory serves correctly they are 42mm or 42.8mm.

[bignum]

Next we`ll be having some braking competitions on a runway somewhere

[JamieP]

Next we`ll be having some braking competitions on a runway somewhere

 

0-150-0?

[Bobbeh]

That would be interesting, we already have figures for UK Spec brakes

[jevansio]

My racelogic performance box can measure stuff like that no probs

[jevansio]

My racelogic performance box can measure stuff like that no probs

[jevansio]

OK, I have another question, for the guys who upragraded the fronts first, then followed with the rears later, did you feel the rear upgrade was worth making a priority job? I am def going to do it, I just want to know will I feel the same "increase" in braking performance I did with the rears that I did with the fronts?

[JamieP]

OK, I have another question, for the guys who upragraded the fronts first, then followed with the rears later, did you feel the rear upgrade was worth making a priority job? I am def going to do it, I just want to know will I feel the same "increase" in braking performance I did with the rears that I did with the fronts?

 

Yeah its worth doing and you will see an improvement, i take my rears off and put jap specs on every now and then for when i have the drag wheels on, i can notice the difference right off.

[jevansio]

Thanks mate. Going to get new cams in first and will fit the rears in December as my Xmas box

[TLicense]

The problem is that the rears, especially if they're j-specs, is that they aren't designed to do quite as much work as they can end up doing.

Certainly when I just had AP fronts and J-spec rears, the rears just got absolutely hammered, and even more so as I increased the engine power and started to drive at much higher speeds than the j-specs were ever designed to see.

I cracked the original discs fairly quickly, and fitted a new set, which lasted a couple of months before they cracked as well. I also went through pads at a much higher rate than acceptable.

At one point I thought I had a sticking caliper and re-furbished them, but they were actually fine.

 

If I had a set of UK rears, I would buy some temperature stickers and put them on both the front and rear calipers. If the temperatures are the same or close, front and rear, I would leave them. If there was a large disparity then I'd probably look at upgrading.