Martin J Stirling

When upgrading to better brakes, which single element is most important in giving greater braking performance; is it the size of the pad, the total piston area or the size of the disc?

Will a 355mm disc with AP four pots give greater braking performance than a 335mm disc with 6 pots?

Any help appreciated..

MS

Matt Churchill

I thought it was something to do with contact area - therefore the bigger the pad and disc, the more contact there is, and thus the more force can be exerted.

Just a guess mind you, but sounds right

Hoppy

What is "greater braking performance"? Do you mean stop quicker? In which case, all other things being equal (which they never are but let's pretent) bigger discs will do it best/cheapest. Extra mechanical leverage makes a big difference. However, with even a modest brake upgrade your braking from normal speeds will probably be limited by the ABS cutting in. This is why the Godspeed upgrade using standard calipers but with bigger discs makes such a big difference at sensible money. Using the same principal, longer pads (eg APR 6-pots) will stop quicker as more of the pad area is closer to the outside of the disc.

But if you want to stop quickly again, and again and again, as in a track day, a whole new set of factors come in to play as the brakes have got to absorb and disperse absolutely huge amounts of heat very quickly. The mass, design and construction of the discs is the most important factor for Scoobs with poor brake cooling.

I've posted enough boring stuff about brakes on here so I'll stop now and just leave you with this to dwell on. In a full-on stop from 100mph, your brakes will absorb enough heat to boil three kettles of water at 50 deg, in about four seconds In a 3000w kettle that will take 12 minutes.

Richard.

Martin J Stirling

So if you could choose between a 325mm disc and a 6 pot or a 355mm disc and a 4 pot, which would you choose?

Cheers Hoppy,

MS

Hoppy

Hi Mart, sorry to dodge the question but it's not just a matter of size (missus) because, as said above all things are never equal.

In my view, and for my application (ie track days) the disc is paramount. APR make the best discs. Fact. There may be others as good, but certainly none better. So it's 330mm x 28mm 48-vane grooved, with alloy bells, as in their branded kit. They can take ten laps of Dono without batting an eyelid, which is more than is good for me, or the car. Full stop There is no tougher test.

The next bit is tricky, ie 4-pot or 6-pot calipers? The main advanatge is the alloy construction for better cooling (no boiled fluid) although big savings in unsprung weight, especially right at the end of the axle, are obviously good. Okay, I've got APR 6-pots because they are the best and that gives me some peculiar pleasure, albeit not very objectively. Frankly, I think the smart money is on 4-pots as they're cheaper and pads are cheaper with a wider choice of componds. Six-pots are just over the top. Bu99er me, my ex APR 4-pots for 16in wheels were awsome enough.

So I would say, get the best discs you can - APR - and clamp them with some nice alloy calipers and the pads of your choice (according to application). APR, Alcon and Brembo are proven, but that is not to say that other alloy calipers are not as good, provided they are properly dust-sealed and have a robust finish.

Best regards,

Richard.

Sigmund

I must say I agree 100% with hoppy there. I have AP 4-pots with AP 330x28mm discs.
You can't go wrong with that setup.