AP racing Radi-CAL 2 calipers?

AP racing Radi-CAL 2 calipers?

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Discussion

m.barnes

Original Poster:

184 posts

210 months

Tuesday 16th June 2020
quotequote all
Anyone got these? The performance versions (particularly the CP9560)

https://apracing.com/performance-upgrades/performa...

Thinking of upgrading the brakes on my v8 vantage which has the 4pot front calipers. It’s a “cheaper” option than the OE 6 pot brembo and I believe they are a “better” caliper but that’s a grey line.

Anyone using them?
Looked at the more race version too but this is more a road car than a track car just looking at upgrading the calipers as need new discs and pads anyway.

Thanks

ATM

18,096 posts

218 months

Tuesday 7th July 2020
quotequote all
Can you just bolt these on in place of your current calipers or do you need a complete change of setup so discs calipers and whatever brackets required to locate the caliper?

I had a massive 6 pot ap caliper setup on a car I bought. They were an older caliper design but worked fine. The only real changes between different calipers is their weight and their torsional rigidity. No human would be able to detect the difference between one ap caliper and another from the driving seat if all else was equal.

The main change between using one brake setup and another is the disc diameter and disc thickness and pad area. By increasing any or all of these variables you get more braking force and can therefore brake harder and longer without cooking everything.

Ultimately though the tyre is a limiting factor. So if you have a load more braking force available then its useless if your tyre can't cope.

Even if your tyre can cope with the added force but the car itself can't then accelerate hard enough after a braking event to make it go quick enough to then need to brake hard again without time to cool the brakes from that braking event then it is all useless. Basically if your car takes too long to accelerate after hard braking then the brakes don't need to work well hot because they will have time to cool.

I see a lot of people getting excited about bigger brakes but they forget about the added weight a bigger brake setup brings with it. More rotational mass is bad and means your car will accelerate slower as it requires more energy and then that extra energy will generate more heat in the brakes when slowing down.

Sometimes less is more.

GreenV8S

30,150 posts

283 months

Tuesday 7th July 2020
quotequote all
ATM said:
By increasing any or all of these variables you get more braking force and can therefore brake harder and longer without cooking everything.
If you do get significantly more braking force then you'll need to correct the brake balance too.

ATM

18,096 posts

218 months

Wednesday 8th July 2020
quotequote all
GreenV8S said:
ATM said:
By increasing any or all of these variables you get more braking force and can therefore brake harder and longer without cooking everything.
If you do get significantly more braking force then you'll need to correct the brake balance too.
True

You can read the specs of the calipers which talk about piston sizing. Generally older 4 pots have equal sized pistons. The 6 pots can have different sizes.

Generally on a road car bias isn't adjustable. So you can only really alter this by changing rear brakes too.

I've seen some claims that bigger brakes do not generate much more braking force amd instead just go about their business and generate less heat therefore remaining consistent over the smaller setup. We've all had brake fade - I assume - the bigger setup should mot fade or not fade as easily.

Ultimately all the brake does it change energy stored in a car into heat.

Some people might say a better caliper allows better feel and modulation but again I'm not sure if you could really notice the difference comparing 2 different calipers from the driving seat. I will buy into the longevity of a caliper being better from one manufacturer to another. But a brake caliper is a very simple device.

I watched a video on you tube I think from someone like maclaren testing a brake caliper they had 3d printed. It did surprisingly well.

E-bmw

9,106 posts

151 months

Wednesday 8th July 2020
quotequote all
ATM said:
I've seen some claims that bigger brakes do not generate much more braking force
Larger diameter discs = more leverage for the same caliper so more braking force.

Greater pad area using larger caliper = more friction on the discs and so more braking force.

Yes, these are obviously relative, but equally both true.

There are many examples of simple upgrades ( using brakes from the same stable) that are used all over the world and all are effective.

Here are 2 I have done myself:

e36 325 - e46 330 caliper & discs

R53 - r56 front discs & calipers.

Both are very noticeable with even my insensitive seat.

So, not sure where you saw that.

ATM

18,096 posts

218 months

Wednesday 8th July 2020
quotequote all
E-bmw said:
ATM said:
I've seen some claims that bigger brakes do not generate much more braking force
Larger diameter discs = more leverage for the same caliper so more braking force.

Greater pad area using larger caliper = more friction on the discs and so more braking force.

Yes, these are obviously relative, but equally both true.

There are many examples of simple upgrades ( using brakes from the same stable) that are used all over the world and all are effective.

Here are 2 I have done myself:

e36 325 - e46 330 caliper & discs

R53 - r56 front discs & calipers.

Both are very noticeable with even my insensitive seat.

So, not sure where you saw that.
It seems to make the most sense that bigger brakes will give more stopping force. Although if the new brake calipers have very different piston sizes to the ones they replaced then you will need to move more fluid to get the same clamping pressure so you can see an argument there for it not changing the forces applied. But personally I dont buy it.

rustednut

807 posts

46 months

Wednesday 8th July 2020
quotequote all
Braking force is relative. Balance, tyres and suspension all make a difference.

If you can lock up the wheels/tyres (or force abs to activate) then you cannot stop any quicker, no matter what size and types of brakes are fitted.

Then it becomes a cooling issue, and the ability to repeatedly brake to that force. Materials and air flow then become more essential.

More can often become less with brakes.

Is there actually an issue that needs to be addressed ? Or is it more for cosmetic appeal etc?

GreenV8S

30,150 posts

283 months

Wednesday 8th July 2020
quotequote all
ATM said:
Although if the new brake calipers have very different piston sizes to the ones they replaced then you will need to move more fluid to get the same clamping pressure so you can see an argument there for it not changing the forces applied. But personally I dont buy it.
No, there is no argument for anything of the sort.

What there is, is the additional risk of running out of travel at the master cylinder especially if a tandem cylinder is used.

Dave Brand

928 posts

267 months

Thursday 9th July 2020
quotequote all
E-bmw said:
Greater pad area using larger caliper = more friction on the discs and so more braking force.
For all practical purposes pad area is irrelevant. The frictional force acting on the disc is the product of clamping force x coefficient of friction.

Larger calipers will have a bigger piston area, which will increase the clamping force for a given pedal pressure, at the expense of longer pedal movement.

ATM

18,096 posts

218 months

Thursday 9th July 2020
quotequote all
Dave Brand said:
E-bmw said:
Greater pad area using larger caliper = more friction on the discs and so more braking force.
For all practical purposes pad area is irrelevant. The frictional force acting on the disc is the product of clamping force x coefficient of friction.

Larger calipers will have a bigger piston area, which will increase the clamping force for a given pedal pressure, at the expense of longer pedal movement.
Come on Brand

You cant throw the irrelevant word around and not expect some come back. Surely if the pad area was so small as to be the size of a pin head then there would be a lot less friction right? Or is the friction the same but the bigger pad just lasts longer?

stevesingo

4,848 posts

221 months

Thursday 16th July 2020
quotequote all
ATM said:
Sometimes less is more.
IME, true. I changed the brakes on my E30 M3 (286x25.4mm disc). Where most were going for 330x28mm disc with a d50 and having to use a 17" wheel, I went for 315x25.4mm and d46 pad. Less weight in the disc and wheel, no issues with brake performance on track even when using a mild track pad (CL RC5+).

WRT pad area, a pad with less area will have lower volume, so it's ability to absorb heat will be less. This would mean the pad temperature will increase faster than a pad of a larger size leading to the earlier onset of pad related (gassing) fade and higher heat transfer to the fluid via pistons and caliper. Also, if the disc is sized correctly for the pad, the disc will have a smaller area and again, will heat up faster.

If the caliper the OP has identified has the same piston area and can use the same size pad, here should be no discernible difference in performance. The issue then become mounting centres and offset.



Slippydiff

14,742 posts

222 months

Tuesday 28th July 2020
quotequote all
To those that doubt bigger is better, I'd suggest finding a couple of M3 CSL's, one with standard brakes, and the other with the well proven AP 6 pot/365mm front BBK upgrade.

Drive them back to back along here :

https://goo.gl/maps/jYfC5cYeYHBHSZVV7

as quickly as humanely possible with no regard for other road users whatsoever (or alternatively get up very early and drive it when there's no one else on the road) smile

and tell me big brakes aren't better than small brakes ...

Slippydiff

14,742 posts

222 months

Tuesday 28th July 2020
quotequote all
m.barnes said:
Anyone got these? The performance versions (particularly the CP9560)

https://apracing.com/performance-upgrades/performa...

Thinking of upgrading the brakes on my v8 vantage which has the 4pot front calipers. It’s a “cheaper” option than the OE 6 pot brembo and I believe they are a “better” caliper but that’s a grey line.

Anyone using them?
Looked at the more race version too but this is more a road car than a track car just looking at upgrading the calipers as need new discs and pads anyway.

Thanks
I made my recommendations to another PH'er with regards to the Radi Cal 2 calipers here previously :

https://www.pistonheads.com/gassing/topic.asp?h=0&...

Give David at BG a ring, he'll sort you out smile

stevesingo

4,848 posts

221 months

Tuesday 28th July 2020
quotequote all
Slippydiff said:
To those that doubt bigger is better, I'd suggest finding a couple of M3 CSL's, one with standard brakes, and the other with the well proven AP 6 pot/365mm front BBK upgrade.

Drive them back to back along here :

https://goo.gl/maps/jYfC5cYeYHBHSZVV7

as quickly as humanely possible with no regard for other road users whatsoever (or alternatively get up very early and drive it when there's no one else on the road) smile

and tell me big brakes aren't better than small brakes ...
It all depends from where you start. If the starting point is too small, then bigger is better. I'm an advocate of right size, not oversize.

Slippydiff

14,742 posts

222 months

Tuesday 28th July 2020
quotequote all
stevesingo said:
It all depends from where you start. If the starting point is too small, then bigger is better. I'm an advocate of right size, not oversize.
Agreed, but most (and I stress, most) manufacturers specify brake discs/calipers that are commensurate with the performance of the vehicles they manufacture. More often than not, a change of flexible hoses, some decent brake fluid and the fitment of upgraded pad material to such systems will see them suitable for occasional track usage.

However some manufacturers (more often than not the one with the blue and white propeller roundel on the bonnet...) were guilty of specifying brakes that were just plain cheap and fell well short of what could have been expected/should have been fitted, in such instances the customer had every right to be aggrieved.

The E46 M3 CSL & V10 M5/6 were prime examples, the E9X (and thus the 1M Coupe) were similarly hamstrung by questionable OE brakes.

I'm sorry, but cheap sh*t 2 pot cast iron sliding calipers such as these E63 M6 items :



have no place on an 1800kg, 500hp, halo M car. Never did have, and never will. But the fact that they're fashioned from cast iron, only served to exacerbate the heat sink issues.

It took years of criticism before BMW addressed this issue, and whilst the Performance brake upgrade on the F20 3 Series uses large 370mm ventilated, floating (of sorts) front discs, the spangly and large looking four pot front calipers utilise the same pad shape and size as those used in the "standard" single pot sliding calipers ...

The standard E46 M3/CSL brakes were parlous, so I ensured the car I bought (and subsequently ran for 3 years/30K miles) had the AP 6 pot/365mm disc front brake conversion.



Fitted with new discs (PF rather than the AP items) and RS 29 pads, along with the AP 4 pot rear calipers and RS16 pads, they were quite simply the best brakes I've experienced, ever.

Having owned an array of Porsche 996/997 GT2's and 3's (the 997 GT3 had PCCB's) that's quite a bold claim. But I stand by it, as the AP's were staggeringly good.

The confidence they inspired, the sheer power of them AND the ability to modulate them, meant they had no peers from my perspective.

I fitted a similar, slightly larger set up to the front of my 1M (6 pot calipers and 378mm strap drive discs)



The results were quite frankly, mind boggling. The reduction in unsprung weight along with their stopping power, made the OE equipment look like a very unpleasant joke.

Anyone who alleges big brakes are no better than small OE brakes "because the limit of the coefficient of friction betwixt the Tarmac and the tyre is the limiting factor in brake performance" is I'm afraid, rather missing the point.

Rest assured, the first time the steering wheel starts shaking violently in your hands after a couple of high speed stops in a V10 M6, M3 CSL or a 1M Coupe equipped with standard brakes, your confidence in them, never mind the ability to drive the car as its makers intended, will disappear as quickly as a fart in the wind the brake pedal sinks to the floor.

smile





ATM

18,096 posts

218 months

Tuesday 28th July 2020
quotequote all
Slippy

How much of this performance would you say came from the caliper itself. Do you think you would see or feel similar performance from a Brembo or Stoptech caliper with everything else the same?


Slippydiff

14,742 posts

222 months

Tuesday 28th July 2020
quotequote all
Yep, Stoptech, Brembo and Alcon are all much of a muchness. However AP seemed to have found a bit of a sweet spot when it comes to their choice of annulus width (and a competitor who is linked to one of the other three mentioned above, said as much).

I asked him why Porsche use such a wide annulus, to which he replied Porsche have very specific brake tests which are conducted from Vmax, so for example their criteria may be 5 stops back to back from Vmax, with no fade or no more than a 10% increase in pedal pressure. To pass their tests requires the discs to have a huge mass to ensure they have sufficient capacity to cope with the thermal loads created by such harsh testing regime.

Aftermarket manufacturers will have differing criteria for testing their kits.

The downside of the AP’s on my CSL was the front calipers partially seized because they had no primary dust seals, something that wouldn’t be acceptable on a £100K 992 or indeed a £50K 718.

It wasn’t a big deal, I pulled the callipers, pumped the pistons out, cleaned them up, greased them and refitted them with new seals. Good for another 5 years/50K Miles and probably more.

There is cost difference too. A single 996 GT2/3 front 6 pot Brembo will now cost just over £1000 each, whereas the AP RadiCal 2 calipers were waaaaay cheaper when I last checked.

The Wookie

13,909 posts

227 months

Tuesday 28th July 2020
quotequote all
ATM said:
But a brake caliper is a very simple device.
A brake caliper seems like a simple device but getting it right is hard.

There’s more to a brake setup than just caliper stiffness too, it’s only one aspect of a lot of details that add up to a consistent, feelsome pedal without parasitic drag if it’s done right.

That all said, the OP is in for a not inconsiderable or cheap exercise to build a brake kit. On a road car it won’t be worth it unless the brakes really are pants and you’re risking introducing annoying NVH problems like squeal

ATM

18,096 posts

218 months

Tuesday 28th July 2020
quotequote all
There seems to be more people concerned about the dust produced by brakes. I've seen comments from people saying they chose ceramic disc brakes for this reason. I suppose a massive brake kit with a gentle dust free type pad could still produce some stopping power. Personally I don't understand this fascination with trying to keep cars clean. But mine live outside and get used.

The Wookie

13,909 posts

227 months

Tuesday 28th July 2020
quotequote all
Slippydiff said:
The E46 M3 CSL & V10 M5/6 were prime examples, the E9X (and thus the 1M Coupe) were similarly hamstrung by questionable OE brakes.
Good example of a car where the OEM brakes really are pants and worth an upgrade. On my E92 I went from a baggy pedal that would fade and start juddering after a few laps of most track to being able to pound round all day without a hint of fade