The AP Racing big brake kit?

[steve b]

Does anyone have any experience with it?  Lots of cash but thinking it maybe a worthwhile upgrade as i'm a trackday regular.  Should also weigh a fair bit less than standard, my old AP 4 pots on my VX were feather light..

Is it definate you need to go to 16" wheels?

[Wabbitkilla]

It's been debated a few times whether the big brake kits are worth anything on the MR2.
The standard brakes, in good condition, are excellent and can be improved with braided brake lines and decent fluid.

It's normal to need bigger wheels to fit big brake kits ... because the brakes are bigger than standard (go figure).
If you're hung up on Big Brakes, have a look as the KSport packages too  m http://www.ksport.co.uk/order.asp?id=344&loc=2 m  they're a bit different and give you options for different sized wheels. Worth calling them for a chat as the guys are very experienced and happy to help.

What bugs me mainly about BB kits is that it's fine replacing the fronts, but really to balance the car you need to replace all four, and it's nigh on impossible to get rears with MOT approved mechanical handbrakes. Unless you want to get some fabricated that is ... then you're talking money.

[steve b]

Yes the stock brakes are good with carbotech pads which do seem to be lasting ok, the APs should drop quite a bit of weight from an important area as well as giving a bit better modulation I'd hope.  Opens up a much wider range of reasonably priced good pads as well.


I don't think the balance will be that much altered as long as high friction pads are used on the rear.  I tested this theory by running carbotech pads front only for a trackday then the next day fitted the rears, braking was slightly more stable but not dramatic.  Standard to carbotech on the front made a huge difference.

[steve b]

Not heard of K sport are they just bling rather than a quality proven brake?  £1000 cheaper than the APs...

[dj2k21]

K sport are very good, there suspension kits a excellent and basically the same as BC racing stuff iirc?

[dj2k21]

Also I have a D2 8pot conversion on my mr2 and it's brilliant

[Steve Green]

It's been debated a few times whether the big brake kits are worth anything on the MR2.
The standard brakes, in good condition, are excellent and can be improved with braided brake lines and decent fluid.

It's normal to need bigger wheels to fit big brake kits ... because the brakes are bigger than standard (go figure).
If you're hung up on Big Brakes, have a look as the KSport packages too  m http://www.ksport.co.uk/order.asp?id=344&loc=2 m  they're a bit different and give you options for different sized wheels. Worth calling them for a chat as the guys are very experienced and happy to help.

What bugs me mainly about BB kits is that it's fine replacing the fronts, but really to balance the car you need to replace all four, and it's nigh on impossible to get rears with MOT approved mechanical handbrakes. Unless you want to get some fabricated that is ... then you're talking money.

+1
Bear in mind that most braking is carried out by friction between tyre and road, and the greatest braking effort happens just before the wheels stop turning, Thats why ABS works! Bigger brakes will not change any of that.

The job of the brake pad/disc is to convert rotating enregy into heat, and that is largely based on inertia or the weight of the car, speed has a reducing factor (because you are slowing down). To put it into persepective the Mondeo repmobile has the same size front disk as a Mk3 but the weight of the car, not to mention the weight distribution is entirely different.

Bigger brakes may dissapapate heat a little quicker but if they fill the wheel, there will be less air getting to them.

IMHO Big brake kits have a bling factor, and thats about it. A good set of rubber on the road and well maintained calipers, with braided lines and perhaps better pads will pay dividends.

To reinforce something said above, its the balance between front and rear that needs to be right to cope with the weight transfer. MR2 Mk3 discs are larger at the rear (263mm) than the front (255mm) unlike just about every front engined car!

Don't play with brakes unless you really know what you are doing.

Spend your money on rubber on the road, not bling.

[Jubal]

One of my previous cars was an MR2 Mk2 Turbo. The previous owner was a well respected community member who had modded it nicely for track work but the brakes were a disaster.

It may not compare exactly but bigger brakes at the front had ruined the rears causing them to lock up early. It was a combination of weight transfer and brake bias. Going into corners backwards was no fun at all. I chased a cure for ages without success and then blew the engine!

Anyway, lesson learnt so I've stayed standard with just track fluid and pads on the Mk3. Much, much better unless you are chasing the last tenth on track.

My old car has shown up on PH at 16k having had 30k poured into it to go racing in Super GT!

 m http://mobile.pistonheads.com/sales/4105929.htm m

[steve b]

Also I have a D2 8pot conversion on my mr2 and it's brilliant

You've not experience any issue with them as others have alluded to?

Must say my Elise / VX220 experience doesn't follow the problems mention in the thread.  Lotus track pack includes an AP 4 pot upgrade and larger discs for example at the front no change to the rear.

I also went big AP discs and calliper spaced back on my VX220 up front and that was perfect.

[Wabbitkilla]

I'm sure everyone's experience is going to be different regarding bb kits. Thu I would like better calipers with opposed pistons if I wanted to spend the money, but I find my brakes are great and the cost for fabrication prohibitive.

I just think that you should really balance front big brakes with rear big brakes. But then I'm a person who likes balance.

sent from a planet somewhere nearby

[MattPerformance]

I just think that you should really balance front big brakes with rear big brakes. But then I'm a person who likes balance.

I agree.  I did that on my old car and the results were epic. (AP 4-pots front, AP 2-pots rear)

[dj2k21]

I've not experienced any issues at all with my brakes, my friend has stop techs on his civic and they are apparently self bias balancing, not sure how that works though

[steve b]

So the person with direct experience of a front brake upgrade says the setup works well, those without say it'll cause problems :-/

The mk3 is very similar in many ways to a late S2 Elise, only a little bit heavier.  The Elise has 288mm discs all round single pot rears like ours but AP 2 or 4 pots up front and regularly bigger discs 295 or 304 being the most popular put on the front.  My upgrade to 295mm was one of the best upgrades I did with the VX, I ran Exige wheels with 195 tyres instead of the skinny less track focused Elise setup, the MR2 I'm running AD08 205's on the front.  Mirroring the way the Lotus setup goes and using it as a guide, it'd appear for a more track focused car the MR2 is a bit under braked.   I've taken the MR2 on track every month i've had it running (6) now, so I'm not thinking of a brake upgrade for bling reasons.  Car is running over 190bhp as well so I'm arriving at bends faster than a standard engined car is likely to as well.

Anyone else got a kit fitted?  It appears K-sport use AP's discs from 304 upwards, 304 AP kit requires 16" wheels so presumably the smallest K-sport would fit under 15".

[Wabbitkilla]

I think you're taking us a bit too seriously there, we're only questioning its effectiveness and whether it upsets the balance of the car.
It's always subjective as we all have different driving styles, I only suggested the K-Sports as an alternative that might offer you more options and the possibility of keeping standard wheel sizes. If you do it, then please let us know how you get on and how it all behaves afterwards.

[steve b]

I think you're taking us a bit too seriously there, we're only questioning its effectiveness and whether it upsets the balance of the car.
It's always subjective as we all have different driving styles, I only suggested the K-Sports as an alternative that might offer you more options and the possibility of keeping standard wheel sizes. If you do it, then please let us know how you get on and how it all behaves afterwards.

Oh it is appreciated  :-) :-) :-)

I'd never heard of K sport before and so trying to find out more info, I have been in touch with them.  Kits have changed and their website out if date.  Now only the 356mm kit uses AP spec discs, that I agree is too big.  My worry is that if they are in house discs supply may not be great in the future.  So waiting to see if they use Alcon sizes now ..

The much cheaper cost of the k-sports does appeal.  In regular AP / Alcon sizes 304mm would be the biggest I'd go, 295 would probably be idea and is cheaper as a popular size.

[Steve Green]

One thing not mentioned yet is the volume of the master cylinder relative to the various slaves.
Not a massive issue as the brake pads don't move very far but it could have an effect on pedal travel and feel.

[Wabbitkilla]

One thing not mentioned yet is the volume of the master cylinder relative to the various slaves.
Not a massive issue as the brake pads don't move very far but it could have an effect on pedal travel and feel.

The difference is probably very marginal tbh, there is a fair amount of room for changes when you consider how oem flexi pipes end up expanding under pressure.
I quite liked Matts setup of Elise brakes on the MR2, something I would consider if it were the right price.

[MattPerformance]

I found the brake pedal feel massively improved with the race calipers - with stock brakes the pedal is spongy, even with braided hoses the flex is transferred to the bulkhead, whereas with the big calipers you don't push the pedal so hard so there is no flex and the feel is really good.

My car had 304 front and 288 rear which was a really balanced set-up on track IMO, and because of the twin pot rears meant there was considerably more braking effort at the rear than there would have been with stock calipers/ discs at the back.  My suspension was mega hard which will have had a significant impact on weight transfer.

I think it's fair to say that no-one knows the answer to your question.  One person has big brakes on the front (road car) and says it's great.  One person had big brakes on front and back (track) and says it's great (well, epic actually).  The only drawbacks for me were the cost of the AP rotors and the extra cost of converting the handbrake to hydraulic for the rear upgrade.  The new project will be following a similar formula but it's still a few months away...

[markiii]

and still the control tower?


sorry couldn't resist   s:D s:D

[MattPerformance]

Let's just say that many lessons have been learned from the "old" car  s:wink: :wink: s:wink:

[steve b]

K Sport 286mm 6 pot kit with Pagid RS4-2 pads turned up today  :-) :-) :-)

Looks all well put together very comprehensive kits calipers look massive, weigh in at 2010g each how does that compare to stock steel calipers?

Will weigh everything when I do the swap  :-) :-) :-)

[dj2k21]

Great news. Did u go for a rear kit too? Thats on the cards for me when the wider rims go on the back I think

[Mark A]

Taken from 22b forum, posted by John Felstead who's business prepares and manages racing cars. interesting reading.

Key to brakes is getting the disk bulk temperature into the working range of the disk material and pad material, and keeping it there, plus keeping the caliper and fluid in it's working range. Correct disk Bulk temperature and pad temperature is something not easy to achieve on a road or sprint car, far easier to achieve on a race car. Outside the working range (both too hot and too cold) you get much higher disk and pad wear rates, ignoring the issues with coeficiant of friction changes as the disks and pads heat up.

With regards to the K sports, you may have 8 pots, but the surface area of those 8 pots is almost identical to the WRX 4 pot and less than OEM Brembo's. The K sports have two small leading pistons working on the area of the pad that provides the main performance of the pad, which will give less bite from the pad than the larger leading 4 pot piston. You will get a better performance from a 6 pot caliper with properly stepped diferential pistons. The equivilent D2 6 pot caliper has larger piston surface area and a larger leading piston than the 8 pot K sport, so gives better initial bite and more brake force for the same pedal pressure.

AP 6 pots have better differential piston sizing than both the K sport and D2, with 3 piston sizes in use to ensure the pressure on the pad is well matched to the requirement to provide less taper wear and give a better match to the required pressure increase as you move away from the leading edge of the pad, which is where all the work occurs. The D2 6 pot has 2 small and 4 large pistons per caliper, so the pressure required is less well distributed than the AP, but not too far away, the K sport has 4 small and 4 large pistons per caliper, which gives a less even pressure match accross the pad length. This means the AP will give the better brake feel and modultion, with the D2 6 pot next, the K sport a bit further away.

With regards to piston surface area, pad surface and the total brake torque resulting from that, on a 330mm disk the D2 6 pot gives the most total brake torque, K sport next and then the AP 6 pot last. None of these give as much brake torque as a Brembo OEM caliper on a stock newage disk. Even a 356mm AP 6 pot kit gives less brake torque than an OEM Brembo setup. Where the AP, D2 and K sport win is in handling the elevated temperatures seen on track.

There are differences throughout the Subaru range with regards to the master cylinder bore size, and also pedal ratio, this will also influence the amount of force required at the pedal to give the required brake force. So a brake kit on a classic will work differently on a Newage STi, Newage WRX or Legacy. And we havn't touched on brake balance matching for the rears, or the way the ABS system will work when you change that balance.

[steve b]

I worked out the pad sizes and areas and posted them in another thread, the K sport 6 pot uses the identical pad to the AP 4 pot, it's a fair bit bigger than a stock pad.

I have the standard rear caliper and Carbotech pads, will see how I get on with them.

I will post some up close photos in the next few days and then when I fit them although that will be in about 10 days time as the cars going away to have its T45 rear cage put in tomorrow  :-) :-) :-)


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[dj2k21]

Im thinking of ordering the rear d2 kit for a honda civic as they are 4 x 100 also and just modifying to suit. That way I keep d2 all round pkus their rebuild kits and pads are supplied by a p racing anyways so they are basically a cheap ap kit as far I can tell