jasonius

iTrader: (1)

About to fit some AP 4 pots to the front of my 05 WRX and have been told conflicting information (from people in the know ) regarding the need for uprating the rear pads (oem brakes).

Some say the AP's at the front will be more efficient so the rears have less work to do, whilst others say the rears will be required to 'keep up' with the fronts, therefore working harder and so requiring uprated pads..!!??

Following on from this I've read posts where people have reported overheating rear std pads, when doing track work, with 'big brake' fronts. This obviously seems to confirming the upgrade school of thought.

Before anyone directs me to it, I've read the Stoptech guides through and through so please don't point me there..

I'd like technical reasons only for the different theories, or at the very least personal experience..

Thanks in advance,
J

finchyboy

I run 330mm ap 6 pots on my 05 wrx with bog standard rears no problem's at all. For what it's worth a friend of mine is a very quick tarmac rally driver he runs ap for pots with ferodo ds3000 pads but cheap motor factor rear pads on his Mark 2 escort rally car!

My opinion is that they don't do much work and uprated pads will give a minimal improvement in braking performance

MaDaSS

You know all about my setup jasonius, and i too run standard rear pads. I did think about uprated ones a few months back when they were due a change, but never bothered after asking advice myself.
It is 'horses for courses' though. My driving does not need anything else! lol.

WRX_Rich

iTrader: (5)

i was running std rears with ap 6 pots

hard braking from high speeds ( 100 + ) the rear end seemed to go light, this could be something to do wth the stuidly heavy audio system i have

I ve swapped to a better pad and braided hoses - will let you know if it changes anything

terryb

I would suggest uprating the rear pads, in order to maintain the brake balance, otherwise the front brakes could overheat, resulting in reduced pad and disc life on your expensive APs.

Speak to Alyn at AS Performance - he will advse you on a suitable uprated rear pad.

jasonius

iTrader: (1)

Just what I've been finding, a tale of two opinions..

172sport

iTrader: (6)

Never had any issues with std rears myself.

stockcar

like all things it depends on your exact use and how you drive or braking style....................
personally i find that most tubo's are underbraked on the rear even as std, and its a no brainer for us to uprate the rears to help maintain a flatter more stable platform under extreme use

alyn

Tazz Kill Er

Just taking pad compound into consideration for a moment, if the coefficient of friction is higher on the front as opposed to std, then the same pedal pressure will cause the car to stop faster, this usually is not a problem unless on the road when you would not use the same pedal pressure and less pedal pressure is required, this means the rears can be doing less work, unless you have a brake bais adjuster installed.

When giving it the berries as it were, you would use more pedal pressure and this would involve a higher pressure on both front and rear pads, this can lead to the rears overheating though not usually enough to cause major problems.

Performance brakes tend to have a harder pad compound and do not compress as much as std, this means that you have to press the pedal harder to effect the same braking forces, this means front and rear pressure goes up which causes the rears to heat up more.

Bigger brakes use a better leverage ratio to stop the car and have more material to aid in heat dissipation. This can again increase pressure on the rears when you start to use them harder, as you increase braking forces on the front and the pressure on the rear goes up accordingly.

So far in my car experience as the braking forces are shared, the rears usually need better cooling or an increase in pad compound to compensate the increase in front braking efficiency.

There are so many variables in a braking system to be taken into account, wether your pads use cohesive braking forces or friction braking forces or even a mix of both, then performance at different pad/disc temperatures.

Puff The Magic Wagon!

iTrader: (2)

Brembo/AP set up on PTMW! and I would do a set of fronts in 1 to 1.5 track days compared to 5 or 6 track days on the rear.

Braided hoses all round.

Contemplating u/grading the rears to STi Brembos & fitting a bias bar.


Interestingly on my XC70, I have only just replaced the rear pads at dealers suggestion, at 108,000 miles. To do the job properly, I replaced the discs too.

I then went to change the fronts to Brembo discs and DS2500s as a sort of minor upgrade and on the basis they surely must need the change after all those miles, to find that I had 60% left on the pads and less than 1mm lip on the discs

These were the original fit ones!! But its interesting that on the XC the rears wear faster than the fronts (by some margin!),

Mother Theresa

My OEM rear pads were trashed after a track day, they didn't even take the rust off the discs any more. The obvious solution was to get better pads for the rears.

MaDaSS

There, i think we have it then!
For road cars only, ie me, then uprated fronts and standard rears are ok.
For most ppl who do track days then uprated rears too must make sense.
And apart from that, if i ever wear out my rear pads again, i will uprate em.
LOL.

Aztec Performance Ltd

iTrader: (234)

Having uprated fronts and std pads rear can cause brakes to overheat.

Butty

iTrader: (2)

I had the Prodrive set up and braided hose all round on my 04 wagon.
Whne the Prodrives were fitted, the rear used to go light and move around quite a bit under heavy braking. It was eased with uprated pads but I still had an ongoing problem with the front ABS triggering on rippled surfaces.

I always thought that the back needed more bias to help out but never got around to sorting it.

Nick

jasonius

iTrader: (1)

^^^^

This is an interesting point, if you have the PD/alcon big brake kit fitted by a main stealer they don't recommend a rear pad upgrade..!

Where/how do these bias valves fit and I presume they're compatible with the ABS system..?

Good feedback BTW..

WRX_Rich

iTrader: (5)

Just what mine does !!!

Hoppy

This is not a simple subject. Speak to Alyn about your particular circumstances for good advice.

Suspension has a lot to do with front/rear bias when you fit big front brakes. Knackered old suspension will nose-dive more, the rears will be practically air-born, and you'll be driving a snake. The last thing you want is the ABS being triggered by the rears. You'll die.

In my view, uprated front brakes also means up-rated suspension and up-rated rears. You can achive a lot with front/rear bias by carefully mixing pad compounds. I know some people who have fiddled with the front/rear bias valve but I'm not sure the results have been dramatically better and the potential for a major **** up is huge. Heaven help you if you have a big off and the insurance company finds out about it

Richard.

jasonius

iTrader: (1)

Very true, hadn't thought about that..!

Hopefully the fact that my WRX has the full T25 suspension setup should help, as I won't be too happy if the AP's start producing premature ABS application..!

I'll see how they go and get a set of uprated rear pads if it seems skittish.

Once again, thanks for the input guys..


BTW does this thing about the ABS kicking in with uprated fronts only effect WRX's and not STi's..?

Hoppy

All ABS systems kick in when they detect a wheel locking. Of course all cars are different (tyres, suspension etc) and all driving circumstances different.

Not sure exactly what systems are fitted to which Imprezas, but I think the Classics are three-way, ie the fronts operate indpendently, but if one of the rears detects lock-up both rears are moderated together. Newer models may be different but what you do not want is the ABS at the rear kicking in before the fronts - you'll never bl00dy stop! Well, you will when you hit the ditch

Richard.

PS Would be really interested to know how Impreza ABS works on which wheels, and when. Never got a conclusive answer, even from my main dealer's chief mechanic!!!

Butty

iTrader: (2)

Yes - I've now got a Spec D and drive the same roads that used to cause the 04 WRX problems, but the Brembos are fine.
I seem to remember that the STi ABS system is called a "supersport" version.
I've no idea how this differs from the WRX type.

Nick

jasonius

iTrader: (1)

It would be interesting to have Mike Wood comment on this..

Anyone fancy sending him PM..?

jasonius

iTrader: (1)

When did Subaru introduce EBD (electronic brake distribution) to the Impreza..?

I'm wondering/hoping that this may help the front/rear brake balance.

So those of you who've experienced this problem of premature ABS function after fitting big brakes to a WRX know if your MY had EBD..?

MaDaSS

The only time i get the ABS on with my StopTech's is when the pads are glazed over with my normal boring driving. Once i start using them in anger and get rid of the glazed pads then i very rarely get any ABS action at all. I have to say the StopTech's seem to be very good for this. Apart from sh@t roads when you brake they are good.

Hoppy

That doesn't make sense Mad. Should be the other way around

jasonius

iTrader: (1)

So does anyone know when EBD was introduced..?

The Mad Doc

Just of interest, reading this thread reminded me of a recent experience of mine. I ordered a new set of discs front and back from EBC and wanted new pads as well. Initially I thought of having Yellowstuff on the front and Redstuff on the rear given that they would wear less. The guys at EBC wouldn't let me mix compunds as the friction coefficients were different so I had to get Yellowstuff all round! Is this a common phenomenon?

WRX_Rich

iTrader: (5)

had a good test of this today

IMHO don't fit big brake kits to new age wrx's with out coil overs

i was never truley happy with the way the car felt under heavy braking after the AP's went on, yes they never faded and this was a problem with the std 4pots but with it came a really un easy feeling under heavy braking, as the car was mainly used on the road i put up and shut up thinking it was the way it was supposed to be.

recently I upgraded the rear pads and hoses but it made very little difference ( to be honest i didn't notice it )

just had the car back after a set of exe tc coil overs, not used it all to much but can say the car feels stunning and no abs what so ever

sad fact is subaru balance the car out to feel good out of the shop you can't go changing one major componet with out the other or it becomes un balanced

for sure im no Damon Hill but i know what feels right and what gives you confidence and im sure thats what 99% of us are wanting

car feels so good now

a happy man

jasonius

iTrader: (1)

Glad to hear this mate..

Having the full T25 setup (AST's etc) I'm hoping there shouldn't be any ABS/balance issues..

jasonius

iTrader: (1)

Well had AP's fitted at weekend and they're just about bedded in.

All I can say is OH YES..!!!

Even with all the 'other' stuff I've done to this car these have to probably be the best (even though they're the most expensive) mod I've done..!

With regards to the balance, I've given them the 85% required to bed in with no sign of any premature ABS..

What I have noticed is the rear disc is now shiny, where it always used to be tarnished looking, regardless of how hard I'd been hitting the brakes..!

The only slight problem it there's a faint "shussh-shussh-shussh" from the O/S front when they're really hot that I think is the dust shield. Just need to prise it back a little more.

I finally feel that I've got a really well balanced package, lol only taken 2.5 years..! It's a pity they don;t come from the factory like this, then again the car would have cost me a lot more than it has..

MOT next and that's going to be a bit of a PITA given it's a full decat..

jasonius

iTrader: (1)

Just to update this discussion for future reference..

After recently fitting new disc's (ASP 8 groove and PF 097 pads) to the otherwise std rear (braided hoses only) on my AP fronted 05 WRX, I can now say with some confidence that improving the rear in some way certainly helps keep the car flatter during hard/high speed braking.. Reduces that feeling of the rear going light/skittish..

I can now actually see evidence of the rears doing something lol, disc/pad contact marks, especially when giving them a hard time. Only downside, lol, the rears now get as dirty as the fronts..

One other thing, the 'tish tish tish' noise I was getting on my AP's was down to the caliper-disc clearance not being enough. When they got very hot heat expansion increased the effective diameter of the disc and the outer surface rubbed on the pad spring plate. AP themselves (not original fitters) kindly re shimmed/spaced the calipers and that sorted it. Although I still get it a little if the car isn't used for a while and rust builds up on the outer rim, again effectively increasing the diameter of the disc. A few mins with a hammer, gently tapping the outer edge of the disc soon 'flakes' this off and normal service is resumed..

Note: this is an issue that can arise with the AP 4pot CP5200 caliper family only. The 6 pots have a different design and therefore clearance isn't an issue..

Might be the simple answer for some people who think the discs are warped, as when the rust gets bad enough you do also get some vibration..! Worth a try imho..