Rear Brake Pad Upgrades....

[RedRobin]

....

I have it on good authority (AP Racing) that the Golf GTI does about 85% of its braking on the front wheels and consequently most big brake upgrades are front kits. For normal road use it's considered fine to leave the rear brakes as oem, but for trackday use it's advisable to at least upgrade your rear pads. If you don't, you may experience fade on them quite quickly and without fully realising.

Many of us have front brake kits using the ubiquitous Ferodo DS2500 pad and so a DS2500 pad is wanted to fit the oem rear brake calipers. My initial attempts to source some discovered that they don't appear to be listed as such for the Mk5 GTI but with Kate's help at JKM I found that their Ferodo part# is FCP1636 (she wanted some for her car too).

Unless you want it as eye-candy you don't really need to change the rear discs on the Mk5 GTI to something grooved and/or drilled - For the 15% work they do the plain discs are quite sufficient.

If anyone needs some rear DS2500's I recommend contacting JKM - 023 9263 9933 - They supply at the best prices for Ferodo products and can supply quickly.

HTH

[Poppa Dom]

Top man - thanks for this Robin!

[Hurdy]

Spot on Robin

Still considering rear TAR-OX grooved discs for the ED30 beastie, but this could be a quick fix for now

[gillm]

never had a problem with them on track and don't really see the point . braided hoses will help tho

[RedRobin]

Spot on Robin

Still considering rear TAR-OX grooved discs for the ED30 beastie, but this could be a quick fix for now

....I nearly added something in my original post to cover the likes of your goodself who have modified cars somewhat beyond most others. Especially with the power you're going to be having 'a la Garrett', methinks you'll need some big rear stoppers even if only ~15%.

Am I right in thinking that any increase in rear braking capability will keep the ESP more at bay?

[RedRobin]

never had a problem with them on track and don't really see the point . braided hoses will help tho

....Weeeell, I'm inclined to take AP Racing's advice.

Perhaps adding braided hoses to the rear may also help but I won't bother with that until my next brake fluid change and also until speaking with AP and VWR again.

[Hurdy]

never had a problem with them on track and don't really see the point . braided hoses will help tho

....Weeeell, I'm inclined to take AP Racing's advice.

Perhaps adding braided hoses to the rear may also help but I won't bother with that until my next brake fluid change and also until speaking with AP and VWR again.

I remember asking T_T (Sean) about braided hoses in the past. He said that the OEM hoses are banded internally anyway and that they are more than up to the job.

[DaveB@Vagbremtechnic]

I'd be very surprised if the bias figure was 85/15, the figure for the Mk4 was calculated at 74/26 and with the Mk5 Gti having 286 rear discs as opposed to 256's then the bias would probably be rearward from the Mk4

This despite the fact that the MK5's front piston is 1.5mm bigger on radius than the Mk1 TT/Mk4 setup, same rear piston, same MC

if the number was 85/15 then the car would feel absolutely awful to drive with excessive wear put on the front suspension to alleviate the massive dive that it would generate.

Whilst I appreciate the advice came from AP (who sell brakes...front brakes.....) I would be sceptical that its actualy that bad in reality, sometimes generic flippant remarks come out with no real substance......

Now having said all that if that figure arrived from a conversation that took into account disc size, piston surface area,pad surface area, master cylinder piston stroke and surface area, pad material and piston rollback measurements then I stand to be corrected and please accept my apologies

If the bias was indeed as bad as that the first thing on my shopping list would be a huge rear brake kit IMHO

Braking is about balance - 85/15 sound right to you???

[RedRobin]

^^^^
@ DaveB,

My AP Big Brake Kit was fitted by their Senior Engineer at Coventry with myself present. At that time in 2006, I asked him whether he thought it was worth also fitting their AP brakes to the rear and he said no, saying that about 85% of braking on the Mk5 Golf was done by the front brakes and the power of the front AP's would 'do the job'.

The 85% value has been mentioned by him again since 2006 in our conversations and also yesterday when I specifically asked for his advice about what would be best to do now that I occasionally track (Nurburgring).

Now, it is of course possible that his use of the term "85%" is more to emphasise that the rear brakes do relatively little. "85%" possibly over emphasising? But "flippant"? - I very much doubt it. In our chat yesterday he also made the comment that the oem rears on the GTI were more designed for 'street' stopping as opposed to a workout on The Ring.

AP Racing (once known as Lockheed) do far more than sell brakes - They design and test brakes and clutches for car manufacturers (they are an autonomous arm of Brembo), F1 (first 9 of the finishers at Spa last weekend), and NASCAR etc etc. When I first visited them they were 24/7 bench testing calipers for the Bugatti Veyron for example.

Now having said all that if that figure arrived from a conversation that took into account disc size, piston surface area,pad surface area, master cylinder piston stroke and surface area, pad material and piston rollback measurements then I stand to be corrected and please accept my apologies.

....I'm confident that his knowledge as AP's Senior Engineer will have taken such technical factors into account.

The question is whether his "85%" comment is to be taken literally or as emphasis - I would have to ask him when we next speak.

[RedRobin]

R32's have vented 312mm discs on rear which are larger than a standard GTI fronts!

Also it's a cheap oem upgrade (I gave £280 for a complete F&R setup).

I think the rear pads are the same also, just the caliper carrier is moved out in comparison to accomodate the larger disc size.

....Do you know how much R32 312mm discs weigh?

Are you saying you bought a new set of front and rear R32 brakes for £280?

One of the reasons for upgrading the pads to DS2500's on oem GTI rears is to reduce generated heat and its ramifications.

[Hurdy]

Dave also knows his stuff Robin

This could be a good thread to look in on as some decent technical info could come out of it

[RedRobin]

Dave also knows his stuff Robin

....So I'm told.

I'm just piggy-in-the-middle trying to help people (and myself) by posting and sharing information which can only ever be to the best of my knowledge.

T_T Sean knows his stuff too, but all these experts don't always agree - Brake fluid for example.

The bottom line for me is that I run AP Racing front brakes and I'd be a fool not to take their advice about brake related subjects on my car, especially considering their indisputable experience and reputation. The AP kit I run has been designed by them for Performance Road as opposed to eyeballs-out Competition.

[QD MBE]

R32's have vented 312mm discs on rear which are larger than a standard GTI fronts!

Also it's a cheap oem upgrade (I gave £280 for a complete F&R setup).

I think the rear pads are the same also, just the caliper carrier is moved out in comparison to accomodate the larger disc size.

....Do you know how much R32 312mm discs weigh?

Are you saying you bought a new set of front and rear R32 brakes for £280?

One of the reasons for upgrading the pads to DS2500's on oem GTI rears is to reduce generated heat and its ramifications.

More friction = More heat?

Since i fitted my S3 rears the car is a joy to drive, the car feels balanced under braking, and the rear never gets "tail happy" under braking.  

i was asked by an independent engineer as to what brakes I have fitted, he was impressed by the overall feel of the car, and he has the pick of any braking system, being in the 'race preparation' enviroiment.

I therefore rate the S3 rears was the 2nd best mod behind fitting my RNS510.  

This is my opinion, and I would do the same again.

[DaveB@Vagbremtechnic]

^^^^

Now, it is of course possible that his use of the term "85%" is more to emphasise that the rear brakes do relatively little. "85%" possibly over emphasising? But "flippant"? - I very much doubt it. In our chat yesterday he also made the comment that the oem rears on the GTI were more designed for 'street' stopping as opposed to a workout on The Ring.

Now having said all that if that figure arrived from a conversation that took into account disc size, piston surface area,pad surface area, master cylinder piston stroke and surface area, pad material and piston rollback measurements then I stand to be corrected and please accept my apologies.

....I'm confident that his knowledge as AP's Senior Engineer will have taken such technical factors into account.

The question is whether his "85%" comment is to be taken literally or as emphasis - I would have to ask him when we next speak.

robin 85/15 would drive crap and thats the sort of split I would expect from a ford fiesta with rear drums.....

emphasis/flippant - tomayto/tomarto - its not 85/15 maybe it would be worthwhile asking your senior engineer mate to clarify.

Front end dive is not a good trait - wherever possible 60/40's /////  70/30 is the figure normally aspired to (depending on configuration) , mid engined cars can have 50/50 - I've had many pairs of  Ferrari 360 calipers the psiton sizes are the same at 38/42 front and rear, discs sizes are 330mm front and rear, Audi R8 rears are big at 38/42 as examples

The rears should be encouraged to share the load, redistribute the forward energy in to heat front and rear if you're brakes are really 85/15 then you should get it sorted you'll be amazed at what it'll do for your lap times.

I do a 300mm S4 conversion for 4WD mk4's which upgrade them from 256mm - we've had tangible positive results reported at the first stop, trackers and ringers also reported flatter braking, less weight transfer and better turn in and into corner confidence.

I think the 310mm R32 rears are a worthy upgrade, for a given (similar) pad area and piston size.... in easy terms its the difference between trying to move the rear ABS locking wheel with a ratchet as opposed to a breaker bar. If the rear ABS is kicking in then you need a bigger disc - think about it

One of the reasons for upgrading the pads to DS2500's on oem GTI rears is to reduce generated heat and its ramifications.

The pads reason d'etre is to deal with the heat generated - they dont reduce or increase the amount of heat generated you adjust that by hard you press and for how long, the generation of heat is a positive thing..... its how your setup deals with that through cooling, materials that gives you a good installation. As you probably know pads are classified by their reccomended operating ranges.

heat is a good thing - no heat no stopping the energy has to go somewhere!

Dont know whether its an installation issue but the 2500 compund has been getting a bit of a slating recently over on uk-mkivs, the pad of choice over there at the moment seems to be the pagid blues

Just my £0.02

[RedRobin]

....

My understanding is that the DS2500 pad performs better than the oem pad regarding whatever heat generation there is or isn't.

So, stokey, tell us more about your S3 rear brakes - Disc size, pads used, weight, any pics?