Rear Brake Pad Upgrades....

[DaveB@Vagbremtechnic]

What's the rear setup that I should go for? TT?

R32=S3=TT= All the same

[Teutonic_Tamer]

The only real options would seem to be the S3/R32 set up.  That is what I shall be going for.

And perfectly suitable -going much bigger than 310mm on the rear quickly gets you into the realms of diminishing returns.

Any upgrade front and rear must always consider the size of the fairly small master cylinder on the Mk5, theres been a couple of people over on the Mk4 forum who have gone for S4 fronts on a Mk5, the problem being the piston size is bigger.

Eeek - the S4 caliper, whilst being physically identical to the R32/S3 front caliper, has a 60mm dia piston, whereas the R32/S3 is 57mm.  3mm diameter difference doesn't sound much, but it has quite an effect on surface area!

So what size diameter is the Mk5 master cyl - 22mm? 

The 286mm caliper and the 310mm caliper both share the 38mm piston so for all intents and purposes its rearward bias but without all the other baggage that would accompany either a 2 or 4 pot upgrade.

Are you sure on that?  The 286mm rear caliper is 38mm, but according to all the data I have, the 310mm caliper for the S3/R32 uses a 41mm piston!

I drew and fabbed a bracket to use Evo 2 pot rears and compbrake handbrake calipers but quickly realised that the R32/S3 rear setup ticked all the boxes and more importantly wouldn't compromise hydraulically any front upgrades already done.

That's really good to know. 

Ive got a fitting kit for RS4 rears here - but to go from the Mk5 38mm piston to the RS4 43mm piston whilst only 5mm is volumetically a country mile and would drive crap, looked into MC upgrades for the Mk4 with no joy but theres too much parts bin engineering in the Mk5 for there not to be a 25mm+ MC in group that would really open up some serious rear upgrade options.

Tell me more! 

[Tfsi_Mike]

What's the rear setup that I should go for? TT?

R32=S3=Cupra?=TT= All the same

[xxx_mojo_xxx]

What's the rear setup that I should go for? TT?

R32=S3=TT= All the same

OK, that settles it.  Gotta find a R32 rear kit to install.... thanks everyone.

[DaveB@Vagbremtechnic]

@TT

You are indeed correct sir   2 mins on google has found me out! 41mm is the figure!

So.....

R32/S3 Front is 57mm compared to 54mm for the Gti
R32/S3 rear is 41mm compared to 38mm for the Gti

Total surface area of all 4 pistons on the GTi = 6850 mm2
Total surface area of all 4 pistons on the R32/S3 = 7745mm2

A 13% increase on the same (23.8mm)??? master cylinder (confidently assuming 23.8mm as the Gti piston sizes are the same as the Mk4)

So 13% is the figure that we can hydraulically upgrade to and keep an OEM Pedal

TT you aware of any proportioning that goes on front to rear?

So just considering MC upgrades from within the VAG group, you could calculate as a percentage the master cylinder surface area against total piston area which works out for the GTi at 6.5% and for the R32/S3 5.75%. Interestingly enough the S4 with the 60/43mm pistons works out at a middlingish 6% dead with the 25.6mm master cylinder.

So assuming you could reduce that OEM 6% by 13% to 5.22% on the S4 or similar Master Cylinder in much the same way that VW did with the S3/R32 against the Gti it would give you a total piston surface area of approx 9850mm2 which would be handy and would maybe open up the possibility of some 4 pot rear conversions  

So im off to scour EKTA for a master cylinder within group that would suit, I normally try to find the servo/MC seal part number from the unit Im trying to replace and search for that as a starting point - anybody else any other ideas or candidates???

With the ESP sensor being downroute of the MC now Im thinking maybe something like a transporter van, we could also do with somebody with a Mk5 track slag that we could experiment with as opposed to a road car.

Its funny how history repeats itself - sticking a Mk2 Gti MC into a Mk1 Gti was a popular upgrade in the eighties  

E&OE !!!!!!! Somebody for fecks sake check my maths

[Top Cat]

I just did a quick calculation Dave and all your figures above are correct.   

[QD MBE]

I just did a quick calculation Dave and all your figures above are correct.   

I thought so too Tom!
 

[RedRobin]

Interestingly enough the S4 with the 60/43mm pistons works out at a middlingish 6% dead with the 25.6mm master cylinder.

....Was at Brands Hatch today and one of the VW Cup teams was running S4 brakes but ALL the teams I saw were running oem brakes on the rears of the Mk5 GTI.

[DaveB@Vagbremtechnic]

Without locking horns again Robin and covering old ground, track cars no problem, no road ride height, uber stiff suspension.

The adverse dive can be dialed out when there are no other compromises to make

The S4 brakes just look like R32/S3 brakes from the front, you'd need to strip them and measure the piston to be sure...

Unless you asked of course in which case I'll stfu! 

[RedRobin]

Without locking horns again Robin and covering old ground, track cars no problem, no road ride height, uber stiff suspension.

The adverse dive can be dialed out when there are no other compromises to make

The S4 brakes just look like R32/S3 brakes from the front, you'd need to strip them and measure the piston to be sure...

Unless you asked of course in which case I'll stfu!  

....No locking of horns - Just discussion. We don't have to agree about everything.

At least you've now written it in plain English I can understand (re track cars) - The highly detailed tech stuff goes over my head.

No I didn't ask about if they were S4 brakes - I would have felt a bit stupid as they had S4 written on them.

[DaveB@Vagbremtechnic]

Yeh sorry mate, they started putting S4 on them after they went B7. Just done some GT40 fronts onto a B6 S4 and they looked like scruffy R32 unpainted calipers

[xxx_mojo_xxx]

DaveB1970 - good stuff about the master cylinders.  Are they easy to change?  

As I'm looking to upgrade the rear brakes with the ones from the Seat Cupra, I might as well do the master cylinders from the R32.

Are there two separate master cylinders, front and rear?  

Presumably, the Seat's rear brake kit will be a straight fit on the GTi?

Part numbers for all this would be very helpful... Many thanks in advance.

[RedRobin]

....

Back on the subject of rear brake pad upgrades, inspection of mine shows that whereas I wore my front DS2500's almost to the metal there is still loads of pad thickness on my rears, so I shan't be putting new pads on yet.

Any rear end 'twitchiness' I've experienced under harder driving is most definitely the ESP kicking in but I've found that it's best to ignore and drive through it, taking it on board as feedback information.

[Hurdy]

If there is so much difference with the pad wear, do you think that you could get VWR or JKM to alter the brake bias to give more bite at the rear?

[RedRobin]

If there is so much difference with the pad wear, do you think that you could get VWR or JKM to alter the brake bias to give more bite at the rear?

....Is this done via software? If so, then Keith at JKM would be best to do it.