The definitive 312mm brakes onto a VR thread

[Henny 0]

why bother with larger rear brakes when you still have the automatic brake bias compensator on there? I'd have thought that you're just likely to mess up the brake bias causing the rears to lock up under heavy braking if you upsize the rear disks without adjusting the rear bias accurately... :|

[Taggart 0]

I thought it might be a bit of a stupid question! :D, thought I'd ask anyways.

 

cheers

[Kevin Bacon 5]

why bother with larger rear brakes when you still have the automatic brake bias compensator on there? I'd have thought that you're just likely to mess up the brake bias causing the rears to lock up under heavy braking if you upsize the rear disks without adjusting the rear bias accurately... :|

 

IMO uprating the WHOLE braking package is a must when modding a car, not just the fronts.

 

Compensator issue or not, it still doesn't solve the problem that the A2/A3 rear brakes are utterly shite and always have been. Uprating just the front brakes and not the rears can cause the rears to go light aswell....but ABS will stop them locking.

 

VW felt the 239 setup was pants and duly fitted the much better 256 setup and I agree with them. It's all OE stock parts and fits, so what's the problem?

[Henny 0]

so will you be fitting the MKIV brake compensator too to make sure all the biases (is that the correct word, or is it biasi or biasus?!? :lol: ) stay matched then?

 

I know all about getting the rears to lock due to uprated fronts and no ABS, that's how I flat spotted the rear tyres during my accident in J-DUB! :oops:

 

I agree that the rear A2/A3 brakes are crap, I was just wondering if putting bigger rears on wasn't going to cause as many problems with braking bias as it'll sort out the with the rear brakes? :?

 

p.s. these are genuine questions 'cos I'm interested, not me being arsey and thinking I'm right... I'm genuinely not sure about any problems this may/may not cause 8)

[Kevin Bacon 5]

Sorry mate, I wasn't trying to be arsey either, I suppose it can come across that way sometimes, LOL!

 

Nah, no need for the MK4 bias valve.... in fact I don't think they even use them! The ABS pump, IIRC, takes care of pressure regulation, Mr Renshaw will know as he has all MK4 stuff on his.

 

My aim is to get more initial bite from the rear brakes with what fluid pressure they're given from the compensator. Sure the rears will go light, often, but that's the nature of the beast. But what I have found since fitting the MK4 callies and discs etc is the rears do have a profound effect on overall braking....and obviously a proper handbrake would be nice too.

 

But that aside, it's just a nicer setup anyway as it's a proper hub and you don't have to feck about with bearings every time you change the discs.

[dinkus 10]

I was under the impression that bigger front brakes meant that more weight is transferred forwards, so the rear brakes actually do less. So if you uprate the rear disk sizes, you're going to end up locking the rear wheels much sooner.

 

I would suspect that the reason VW uprated the rear disk sizes (when did they do this? For the Mk4?) was because the cars weighed more, thus you could safely apply more rear braking power.

 

Of course, it's a completely different kettle of fish if the car is RWD and I'm just speculating - if anyone can provide a concrete answer it would be good :)

[Kevin Bacon 5]

That is true Dinks. You don't need bigger rear brakes, I just want bigger rear brakes :-)

 

VW fitted the vented setup at the rear because the 239 setup was ancient. It's not a weight thing as MK4 Golfs are roughly the same weight as a VR.

 

I want them mainly for a better handbrake, better initial bite and additional cooling (the 239s do get hot, very hot, on a hard thrape) and the far superior bearing arrangement.

 

But it's all academical at this stage anyway as I haven't even got the 312s on yet!

[Chris VR6nos 0]

Not sure if the 312mm will make much of a difference from the 288mm ones anyway, mine are so good, i need to see the 312mm setup work properly.

 

 

Chris

[Kevin Bacon 5]

I think it depends on pad choice tbh which is why I'm trying Ferodos DS2500s this time round. I like the 288s aswell but I'll have the option to use either, depending on what wheels I'm using.

 

The DS2500s have a constant friction coefficient of 0.5 from 0 to +900 deg. They don't smell of ammonia either!

 

Friction Coeff' 0 is Ice on Ice, and 1 (the highest) is akin to shoving a metal bar in your spokes. OE pads are FCo 0.2 Pagid FRs are 0.3, so the Ferodos are sticky like.

 

I'll try them and report my findings.

[Chris VR6nos 0]

From memory the Ferodo's are pretty good but very dusty

 

 

Chris

[Kevin Bacon 5]

Yes mate, they are VERY dusty but black wheels nay bother me. As I've said on the blower to you in the past, I like the dirty, well used look on Corrados ;-)

 

Ferodo are a laugh. The box they came in was filled with off cuts of random cardboard boxes and cereal packets and were packed by a two year old....and for £122, yes, that much, one expects better......but the DS2500 compound has a brilliant reputation.....we'll see.

[Joe M 0]

I was under the impression that bigger front brakes meant that more weight is transferred forwards, so the rear brakes actually do less. So if you uprate the rear disk sizes, you're going to end up locking the rear wheels much sooner.

 

I would suspect that the reason VW uprated the rear disk sizes (when did they do this? For the Mk4?) was because the cars weighed more, thus you could safely apply more rear braking power.

 

 

The main advantage of larger disks isnt to improve braking power, the standard brakes in good condition are plenty powerful enough to lock the wheels up at will.

The main reason to fit larger disks is to provide more surface area to increase heat dispersal, decreasing brake fade.

The rears do more braking than you would think as well, my car is currently going through rear pads faster than fronts, and I have no issues with sticking calipers or anything like that.

[CoxyLaad 0]

well I dont speak from full experience, but I had 288s on my VR mk2 without ABS and I can honestly it was best stopping car I have ever been in, it was absolutely class. Daz who I bought the banana off ran with 288s for a while and said they were excellent too. He then fitted 312s and said the difference is like night and day. Ask anyone who knows him, he is an absolutely nutter on the brakes!

 

Interestingly he said that he disconnected the ABS as it was 'rubbish' and heated up the brake fliud too much on a track day

[dinkus 10]

Yeah, if you're doing a track day, definitely disconnect the ABS as you'll cook the pump unit

[Taggart 0]

Anyone got anywhere with the 6mm spacers? I'm getting my brakes fitted saturday week.

[bix 0]

I was under the impression that bigger front brakes meant that more weight is transferred forwards, so the rear brakes actually do less. So if you uprate the rear disk sizes, you're going to end up locking the rear wheels much sooner.

 

I would suspect that the reason VW uprated the rear disk sizes (when did they do this? For the Mk4?) was because the cars weighed more, thus you could safely apply more rear braking power.

 

 

The main advantage of larger disks isnt to improve braking power, the standard brakes in good condition are plenty powerful enough to lock the wheels up at will.

The main reason to fit larger disks is to provide more surface area to increase heat dispersal, decreasing brake fade.

The rears do more braking than you would think as well, my car is currently going through rear pads faster than fronts, and I have no issues with sticking calipers or anything like that.

 

I'd like to see someone without an arnie size leg lock the wheels up at 140mph!

[Joe M 0]

Its more a case of having the bottle to press the brakes that hard at 140mph. After all, the tyres have the same amount of grip at 40 as they do at 140..... Only difference is the wheels are spinning faster.

[bix 0]

Yes and dont you think even a free spinning wheel, say off the ground, at 140mph is going to require a little more force to lock-up than one spinning at 1mph, and thats before you have a ton of car, and the traction on the road!

[Joe M 0]

Yes, but locking the wheels up only means the wheel is decelerating faster than the car, it doesnt need to completely stop.

[bix 0]

Ok, but still I'd like to see someone without an arnie size leg lock the wheels up at 140mph! You think you could?

[Joe M 0]

Ive done it at about 100mph on track and it was scary enough. Ive also felt the abs kick in at about 130. Im not daft enough to try disconnecting the abs and hitting the pedal that hard at 140 though.

[daves16v 1]

Anyone got anywhere with the 6mm spacers? I'm getting my brakes fitted saturday week.

 

Kev has asked me to supply them, hopefully you should see them next week.

 

Dave

[Taggart 0]

Cool, I'm down at Kev's on Thursday/Friday, so if you could 'ave em by then it would be awesome :cheers:

 

If not I'll get some washer set-up like Dinks'.

[Kevin Bacon 5]

Here are the lovely washers Dave very kindly agreed to make for us. 11m inside diameter, 25mm outside diameter, which I've checked against my bolts and carriers.

 

If Dave can run off 2 batches for next week, that would be most excellent.

 

Joe, the reason for larger discs is to increase the mechanical advantage, i.e. extra leverage. I found the 280s to be rubbish and was forever warping them. 288s so far, so good on the warpage front. I have a formula somewhere for calculating pedal effort against disc size against Master cylinder bore size etc etc. Heat dispersal is a secondary effect of larger discs and a bonus.

[dinkus 10]

Oooh purdy :)

 

My 312s are starting to bed in properly now and they're constantly getting better and better.

 

The problem is, there's still that dead area at the top of the pedal travel that makes the initial bite feel a bit spongey.

 

Anybody thought of fitting a Mk4 master cylinder? Is it an item that you could just swap in and it would solve the dead-zone, or is it more complex than that?