Vented Rear Discs

[Cameron 16]

I've seen a couple of pics of vented discs on the back of 205s, but are they ever actually necessary? I only ask as I'm spec'ing up my brake system for my upcoming project (double wisbones & slicks for those who haven't read the thread) and have to make a pretty important choice between solid or vented rotors for the back. Currently I run Lotus 2-pots up front on 280mm AP rotors/bells and standard GTi6 setup at the back, using Yoko A048 tyres all round. The brakes are awesome on track so I'm not too worried at the moment, I'm just not sure how the extra heat from running slicks will affect things.

 

There's pros and cons for both really.. Solid discs are about half the price, but means I will need to buy discs and calipers as I want to upsize to 280mm rotors, they're also about 2/3rds of the weight. If I go for vented discs then I can use my current front brakes on the back, but there's a fairly large weight penalty and also the chance that they'll run too cool. (The rotors are also bloody expensive when they need to be replaced!)

 

So yeah, thoughts and suggestions please! If anyone's run them, how do you think they compare to solid discs? For people who still run solid discs, do you reckon vented ones would ever be necessary?

Edited October 5, 2011 by Cameron

[Batfink 201]

I think you have to remember that you are also going to be a lot lighter than standard. The standard rear brakes found their way onto much heavier cars than the 205 so I personally think they are unnecessary to upgrade so significantly. I would rather run lighter and use the right pad compound to cope with the heat demands. You could always look at running motorbike discs and brake calipers to save more weight

Edited October 5, 2011 by Batfink

[welshpug 1,655]

ever heard of anyone cooking rear pads?

[Cameron 16]

That's what I was hoping to hear! Motorbike brakes would be a cool idea, could maybe get some tiny 4-pots on there.

[welshpug 1,655]

http://forum.205gtidrivers.com/index.php?showtopic=89678&view=findpost&p=939949

 

[Baz 421]

In the words of Mark & lard; ''No neeeeeeed!!!''

[Cameron 16]

Motorbike calipers looks like a really interesting option, what's the pad contact on those rear discs like though? I was looking at 2006 R1 calipers as they're 4-pots, but they normally run huge 310mm so I'd be a little worried about the pads overlapping with smaller diameter rotors.

 

It's a good idea though and I'll look in to it more, can quite easily get rotors laser cut too.

[Batfink 201]

There must be plenty of bikes running smaller discs?. As you would be making custom mounting points I doubt you would have overlap with the right pad and calliper shape. My first port of call would be a bike shop with a tape measure lol

Edited October 5, 2011 by Batfink

[Cameron 16]

I'm just thinking the smaller disc diameter could mean the corners of the pads overlap the disc.. I need to go measure someone's R1!

[Batfink 201]

Theres surprisingly few pad shapes on bikes compared to cars. Many are universal for loads of models.

[B1ack_Mi16 67]

I agree there is no need. Only reason to why I did it was because I could.

 

I did consider removing the vented rear ones on mine when I changed the beam, but couldn't be bothered by buying the discs.

They are indeed more show than go

[Cameron 16]

Cool, in that case I'll go down the weight saving route and fit solid discs to the rear, also means I can sell my current front brake setup to raise a bit of cash.

 

I reckon I'll invest in a heat-sensitive paint set to get an accurate indication of how hot the brakes are when running. I have some temps from after a run round the 'ring but they would have cooled down a fair bit by that time so aren't representative of the actual running temps.

[Batfink 201]

just get a decent race pad that works at all temperatures then go light!

[Cameron 16]

Rotors are expensive though, I don't want to kill them by overheating.

[welshpug 1,655]

naaah, depends where you get them from

 

http://forum.205gtidrivers.com/index.php?showtopic=101836&st=0

[Cameron 16]

naaah, depends where you get them from

 

http://forum.205gtidrivers.com/index.php?showtopic=101836&st=0

 

If they overheat they're still going to get mullered though, having lovely wavey edges won't help that.

[welshpug 1,655]

I was meaning the cost not the waveyness, though that will aid cooling

[Cameron 16]

Ahhhhh I seeeeeeeeeee! I'm not a massive fan of wavey discs though.. would rather stick to good old fasioned round ones.

[Rippthrough 98]

Just lets you use a nice big pad while still keeping a large effective radius over a smaller/thinner disc.

 

I'd be very surprised if you overheat a couple of bike discs on the rear though tbh...

[Cameron 16]

I doubt it either tbh.. thinking about using some early R6 calipers at the moment - see this link - they're lug mounted rather than radial which means they can be tucked in next to the upright with a simple bracket rather than have to have an awkward shaped post mount.

[Cameron 16]

Well I don't take much convincing..

 

Bought a set of R6 calipers on eGay for £80 delivered so I can measure the piston sizes and get an idea of whether it will work. They need to be at least 32mm diameter on average so they'll work with the front calipers without having a silly sized master cylinder.

 

I reckon some laser cut stainless discs are gonna be the way to go as I want them to be 280mm diameter.

[Rippthrough 98]

I've got a pair of those but radial mounted to go with my new rear suspension.

 

If you want 280mm discs have a look for some off the rear of a bike, generally in the 270/280mm area.

[Cameron 16]

Do you know what the piston diameters are?

 

Not sure about a bike rotor, they're generally riveted to an aluminium centre aren't they? Will have to investigate.

[Rippthrough 98]

They usually float on stainless bobbins, but you can bolted rears on many bikes.

 

Mine are the radial mono-block type that take 4 seperate pads - IIRC (have to measure for you) 30mm trailing piston, 28mm leading.

Edited October 11, 2011 by Rippthrough

[Cameron 16]

Ah cool, I'm hoping these are a similar size then. If they're any larger than 32mm average then master cylinder selection is going to be tricky.