I think you lot r probably fed up with all my questions now lol but you lot r my bible. Rite well neway I wanna convert me Focus to rear discs, now while gettin the parts arent a prob, am I lead to believe that I need to change my brake master cylinder? The car has ABS but no traction control. Also shall I just go for std rear discs for my car but I will eventually go for poss bigger ones on the front, i.e Fezza ST150? Help please lol

 

Why do people go for rear disc conversions? Most of the braking is done by the front wheels, you wont feel any extra braking force.

 

A waste of time imo on the focus, unless you are hard on brakes ?, but your current master cylinder can stay put, just ensure you fit a pressure reduction valve in the rear lines from a disc brakes focus.
tabetha

 

Or run a Brake Bias valve so you can have what you like.

 

Too dangerous, don't forget this advice is going to be read by lots of people, some not experienced with bias valves, so if they were to say set it on the limit in the dry then tamp on the brakes in the wet!!!!
The oe fit pressure valve is set softer than it seems it needs to be for a reason, it can cope with all conditions.
tabetha

 

Tabetha, I'm not really hard on the brakes if I'm totally honest but I will brake at the latest possible point but thats just my drivin style but its 4 more asthestics than nethin else but could just the front brakes be up2 the job for wen I put the bigger engine in as poss thinking of a 250bhp engine

 

Can always buy big bastard 4 pots. Lots of people think "If i put big discs on the brakes are better" this is not the case, it's all about pad area, then you might need master cylinders to suit your new set up for full braking efficiency.

 

So could in theory keep drums on the back (though looks crap) n just say have poss 2 Master cylinders 2 cope with the uprated brakes, I think I'd only go for bigger discs n pads but obviously change calipers aswell?

 

The brake set up I had on my focus worked well. focus 2.0l rear discs. mondeo mk3 calipers and st170 discs on the front. with braided brake lines and descent fluid. It stopped like hitting a wall.

 

You don't have two master cylinders, just the one, but it will be one designed to suit the new piston set up.

 

It's actually very little to do with pad area, it's a lot more to do with co efficient of friction, that's why uprated pads have a higher cof, larger pads tend to use more pistons in the calipers, or a larger single in a lot of cases, putting larger diameter/bigger discs will make the pedal lighter for the same amount of "stop", as it exerts a larger lever effect on the disc with the caliper being further away.
It's easy to over brake a car, a lot of rear discs fitted on smaller lighter cars do next to nothing due to the fact they have very little traction due to lack of weight over them, indeed some race series like hot hatch actually brake ONLY on the front and disconnect the rear brakes!!
On a fwd set up around 85-90% of the braking comes from the front, but by all means put discs on rear if you want the looks.
tabetha

 

But with bigger pads comes higher Cof. With little pads there is a small amount of material to stop a much bigger disc down also, the heat is all contained within a smaller area. Larger pads cover much more of the disc so there is more contact material.

 

Doesn't work that way, you're forgetting that the same force applied over a greater area = less pressure, same force over greater area = more force at contact point.
It's a fine balance between keeping enough heat in the pad and not too much, granted smaller pads will create more heat due to higher pressure, all else being equal, but there's also less pad material to retain heat.
As a very rough rule the smaller/lighter the car the smaller the pad it can get away with, bigger pads could be used just not to their best, as won't get hot enough if a sporty pad.
Add to this some cars using aluminum discs and the whole pad material changes again, the way it is driven plays a big part of course.
The 1.4 astra auto I drive has greenstuff pads, but only 236mm discs, so fade nearly every day when I'm driving it, this is being swapped for 288mm vectra b discs with yellowstuff pads, on a car weighing around 930kg, but this is entirely down to my driving.
Having used yellows for years and my cossie all through 4 winters even ice snow etc I know they work ace when cold.
tabetha

 

Yeah? I thought Yellow stuff was quite a racey pad? I've seen people using Carbon Metallic on the road and they get down the end of the road and it wont stop because they're cold so i really don't know why they keep using them lol.

 

So I cud essentially go 4 say std 1.8/2.0 rear discs for my car 4 the look I'm after but run bigger discs up front when I put the bigger 2.0ltr in. I queried the master cylinder as I spoke 2 EBC tech as they say I need 2 change said item 2 cope or as u say run a pressure reduction valve which I think may be a cheaper option but ne ideas peeps on where 2 get one?

 

It's not about how big the discs are, we run an ST170 with 292BHP Normally Aspirated and that's got 280mm on the front (With 6 pot Wilwoods) and it stops like someone getting hit by a train and people seem to be putting 300mm's on standard Escorts, i don't see the logic.

 

they look damn sweet when you have a massive set off stoppers.

 

What does?

 

having a full alloy. instead of 17" wolfrace alloys with 240mm discs.

 

Oh i see what you mean, yeah i suppose it does.