280mm rear discs

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mgtfnut
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280mm rear discs

Post by mgtfnut » Tue Aug 14, 2012 10:06 pm

Does anyone here use 280mm rear discs?

I've been using Ford Focus ST170 discs for a couple of years now, and could do with sharing some experiences.
Jerry
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Rob Bell
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Re: 280mm rear discs

Post by Rob Bell » Wed Aug 15, 2012 2:19 pm

On Project Shed - I've got BG Development floating rotors front and rear. Unfortunately with the Shed not yet road registered, I've not been able to do much in the way of brake testing, but a short drive up and down a private road has revealed the potential for brilliant braking performance without triggering ABS - and that's with standard-spec Mintex pads! :thumbsu:

Feeling even more tempted than ever to get some 304mm rear discs made up for the other F to match the 304mm AP fronts!

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Re: 280mm rear discs

Post by mgtfnut » Wed Aug 15, 2012 8:03 pm

Rob, I was talking him for some time, but as I've got 304mm on the front it seemed logical to go further and increase the rears relatively cheaply.

I've got a local brake supplier who can re-drill the Focus discs with wear related grooves etc.
I was after some findings of other people, possibly not many on here then.

I've found the rears heat up very quickly, in fact I've burnt out one set of Greenstuff pads already. The discs are showing signs of wear after eight months limited use :roll:
I've tried downhill braking on gravel and the fronts still lock up first. I know the limited mass means they warm up faster, but looking at the pad/disc wear they must be doing some serious braking. The overall braking is fine and reassuring when you want to kill off speed quickly on a twisty downhill Welsh mountain road :oops:

I'm wondering if it is worth trying larger rear discs, or even ventilated rears. The fronts stay relatively warm, never really getting hot. The pistons and pads are all free.
I don't have ABS, and I'm wondering if the rear brake bias valve is empty :o

Is there something I'm missing here?
Jerry
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Rob Bell
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Re: 280mm rear discs

Post by Rob Bell » Wed Aug 15, 2012 8:19 pm

We chatted about this at Silverstone, and I have had exactly the same problem as you do with the rear brakes. Like you, I have long maintained that the rear brakes of our little roadsters work far harder than on most cars (usually front-heavy with the engine at the front). Have you also noticed how Porsche Boxsters and Lotus Elises also have practically the same size rear discs as they do at the front? Of course, there may be marketing reasons for this, but I also suspect that the reason is that you need brake-torque balance, and you also need to dissipate heat.

Perhaps the small rear pad surface area has something to do with heat build up too?

Al Phillips did the calculations and figured that 266mm rears would be sufficient to dissipate the heat on an MGF - but I am not so sure.

Regarding the brake bias valve, this is set up assuming the same diameter rotor front and rear (240mm F/R) - so having 280mm rotors all round should pose no problems. Nor should 304mm rotors come to that! Perhaps I should approach either AP or BGD to see whether they'd do 304 floating rotors. Or perhaps I could fit 304 front discs to the rear - but then I'd need to find a rear caliper suitable that can fit over the vented disc and have a mechanical handbrake mechanism... Suggestions on a post card to the usual address! :lol:

Not sure how many folks here have larger rear discs; my road F runs the aforementioned 266 rear conversion, and I can confirm that I still eat through rear pads far faster than fronts (again, small pad area may contribute, but I also suspect that there is disproportionate heat build up - I'll have to check this out sometime).

Would be interesting to hear from others with 280mm rear or 266mm rear discs?

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Re: 280mm rear discs

Post by Bigfootmgf » Wed Aug 15, 2012 8:49 pm

I have the same problem of eating the rear pads first but all options seem to be rather exspensive so its cheaper just to replace them(track days don't help this)
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Re: 280mm rear discs

Post by Rob Bell » Wed Aug 15, 2012 9:03 pm

What pads do you use? Mintex pads other than standard road spec cost over 100 an axle set these days! Not good if they're being eating through at a rate of knots! :(

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Re: 280mm rear discs

Post by Bigfootmgf » Wed Aug 15, 2012 10:52 pm

i have tryed mintex standard pads along time ago that i got for cost when my uncle worked for a motor factors( he's retired now), also tryed black diamond pads they did not last very long and made a loud vibrating sound when they got hot and had no bite at all when cold. at the mo i have green stuff pads as i had worn the pads down to the metal and needed them in a hurry and found mintex hard to get and priced high!
I keep looking at other options of discs and pads but i want to keep the alloys i have so that stops me having AP's
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Re: 280mm rear discs

Post by Rob Bell » Thu Aug 16, 2012 10:41 am

280mm discs all round is a good solution - fit nicely within both 15 and 16" standard wheels. However the problem is the front calipers which were originally found on Metro GTi and MG Maestros - they are designed for 240mm disc fitments, and when fitted over a larger disc, the pad material runs over the edge of the disc.

I saw in MG Enthusiast that there is a Tarox 4-pot caliper conversion originally designed for the Metro GTi, but fits just as nicely on the MGF. Might be a solution for 280mm front discs?

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Re: 280mm rear discs

Post by Rich in Vancouver » Fri Aug 17, 2012 6:30 am

I have been lusting over Hi-Spec's big brake kits. Only the price is stopping me. :(
They even come in snazzy anodized colours. :thumbsu:

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Re: 280mm rear discs

Post by Steve White » Fri Aug 17, 2012 7:36 am

I like the look of them too, and was also wondering if thier 4 pot rear calliper with handbrake spot pad could be fitted with thier MGF big rear disc conversion (would beinteresting to find out if this uses a solid or vented disc).

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Re: 280mm rear discs

Post by mgtfnut » Fri Aug 17, 2012 8:53 pm

Steve White wrote:I like the look of them too, and was also wondering if thier 4 pot rear calliper with handbrake spot pad could be fitted with thier MGF big rear disc conversion (would beinteresting to find out if this uses a solid or vented disc).
Careful how you go with that ;) The piston numbers mean the fluid displacement would be more, and might lead to excessive brake pedal travel. Also the balance would again be thrown out with different front to rear ratios.

I'm still messing around with the Golf Mk4 handbrake caliper, as it's a kit car favourite for reliable action, and the piston is the same diameter as in the OEM caliper. A bit wary of future MoT requiremnts - the OEM caliper on 280mm discs look OEM anyway :roll:
Jerry
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Re: 280mm rear discs

Post by Rob Bell » Thu Aug 23, 2012 10:03 am

Just wondered whether all VAG brakes use the same piston sizes Gerry? I'd be after a set of front calipers with the same (32mm?) pistons as the Rover originals...

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Re: 280mm rear discs

Post by mgtfnut » Thu Aug 23, 2012 12:04 pm

I think we're well catered for in front brakes/calipers - it's the rear ones that intrigue me :roll: I've never looked at alternative front calipers
If I get surface "rust" from overnight rain, the staining rubs off the rears within a few hundred metres, the fronts can run around all day and still show rust stains. The front pads and pistons are all free, I just think that, due to their size, they don't have to work hard at all.
That's why I raised the question of people running 280mm rears.
Logically, the next step would be ventilated rears to overcome the heat build up. Fortunately, I have access to a rally car testing stage where I can check out downhill braking on loose surfaces for premature rear lock-up.
I've got the Golf rear caliper conversion on hold, as I think I read somewhere about future MoT testing requirements becoming more in line with EU rules, ie TUV etc. At least what I have looks OEM, pretty much so as to be able to convince my local MoT man that there was any apparent diffence :o
Jerry
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Re: 280mm rear discs

Post by Rob Bell » Fri Aug 24, 2012 9:34 am

The reason for thinking about calipers for my 280mm front discs are because the standard front calipers are designed for 240mm discs, and with larger discs, the pad overlaps the edge of the disc. A standard caliper from a scrappie is cheaper than going to Tarox or HiSpec, and should still fit nicely within 15" wheel rims...

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Re: 280mm rear discs

Post by Mikeadman » Tue Oct 18, 2016 9:21 pm

Any update on this four years on?

Cheers

Mike.

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Re: 280mm rear discs

Post by talkingcars » Tue Oct 18, 2016 9:42 pm

mgtfnut wrote:......as I think I read somewhere about future MoT testing requirements becoming more in line with EU rules, ie TUV etc.
Mikeadman wrote:Any update on this four years on?

Cheers

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Re: 280mm rear discs

Post by Larry Nicoll » Wed Oct 19, 2016 4:14 pm

I have been running 280mm all round for a few months now with no problems and a noticeable improvement together with a servo brace.

if you want to keep the 15" wheels the next logical step would be multi-pot front callipers from the likes of Hispec or similar. I was doubtful of their solution for the rear on the basis if the small handbrake pad but am sure better callipers at the front would improve he situation if you are prepared to pay the money!
MGTF : 2005; 15" wheels; 280mm discs all round; servo brace; Mike Satur gear change; Mike Satur 4:2:1 manifold; sports cat; Daytona silencer; KMaps remap

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