Upgrading 15 inch brakes.

A very worthwhile read!
Loved the adventure.

An interesting discussion David and confirms to me that somehow arranging for appropriate balance front/rear is important.
It also tells me that arranging an upgrade is worth it although in my case it will be by the simpler 280 diameter route at the rear (or 260 if I can locate one) and this will be regardless of weather it is a 208 or 304 route at the front.

My motoring is not as adventurous as others seem to contend with and the choice of pad may also be important to achieve reliable performance.

 

  I’d like to thank TA22 for the “exploded” balance valve. I’ve been there but returned things to original due to being awash in brake fluid, it was pissing from every possible place at that time & to staunch the fluid loss took prime position.
I’ll return to it once I’ve visited the scrappy.
I’ll add a picture of my Mini one brake callipers grafted onto my updated system.
M

If I had the wherewithall I would have gone the Mini calliper route because there are dozens of great pads for the Mini.
Good luck with finishing the project.

After a lot of searching I think I have found the origins of a disc that might fit the rear hub without any additional support ring . It would need re drilling and the centre boring out by approximately 2mm on diameter.
If I’m right I think it would be from a mini. OEM -Number BMW -MINI 3421 6784 38. As this seems to have been replaced with a different disc with slightly different machining details I do not know if it fits flush on the face of the hub.

Can anyone tell me if there is a suitable part number for the font disc that does away with the need for a support ring and accepts re drilling if the PCD does not match that of the TF and which can use the existing caliper with the “block” spacer?

regarding the difference between 240, 260 and 280mm loading on the hub and potential increased stresses caused- once the wheels are locked up, and skidding or inducing ABS for those that have it, the loading from the caliper on the hub is essentially the same because the tyre to road contact has broken first hasn't it, or am I being dense?

I can lock all 4 wheels with my stock 240mm setup if I need to do, on decent 16" falken road tyres for what it's worth. For any of these brake variations, the clamping force is able to overcome the mechanical grip on the road with a suitably hard stomp on the pedal (aided by other mods such as bulkhead reinforcement or the now patented Pineapple servo relocation)

I guess these concerns around stress on components from larger caliper spacing would be increased with a better / gripper tire such as a slick or semi slick in ideal conditions though...

Cheers

The MGF/MGTF rear brake discs have a height of 35mm as does the ST170 and MX5 disc. The Mini disc has a height of 43.9mm so you would need a 9mm spacer between disc and hub to get the heights correct. Although not a major problem to overcome it would be add additional load to the rear wheel bearings which are a weak spot in themselves. using the ST170 discs with a spacer ring, is still likely to be the simplest solution. OTOH if you are replacing the rear wheel bearings then you might turn the hubs down to take the MX5 discs and then just file or re drill the
bolt holes.Edit, when I looked I couldn’t find a Mini or BMW disc with the part number; 3421 6784 38 the only one that I found was 3421 6784 389, it’s quite possible the original number does give the correct height but I didn’t find it. 

From the information I can find and according to Delphi and others the MGTF 135 has a rear disc thickness closer to 43mm.
The thickness I can see without the thickness of the part that mounts to the hub is recorded as 36.7mm. So adding that dimension of 7mm I see 43.7

As it happens and for what is worth “Reddit” shows 43mm.
Brembo confirms 43mm

Edit, I believe the front has a similar value
Second edit : apologies thickness should have been height.

You are absolutely correct about the disc heights and I will remember to read what I have written in the future. What I really meant to say is that due to the thickness of the bracket you need the discs with the lower height, ie the MX5 or ST170 ones. If you use the Mini disc then you will need to put either a 8 or 10mm spacer between the disc and the hub depending on the thickness of the adapter bracket. I said 9mm because it would cover either thickness bracket. My final sentence still stands scrutiny in that the ST170 disc is probably the easiest to use. 
Sorry for posting the misleading information. 

Re # 220397 and the photo of the rear disc.
That looks rather like a EBC disc. Can you please tell us if that also came from TT or was that sourced elsewhere? Is the part number identified on it?
It looks as though the centre fits “exactly” on the hub and if so might have been machined to match when re drilling for the studs. Any additional detail would be most welcome.
Thanks.

Both the disc and the brackets were supplied by TTPerformance.
I don't have the original packaging but it was all labelled TTPerformance and not an EBC box with brackets shoved inside.
I honestly don't know what car they were originally meant to be oem.
I am not certain but I don't believe the centre was machined out but he did make a very good job of centring the PCD as the new holes are a nice snug fit.
Perhaps if you sent an email directly you might elicit more information?
Next time I have the wheels off I will see if I can determine the source of front and rear discs.

Thank you for the response much appreciated