What size master cylinder do I need

[Mad Hatter]

I’m fitting a KTM 690 Enduro front end to my R80GS, with the KTM disc & caliper. I want to use the standard BMW master cylinder but there are 13mm, 15mm and 16mm ones available. I think the two larger sized ones are for twin disc BMWs. Can anyone tell me which size master cylinder I should get to use with the 2 piston KTM caliper?

 

[Smug]

Why not use the same diameter master cylinder as is fitted to the KTM 690 Enduro?

 

[Mad Hatter]

Why not use the same diameter master cylinder as is fitted to the KTM 690 Enduro?

I would if I knew what size it was…….

 

[Timolgra]

Pretty sure you'll need 11mm which would be the same as 950SE, you can use one from a single cylinder bmw 650 but that's 13mm and doesn't work quite as well but still OK, so for your needs that might be the best option.
Any bigger and the brake will feel wooden.
I seem to remember an exc master cylinder being too small and no power as the older ones are 9mm.
I had to find this out when converting my 640adv to single disc.

If you phone the parts dept at Trevor Pope they'll confirm.

 

[Nin]

I’ve done exactly that on my R80G/S build. Standard BMW 13mm is more than enough to lock the front wheel with the 690 caliper.

 

[Mad Hatter]

I’ve done exactly that on my R80G/S build. Standard BMW 13mm is more than enough to lock the front wheel with the 690 caliper.

Thanks gents. I wanted to stick with the airhead perch’s, switches and master cylinder rather than use KTM ones. Nin’s answer above is what I needed. I know which one to go for now (13mm).

 

[Joe Bar]

FWIW my R80ST has a 12mm fitted.

 

[Nin]

My setup