Better disk on '75 R75/6

[Ken in Oklahoma]

. . .With this setup, I think I'd need about a 12mm MC (currently have 14mm).

But I have a pair of R100 or somesuch forks on the way from the 'Bay, so I'll have the easy opportunity to fit a better caliper, maybe a 4-pot, in which case the 14mm may be better.

I'm afraid not, Abstrese, that is unless you've done the research on the old master cylinder ratio to caliper piston(s) area compared to the ratio with your envisioned solution (same master cylinder brand and style). All other factors being equal it's all about that ratio, both for braking power and feel.

But then you may be fully aware of that and are planning to take such into account.

Ken

[Abstruse1]

Ken, I can do this. I'd calculate the ratio as-is and with a 12mm MC, then look at one or more caliper combined piston areas and get a sense of about what MC would give me a happy ratio.

On the topic, my assumption is that dual disks don't add to the stopping ability of a well designed system, except as to heat dissipation; and where adding a disk helps cold braking, the second disk simply helps correct a system that wasn't optimum.

Consider my KTM Duke 690, single front disk. Maximum braking easily achieved with very little lever force (yes, I need to look at that ratio).

Do you agree?

[mattcfish]

There are other ways to make it stop. I finally found my way.
viewtopic.php?f=1&t=9081

[Zombie Master]

Single disc can work fine but will always pull.

[Abstruse1]

Well, I decided to go ahead and install the twin disk forks (eBay) that are set up for conventional calipers (e.g. Brembo). I'll start with one disk and see how it works, then most likely add the second disk and caliper. Stay tuned.

[chasbmw]

Your existing wire wheel wont fit the Brembo set up.......unless you have obtained the wire wheels fitted to some Police bikes in the UK.

A snowflake cast wheel will fit fine but will look odd.

twin discs on a R90/6 with a 13MM MC work very well, giving you both power and control, if adjusted properly about 95% as good as Brembos. works very well with a decent front tyre. Grip in the dry and wet is a good thing

[Abstruse1]

Chasbmw, I hope you're wrong. If not, this tail I'm chasing gets longer and longer.

I hope I'm not force to go to a different alloy rim, e.g. something from Buchannan.

BTW, from what I read, many of the snowflake wheels were recalled for some serious defect. Anyone know how to tell which ones are good? But then, I'd rather stick with wire wheels.

[khittner1]

The recalled snowflake cast front wheels lacked the tapered cast reinforcements at each "spoke's" juncture with the center hub that their replacements have. There are comparison photos that show the differences (google "BMW recalled snowflake wheel"), and they're easily spotted once you know what you're looking for/at.

I don't know the particular details, but I think the issue with putting Brembos onto an ordinary /7 spoked wheel has to do with the comparative dimensions of the hub, not the rims. Read Snowbum's treatise on the topic of swapping wheels between various years.

[SteveD]

BTW, from what I read, many of the snowflake wheels were recalled for some serious defect. Anyone know how to tell which ones are good?

This topic is considered a bit like an oil thread around here!
viewtopic.php?f=1&t=8763&hilit=recall+snowflake

[chasbmw]

Chasbmw, I hope you're wrong. If not, this tail I'm chasing gets longer and longer.

I hope I'm not force to go to a different alloy rim, e.g. something from Buchannan.

BTW, from what I read, many of the snowflake wheels were recalled for some serious defect. Anyone know how to tell which ones are good? But then, I'd rather stick with wire wheels.

I'm not wrong......If you want wire wheels they need to have a narrower hub, 2 ribs rather than (3?). The UK police specified wire wheels on their bikes after 1981-84, so BMW made the narrower hubs, I don't know if other service bikes also had wire wheels during that period, but most of the available stock has been sold to people making Cafe racers and the like so they are as rare as Rocking horse SH*T. People have cut down the wider hubs, but I would not want anyone to go down this route unless they really know what they are doing.

To go back to the beginning a twin Disc ATE braked bike with a Smaller 13MM handlebar Master cylinder will get you 95% of what Brembos give you and being much truer to the original bike than going down the Brembo/Snowflake route will add rather than detract value. its easy enough to sell stuff on EBay.