Front brake on the R 100?

[Tapio]

I’ve been wondering about this for a long time. What’s the point of this feature?
First you have a cable at the handle bar, that goes to a hydraulic cylinder that sits below the triple tree. From there hoses to the brakes. It just seems daft. Why not have the brake cylinder at the handle bar?

[llanellybmw]

It works fine if all set up properly and is out of the weather. I have a twin disk system on a 79 R80/7 that runs this system. The only real issue is you cannot check the fluid level quickly, but there is a low level warning system built in. Lots do change to the later handlebar version ( I have that on a R100RT) but there's no real need.

[The Teutonic Tangerine]

We all know what great innovators BMW Mottorad are (I'd not come across this cable hydraulic set up before) but I guess not all innovations are deemed the greatest success and are quietly discontinued.

[Tapio]

It works fine if all set up properly and is out of the weather. I have a twin disk system on a 79 R80/7 that runs this system. The only real issue is you cannot check the fluid level quickly, but there is a low level warning system built in. Lots do change to the later handlebar version ( I have that on a R100RT) but there's no real need.

I wasn’t implying that the system performs poorly. Only that the shift from mechanical force to hydraulic force is unnecessary.
Force is force.
You could just as well have the cable push on the brake pads directly (even though, the only such mechanical brake system, as I can recall, was on the 80’s CB 125), or, you could have the hydraulic cylinder at the bar.

Sure, the cable flexes a bit when strained, but hoses expand when pressurised, so no advantage for either system.

So, why have two ways of transmitting force in one system? It doesn’t make sense.

P.S. I see your posting above is your first. Even though i'm not a frequent poster here, i'd like to greet you a welcome!

[Tapio]

Ok.
So, nobody knows for sure.
So here comes my theory on it: Tank slappers.

Anything that has a degree of freedom to move (in this case rotation) also has a resonating frequency. There’s a wiki on this: https://en.wikipedia.org/wiki/Moment_of_inertia
That’s too much to “digest” for a man born of a woman.

The lower the moment of inertia for the front end, as I understand it, the bigger probability for a tank slapper. Hence a cable at the handlebar. A master cylinder there would add weight. Unwanted. Thus two systems.

Historically, BMW have been anal about this (don’t know for a fact, but it looks so): short, narrow handlebars are good. Your arms contribute, lowering the resonating frequency.

[Jeff Highland]

I don't really see a problem with this arrangement, BMW just wanted to locate the MC more discretely.
Most every car has a pushrod from brake pedal to MC.
The main problems early 20th century vehicles had with mechanical brakes was balancing out forces to each wheel and accounting for wear of brake shoes. Neither of these would apply to a short cable to the MC.

[slparry]

I don't really see a problem with this arrangement, BMW just wanted to locate the MC more discretely.
Most every car has a pushrod from brake pedal to MC.
The main problems early 20th century vehicles had with mechanical brakes was balancing out forces to each wheel and accounting for wear of brake shoes. Neither of these would apply to a short cable to the MC.

As did Kawasaki with the Z1R. The master cylinder on my Z1R was down on the right fork leg near the headlight if I recall. It meant (on both bikes) that the cockpit fairings could be "tighter" to the 'bars

[The Teutonic Tangerine]

"You could just as well have the cable push on the brake pads directly (even though, the only such mechanical brake system, as I can recall, was on the 80’s CB 125), "

This appeared first IMHO on the Honda CB200 in 1974. My own CB200 though was 9 months old when I bought it in 1975 and it had a twin leading shoe drum on the front – and there are pictures of both set ups on the internet so assume mine was an early version of the Marque. The twin leading shoe was the identical set up to the CB175. (Interestingly the CB175 had 3 BHP more than the CB200, 20 and 17 respectively but the CB200 had more Torque) My mate had the cable disc brake on his CB200 and mine stopped a tad better than his - early days for disc brakes and the cable set up just wasn't man enough.

TLS: https://goo.gl/images/zjnPP5 You can just about see the TLS set up.
Disc: https://goo.gl/images/kvcBZZ