Handlebar Master cylinder query

[Darryl Flynn]

Hi, i am gathering bits at the moment to change from my undertank master cylinder onto a handlebar mounted one on my 1980 R100RS. The bike currently has 40mm ATE calipers and braided hoses leading to them.

I have been offered a 16mm master cylinder assembly VERY cheap and in great condition. This is from an 83 airhead.

Reading the posts on this conversion it seems that 13 mm is the favoured option but can someone please in laymans terms explain to me the difference that i will experience if i use 16mm as against 13mm. The term " wooden feel " is often used when referring to the use of a larger MC.

Does this mean that the lever requires more physical effort to impart the same braking force as a 13 mm OR does it mean that the brakes have little feel and are over sensitive ie easily lock the front end up.

Thanks Darryl

[Kurt in S.A.]

http://www.vintagebrake.com/mastercylinder.htm

Kurt in S.A.

[George Ryals]

With the 16 mm, it takes more effort with less lever travel to achieve the same braking force as with a 13 mm and more lever travel.

[Darryl Flynn]

With the 16 mm, it takes more effort with less lever travel to achieve the same braking force as with a 13 mm and more lever travel.

Thanks for that. Exactly what i was after.

[SteveD]

With the 16 mm, it takes more effort with less lever travel to achieve the same braking force as with a 13 mm and more lever travel.

Thanks for that. Exactly what i was after.

I converted my 15mm 1982 mc to a 13mm from a R80 mono and the lever travels further but the feel is much more progressive.

[Darryl Flynn]

Thanks Steve.

Does anyone know which airheads were fitted with the 16mm handlebar MC ?

The reason i ask is to get some understanding as to why BMW seemed to shuffle betwen 13mm and 16mm MC's on presumably similar bikes with similar calipers.

Darryl

[SteveD]

Does anyone know which airheads were fitted with the 16mm handlebar MC ?
The reason i ask is to get some understanding as to why BMW seemed to shuffle betwen 13mm and 16mm MC's on presumably similar bikes with similar calipers.

R100CS, R100RS, R100RT, 32 72 2 302 363 HANDLE UNIT, RIGHT - D=16MM (09/80 to 09/81)
The bigger model twin shocks from 10/81 on (including R80RT) had the 15mm.
The initial monos had 13mm, then the later ones had 14mm.
Not sure it'll help understand though?

[chasbmw]

I think that BMW started off at maybe 17mm for the earliest twin discs on the 74 ATE bikes.

My view was that BMW were very conservative in their choice of MC ratios because they were wary of riders locking up the brakes with these new tangled discs. This was a time when tyres were skinny and rubber compounds were not nearly as good as they are now and rider education was almost non existent. In the US in paticular a proportion of riders almost never used the front brake. The front disc on my 73 norton was not much better than the BMW single disc.

The ratios changed as BMW changed brake calipers and brake performance became more important. 13mm is good on my 38Mm ATEs but the stock brembos on my 82 are better. One advantage of the 13mm MCs is that they have twin pull throttle cables same as the 74 on bikes and the switch gear from the 1975 bikes will fit.

[Jean]

Maybe the larger cyl was used with a longer lever.
If you calculate the difference in AREA of the 13mm piston vs. the 16mm piston you will see how much more lever-effort is required to get the same effective pressure at the brakes. Roughly, it takes half-again as much hand effort to give the same pressure with the bigger one, and the brake effect will be a LOT quicker...easier to lock-up and less control.

[chasbmw]

It's looks to me that the brake pivot point on BMW handlebar MCs is the same, and the position of your hand is also the same as it is determined by the twist grip position, so a longer lever would not have much effect. Is it not the ratio between the master and slave cylinders that is important?