17mm vs 19mm master brake cylinder, pros and cons? Options

[914 RZ-1]

I need a new M/C. Stock is 17mm, but it seems everyone is selling 19mm. I'll get a firmer pedal and less stroke with the 19mm, correct? Is this good or bad or personal preference?

What are the advantages/disadvantages of both?

Thanks!
-Jeff
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[Superhawk996]

(IMG:style_emoticons/default/agree.gif)

People have become used to overboosted brakes and power steering. Very few people recall driving an early 70s Chevelle without power steering, drum brakes, and without power brake boosters.

Even when domestics finally went with discs up front and power assisted brakes, they were terribly overboosted and difficult to modulate vs a 914.

@bkrantz

500N (112 lbs) is the force to be applied to the brake pedal during the failed power portion of FMVSS 135 testing which would be conducted for a power assisted brake system with a failed brake booster. There are other tests within FMVSS 135 that allow up to 1000N (225 lbs) of brake pedal force. Any human in reasonable physical condition should be able to obtain these pedal forces.

At 100 kph the vehicle must stop in less than 168m (551 ft) with a failed booster and 500N of pedal force.

That is a bare minimum accepted performance that you should be able easily beat.

I don’t have any easy recipe to set up a cheap foot operated load cell so that you can directly measure these pedal forces but I outline them so you have some sense of what is considered normal pedal forces that can easily be achieved and the stopping distance that must be met by any new production vehicle.

[bkrantz]

(IMG:style_emoticons/default/agree.gif)

People have become used to overboosted brakes and power steering. Very few people recall driving an early 70s Chevelle without power steering, drum brakes, and without power brake boosters.

Even when domestics finally went with discs up front and power assisted brakes, they were terribly overboosted and difficult to modulate vs a 914.

@bkrantz

500N (112 lbs) is the force to be applied to the brake pedal during the failed power portion of FMVSS 135 testing which would be conducted for a power assisted brake system with a failed brake booster. There are other tests within FMVSS 135 that allow up to 1000N (225 lbs) of brake pedal force. Any human in reasonable physical condition should be able to obtain these pedal forces.

At 100 kph the vehicle must stop in less than 168m (551 ft) with a failed booster and 500N of pedal force.

That is a bare minimum accepted performance that you should be able easily beat.

I don’t have any easy recipe to set up a cheap foot operated load cell so that you can directly measure these pedal forces but I outline them so you have some sense of what is considered normal pedal forces that can easily be achieved and the stopping distance that must be met by any new production vehicle.

Thanks. I certainly have gotten used to modern brakes. But at 220 lbs and 6-2, and fairly healthy, I am pretty sure I can apply a fair amount of foot pressure. And I have memories of 914s (my own and others) where we had to practice threshold braking to avoid lock-up. Once the snow is gone, and the roads get cleaned up, I can try again.