Master Cylinder Sizes

[SlowOldGuy]

Anyone noticed the sizes of front brake master cylinders on new Yamahas lately? 
They're 16mm. 
I wonder if too many newbies were putting themselves on their face with overly sensitive frony brakes?

And I saw an FZ8 on the showroom floor.  My only question is WHY?  I didn't think BMW was knocking them dead with their 800cc, or are they?  I'm still trying to catch up on my magazines, I think I'm in late 2009.  :-)

DavidR.

[Arnie]

Anyone noticed the sizes of front brake master cylinders on new Yamahas lately? 
They're 16mm. 
I wonder if too many newbies were putting themselves on their face with overly sensitive frony brakes?

And I saw an FZ8 on the showroom floor.  My only question is WHY?  I didn't think BMW was knocking them dead with their 800cc, or are they?  I'm still trying to catch up on my magazines, I think I'm in late 2009.  :-)

DavidR.

Wouldn't the lager size master make the brakes MORE sensitive?  It would be pushing more fluid/mm of stroke, right?

I'd guess that the 800's are an attempt to cash in on MotoGP sized bikes before they return to 1 litre again.  They're probably a better choice for most riders being lighter and easier to handle as well as having lower emissions.  I don't know what the regs are in Europe, but maybe they're getting a CAFE type limit on bikes too.  Or maybe the bike manufacturers are trying to hold off top speed limits.

Arnie

[SlowOldGuy]

Arnie,
It's one of those reverse logic areas.  You get more power and hydraulic advantage using a small master cylinder piston to pressurize a larger working piston.  The cost is more lever stroke is required to pump additional fluid.

Here's how it works:
Squeezing the lever produces a force on the master piston (pounds).  Applying this force to the area of the master piston (in^2) produces a pressure in the line (lb/in^2 or psi).  So, the smaller the master piston, the greater the fluid pressure produced for a given lever force.

Down at the caliper, a greater clamping/braking force is produced by a large piston.  The fluid pressure (lb/in^2) is acting on a large piston area (in^2) to produce the braking force (lb).  In this case a larger caliper piston produces greater force.  But, the system has to deliver enough fluid with a single "reasonable" stroke to move the caliper piston. 

Balancing the piston sizes provides optimum lever force with reasonable lever travel to produce the desired braking force.   The extra travel and lighter force of the smaller master usually equate to better lever "feel" and "sensitivity."

DavidR.

[racerman_27410]

the price of fuel keeps going up...     mid sized bikes that get respectable fuel economy will sell.

i know i wouldnt be happy on a 600 but i could prolly get by on a 800cc bike that gets 50mpg.


KOokaloo!