O.K.- I agree that if you have a system running 2 masters ( 1 for the front,
and 1 for the rear) that this is true-bigger wheel cylinders = bigger
brakes. However, if you're running a single master, with dual outputs, then
won't the increased volume necessary to bring the rears to bear cause a
substantial front bias? The 2 pistons are traveling the same distance, the
volume output is proportional front to rear, but the front (discs) which
have less runout, and less free movement will come on-line first, before the
rears with more volume to take up have even started to act on the drums?-I
realize that I'm talking about a specific case, and not a generalization
here, so please bear with my long windedness (and possibly my
bull-headedness)
Mark Haynes
'65 Spitfire RMVR #162
> -----Original Message-----
> From: Greg Burrowes [SMTP:gregb@datafast.com.au]
> Sent: Wednesday, May 12, 1999 12:28 AM
> To: Simon Favre
> Cc: Vintage Race
> Subject: RE: beginners tech question
>
> Hey, you got it right! Bigger wheel cylinders = more pressure on the
> pads.
> I was amazed at the opposite opinions. We increased the size until we
> went
> too far & loacked up the rear wheels easily and then came back. @ $12 a
> cylinder it was the easiest way.
>
> Think about a trolley floor jack. A small pump pistons pushes a large
> piston in the lifting ram. A small piston pushing a large one takes more
> strokes but the large piston will exert more force (but with less travel).
>
> Greg Burrowes
> GM Holden Torana XU1 #50
> Historic Touring Cars Australia
>
>
> -----Original Message-----
> From: owner-vintage-race@autox.team.net
> [mailto:owner-vintage-race@autox.team.net] On Behalf Of Simon Favre
> Sent: Wednesday, 12 May 1999 4:21
> To: Haynes, Mark
> Cc: 'Greg Burrowes'; Vintage Race
> Subject: Re: beginners tech question
>
> What you apply to the pedal is a force. Multiply that by whatever pedal
> ratio you have and you still have a force. Divide that by the area of the
> master cylinder piston and you get a pressure. Multiply that pressure by
> the total area of wheel cylinder pistons and you get back to a force which
> is applied to the brake pads or shoes. It's the ratio of master cylinder
> area to wheel cylinder (or caliper) piston area that determines stopping
> power. A smaller master cylinder piston means more pressure in the lines
> because the force is divided by a smaller area. This makes for less pedal
> effort, at the expense of more pedal travel. A larger master cylinder
> gives
> less brake line pressure because the force is divided by a larger area.
> This makes for greater pedal effort, and reduced pedal travel. The
> opposite
> is true for wheel cylinders. A smaller wheel cylinder produces less force
> on the shoes or pads for the same line pressure. On some cars, it's easier
> to change the master cylinder, on some the wheel cylinders.
>
> At the wheel cylinder, the relationship is intuitive, that is, bigger
> cylinder = more stopping power = less pedal effort. At the master
> cylinder,
> the relationship is counter-intuitive, that is, SMALLER cylinder = more
> stopping power = less pedal effort.
>
> "Haynes, Mark" wrote:
> >
> > Greg- By my recollection (which may be faulty) of hydraulic theory, if
> you
> > take a specific traveling volume of fluid (hydraulic line), and apply
> the
> > pressure over a larger applied area (i.e. a larger piston diameter) you
> wind
> > up with less pressure per unit area, thus decreasing the braking effect
> > (actually the same pressure over a greater area). Anyone know for sure
> if
> > my theory of hydraulics is correct??
> > Mark Haynes
> ...
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