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Old 05-16-2013, 09:06 AM   #1
iminhell
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MK1 Rear Wheel Cylinder?

Can someone verify my fluid dynamics 101 is correct?

Foci built before mid 2001 had a different WC then after. The early ones had a smaller bore (20.6mm) than the later (22.24mm).

So, to increase braking pressure in the rear one (me) would want to ensure they have the smaller diameter bore WC's, correct?
(believe I understand hydraulic theory)


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Old 05-16-2013, 09:38 AM   #2
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You would want the bigger bore. That would give you a larger surface area (piston) for the fluid to work against. Hydraulic formula is F (force) divided by P (pressure) x A (area). A smaller bore willnot give you more pressure. Pressure is resistance to flow. Both are dead ends, so pressure remains constant. So in your situation, if you have 1000 psi, (not sure if that is really what it is) you would multiply it times the area available for the fluid to work on. Your would need to find the area of the cylinder. Say the wheel cylinder is 2 inches long. converting the cylinder size to inches it would be .811 (20.6mm) inches and .875 inches (22.24mm) x .8754 x 2= 1.41. area of smaller cyl or 1.53 in area of larger cyl. Then multiply by pressure to find your force is 1410 lbs. for smaller cyl or 1530 lbs. for larger cyl.

Sorry for the long windedness, and this is probably much more than your are after, but it helps explain why the bigger one is better for force.
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Old 05-16-2013, 11:32 AM   #3
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Viscosity is resistance to flow. Pressure is an omnidirectional force exerted over an area due to the momentum of fluid particles.

He's right, though—same pressure on a larger area means more force.
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Old 05-16-2013, 07:24 PM   #4
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Guess I'll return my little ones for the big ones tomorrow.


Thanks guys.
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Old 05-19-2013, 01:20 AM   #5
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There is no momentum in a closed in system that is pressure maintained, the particles are under pressure but not moving. Pressure in that case would indeed be resistance to flow.

Bigger wheel cylinder has more force since more area to work on with whatever force coming from M/C.
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