Stock Miata brake proportioning valves
If you're interested in changing the brake balance of your Miata, one option is to change the stock proportioning valve for one from another Miata. A number of things can alter the ideal brake proportioning, ranging from brake pad selection, tire choice and even the traction of the surface you're on.
Another option would be to install an aftermarket adjustable proportioning valve. If this is done, the factory valve should be removed and the adjustable put in its place. Do not put the adjustable valve on the front brake lines to drop their pressure.
The following table will refer to this chart. Up to pressure A, the front and rear pressures are equal. After this point - termed the "knee point" - the rear pressure is a fixed percentage of the front.
Note - it is unclear whether the 1999-00 valves are the same as the 1994-97 ones although it is likely. The master cylinder sizing was changed in 2001. The 2006+ non-ABS cars use a dual proportioning valve with two rear inputs and outputs that is not interchangeable with the earlier cars. Cars with no proportioning valves use Electronic Brake Distribution that is integrated into the ABS system.
Here are the various valves overlaid. The X-axis is front pressure, the Y is rear. It's interesting to note that the post-knee slope of the 1994 valves are both the same, but the ABS has a higher knee point and provides nearly 100 psi more pressure to the rear at 800 front psi.
|1994-97, no ABS||427||850||597|
|2002, no ABS||569||853||702|
|2002, ABS||No proportioning valve|
|2006, no ABS||497||852||639|
|2006, ABS||No proportioning valve|
|All ND||No proportioning valve|
Want to know more about performance brake theory? Here's a rundown on how it all works.