Fitting HiSpec Princess Calipers

[Paul318UK]

Hi everyone,
I know people have been upgrading brakes on spitfires by fitting Princess calipers.

Having spoken to HiSpec about there 4pot proncess pattern utralites they say they are designed to be used with a 260mm disc.

The standard Spit disc is about 225mm. Is the GT6 disc bigger? Do I fit it on the Spit hub or with its origional hub? Or does someone know of a better combination of bits?

Cheers, Paul

[Nick Moore]

The specs for HiSpec's billet calipers are on their site. Their M14, M16 and Princess alloy 4-pots all have the same 82.55mm bolt hole spacing, and I know a friend put Princess calipers on his Vitesse as a straight swap. According to Paul Tegler's website, GT6/Vitesse discs are 246mm (9.7") - certainly a bit bigger than Spitfire ones but not quite 260mm. So maybe the Princess calipers would fit, maybe not. As HiSpec also make a 4-pot M14 caliper replacement, and Spitfires have M14s, you could presumably fit a pair on your existing Spitfire setup. Or, if you want bigger discs you could fit GT6 uprights, hubs and discs and HiSpec's M16s.

I was thinking about fitting HiSpec calipers as well (they certainly look well made), but read a few stories about poor customer service. Granted, an unhappy customer makes a lot more noise than a happy one, but in the end I went for Wilwood calipers. Photos (small, low bandwidth!) in a couple of weeks.

[Paul318UK]

For me its a case of I want the extra piston area of type16's to reduce the pedal effort so thats the route I am taking. Interested to know how the price and spec of wilwood compare. Basic ultralight is £95. I will probable buy these and gt6 discs and try the fit on Spit uprights before I get GT6 ones

[Deleted User]

The willwoods and gt6 discs and uprights work perfectly, if you want to reduce pedal effort fit a servo, if you want to increase braking power fit bigger discs. Fitting bigger callipers wont decrease pedal effort significantly

[Paul318UK]

I'm going the calipere route rather than servo as I have a late spit with dual line brakes

[2litre-e]

i had the princess lug ultralites on standard spitfire uprights with the capri vented discs. just needed some spacers to centre everything.

[JohnD]

Paul,
"I want the extra piston area of type16's to reduce the pedal effort"
This is the old class room paradox about friction NOT being proportional to area.   Just increasing the brake pad area does not lessen the effort you need to exert on the brake pedal.   A servo does that, possibly at the expence of some 'feel',but by increasing the pressure.   The apparent paradox is because the force you exert is the same, but the greater area means less pressure/unit of area. Less pressure >> less friction.

Increase the squeezing force of the calipers and your foot need not work so hard either.  Use a master cylinder with a smaller cross sectional area, and you need not press so hard.  But you will have to press further as the pedal travel will increase.

Like so much in car design and tuning, it's a compromise.

With braking, heat is the enemy.   Brake compounds that will withstand more heat need heat to work, but they are lousy when cold.   They will be cold most of the time when driving on the road, because even with 'spirited' road driving, you don't cycle the acceleration and braking vigourously and often enough.   Fit them by all means but I fear they will be wasted and may not stop you well most of the time.

Race driving is different.  The Sb's ability to stop was not improved by 4-pots, vented Capri discs and 1155 pads, but it now maintains that ability all through the race.   Previously the  brakes would overheat and fade after a few laps.

John