Brake options

[MartG]

I'd be interested to see what your bias calculations would be for my trackday car - it's a 1a SC conversion, with ST165 twin pots up front ( 2 x 42.7mm pistons ) with 1B disks, and 1B rears with a gutted bias valve - the master cyl is the original 1a item. Also what effect would re-instating the bias valve have on the bias.

[AdrianS]

I've got:

AW11 f = 51.0 x 1
AW11 r = 36.3 x 1
SW20 late f = 36.4 x 2
SW20 late r = 42.75 x 1
ZZW30 f = 51.0 x 1
ZZW30 r = 44.25 x 1

...all from direct measurements - hope that helps!

Thanks heaps! That's all within a whisker of my figures now.
What I need now is data for the various non-mk1 calipers. Then I can update my bias graphs for various combinations.

I was thinking mk1b and late sw20 rears, with mk1a / st165/st185/st205/BZR fronts. (I think the BZR fronts are a celica caliper anyway).

Questions :
Are my piston sizes for the celica calipers correct ?
Are st165 pistons opposed, or side by side ?
What disk diameters are used for the various non-standard calipers in a mk1 ?

ps Sorry for hijacking this thread

[System-G]

Very interesting - thanks Adrian

[Keri-WMS]

Questions :
Are my piston sizes for the celica calipers correct ?
Are st165 pistons opposed, or side by side ?
What disk diameters are used for the various non-standard calipers in a mk1 ?

ST165 pistons are side by side, the only opposed piston Celica caliper Iknow of is the ST205 4 pot.

I only have:

ST185 = "52.5mm" x1 <<<< but this is a very old note, and might be wrong.
ST202 import/AT200 etc 255mm disc fit = 57.1mm measured.

The AW11 with ST185 front calipers uses 277mm discs, BUT you get a fraction of the pad overhanging - most people don't notice and its not a big issue.

[MartG]

There is a table of caliper piston sizes on Twobrutal. From that

ST185 1x 57.2mm
ST205 4 x 40.4mm

[Keri-WMS]

ST185 1x 57.2mm

This is probably more likely to be right than my old note! I don't regard any brake specs as "fact" unless I've measured them myself, and I don't have a reference ST185 caliper...

[AdrianS]

Here are the amended specs

Master Cylinders :


Calipers and disks :


And here is the static bias and pedal feel.
Pedal travel is ratio of master cylinder to pad travel, eg m/c stroke reqd to move all pads 1mm. More is worse.
Pedal pressure is the ratio of force on the master cylinder piston to braking force (retardation). This ignores the effect of the brake booster (anyone got data on boosters ?).

Note that brake bias curves will be different with bigger brakes. As the brake piston area goes up, the line pressure required decreases for a given braking force (deceleration), so the bias valve will have less effect.

These figures show that
a) Fitting larger brakes to the front with standard rears increases the front bias considerably (duh!)
b) Fitting a 15/16" or 1" master cylinder will keep the pedal travel close to standard with bigger brakes (also duh!)

I'd love to add disk + caliper weights one day - big iron disks + big iron calipers are surprisingly heavy.
Alloy calipers and hats are the way I'd go, if I had the money, with careful selection of master cyl & bias valve.

I think I've gone on long enough for now; hope this has been of interest.

[JMR_AW11]

My F/R pads need replacing soon on my red mk1b according to the last MOT.

Can anyone recommend better aftermarket pads for road use?

Possibly because I'm an ex motorcyclist I'm not a 'braker' (been on the same Toyota pads/discs since 1994 in this car)

I'm concerned about brake balance so I'd only choose an aftermarket pad if it outbraked the Toyota pads without upsetting the brake balance.

I did once have to brake hard mid bend in my mk1 at about 60mph and I was amazed the car didn't spin despite mega tyre smoke. I don't want to lose this balance.

I'm not bothered about brake fade as I never get this on the road but I've always thought the stock brakes were adequate at best. You can really feel the weight of the car when trying to brake hard, especially downhill.

I've changed the fluid several times but never the brake hoses/lines.

[MartG]

Jeremey - if you're light on the brakes like you say, avoid any performance pad as you'll never get them hot enough to work properly. Go for an OEM equivalent from a reputable manufacturer like Mintex, or try EBC Blacks

[JMR_AW11]

Jeremey - if you're light on the brakes like you say, avoid any performance pad as you'll never get them hot enough to work properly. Go for an OEM equivalent from a reputable manufacturer like Mintex, or try EBC Blacks

Thanks.

Would I be mad to go for OEM pads again? I don't have a clue how much OEM pads cost but I need a full set for the whole car plus it's 2 years since I had the fluid replaced.

AFAIK the car is on its second set of pads since new. They were replaced at about 27k before I bought the car and it's now done just over 60k miles.

BTW It's still on the same rear exhaust since I bought it in 1994 and the exhaust looks good for another few years. I'm an unashamed fairweather driver of this car and I try to give it a good run whenever it goes out so this is why it's only on exhaust #2

[toxo]

Last time I bought OEM pads for my SW20 they were £25 an end. I get 25% off pads and discs though so they'd be £33 ish an end I would imagine.

[Keri-WMS]

Would I be mad to go for OEM pads again?

If I were you I would either:

1 - Get gen Toyota pads F+R (as motor factor pads can vary a lot) but with new cheap discs.

2 - Or for the same price try EBC Reds on plain discs, if you fancy a change or might end up driving it harder at some point - they really are fine from cold.

Either will do you fine for road use in my opinion, don't waste money on "performance discs" but do get new ones to go with the new pads.

[System-G]

EBC Reds are good on a road car. Blacks & Greens are a waste of time & money. The reds don't need much temperature in them as they have excellent cold bite.

[un1eash]

Never had any problems stoping with my standard disks and EBC green pads all round.

[Keri-WMS]

Never had any problems stoping with my standard disks and EBC green pads all round.

Have you ever tried Reds for comparison though?

[un1eash]

Havent finished with the greens yet, i might be tempted to try the reds but the greens work perfectly fine for my driving style on the road.

May be a different story when i finally get round to putting the mk1 back on the road and try out some track days.

[Keri-WMS]

Far later than planned, I've done the brake bias comparisons for the Mk1b and upgrades:

It only looks at the torque generated for a fixed line pressure (isolates the caliper and disc for comparison), master-cyl and tyre diameter etc etc are ignored.

Standard AW11-b (late Mk1 MR2):


...that's the standard car, here are the upgraded options....

Standard rear brakes matched with 277mm disc / 1.38" piston WMS kit:


Standard rear brakes matched with 277mm disc / 1.25" piston WMS kit:


"22v" (Rev 2>on Mk2 MR2) rear brakes matched with 277mm disc / 1.38" piston WMS kit:


So there are a few options there, the 1.38 and the 1.25 pistons both work fine for the std car, but I would probably opt for the 1.25 in most cases.

Hope that helps, more grist for the brake mill!

[rikster]

what will be the best setup for what i have

Front Hi-Spec racing 4 pots & racing pads + 300mm disks or st165 2pot & mk1b discs

rear 22v mr2 mk2 discs

bias in or out?

car is for racing in the tss its 4agte setup

[ulysess1966]

im sorry,i dont mean to argue but this statement is not true,i had huge st205 4 pot calipers and 300mm discs on my last mk1 and it didnt upset the bias at all and it didnt lock up easier.If anything id just made the car stop very very quickly,almost an ABS feel.

I was told at my last MOT the car's braking was biased too much to the front, but it was still passed. The only thing different from the previous MOT was the ST165 2-piston calipers.

Is there any simple way to adjust this? All those graphs are giving me nightmares.

[MartG]

You can shift the bias rearward by gutting the bias valve, or by upgrading the rear brakes