ST 185 Brake conversion

[Lauren]

I think you have to do the rears as well. Years ago I tried that old mk1 race car (with all the spaceframing D800 FHM or something?) anyways that car had big aftermarket discs on the front but no upgrade on the rears, think they were willwood.

All it did was continually lock the fronts up. The rears do a lot more braking than you would expect as they need to for a mid-engined setup.

So i'd never advocate just upgrading the fronts.

FWIW i've raced mk1s on standard brakes with no issues. I've done loads and loads of trackdays with no issues on standard brakes with a modded SC. If they are working 100% well then they are actually good enough for purpose even on track.

[PW@Woodsport]

I disagree with that,stock mk1 brakes are known to fade under heavy braking,to be honest lauren im very surprised you of all people would have felt the fade by now?

[IanClements]

ST single pot 185 calipers - More brake power, don't fade, pads last for ages. These are what the car should have had in the first place.

Just watch it in the wet if you're tyres are knackered.

[Lauren]

I disagree with that,stock mk1 brakes are known to fade under heavy braking,to be honest lauren im very surprised you of all people would have felt the fade by now?

I really think pad choice has a lot to do with it. Even Tom who is notoriously hard on the brakes (i'm always fairly easy on brakes as a rule) has been happy (I think) with the carbotechs.

None of the trackday lot that I hang around with are running bigger discs AFAIK.

[SySanguinary]

I don't know ...

When Tom built the 1.5 for/with me we looked at upgrading the disks and calipers but the budget and timescales simply didn't allow us. I ended up with refurbished calipers and new standard disks (not even grooved). I then opted for yellow stuff pads (couldn't afford carbotechs).

The brakes work more than well enough when cold but when they warm up they're fantastic.
I've had the car at Donnington and Anglesea this year driving for long sessions (30mins+) and never had a problem. The pedal hasn't even gone spongey on me. On one session in the 1.5 I managed to turn the disks a nice shade of blue! I always seem to give up before the car does.

I'm told I drive the car quite hard on track, so for me well maintained standard brakes are the way to go.

[Jim-SR]

......with the carbotechs......

for the price of carbotech pads every time you wear them out you could just upgrade the brakes and run Ferrodo DS2500's though!!

the carbotechs are excellent pads, but id expect them to be for their price, and youd still potentially get fluid fade issues on long runs, especially as the pads have a higher friction coefficient and generate more heat. so then youre spending £40/litre on Castrol SRF instead of £10 on AP or Motul fluid and there is yet further costs, plus the added risks of warping stock discs as they wear down

if youre running carbotech pads then id argue that you actually need to upgrade the rest of the braking system in the first place

[Lauren]

if youre running carbotech pads then id argue that you actually need to upgrade the rest of the braking system in the first place

I've never run them. Pagid fast road pads have been fine for me. I've never come in after a track session or even a race and thought, 'those brakes aren't up to scratch'.

[mr2mk1chick]

Jo, Are you still running the 1a brakes? or have you replaced them with 1Bs?

Stuart

We have the 1a brakes on the track car and std sc brakes (1b) on the SC, both with yellowstuff

[mr2mk1chick]

I still don't know why people bother with this upgrade.

Jo you pretty much answered your own question,reason being it IS an upgrade over stock brakes.

Tim we discovered the celica upgrade back in 99,ive no idea if the US guys were using corolla calipers before then or not,or if the corolla caliper is the same as a celica? ,but certainly here in the UK we were fitting celica calipers to mk1's before anyone else.

What i meant was why bother with this particular upgrade, when keeping stock calipers, grooved discs or std, and really good pads will perfectly suffice. (whether the mk1 is std or not. our sc has big pulley etc and not lightened, and Sy's 1.5 dosen't hang about either)
(As others who dive the cars hard on track have agreed too: Lauren, Sy et al)

[PW@Woodsport]

People ugrade to celica calipers because they want more stopping power i guess....which is exactly what this upgrade does.

[Xhermes]

I had refurbed calipers all around, Ferodo DS2500 pads on the front, Porterfield R4S brakes in the back. Dot 5.1 fluid, Goodridge lines and Advan semi slicks. I used it on Zandvoort racetrack here in Holland and after about 3/4 of the 20 minute runs fading would start. Not really serious but enough to notice. When I'm done with the MK1 I also want to go to Zolder, a track notorious for fading. Might aswell already put the Celica calipers on and benefit from the larger discs. Thus better cooling as stated above.

[Flat Pack]

I can see that a case can be made for better heat dissipation and so fade resistance from bigger brakes (whether or not anyone actually needs that is subjective and down to the individual).

Just changing the front brakes and so moving the brake bias fowards is the bit I don't understand. How does this increase stopping power on a mk1 (with arguably too much front brake bias already)? Under tricky braking conditions where you could lock a front wheel it should make things worse as the rears will be doing less work at that point and so increasing overall stopping distance.

[PW@Woodsport]

without going into too much detail you have to remember fitting bigger calipers means more piston chamber volume for the master cylinder to move fluid into,so that will decrease lock up on the fronts at the expense of maybe a little more pedal travel.

It requires someone more clued up on the mathematics of volumetric fluid movement and pressure to explain whats going on on a physics level,all i can say from real world experience is that going with bigger diameter or twin pistons,or even quad... does not give more lock up with the stock master cylinder.Perhaps thats the problem with the stock brakes? the piston chambers are too small?

Who knows,all i know is its a great upgrade that works.

[Jim-SR]

I can see that a case can be made for better heat dissipation and so fade resistance from bigger brakes (whether or not anyone actually needs that is subjective and down to the individual).

Just changing the front brakes and so moving the brake bias fowards is the bit I don't understand. How does this increase stopping power on a mk1 (with arguably too much front brake bias already)? Under tricky braking conditions where you could lock a front wheel it should make things worse as the rears will be doing less work at that point and so increasing overall stopping distance.

in a dead straight line this might be the case, but moving the brake bias rearwards will destabilise the car when braking under yaw conditions (e.g. braking with steering applied). youd end up with the back end breaking traction and stepping out. the stock brake bias favours the rear, but weight is tranferred forwards under braking, so having as much braking at the rear prevents locking up, but its sacrificing ultimate braking performance. the grip of the tyres is relative to the amount of vertical load on the tyre. the more vertical load, the more grip. if you increase front brake bias (up to a point) then you will transfer more weight forwards, and more weight means you can apply more braking force without breaking traction. obviously there is a limit to this, and eventually youll overload the tyres and lock up. but if youre fitting a brake upgrade it has to be assumed that you possess the driving ability to use it (if you dont then youd be better off with stock brakes), and if youve got a feel for the car you should be able to find the critical point of wheel lockup and work around it.

if you use the upgraded brakes to their maximum potential on stock suspension and road tyres then you will be able to lock the front brakes more easily, but youll be able to carry more braking into corners without unsettling the car so easily. alternatively, if you have more powerful brakes up front you can then apply less braking force for the same results as before, and thus reduce the temperature in the system and the problems of brake fade.

in an ideal world you would also upgrade the rear braking system, and then have an adjustable proportioning valve to tweak the bias until you find a sweet spot. however that will only apply to track cars, on the road its far safer to have the braking biassed towards the front, the worse case scenario then is understeer, which can be easily counteracted by cadence braking (lifting your foot off the pedal and then reapplying it). if you encounter oversteer under braking then you need a pretty impressive skill set to catch it (whilst still slowing down!!) if youre not fully expecting it.

[crazybrightman]

what im confused about is people complaining of fade on standard brakes. this is either caused by the pads or excess heat (assuming your brake fluid is ok, but that causes a soft pedal not fade). now as upgraded pads are available thats easily dealt with. now the next problem is the discs if these get too hot you will have fade, fitting bigger calipers to the same discs wont help this. the only way is larger brakes that have a larger heat sink effect and therefore reduce the chances of fade. the problem is you have then increased rotational mass, unsprung weight and so on all seems a bit ott realy. if your running a 1.5 or 1.6 then obviously thats a bit different but for a n/a or s/c i cant honestly see why you would fit different calipers or larger discs.

[Jim-SR]

what im confused about is people complaining of fade on standard brakes. this is either caused by the pads or excess heat (assuming your brake fluid is ok, but that causes a soft pedal not fade). now as upgraded pads are available thats easily dealt with. now the next problem is the discs if these get too hot you will have fade, fitting bigger calipers to the same discs wont help this. the only way is larger brakes that have a larger heat sink effect and therefore reduce the chances of fade. the problem is you have then increased rotational mass, unsprung weight and so on all seems a bit ott realy. if your running a 1.5 or 1.6 then obviously thats a bit different but for a n/a or s/c i cant honestly see why you would fit different calipers or larger discs.

when people refer to "brake fade" they are almost always referring to fluid fade, where the pedal goes soft and long. pad fade is just another type of brake fade, both are caused by heat

upgrading pads is indeed the first way to go, but you can only go so far with fluid. the ST185 brake conversion exists in 2 forms - single pot calipers with bigger discs, and twin pot calipers on standard discs. the one ive been referring to in all of my posts is the conversion with larger discs. youre talking about an extra 23mm of disc diameter, the discs are slightly fatter, the calipers themselves barely weigh more than the standard items. its not really OTT at all, its just a sensible upgrade that is a lot cheaper than going to single piece aluminium calipers on floating discs and spending £1000 on brakes for a road car!!

[silentk]

I've got the single pot ST185 callipers on the front of my mostly standard MK1b (the only mods are new shocks and springs, and braided hoses). The reason I've got them is that basically it worked out just as cheap as refurbing the existing brakes, which were terrible.

I got the callipers for 50 quid (in perfect working order so no need to refurb), which is how much a refurb kit cost. I also got standard discs and pads. So have very good front brakes without having to go for Porterfield or Carbotech pads (which are what £100 a set?), I can just use the normal £15 pads, so running costs are very low.

On track they're very good, no fade at all, just if you are too enthusiastic they do lock up, but it's easy to control and to be honest my rear brakes are probably doing nothing at all at the as they've not even been looked at since I got the car. When I get a chance I'm going to look at refurbing the rears and maybe gutting the bias valve.

[eRATic]

on my first mk1 i pit the twin pot Celica calipers on and let the rears. the front wheels would lock up on a hard pedal push and i thought the brakes were fantastic and could not be bettered. on my second mk1 i have the WMS 4 pot calipers on and mk2 rear brakes with a Corrado G60 front disc on the back. the set uo is awesome. both in stopping power but also feel.

By just upgrading the fronts you upset the brake balance of the car so any upgrade in terms of better caliper at the front will be complimented by improving the performance of the rear brakes.

a lot of people put the Celica ST185 caliper on and think they have the best set up purely because they dont have the opportunity to try other set ups using modified rear brakes and/or ST205 or WMS front calipers(which allow you to use 15" rims)

[Tom G]

without going into too much detail you have to remember fitting bigger calipers means more piston chamber volume for the master cylinder to move fluid into,so that will decrease lock up on the fronts at the expense of maybe a little more pedal travel.

It requires someone more clued up on the mathematics of volumetric fluid movement and pressure to explain whats going on on a physics level,all i can say from real world experience is that going with bigger diameter or twin pistons,or even quad... does not give more lock up with the stock master cylinder.Perhaps thats the problem with the stock brakes? the piston chambers are too small?

The maths is quite simple - For a given (fixed) brake fluid pressure:
larger caliper piston area = more pressure exerted.
(fluid pressure in force per area; more area=more force)

Therefore if front and rear piston size is the same, bias is 50/50.
If front area is twice that of rear, bias is 66/33.

we've had some discussions on TB about this, eg here:
http://forums.twobrutal.com/showthread. ... 490&page=3

the bias with st205front/G60rear conversion is about 85/15. stock is 66/34.
I'm not the first to find the bias problems with these conversions. I guess it depends what you're looking for, like whether you're racing (where minimal stopping distance is as important as fade resistance).
I think with an adjustable proportioning valve it would be a good upgrade.

[Jim-SR]

Therefore if front and rear piston size is the same, bias is 50/50.
If front area is twice that of rear, bias is 66/33.

making the assumption that the master cylinder is doing the same amount of work for both ends of the car. bearing in mind they are 2 seperate circuits, with a proportioning valve thrown in for good measure!