- 1 Basic checks
- 2 Aspects of braking
- 3 Upgrades
Always ensure that your braking components are in full working order and good condition before embarking on any upgrade. Check that the calipers are in full working order (no sticking pistons, seals etc) and the brake hoses are not worn or cracked. Also check the servo is working properly if fitted (a duff servo normally gives you a hard pedal with a lack of braking force) and that the master cylinder seals are good (leaking seals give you a soft pedal, often slowly "sinking" if held under pressure).
Aspects of braking
There are a lot of closely interrelated aspects surrounding brake system operation, many areas can be improved but at the expense of another area. This makes everything a compromise, here are the aspects with their effects on performance etc:
ie torque at the wheel for a given brake fluid pressure. This can be improved in several ways:
1 - Larger discs, this in effect increases the leverage that acts on the wheel. Downsides are increased unsprung mass (and rotational mass due to the larger diameter), a slight increase in cost if it's a re-drilled one-piece disc or a larger increase in cost if it's alloy bells and rotors.
2 - Higher coefficient of friction in the pad material. Downsides are that in most performance pads they work better when warm/hot, and full race pads hardly work at all when cold, plus increased cost.
3 - Larger pistons in the calliper (and/or smaller master cylinder piston/s). This increases the mechanical advantage that the system gives your foot over the force applied to the back of the pads, but like all forms of increased leverage the longer the "lever" the longer the travel needed at the input end. In the case of brakes, the added clamping force at the pad is offset by a longer travel / softer pedal.
This is the effect of the mass of the brakes fitted to the strut, where they are not properly "sprung and damped" by the suspension like the chassis is. The lighter a brake system is, the faster and more controlled the suspension action can be, giving the car more grip. The downsides to lighter brake discs, is that they heat up faster due to the lower "thermal mass", but lighter callipers, pads, alloy bells and mounting brackets all give you "free grip".
The lighter and smaller the brake disc (and wheel/tyre/hub etc) the less energy is needed to spin it faster or slow it down. So a lighter and smaller brake disc will give the car better acceleration, economy and braking (if the brakes magically still worked just the same!). The downsides are reduced brake power, reduced cooling from the smaller disc vents and reduced thermal mass.
Fade (pad) resistance
This is the amount of heat the brake pads can withstand before they overheat into "brake fade", this feels like you have a hard pedal but no brake power (similar to a failed servo). In the olden days pads used to "gas", where the glue in the material boiled and producing a thin layer of high pressure gas that lifted the pad off the disc using the same principles as a hovercraft uses! This lead to people drilling (and grooving) their discs to release this gas. Modern brake materials no longer gas in anything like the same way, so grilled discs are of FAR less use than they used to, and given that they can crack the main reason people buy them is for the "look". Grooved discs DO still have a place as they scrub at the face of the pads, and with many race pads they are needed to stop the pad surface "glazing".
Fade (fluid) resistance
This is the amount of heat the brakes can withstand without the fluid boiling, when the fluid boils the bubbles created are easily squashed by the pressure created when the pedal is pressed, making the pedal sink straight to the floor and allying almost no pressure to the pads at all! This is probably the most dangerous form of brake problem and for the few seconds it happens the effect is as ba as a burst brake line. Fluid boiling can be reduced by:
1 - Running a fluid with a higher boiling point.
2 - Changing the fluid regularly as water is absorbed by most brake fluids, and of course only needs 100 degrees C to boil. Also once brake fluid HAS boiled it's resistance to boiling is actually reduced, and next time it will boil at a LOWER temperature!
3 - Using cooling air from the brake duct to cool the caliper.
4 - Using cooling air from the brake duct to cool a brake fluid radiator.
5 - Running a brake fluid recirculating valve. This clever gadget cycles the fluid into the calliper then back out and up into the main fluid reservoir, this keeps the calliper cooler and stops a stagnant volume of fluid from sitting in the calliper and getting very hot.
This is mainly about keeping the disc cool to stop it "warping" and keep the pads cooler so they can operate properly. You can reduce disc temperatures by:
1 - Having a larger disc with bigger, more efficient vents and larger area to be cooled, the downside is added unsprung/rotational mass (although mass helps in another way, next....).
2 - Having a heavier disc, this provides more "thermal mass". Thermal mass works because it takes twice as much energy to heat twice as much mass to a given temperature, so if you double the mass while keeping the energy input constant you HALVE the temperature (before cooling efficiency etc starts to come into play). The downside is added unsprung/rotational mass.
Disc warping resistance
It should be noted that brake discs juddering through the pedal are not "warped" in the way many people think, in most cases it's because road pads (which are abrasive) have been overheated and a high-spot has formed. This high spot gets VERY hot and into a changes into a different and much harder form of iron. Of course the new hard area is more resistant to the pad's abrasion and so as the material around it is worn away it becomes higher, which makes it hotter, and therefore even harder....and so on. The discs DO warp, but only when you press the pedal and this one high spot gets much hotter, rapidly expanding and warping the disc. The things people miss are that (1) the disc returns to a mostly non-warped state as soon as you back off the brakes or take the disc off the car for inspection, and (2) machining the disc won't fix it as there is still a hard spot in the iron waiting to start the whole process again once the abrasion or use continues! Upgrade pads often work by "smearing" their own pad material onto the disc rather than abrading the disc, thereby dodging the high-spot vicious cycle.
If you assume that the brake system will be used and a hard and sustained way (track-days etc) then the components ARE going to get very hot no matter what cooling you use, but there are ways to allow them to survive the temperatures and work very effectively for a sustained period.
- External piston dust seals on performance callipers often burn off, but they can be omitted without causing any problems in most cases.
- Brake discs get very hot in the area that's in contact with the pads and expend with huge force. In a one-piece disc this makes the disc form cone-shape as the vented "rotor" part expands but the "bell" part stays cooler and unchanged, in (very rare) extreme cases the vented part can crack right off the bell! To reduce these forces there are two options, (1) fit an iron rotor to an aluminium bell (aluminium expends faster with temperature than iron, so the cooler bell partly "keeps up" with the hotter rotor as it expands) and (2) fitting a "radially floating rotor (there are radial slots in the rotor or the bell with sliding "bobbins" in them, this allows the rotor to expand totally freely, with no force applied to the bell)! Floating rotors are very expensive though and are almost exclusively for race-cars only - although BMW have recently used the principle on the M3, the discs have aluminium bells with radial spoke-like pegs, and the cast-iron rotor "floats" on these pegs! Also large light-weight rotors rely less on the effects of thermal mass, and more on effective cooling vents to cool the brakes on each straight section of track.
- Race pads will continue to work happily way after normal pads would have totally failed, and often get better the more abuse they get, and race brake fluid can withstand the continued high temperatures.
- Brake ducts are very handy as the high speeds on the straight pump much more cooling air into the brakes than on a road car.
Main article: 5-Lug Conversion
The E30 M3 was fitted with completely different hubs, allowing it to take 5-lug wheels instead of the standard 4x100 E30 wheels. This allows for much larger wheels, and therefore bigger discs and callipers to fit inside them. Converting to a 5-lug setup is a popular option for serious performance driving.
First would be upgrading the pads as you get some easy extra torque and fade resistance (EBC Red, Mintex M1144/1155, Ferodo DS2500 or similar pads for fast road/light trackdays or EBC Yellow/Blue or similar for more serious track use) - of course all the OEM components need to be checked over at the this stage, including the cooling ducts. Fit fresh standard brake fluid and new standard discs (worn discs have less thermal mass and won't bed in properly with new pads).
Next would be increasing the resistance to the extra heat and pressure the pads can create by fitting stainless braided hoses (like Earls/Goodrich etc) and upgrading the existing brake fluid (like ATE Superblue, or Castrol SRF for a road/trackday oriented car).
A common question regarding brake hoses is "Which kit - 4 or 6 line?" The answer is simple; 4 Line kit for drums, 6 Line kit for rear disks. All ABS-equipped cars have rear discs, so you'll need the 6 Line kit if you have ABS.
Standard discs do the job for most applications perfectly well but do decrease their thermal mass over time, leading to decreased performance. The solution to that is just to replace them with a fresh new set. There is NO NEED to get drilled and/or grooved or funny coloured discs, unless you like the look.
If you want a proper upgrade, you need to increase the size of the discs. Here are the approximate sizes possible in each wheel size:
14" - Very little room, 255mm normally (275mm in some motorsport allys).
15" - 280mm (300mm in some motorsport alloys). There may be a new 290-300mm 4-pot kit available next year specifically for the 15" BBS...
16" - 300mm (320mm in some motorsport alloys). 302mm disks with 4 pot callipers can be made to fit under 16" wheels, according to Baddave.
17" - 325mm (345mm in some motorsport alloys)
Cars with E30 compatible discs
- Audi TT with some drilling ??
- Chrysler Voyager 302x28mm with redrilled holes(disk offset is near perfect)
- Volkswagen Corrado G60 280mm. Centrebore must be enlarged 1mm to fit E30 hub. Can be fitted with Mazda RX7 callipers
Ready made upgrades includes lightweight 4-pot kits and cheaper but heavier sliding caliper kits where the buyer sources second-hand calipers:
- RX7 4-pot calliper brackets with 280mm Corrado rotors sold here
- The 300mm.de kit, this uses a 312mm re-drilled disc and brackets to suit a BMW sliding calliper.
- The Wilwood 280mm and 310mm 4-pot kits which have 1.38" pistons.
- Other kits from mfrs including AP Racing, Brembo, Alcon, and Hi Spec.
Cylinders from the following vehicles are compatible with the E30
If you're fitting bigger discs, you will need compatible calipers that can apply a greater braking force over the increased area of the disc. If you can't stretch your budget to the bolt-on options, then substantial savings can be made by sourcing callipers from other cars and fabricating your own mounts. Scavenging parts from other cars can save you serious cash.
Cars with 4pot callipers
- Aston Martin(various)-DB7
- Alfa Romeo GTV/166
- Audi Possibly RS2,S8,RS8
- BMW E38 730i, 735i
- BMW E34 3.8L M5(very last ones)
- BMW E31 840i,850i,850csi
- Citroen C8 possibly (going by pad shape)
- Ferrari (all newer models)
- Fiat Coupe
- Fiat Ulysee possibly(going by pad shape)
- Ford Focus RS
- Ford Puma(racing) fitted with Alcon 4pots as standard
- Ford Sierra RS Cosworth 3dr
- Jaguar S type R
- Lamborghini(all newer models)
- Lancia Delta(integrale)
- Lancia Phedra
- Lotus Carlton (AP group C spec)
- Range Rover(newer ones have Brembo's)
- Mazda RX-7
- Mercedes ( most of the higher spec AMG variants)
- Mitsibishi 3000GT
- Mitsibishi Lancer ( from Evo 4 onwards iirc)
- Nissan 300ZX
- Nissan Skyline (R33GTR/R34GTR)
- Nissan 350Z
- Peugeot 607(possibly)
- Peugeot 807(possibly)
- Peugeot 406 Coupe
- Porsche 911/928/944/959/968/Boxster/Cayenne/Cayman
- Renault Clio Sport(mid engined version)
- MG MGF
- Seat Cupra R (Ibiza,Leon)
- Subaru Impeza STI
- Toyota Hilux
- Toyota Celica GT4
- Toyota Supra
- TVR ( certain newer models)