I feel sure that one of the first jobs you will want to complete on your track day car is upgrade the road-going brake pads for a higher performance type. The choice of competition brake pads is huge and I’ll leave any discussion on that, including other subjects, to future articles because it’s such a big subject with so many variables. However, one important task, once you’ve decided on an upgrade, is to bed the new pads to the discs properly.
This article outlines typically what’s required, but always check the manufacturer’s information for any specific recommendations as well.
Preliminary Jobs First
Before fitting new pads you might like to check out the condition of the rest of the braking system first. Use a proprietary brake cleaning spray to clean off accumulated brake dust and ensure that the brake callipers are working properly.
Some manufacturers require you to fit new discs if the previously used brake pads were of different material to the new ones. This is because the efficiency of their pad material can be compromised by incompatible pad material on the surface of the used disc. Check the manufacturer’s literature before you start. Some manufacturers also advise against the use of pre-bedded discs.
If you are able to use the old discs but they are badly scored or showing significant wear ridges near their service limit it’ll be worthwhile replacing these anyway, but some wear in the discs can often be preferable to a brand new disc surface. Again a check with the manufacturer will clarify the situation for you.
If you do fit new discs they may need bedding first using a different technique before you fit the new pads. I’ve covered this below.
Change the brake fluid if this hasn’t been done recently and perhaps upgrade to a higher performance Dot 5 fluid, but check that your system is compatible first. Not all braking systems are suitable for Dot 5 fluid if it is silicone based.
Competition cars and advanced driver pure track cars only: Before bedding new pads on old discs you can consider chamfering the edges of the pad at an angle of about 45 degrees so that the pad material is clear of the wear ridges on the non-braking surfaces of the disc.
Why do the discs need bedding?
All discs, whether for road, track day or competition use need to be bedded in to stress relieve the castings. You can purchase discs that have already been pre-bedded, but if this is not done and then if the discs aren’t bedded there is a risk that cracks develop in the disc or even of disc failure resulting in wheel lock-up with all the consequences that might lead into. Check with the brake pad manufacturer’s instructions first about the use of pre-bedded discs as mentioned above.
Disc bedding procedure
Many track day cars are also road legal, so it’s possible to bed the discs on the road, or to start the process on the road and complete it on the track. If the car is a pure track day car then everything is carried out on-circuit and the process on-track is very similar to bedding competition discs.
It’s preferable to use serviceable but used brake pads for this process, but do check about pad compatibility issues first and make sure that any deposited material from the “bedding” pads will not compromise the efficiency of the new pads. On the road for the first 5 – 10 miles try to carry out repeat gentle braking from around 60 mph down to around 30 mph having due regard for other road users, speed limits and the law. Try to do multiple braking applications in succession. Groups of 5 with a gap is generally considered an ideal.
Over the next 100 – 150 miles or so avoid abrupt full stops where possible, but gradually increase braking pressure from the normal braking you would apply in moving traffic up to maximum braking effort by the time you have completed the full distance. During the process, if you examine the discs you may see, depending on the materials, a gradual transition in colour across the disc until it is a uniform light blue tempered colour.
On-circuit it’s all very much easier. Over the first 5 – 10 miles (3 – 6 laps of Castle Combe Circuit) from an initial low speed with light application of the brakes gradually increase speed to full track speed but continuing to only apply a light braking application. That is, apply light braking over a longer than normal distance. Complete the bedding process over a final lap with moderately heavy application of the brakes.
You should then complete a cool down lap trying to avoid using the brakes and return to the paddock.
Again the colour transition should be observable, and for increased sophistication, you could apply thermal paint to the outside rim of the disc to confirm that sufficient temperature had been achieved for the process in the range 400 – 500C.
Note: When you are back to the paddock do not put on the handbrake or sit with your foot on the brake with the car stationary. This can lead to warped discs caused by the uneven cooling where the hot pad is in contact with the hot disc.
Why do the pads need to be bedded?
Particularly if you are bedding new pads to old discs, full contact of the pad surface with the disc won’t be achieved until the new pad conforms to the contours of the worn disc surface.
The new pads are likely to have various volatile chemicals embedded in them left over from the manufacturing process. It’s necessary to boil or burn these off in a controlled manner before the brakes can be used to maximum efficiency. If the brakes are used too hard initially, the very rapid boiling off of these volatile substances can cause the brake pad surface to crack and break up, sometimes catastrophically. Also too hard application immediately can cause these residual resins etc to glaze on the pad and disc surfaces leading to poor performance and brake shudder.
The materials of the pad will have some compressibility when new and the aim should be to stabilise this so that consistent braking and a firm pedal results.
Lastly properly bedded pads will give improved braking performance and last longer.
The initial bedding process
The idea is to get some initial heat into the pads. Approximately 4 – 6 retardations using a moderate brake pressure from a speed of about 90 mph down to around 50 mph should be about right, accelerating back to 90 mph and allowing around 400 yds or so between each brake application.
The idea is to get heat into the brakes without exceeding around 400C. Difficult to judge without fancy equipment or the application of thermal paint to the discs, but following the above procedure should be fine for most applications.
Don’t be tempted to use higher speeds at this stage because the energy being dissipated in the brakes increases exponentially with speed.
It’s also important not to brake and apply power at the same time (dragging the brakes), so no left foot braking for example.
The high speed bedding process
Immediately after the initial bedding process is complete apply medium to high pedal pressure and brake from around 100 mph (some sources recommend 110 mph) to around 50 mph. Do not lock the wheels or induce the ABS, if fitted, to operate.
Regain speed and allow around 4 or 5 light pedal pressure recovery braking periods, then repeat the high speed, high pedal pressure braking allowing a minimum of 500 yds between the high speed braking points.
Repeat this process another 4 or 5 times.
It may be that after the initial and high speed processes the brake pad bedding is not complete ie the full pad surface is not yet in contact with the disc and pad material has not transferred to the disc. If this is the case repeat the whole process from the initial bedding process.
The distance between corners and thus braking points on most racing circuits will naturally allow the above procedures to be carried out without causing any significant inconvenience to other circuit users if a bit of common sense is applied.
Track day cars – good practice for each session once brakes are bedded and in use
On entering the circuit, the brakes (and the tyres for that matter) are cold and need to be brought to their operating temperature such that good brake performance is achieved and warping of the discs is avoided. At the same time as you are increasing speed and warming the tyres, bring the brakes up to temperature by gradually increasing the brake application pressure over at least one lap.
Before leaving the circuit, likewise allow the braking system at least one cooling down lap with minimal or zero braking as far as possible.
When you get back to your spot in the paddock, don’t sit with your foot on the brake or you’ll likely warp the discs.
Similarly don’t apply the handbrake – some handbrake systems work on the rear pads leading again to warped discs.