DBA Longlife Gold - Questions & Answers
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DBA Longlife Gold is the name given to an exciting range of cross drilled-and-slotted rotors manufactured in Australia by Disc Brakes Australia. Designed to give enhanced performance and improved appearance, DBA Longlife Gold rotors can be easily fitted to road cars in place of conventional disc. They bring to the affordable end of the "street" market the sort of braking technology which until now has been seen only on exotic sports machines.
DBA continues to manufacture and sell its huge range of conventional discs, but now offers a wide range of DBA Longlife Gold rotors to enthusiasts as a premium product option.
No. The range of DBA Longlife Gold rotors are designed (and warranted)
for street use only.
The difficulty from our point of view is that what works best under race conditions is not necessarily best for the street. Furthermore, top race teams can afford to replace their discs at the end of each race, but the requirements of street customers are somewhat different.
The sort of motor sport which road cars tend to be involved with (club lap dashes and sprint races) can often be harder on rotors than professional motor sport. Lap dashes and sprints often include very little warm-up and very little cool-down. Drivers often slam their foot on a set of cold brakes into the first corner and, at the end, park the car with the rotors still at 500 degrees Celsius. In such circumstances it is easy to warp discs, or even to weld the pads onto the disc surface.
The expression "cross drilled-and-slotted" refers to two separate processes, both of which are carried out on our DBA Longlife Gold manufactured rotors. The first procedure involves drilling rows of holes through the friction surfaces of the rotor; the second refers to milling a series of specially machined grooves from the centre of the disc towards the edge.
In combination, the processes are aimed at making the disc better ventilated and more effective. And let's not forget the cosmetic side: DBA Longlife Gold rotors look aggressive and purposeful, particularly with today's open-patterned alloy wheels.
Not necessarily. But in order to create a street performance disc suitable for the widest range of applications, we've decided to incorporate both the features into every DBA Longlife Gold manufactured rotor.
Let's talk about cross
The drill holes (which are sometimes called "gas relief openings) provide an exit route for the dust and gas. The holes are also commonly labelled "cooling holes" because of the improvements they make in this area. Better cooling means less fade during repeated heavy brake application. Obviously, the holes reduce mass. They also help dissipate water when driving in poor weather.
Slotting increases the bite of the pads. This helps pull the car up quicker. The process doesn't involve removing as much metal as cross-drilling, so it doesn't result in as great a weight saving. However, slotting is even more effective than cross-drilling in combating the problem known as "out-gassing". This is when, at very high braking temperatures, the bonding agents used in some brake pads produce a gas. Under extreme conditions, this gas can create a pneumatic cushion between pad and rotor, giving a driver a normal pedal feel but reducing the amount of friction being generated. The slots pump away gas and restore full contact.
The "micro-shaving" effect of the slots also serves to de-glaze the pads (this is why the edges of the slots on DBA Longlife Gold rotors are not chamfered or "radiused"). It also tends to even out the wear across the brake pad faces, increasing the effective contact area. This can extend rotor life.
Conventional wisdom once said so - and also dictated that all slots to be swept back from the centre in the same direction. However, with computer modelling we've managed to get slots on DBA Longlife Gold rotors to work in combination with the cross-drilling. This enables us to use a minimum of four grooves arranged in a mirror-image pattern. Such an arrangement saves the buyers the additional expense and inconvenience of having non-interchangeable left-handed and right-handed rotors.
Removing any metal from a rotor can potentially weaken it; working in the DBA Longlife Gold rotor's favour is Disc Brakes Australia's policy of safe, conservative designs (our discs are even over-engineered, some suggest), and the basic strength of the cast-iron alloy we use.
Some potential buyers have expressed concern about the likelihood of cracking. This is reasonable, as even standard factory rotors can suffer cracking under extreme use or abuse. Proper bedding of both rotors and pads should minimise the risk of cracking. Logic suggests that a drilled surface is even more exposed to the problem.
The weakest or most crack-prone part of the rotor is the outer edge, which in the normal course of expanding and contracting with heat, endures more movement than the centre of the disc, which is obviously smaller and is reinforced by the central hub or "hat". This is why DBA Longlife Gold road discs do not follow the practice of some racing rotors which have holes right at the outer edge or run slots off the edge of the disc.
Reports from a few owners confirm the occasional appearance of very small cracks around the holes. These were expected; they are caused by localised stresses and in no way detract from the reliability, durability or "stop-ability" of the disc. Some rotors have been returned with more serious structural cracking; however the number equates to a ratio of just 18 rotors in every 10,000 shipped. And of these, most were used in motor sport applications, something they were not designed or warranted for. To be frank, most of these owners would have destroyed the standard rotors under the same conditions; they were simply asking too much of their standard braking system and should have upgraded to bigger calipers and purpose-built motor sport rotors.
On a typical big Aussie six we take away 180 grams from each disc, or less than 2 per cent of its total weight. Multiply this by four and you have a total vehicle weight saving of 720 grams.
Although this is the sort of gain that a Formula 1 team would spend thousands of dollars attempting to achieve, it is not enormously relevant with a conventional car in normal road conditions. That's one reason we have not over-stressed the benefits of lower mass in our marketing. The other reason is a fear that people will mistakenly associate "lighter" with "less safe".
DBA Longlife Gold rotors will deliver better braking performance than conventional discs, but in most cases the improvement should probably be described as "significant" or "worthwhile" rather than "dramatic".
There are several reasons why it is difficult to quantify exactly how much performance improvement DBA Longlife Gold rotors can bring in typical road applications. It varies with the model of car, its kerb weight, the type of pads used, the type of braking system into which the new rotors are being incorporated and the inherent effectiveness of the standard rotors being replaced. Testing every type of vehicle under all conditions is clearly not possible. Nevertheless, we have tried a wide sample in varied situations. We have also interviewed as many owners as possible and are yet to talk to one who hasn't been pleased with the improvement.
To get an additional expert view, Disc Brakes Australia commissioned respected advanced driving instructor (and three-time NSW Hillclimb Champion) Peter Finlay to conduct a series of independent tests. Finlay - the proprietor of Nationwide Defensive Driving School - is comparing the stopping distances and general brake performance achieved with DBA Longlife Gold and conventional "factory" rotors under identical conditions.
During his most recent tests, using Sydney's Oran Park Raceway as a closed
and safe environment, a current series Holden Commodore fitted with the DBA
Longlife Gold product averaged a theoretical efficiency of 97 per cent over ten
stops from 100 km/h. It recorded a best stop of 38.6 metres. The average
stopping distance from 100km/h was 40.4 metres. This compared with 42.6 metres
(90.25 per cent theoretical efficiency) for the same car tested under similar
conditions with standard rotors.
The Finlay report noted that the DBA Longlife Gold rotors provided greater consistency from stop to stop and delivered good pedal feel. The ability to pull up the car 2.2 metres, or 5 per cent shorter is very encouraging. Such a distance could easily be the difference between an accident and a near miss. However, it can't be classified as a universal gain. Some cars may demonstrate less of an improvement with DBA Longlife Gold rotors, while other cars or perhaps other testing conditions might reveal a bigger performance gain.
We feel, for example, that the DBA Longlife Gold advantage would have been increased even further if the speeds were higher and the cool-down period between stops was reduced. On the other hand, the way the tests were conducted and the speed chosen - 100km/h - is entirely relevant to everyday road requirements, as was the choice of Australia's best selling car for the test.
When a car-manufacturer designs a disc rotor, their aim is to please the "average" owner, placing high priority on such things as quietness, durability and low production costs. When enthusiasts change their cars to improve performance they always have to accept some trade-offs. After all, there's no such thing as something for nothing.
In this case, the main trade-off for improved braking is a higher purchase price. The extra cost is due to there being much more production work in manufacturing cross drilled-and-slotted rotors. The specialist nature of the product also adds to the expense, reducing production economies of scale. However, we've done our best to keep the price premium as small as possible, using low-volume manufacturing techniques. Customers consider that the additional cost of the new DBA Longlife Gold rotors is justified by the performance increase, and are also won over by the appearance of the new rotors. In an emergency situation, every buyer will appreciate the extra stopping power even if they rarely drive hard enough to utilise it.
As any driver knows, the ability to pull up as car even one metre sooner can save a life.
Something to note about slotting: as the rotor wears, the slotting becomes shallower and therefore less effective. The DBA Longlife Gold slots are tailored to each rotor type, but typically they are about 1.5mm deep x 3mm wide. By the time the rotor has reached "minimum thickness" (we are careful to point out that the slots are not intended as a wear indicator!), there is not much slot left. To make them deeper would risk weakening the rotor.
In contrast, the holes remain effective in "out-gassing" for the whole life of the disc. As with slots, the pattern is unique for each rotor type; typically we have around 36 holes per disc face, each with a diameter of 6.5mm. To counter the tendency for cracks to form between holes, we normally put just one hole per vane on ventilated discs. This ensures the vane rib will act as a barrier between the holes. Each hole is chamfered around its opening to reduce pad abrasion and provide a smooth transition between hole and friction area (the latter to help combat surface cracking).
The feedback from our customers suggested that in certain circumstances a clicking noise occurs. We'd never noticed it; further research showed it is the sound of the pads running across the holes.
A more powerful engine uses more fuel, and it stands to reason that if brakes do more work, or generate more energy, they must suffer more wear. In the original planning stage we predicated a 10 per cent increase in pad wear. After all, the holes and slots would be abrasive on the pads and, with less metal-to-pad friction area, we expected more as well. Yet the on-road results have surprised us. In normal usage, pad wear is generally no greater, and rotor wear may be extended.
Testing on high-mileage taxis over the past 12 months has shown a totally unexpected benefit. One leading taxi company using DBA Longlife Gold rotors on its fleet has reported that they can last up to 150,000 kilometres with no machining.
This is three times the company norm, and has been achieved without any additional pad wear (the pads continued to be changed at the normal 25,000km intervals). The reason for the improvement relates to the shaving effect of the slots, which ensure improved contact between pad and rotors, plus the lower running temperatures.
Should high-mileage DBA Longlife Gold rotors require machining, this must be performed on a modern, high-speed, low-feed brake lathe. The correct procedure is to machine from the hub to the outer edge, taking 0.25MM (.001") in each pass. A word of caution: Machine in the one direction only; when feeding back, withdraw the tools and recommence from the hub to avoid tip damage. Repeat until required finish is achieved.
Cross-drilling and slotting removes not only weight, but also friction surface (or "swept" area). The figures are relatively small and the enhanced performance shows that the reduction in swept area is more than made up for by the improved ventilation that cross-drilling and slotting achieves.
For the record, the four disc rotors on a typical big sedan have a total swept area of 351.5cm2. With the cross-drilling we remove 22.9cm2, while the slots take away another 5.4cms. That's a total of 28.3cm3, or 8.1 per cent of the surface area.
There's no intrinsic reason. But you'll need to do plenty of testing and research. At DBA, we spent two years getting all aspects right before launching the product to the public. This research and development included perfecting the symmetrical hole pattern which ensures that the discs have correct balance, optimum cooling properties and sufficient contact area with the pads.
We've also put a lot of time into programming our computer-controlled (CNC) milling machines to carefully chamfer the edges of the holes to avoid tearing up brake pads. And we are using manufacturing equipment accurate to within three one-millionths of a metre.
There are already DBA Longlife Gold rotors available to fit most
Rolls Royce & Bentley models.
No, just choose the exact model BAE specifies for your car. The diameter and thickness specifications of a DBA Longlife Gold rotor are the same as with an original equipment component, so it bolts straight into the standard braking system.
The minimum thickness (stamped onto the disc) also remains the same, as the rotor's improved cooling properties compensate for the slightly reduced mass. However you must remember that, as you are asking your brake system to do more work, it must be in first class condition. This means the caliper slides, caliper springs and disc brake pistons must be operating freely, while a general check of all other parts in the system is a good idea.
We recommend you use the brake fluid Rolls Royce or Bentley suggest for your
model car, high
quality brake pads. These can be any pads made by a recognized manufacturer, but
make sure you observe the recommended "bedding-in" procedures. Equally
importantly, if you remove and reinstall the pads for inspection, make sure you
put them back the same way they came out. If reversed, the slightly raised lip
of what was previously the pad's trailing edge can catch in the groove, causing
increased heat and noise.
DBA Longlife Gold rotors are two-tone rather than silver. What's the story?
To give DBA Longlife Gold rotors an even greater visual appeal, Disc Brakes Australia is using Gold-coloured zinc di-chromate passivate plating on some versions and a high-temperature Gold paint on others, particularly the bigger hub-type rotors.
We reckon the two-tone Gold-and-silver effect looks great, whether behind
silver or coloured wheels.
DBA is one of Australia's most awarded component companies and has the largest single share of the local market for replacement rotors. We manufacture in a state-of-the-art facility in Sydney and take the attitude that, with brakes, second best is not nearly good enough. Therefore, DBA works to the industry leading QS-9000 quality standard, using factory components as the minimum benchmark and aiming to exceed their quality by as large a margin as possible.
Need further proof? DBA is the 1998 "AAAA Manufacturer of the Year". It is also an original equipment and/or replacement part supplier to some of the world's largest car companies.Top
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