DBA Longlife Gold - Questions & Answers
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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.
For this reason, specialised rotors are required for racing, and
specialised rotors for the street. With the DBA Longlife Gold
product, we've carefully found a balance between extra performance
and the safety, durability and affordability required by everyday
street users.
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 drilling first.
When the friction surfaces of a rotor are smooth and flat, there
is no means of escape for the gases and dust which build up between
pad and rotor. This is not a huge problem in normal motoring, but
is an important consideration in street performance applications.
These contaminants tend to "wedge up" and reduce braking
performance. The bigger the pads and the higher the braking temperatures,
the more likely the problem.
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.
On both occasions, the car was fitted with similar brake pads, tyres
and wheels. Finlay was the sole driver throughout and supervised
the testing procedures to ensure a valid comparison.
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.
Perhaps. There are already DBA Longlife Gold rotors available
to fit nearly 150 different applications, including GMH and Ford
and popular Subaru, Toyota, Honda, Daihatsu, Mazda and Mitsubishi
models.
The plan is to continue to increase the DBA Longlife Gold
range. Check with your local brake specialist for exact availability.
No, just choose the exact model DBA 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 brake fluid of a least Dot 4 standard and
new, high quality brake pads. These can be any pads made by a recognised
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.
Lastly, we don't recommend mixing conventional and DBA Longlife
Gold rotors on the same axle. The difference in performance
from side-to-side will upset the braking balance of the vehicle.
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 Longlife Gold rotors are made of Disc Brakes Australia's
proven cast iron alloy. When the zinc plating wears off the brake
pad swept area, it gives a two-tone Gold-and-silver effect. (The
high temperature paint does not cover the swept area). Although
developed for cosmetic enhancement, the coatings have the added
benefit inhibiting the surface rust which can develop on rotors.
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.
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