DBA Steve
11-10-2009, 04:11 PM
From the DBA FAQ at www.dba.com.au
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Disc Brakes Australia (DBA) frankly answers questions about the company’s popular range of slotted and cross-drilled Street Series rotors.
http://www.racedotcom.com/attachment.php?attachmentid=76&d=1255240189
HOW MUCH METAL IS TAKEN AWAY WITH CROSS-DRILLING
AND SLOTTING?On a typical large sedan/wagon street vehicle we take away 180 grams from each cross-drilled and slotted disc, or less than 2 per cent of its total weight. Multiply this by four and you have your total vehicle weight saving 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’.
CAN I EXPECT DRAMATICALLY IMPROVED BRAKING?
DBA Street Series rotors will deliver better braking performance than conventional discs, but in most cases the improvement should 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 Street Series rotors can bring in typical road applications. It varies with the model of car, its kerb weight, the type of pads used (and how well they have been bedded in), the type of braking system into which the new rotors are being incorporated and the inherit 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 Australian NSW Hillclimb Champion) Peter Finlay to conduct a series of independent tests.
During tests using Sydney’s Oran Park Raceway as a closed and safe environment, a Holden/GM Commodore fitted with the DBA Gold cross-drilled and slotted 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 100 km/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.
For more on this test click the link to Testing the DBA performance rotor (http://www.racedotcom.com/showthread.php?p=30959#post30959).
ARE THERE TRADE-OFFS?
When a car-manufacturer designs a disc rotor, the 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 tradeoffs. After all, there’s no such thing as something for nothing. In this case, the main trade-off for improved braking is higher purchase price. The extra cost is due to there being a great deal more production work in manufacturing rotors that are slotted, or crossdrilled and slotted. 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 premiums as small as possible, using innovative lowvolume manufacturing techniques. Many customers feel the additional cost of the DBA Slotted or DBA
Gold rotors is justified by the enhanced performance alone, and consider that the attractive appearance is merely a bonus. 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 a 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 Street Series 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 combating ‘out-gassing’ for the whole life of the disc. As with slots, the pattern is unique for each rotor type, typically we have between 24 and 36 holes per disc face, each with a diameter of 5mm. To counter the tendency for cracks to form between holes, we previously put just one hole per vane on ventilated discs to ensure the walls between the vanes would act as a strengthening barrier between the holes. The increasing adoption of the patented Kangaroo Paw ventilation system on DBA Street Series rotors, however, has made this more complex.
The Kangaroo Paw system doesn’t use traditional vanes - it uses a series of diamond shaped pillars to promote greater airflow. The holes now need to be positioned next to these pillars. In a manufacturing sense this is more complex, but from a buyer’s point of view it gives a disc that is stronger as well as better cooled. Each hole is chamfered or ‘radiused’ around its opening to reduce pad abrasion and provide a smooth transition between hole and friction area.
Under some circumstances a small clicking noise may occur as a result of the pads running across the holes.
ARE CROSS-DRILLED AND SLOTTED ROTORS HARD ON BRAKE PADS?
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 predicted 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 rotor wear too.
Yet the on-road results have surprised us. In normal usage, pad wear is generally no greater, and rotor wear is sometimes extended. Testing on high-mileage taxis has shown a totally unexpected benefit. One leading taxi company using DBA Street Series rotors on its fleet has reported that they can last up to 150,000km with no machining. This is three times the company norm, and has been achieved without any additional pad wear (the pads continue 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 Street Series rotors require machining, this must be performed on a modern, high-speed, low-feed brake lathe. The correct procedure is for the technician 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, the technician should withdraw the tools and recommence from the hub to avoid tip damage and repeat until required finish is achieved. Cross-drilling and slotting remove 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. The cross-drilling on a DBA Gold rotor removes 22.9cm2, while the slots take away another 5.4cm2. That’s a total of 28.3cm2, or 8.1 per cent of the surface area.
DO I NEED TO MAKE OTHER CHANGES TO FIT THESE NEW ROTORS?
No, just choose the exact model DBA specifies for your car. The diameter and thickness specifications of all DBA Street Series rotors are the same as with original equipment components, so they bolt 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 of the system is a good idea. We recommend you use brake fluid of at 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 important: 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 Street Series rotors on the same axle. The difference in performance from side-to-side will upset the braking balance of the vehicle.
Don't forget part 1 (http://www.racedotcom.com/showthread.php?p=30957#post30957) for the start of the definitive guide to everything you wanted to know and you might liketo also look at the video series at http://www.youtube.com/watch?v=wdvUx...eature=channel
DBA Steve
www.dba.com.au
-------------------------------------------------------------
Disc Brakes Australia (DBA) frankly answers questions about the company’s popular range of slotted and cross-drilled Street Series rotors.
http://www.racedotcom.com/attachment.php?attachmentid=76&d=1255240189
HOW MUCH METAL IS TAKEN AWAY WITH CROSS-DRILLING
AND SLOTTING?On a typical large sedan/wagon street vehicle we take away 180 grams from each cross-drilled and slotted disc, or less than 2 per cent of its total weight. Multiply this by four and you have your total vehicle weight saving 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’.
CAN I EXPECT DRAMATICALLY IMPROVED BRAKING?
DBA Street Series rotors will deliver better braking performance than conventional discs, but in most cases the improvement should 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 Street Series rotors can bring in typical road applications. It varies with the model of car, its kerb weight, the type of pads used (and how well they have been bedded in), the type of braking system into which the new rotors are being incorporated and the inherit 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 Australian NSW Hillclimb Champion) Peter Finlay to conduct a series of independent tests.
During tests using Sydney’s Oran Park Raceway as a closed and safe environment, a Holden/GM Commodore fitted with the DBA Gold cross-drilled and slotted 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 100 km/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.
For more on this test click the link to Testing the DBA performance rotor (http://www.racedotcom.com/showthread.php?p=30959#post30959).
ARE THERE TRADE-OFFS?
When a car-manufacturer designs a disc rotor, the 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 tradeoffs. After all, there’s no such thing as something for nothing. In this case, the main trade-off for improved braking is higher purchase price. The extra cost is due to there being a great deal more production work in manufacturing rotors that are slotted, or crossdrilled and slotted. 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 premiums as small as possible, using innovative lowvolume manufacturing techniques. Many customers feel the additional cost of the DBA Slotted or DBA
Gold rotors is justified by the enhanced performance alone, and consider that the attractive appearance is merely a bonus. 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 a 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 Street Series 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 combating ‘out-gassing’ for the whole life of the disc. As with slots, the pattern is unique for each rotor type, typically we have between 24 and 36 holes per disc face, each with a diameter of 5mm. To counter the tendency for cracks to form between holes, we previously put just one hole per vane on ventilated discs to ensure the walls between the vanes would act as a strengthening barrier between the holes. The increasing adoption of the patented Kangaroo Paw ventilation system on DBA Street Series rotors, however, has made this more complex.
The Kangaroo Paw system doesn’t use traditional vanes - it uses a series of diamond shaped pillars to promote greater airflow. The holes now need to be positioned next to these pillars. In a manufacturing sense this is more complex, but from a buyer’s point of view it gives a disc that is stronger as well as better cooled. Each hole is chamfered or ‘radiused’ around its opening to reduce pad abrasion and provide a smooth transition between hole and friction area.
Under some circumstances a small clicking noise may occur as a result of the pads running across the holes.
ARE CROSS-DRILLED AND SLOTTED ROTORS HARD ON BRAKE PADS?
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 predicted 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 rotor wear too.
Yet the on-road results have surprised us. In normal usage, pad wear is generally no greater, and rotor wear is sometimes extended. Testing on high-mileage taxis has shown a totally unexpected benefit. One leading taxi company using DBA Street Series rotors on its fleet has reported that they can last up to 150,000km with no machining. This is three times the company norm, and has been achieved without any additional pad wear (the pads continue 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 Street Series rotors require machining, this must be performed on a modern, high-speed, low-feed brake lathe. The correct procedure is for the technician 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, the technician should withdraw the tools and recommence from the hub to avoid tip damage and repeat until required finish is achieved. Cross-drilling and slotting remove 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. The cross-drilling on a DBA Gold rotor removes 22.9cm2, while the slots take away another 5.4cm2. That’s a total of 28.3cm2, or 8.1 per cent of the surface area.
DO I NEED TO MAKE OTHER CHANGES TO FIT THESE NEW ROTORS?
No, just choose the exact model DBA specifies for your car. The diameter and thickness specifications of all DBA Street Series rotors are the same as with original equipment components, so they bolt 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 of the system is a good idea. We recommend you use brake fluid of at 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 important: 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 Street Series rotors on the same axle. The difference in performance from side-to-side will upset the braking balance of the vehicle.
Don't forget part 1 (http://www.racedotcom.com/showthread.php?p=30957#post30957) for the start of the definitive guide to everything you wanted to know and you might liketo also look at the video series at http://www.youtube.com/watch?v=wdvUx...eature=channel
DBA Steve
www.dba.com.au