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  • VXR Performance Centre, AP Racing Brakes, The story so...

    VXR Performance Centre - Astra VXR - AP Racing Front Braking System - The story so far

    The brief was to develop a braking system that would enhance to current O.E. supplied braking system. A braking system designed for road use with a progressive braking feel, and a firm and consistent brake pedal each time it is depressed. This brake package must be able to fit both the standard supplied 18” and 19” Astra VXR wheels (it will also fits under the VXRacing 18” wheel).
    As a secondary aim, to have the ability with a simple brake pad change to change the braking system from the road going application to a motorsport/trackday version.

    In conjunction with AP Racing, VXRacing have chosen to use a 343 mm diameter two piece disc – a very similar system that is used on the VXRacing BTCC Astra. The 343mm diameter x 28mm thick ventilated disc has 48 curved vanes. The operating surface has 8 machined grooves on each face to aid brake pad dust removal. The brake ring is mounted via a hard anodised aluminium disc bell, this gives the optimum weight saving to this disc package.
    The brake calliper is not only an aesthetically pleasing item but is also an extremely efficient Brake.

    The obvious starting point would be the brake pad most commonly used in majority of the AP Racing brake kits that are sold. As you can imagine AP Racing have a huge amount of data regarding all brake pads regarding wear rates, operating temperatures, wet running, etc the list is endless. This brake pad initially chosen was the Ferodo DS2500 this was expected to complete the package for everyday road use. In an ideal world this would be perfect of the shelf choice, then we could move on to test a motorsport/trackday option that will give you that extra brake bite and prolonged performance required for circuit use. A track pad option will probably give you less than half the expected life of the pad and you will replace your brake discs a lot sooner!

    Regarding our test programme, we have had to make modifications alone the way – some have worked, some have not!
    As with most items the brake pads and discs need to be well bedded to each other, this does not take many miles (approx 50 miles would be ideal) during this time you do not want to have any hard braking (possible to pull chunks from the pads) or any long periods of pads rubbing against the disc (possible glazing disc, pad or both).

    The testing has been carried out in three main ways, first normal road driving this is mainly endurance type testing. Second circuit testing, here we can test in safety for those events that can unfortunately sometimes happen on the road, and also other things that should never happen. Third we had the opportunity for Tom Chilton to evaluate the brakes at the Vauxhall Track Day at Thruxton – not a heavy braking circuit unfortunately but we did get some good feed back.

    Initial first road testing was quite disappointing we did not seem to have achieved the progressive brake pedal we set out to! Under hard braking operations it was quite good but both light and medium was quite disappointing. This testing continued for many miles on two separate vehicles (both the Sprint car and the blue development car). Many small modifications were carried out to and improve the system. We were very aware that time was moving on and we have customers out there desperate for the brake up-grade system. All the information we were gathering was being fed back to AP Racing, they were very surprised in the results we were getting. After some long hard technical discussions VXRacing suggested using a different type of brake pad material, something that they had used before on a different project, AP procured and final machined some the brake pads.
    In the mean time testing continued, Tom Chilton drove the Sprint car at Thruxton and was very complimentary about the stopping power and the brake consistency, as in majority of circuit running the soft and medium pedal functions are not often used, the normal late stab on the brake pedal is all that is necessary.

    After fitting the new Obtec (SBS) brake pad the light and medium braking operations were really improved, after a very short road testing programme it was necessary to get some more circuit testing done. On this occasion we went to Bruntingthorpe, with its long and wide main straight you can normally have plenty of space to do some high speed, heavy braking stops with out endangering or effecting other people.

    It was a nice dry sunny day with air temperature of 23°C. During the first few laps we did quite a few light and medium braking operations they were very progressive and constant as the brakes got warmer and the brake retardation (slowing down of the vehicle) got better and better. Next a few hard braking operations. First did a hard stop from 120mph the ABS cut-in all way down to stop - good braking. Then stop from 120mph keeping ABS off - good down to approx 60mph but brakes seemed to get better with heat and just brought on ABS with no extra pedal effort down to a stop. Next was 120mph and stand on brake pedal, ABS obviously, car pulled up very quickly. You could not replicate this test run on the road, although only a distance of 15 miles with a minimum of 80 hard braking operations the car was due a rest! The car was stopped and left to cool, there was a lot of disc cooling noise (pinging and hissing). There were signs of pad deposits on the discs, but not heavy. There was also very little brake dust deposit on the caliper and wheel which is very good.

    After testing some items on another car we go back to the brake test car. The brakes are now cool (you can touch them by hand) were very worried about the initial brake feel there was less retardation with light and medium braking. However with a little temperature in the brakes the retardation was back with all pedal pressures – there possibly had been a slight heat glazing on the pads/discs from previous testing. We then did a very similar brake test programme as described before. Also did a long series of repetitive hard stops from 80mph down to 40mph in very quick succession the pedal felt constant and firm during these tests.

    After a long hard days testing, driving the car back on normal roads the brakes were very good in light, medium and hard braking conditions – we are very happy with this initial test. There will be a lot more road type endurance testing and at least another couple of circuit outings in the very near future just to be able to sign off the brake package completely.

    Unfortunately due to this change in brake pad material AP Racing now have to produce as quickly as possible the new brake pads before the kits will be available to customers. At this time we do not have a confirmed delivery date, they will initially be manufactured in small batches. So to be one of the first to have these fitted to your car please call us now at the VXR Performance Centre (0870 242 4334) to arrange a fitting time.
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