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May 30, 2016 11:07 am
May 30, 2016 11:07 am
Subject: Re: V12 & LG6 brake drums; lightened v standard?
Hi all,
Interesting subject these brake holes.
In the past it was common to make holes in the drums for lightening and for cooling, (supposedly)
However,
The holes obviously do lighten the drums but not as much as you would think. The actual effect of the weight differs with the distance the mass is away from the centre of rotation, so one drum weighing in at several pounds lighter than another can be a little misleading. Motorcycle drums are lightened often by drilling the finned area which is lightening in the best place... BUT
Many years ago we had a problem with brakes overheating on a drum braked race car, (easily capable of 140mph+) under investigation we found that it showed most overheating at the points on the friction area closest to the lightening / cooling holes, we then under test discovered that the largest proportion of heat removed from the brake friction area is done so by heat dissipation into the actual drum material and then into the hub, These big holes actually 'Reduced' the cooling ability and were in fact causing the overheating. We made new drums which were heavier unfortunately but much to our joy, completely eliminated the brake fade and local overheating. Cooling ducts were improved on the backplates later and this again aided cooling to a point where we could even use a softer lining.
Ally drums are the way to go if you want the best of both worlds but stay away from some of the rubbish available as I have seen some shocking quality offered by supposedly reputable manufacturers.
Look out for conformity of thickness of the cast in iron liner, this needs to be dead centre if good wheel balance is to be achieved.
Look also for signs of welding on the cast in iron liner, this is absolutely unacceptable and positively dangerous on a highly stressed drum.
Also a set of drums should be identical, and this means absolutely identical, accept nothing else.
Brakes and crash helmets rule 1.
"Fit the items that match the value of your head"
Regards,
Jules
Hi all,
Interesting subject these brake holes.
In the past it was common to make holes in the drums for lightening and for cooling, (supposedly)
However,
The holes obviously do lighten the drums but not as much as you would think. The actual effect of the weight differs with the distance the mass is away from the centre of rotation, so one drum weighing in at several pounds lighter than another can be a little misleading. Motorcycle drums are lightened often by drilling the finned area which is lightening in the best place... BUT
Many years ago we had a problem with brakes overheating on a drum braked race car, (easily capable of 140mph+) under investigation we found that it showed most overheating at the points on the friction area closest to the lightening / cooling holes, we then under test discovered that the largest proportion of heat removed from the brake friction area is done so by heat dissipation into the actual drum material and then into the hub, These big holes actually 'Reduced' the cooling ability and were in fact causing the overheating. We made new drums which were heavier unfortunately but much to our joy, completely eliminated the brake fade and local overheating. Cooling ducts were improved on the backplates later and this again aided cooling to a point where we could even use a softer lining.
Ally drums are the way to go if you want the best of both worlds but stay away from some of the rubbish available as I have seen some shocking quality offered by supposedly reputable manufacturers.
Look out for conformity of thickness of the cast in iron liner, this needs to be dead centre if good wheel balance is to be achieved.
Look also for signs of welding on the cast in iron liner, this is absolutely unacceptable and positively dangerous on a highly stressed drum.
Also a set of drums should be identical, and this means absolutely identical, accept nothing else.
Brakes and crash helmets rule 1.
"Fit the items that match the value of your head"
Regards,
Jules