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You may have noted that during last years London Athens event the front mudguard support brackets failed on both sides of my Ford based Sportster. Not the first time this has happened with one or more failures on every endurance event we have entered. Sure the roads are more demanding than most but action was clearly required.
The originals were made from 19mm mild steel seamed tube with a wall thickness of 1.5mm. These were either butt welded onto plate or fixed to collars of around 20mm diameter. The mudgards themselves were well made but mighty heavy at 1.4 kilos each.
First step was to reduce the weight of the guards themselves and this was easily done by removing material from the inside. It may have been posssible to go further but I settled for 1 kilo each, so 0.4 kilo reduction. This of course reduces the bending moment at source and the weight benefit is multiplied by the G forces of probably around 2G.
New solid bosses were made for the location points on the caliper bolts of 28mm dia to give a much stiffer mounting. The tube chosen was T45 cold drawn seamless carbon manganese steel of 22mm dia and 2mm section. Frequently used in aircraft and motorsport frame applications, it's mighty tough but not easy to work. With high strength and elastic limit, it requires an 8 degree overbend when forming to achieve the required set, such is the materials natural spring. At close on £20 a metre you don't want too much trial and error so establishing the exact shape to prevent fouling in all steering geometry positions took great care not to mention time.
The fixing plates for the guards themselves were increased from 20X5mm to 30 X5mm as there had been one failure in this area across the threaded section for the mount bolts.
The ensemble was bronze welded to avoid martensite forming within the welded area, as a reliable/controlled slow cooling method was not available. Bronze welding of the material is perfectly sound and again frequently used in airframes. Once in situ with the mudguards mounted , appropriate secondary locations were made and welded into place to provide positive fixed location for both front and rear struts. (previously only the front strut was fixed for location)
A couple of comforting numbers emerged apart from the much strengthened material and mounting: cross section of the tube increased by 54%. Weight of guards reduced by 28% (times 2G).
Completed, the whole system is far stiffer and looks tidier than the original.
Will they break again? Ask me in five years time, but if they do I will really struggle to think of anything better. More photos on request, or see them at Stoneleigh)
Pete C
The originals were made from 19mm mild steel seamed tube with a wall thickness of 1.5mm. These were either butt welded onto plate or fixed to collars of around 20mm diameter. The mudgards themselves were well made but mighty heavy at 1.4 kilos each.
First step was to reduce the weight of the guards themselves and this was easily done by removing material from the inside. It may have been posssible to go further but I settled for 1 kilo each, so 0.4 kilo reduction. This of course reduces the bending moment at source and the weight benefit is multiplied by the G forces of probably around 2G.
New solid bosses were made for the location points on the caliper bolts of 28mm dia to give a much stiffer mounting. The tube chosen was T45 cold drawn seamless carbon manganese steel of 22mm dia and 2mm section. Frequently used in aircraft and motorsport frame applications, it's mighty tough but not easy to work. With high strength and elastic limit, it requires an 8 degree overbend when forming to achieve the required set, such is the materials natural spring. At close on £20 a metre you don't want too much trial and error so establishing the exact shape to prevent fouling in all steering geometry positions took great care not to mention time.
The fixing plates for the guards themselves were increased from 20X5mm to 30 X5mm as there had been one failure in this area across the threaded section for the mount bolts.
The ensemble was bronze welded to avoid martensite forming within the welded area, as a reliable/controlled slow cooling method was not available. Bronze welding of the material is perfectly sound and again frequently used in airframes. Once in situ with the mudguards mounted , appropriate secondary locations were made and welded into place to provide positive fixed location for both front and rear struts. (previously only the front strut was fixed for location)
A couple of comforting numbers emerged apart from the much strengthened material and mounting: cross section of the tube increased by 54%. Weight of guards reduced by 28% (times 2G).
Completed, the whole system is far stiffer and looks tidier than the original.
Will they break again? Ask me in five years time, but if they do I will really struggle to think of anything better. More photos on request, or see them at Stoneleigh)
Pete C
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