When Dahon discontinued their Roo El which used the 20" version of the Sram Sparc hub (which has the attractive feature of incorporating in a single casing a five speed hub gear, two 100 watt motors, and a controller circuit board, ie everything except the battery and the on/off switch) I was concerned that spares for the 20" system might soon become difficult to obtain. However, I have been both relieved, and intrigued, to learn that the 20" version is supplied not only for 20" wheels in the EU, but also for 26-28" wheels in the US. The reason for this is that the 20" version in the larger wheel produces a top cut-off speed of 20 mph which is legally acceptable in North America. For 26-28" wheels in the EU Sparc supply a modified version of the 20" which cuts out at a road speed of 15mph, and is therefore legal in the EU.
What intrigues me however is that a 20" version could be obtained and built into a 26-28" to produce a "delimited" bike for use in the EU. This would be illegal with regard to top cut-out speed, but it would conform to the requirements of under 250 watt nominal power, as well as the non-throttle "pedelec" requirement which ensures that the motor comes on only when the pedals are turned (the Sram Sparc system uses a sophisticated "pedelec" which does not rely on sensors round the cranks, but measures the road speed through the rear sprocket which transmits speed and motion through various internal motor gears to the controller board).
A further consideration with regard to legality is the possible use of the Sram Sparc handlebar "controller" to limit the speed to the legal maximum in the EU. This "controller" is in fact a fairly simple combined battery meter and Off, Econ, and Full switch. With the 20" hub in a 20" wheel and the switch set to Full, the motor cuts out at 15mph, and with it set to Econ it cuts out at 11mph. This suggests that with the 20" hub in a 26-28 " wheel and the switch set to Full the cut-out speed would be 20mph, but with it set to Econ it would be a legal 15 mph or thereabouts.
I suppose to be 100% legal (although I doubt if the 1983 UK regulations are really clear about this) there would have to be some way of locking the switch in the Econ mode while on public roads.
The legality question, of course, is only likely to arise in the event of an accident with insurance companies seeking every which way to evade liability. I doubt if they would notice the "wrong" hub in the the larger wheel as both hubs are outwardly identical, and there would be no way of ascertaining the bike speed just prior to the accident as no witness would be able to swear to the extra 4 to 5 mph if the bike was going at top speed, and that top speed of 20mph would often be less than many non-electrically assisted cyclists readily achieve with pedal power alone (which would make a contributory negligence case for reduced compensation difficult to argue even if an insurance company did notice the hub).
What intrigues me however is that a 20" version could be obtained and built into a 26-28" to produce a "delimited" bike for use in the EU. This would be illegal with regard to top cut-out speed, but it would conform to the requirements of under 250 watt nominal power, as well as the non-throttle "pedelec" requirement which ensures that the motor comes on only when the pedals are turned (the Sram Sparc system uses a sophisticated "pedelec" which does not rely on sensors round the cranks, but measures the road speed through the rear sprocket which transmits speed and motion through various internal motor gears to the controller board).
A further consideration with regard to legality is the possible use of the Sram Sparc handlebar "controller" to limit the speed to the legal maximum in the EU. This "controller" is in fact a fairly simple combined battery meter and Off, Econ, and Full switch. With the 20" hub in a 20" wheel and the switch set to Full, the motor cuts out at 15mph, and with it set to Econ it cuts out at 11mph. This suggests that with the 20" hub in a 26-28 " wheel and the switch set to Full the cut-out speed would be 20mph, but with it set to Econ it would be a legal 15 mph or thereabouts.
I suppose to be 100% legal (although I doubt if the 1983 UK regulations are really clear about this) there would have to be some way of locking the switch in the Econ mode while on public roads.
The legality question, of course, is only likely to arise in the event of an accident with insurance companies seeking every which way to evade liability. I doubt if they would notice the "wrong" hub in the the larger wheel as both hubs are outwardly identical, and there would be no way of ascertaining the bike speed just prior to the accident as no witness would be able to swear to the extra 4 to 5 mph if the bike was going at top speed, and that top speed of 20mph would often be less than many non-electrically assisted cyclists readily achieve with pedal power alone (which would make a contributory negligence case for reduced compensation difficult to argue even if an insurance company did notice the hub).
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