i wrote the complete post last night then lost it so heres a second tryDarrell Taylor wrote:heres a ts1 dyno graph,well set up with 30mm and jl4 ill add a new twist to gearing choices tomorrow thats not been covered yet
I feel theres 2 further elements that play a big role in gearing choice
the first is at what rpm the motor comes onto pipe
the second is what power is at your disposal when it does
the gearbox is designed to maintain as close to useable peak power spread that the ratios will allow from the type of engine tune with a bigger influence coming from the pipe design
Gearing and sprockets are selected which the motors power and torque will dictate what can be pulled in terms of a top speed, as Ian says 70 to 75 would suit most but if you wish to maximise top speed potential and retain good pull through gears based on your motors power characteristic then if a dyno graph is available and using the gearing calculator by avantone the (Lambretta gearbox visualiser) its possible to check out the effects of different gearbox and sprocket combo,s to find out if the selection will drop off the pipe if not then you can keep upping the gearing for a higher top speed providing power is high enough
the ts1 power graph above is a standard ts1 that i set up well on the dyno and is useful as an example this peaks at 6800rpm and comes onto pipe at 4900rpm with 13bhp at that point with available overrev to 8500rpm
so running on li150(probably the best gearbox available due to the least % drop ) 15 46 would do 67mph at peak power 6800 rpm and would find itself in overrev rpm on a falling power curve which is no good for the engine,speed increase potential and fuel economy
17 46 would see 75mph at 6800 and a shift at 7k in 3rd would see 4th engaged at 5400rpm so still well onto the pipe with 18bhp on tap
if gearing is selected that fails to pick up the next gear above 4900 rpm then the motor will fail to pull up onto pipe and stop accellerating but on a high power motor it may not be a problem as it could overcome wind and rolling resistance for example a std motor may have only 8bhp at 4900rpm so 5bhp less than the ts1 has so less chance of pulling
if you check out various pipes you can see there ability to pull gearing is where they come onto pipe so the taff/ads3 type pipes are good for pulling tall gears as they can pull from around 4000 whereas this jl4 set up is 4900 and fran race 5400 the ads race 6000 becoming more difficult to gear effectively