Thanks for the reply. My examples are theoretical and in the second case a rather extreme example, but they are just example to aid my question.
And you are correct, there is physically no way I could fit a 116t spur with a 51t pinion in my car.
Thanks, I hadn't thought about motor position tuning, there is only the physical possibility to shift my motor forward or back by about 7mm so tuning is that respect (wight bias) is limited in my case.
There are of course lots of spur-pinion combinations that would indeed be possible in my car and result in practically the same FDR.
For example if i wanted an FDR of 4.51 I could go with a 100t spur and 41t pinion, or, 105t spur and 43t pinion.
Any thoughts? Thanks again for any help!