Caterham, Surrey, England
My Posts: All Forum Topic
Distance doesn't really matter...The unit counts revolutions, and one rev is one rev regardless how far the magnet is from centre.
I believe the distances are recommended due to the mounting holes and supplied brackets, to ensure that you can line everything up easily. As far as I am aware, most 80s/90's have similar footprints to the 60s, so go with the 60 measurements if you want to use the stock brackets.
Regarding the balance - if you have to drill a hole to mount the magent, then you are removing material and replacing it with the magnet - in this case you can probably just add the one magnet, and unless you are anal about it, the balance will be OK. If you already have holes in the fan, then you will simply be adding weight. In this case I'd recommend fitting the other magnet too, so as to ensure balance. Don't forget to fit it back to front !
Anyone care to bet on how long it is before this thread becomes a push for the optical sensor boys ?