According to my calculation using the overall ratios given in the Riders Handbook, standard Rapide or later Model Black Shadow transmission ratios are:
2.57 to one in First
1.6 to one in Second
1.2 to one in Third
1 to one in Fourth
The current Surtees/Quaife ratios are different than older Quaife ratios. I think they now make a little better use of the extra gear.
First gear is available in two ratios 2.458 to one or 2.07 to one.
Second gear is the same as a standard Vin, 1.6 to one
Third is about midway between second and fourth at 1.34 to one
Fourth gear is a little higher than a standard Vincent 3rd at 1.13 to one
Fifth is one to one.
Fourth gear is the gear that has been changed, lowered from the old Quaife ratio of 1.09 to the new ratio, 1.13 to one.
So according to the info I received from Quaife Surtees, this box does not just give you a new gear between the old Vin 3rd and 4th ratios, it also gives you a new gear between the old Vinc 2nd and third ratios, not a bad thing to have on board.
In addition you have the choice of a little higher or a lot higher first as compared to the Standard Rapide or late model Black Shadow gearing. The 2.458 ratio would be good for bikes primarily used for solo riding and I think it would still be managable with a heavily loaded bike. The 2.07 to one first might be best suited to racing bikes. What was the high Shadow first about 2.2? There is a Shadow in our Club with the high FIRST. On takeoff it sounds like the clutch gets a pretty heavy slip session and that is with two skinny riders on board, probably both add up to not much more than my own weight.
So there seems to be some advantage to the extra gear in the 5 speed, especially now that Quaife has lowered their fourth gear a bit. Talking with owners who have the quaife, the big advantage is that you get a transmission that shifts quickly and positively like a Norton AMC box, rather than somewhat slowly and ponderously like a big old truck.
Terry Prince no longer makes transmissions.
Glen
On edit , from the racing section of the Riders Handbook I see that the high Shadow or Black Lightning first is 2.07, exactly the same as the higher geared first offered by Quaife. I think the 2.458 ratio is the one I will go with, although the higher first might be nice for a bike that is only ever ridden solo and mostly away from stop start traffic.