I read with interest the comments of R. H. Stenning in the March 1976 issue, regarding Overdrives v. 5-speed gearboxes.
There is no doubt that an o/d is not justified, either technically or economically, except on a three-speed gearbox (Vanguard) where the gap between 2nd and top is in the order of 40%, e.g., on a Triumph 2000 3rd gear = 1.39 to 1 which is a gap of 28% from top, the o/d reduces revs by 24% leaving a mean difference of 4% or, if you like 4 m.p.h. in 100. If anybody can say this constitutes an extra useful gear he is more than likely playing with his gearlever.
Clearly then, an o/d is a device, for masking poorly chosen ratios but on a box with well chosen ratios has no use other than for top. The time saved by “flicking the Switch” against “moving the lever” is so small as to be of no practical use.
Finally, are you so short of correspondents that you publish letters from people who don’t know what gear they are in ?
I myself drive an Austin Freeway fitted with a Triumph 2000 gearbox and o/d. The Freeway is a 6-cylinder version of the “B” Series BMC engine in an A60 type bodyshell.
I also have two Austin 7 sports cars and a 1934 Austin 16/6 Sedan with a local body which has not been rebuilt yet.
JOHN NEEDHAM Melbourne, Australia.