We have Lotus “Standardization” to thank here.
The earlier cars had 145X13 tires (first cars with 5.2X13), 3.9 differential, and the close ratio transmission.
This was dodgy once off the back roads. Many people with modified engines and no rev limiters quickly had engine failures.
So, it seems that the SE had 155X13 tires, 3.55 differential, and the wide ratio transmission, which was becomming available from Ford. This cut down on engine failures, since it was relatively more difficult to exceed 7000 rpm with this setup (just shy of 130 mph on 115 advertised hp)
However, during this period, it was possible to order the car in a variety of configurations, so it was possible to get the 3.55 differential with the CR transmission. There are some who consider this the optimum touring combination, provided you didn’t have to start up a steep hill fully loaded.
Later, Lotus seems to have used the 155X13 tires, 3.77 differential, and wide ratio transmission as a relatively standard combination. It may have still been possible to special order the car with 3.9 or 3.55 differential and/or the CR transmission, at least for some time. It is not completely clear, but the 2000E transmission may have some subtle internal changes that makes it more difficult to fit the early CR components. The Dave Bean catalog goes into this in some detail.
I know that when I converted from wide ratio to CR, the mechanic had to do some fiddling and machining to get every thing to work.
I would hope that some of our members with closer ties to the factory during the period could shed more light on the subject. At the current time, unless you have the original build sheet for the car, whether you have 3.9, 3.77, 3.55, CR, or wide ratio is probably due to the POs predilictions if not one of the standard combinations.
David
1968 36/7988 (3.55 CR, not original)