I don't want to change the subject, but I would like to add my experience, which might be of interest to those considering adaptors.
I ordered an adaptor from JC for my 1954, which has the stock 3.9 rear. Because of tall tires, I was reading way low on the odometer compared to actual (GPS). Actually, when speedo said 40, I was actually going about 50.
Now here is the strange thing - With the new adaptor, I am 100% spot on at 40 mpoh. However, above that speed, there starts to be a difference, which gets bigger as I go faster. For example:
40 speedo = 40 actual
50 speedo = 48 actual
55 speedo = 51 actual
60 speedo = 55 actual
70 speedo = 62 actual
I thought the correction would be constant. What am I missing here? Thanks.
Harry
