Location: Surfers Paradise, Queensl...
Registered: May 2002
Re: T50 Gear box - Speedo gears - Experts needed
Tue, 20 April 2004 02:59
from Phil Bradshaws website
Speedometer Drive Corrections
If you change your overall tyre size or differential ratio, or mate the gearbox to a completely different speedo then you will need to make a speedo error correction. My thanks to Neil Fraser for the following information:
"The gearbox speedo worm drive ratios I know of include 5 x 19, 6 x 20, 6 x 22 etc. (ie 5 starts on the worm gear and 19 teeth on the driven gear). Most speedos are 637 rpk, 675 or 1000 rpk (revs per km). So lets say that to cover 1 km of distance your output shaft at the gearbox will turn how many revs?
Say a tyre diameter of 590mm: Circumference = 22/7 x .59 = 1.854m
Axle revs: 1000/1.854 = 539.37
Output shaft revs: 539.37 x 4.11 = 2216.8284
Say your speedo is 675rpk (should be written on back somewhere) - required speedo cable revs: 2216.83/675 = 3.284, so therefore best ratio is about 6x20 (3.33)
The small gear will have written on it the number of starts on the worm it would be compatible with (ie 5 or 6). Using a 5 start gear on a 6 start worm is always terminal. The worm slides off easy enough but requires practically stripping the whole gearbox…"
Tue, 20 April 2004 02:59
