Folks,
I do not understand the Auto industry. If one
takes the published gear ratios of various transmissions
that are normally stated as two decimal points and then
computes the ratios based on the assumed or actual
number of gear teeth I find that the auto industry
sometimes rounds up and sometimes rounds down on the
gear ratios of the same transmission.
On Ford 4 speed transmissions ( and many others)
the drive gear (23 teeth on an HEH CF) drives the
cluster gear. The cluster has 3 other gears attached
that drive the 1st, 2nd and 3rd gears.
The ratio of the drive gear/cluster gear must be multiplied
with any of the other gear ratios to get the effective ratio
in any gear.
The ratios for the Tiger II HEH CF or Tiger I HEH B
are normally published as 2.78:1, 1.93:1,and 1.36:1.
I counted teeth on the drive gear as 23. 1st at 32 teeth
, 2nd at 31 and 3rd at 25 teeth. Assuming that the
cluster gear is 26 to mate with the drive gear,
21 to mate with 3rd , 18 to mate with 2nd and 13
to mate with 1st then I compute:
2.7826 for low or rounded up = 2.78
1.9468 for 2nd or rounded up = 1.95
1.3457 for third or rounded up = 1.35
What gives with 2nd and third compared to the
published figures?
I did a huge spread sheet to try all gear combinations
from 8 to 33 teeth and I could find no consistency
in any of the published numbers including the SROD
and the Close ratio Tiger trans.
Other numbers assumed 22 teeth on the driven cluster
gear and 19 for 3rd, 17 for 2nd and 12 for 1st.
this gives 2.7879, 1.9064 and 1.3756.
For the RUG BP SROD there were 23 teeth on the drive gear,
21 on OD (old third) 31 on 2nd and 32 on first.
Assuming 28 teeth on the cluster driven gear and 21, 14 and 8 on
the other cluster gears I came up with 3.2857, 1.8189 and 0.8214.
This is against the published 3.29, 1.84 and 0.81 numbers.
I guess I will have to actually count the teeth
on the cluster gears. Can do that on the HEH CF, but not on
the RUG BP SROD as it is installed.)
Recommend any one who is in to real
serious rallys pull your transmission apart and count
the teeth.
James Barrett Tiger II 351C and others
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