All-
I have been reading the mailings about RPMs and gear ratios and I believe I
have an answer. In recalling some ME gear equations:
r = n2/n1 where r = velocity ratio (ratio in 1/3.55 format)
n2 = driven gear angular velocity
n1 = driving gear angular velocity
You can create a relationship between two sets of gear ratios by doing the
following algebra:
First state that (a) = current ratio (b) = new ratio
r(a) = n2(a)/n1(a) r(b) = n2(b)/n1(b)
So, if n1(a) = Current RPM
and n2(a) = n2(b) (In both cases the axles spin the same speed)
Then, n2(b) = rb*n1(b)
r(b)*n1(b)
--------- = r(a)
n1(a)
Or simplified:
n1(b) = r(a)*n1(a)
---------
r(b)
Don't forget that r(a) and r(b) is 1/gear ratio or 1/3.55.
So, in summary if you have 3.55 gears that turn 2000 RPM @ 60 MPH and want to
see your new 3.90 gear's RPM:
NewRPM = (2000*3.90)/3.55 = 2197 RPM
For you real gear heads, make an Excel spreadsheet with this formula and graph
the difference.
Thanks,
Rob Weingart (89 Dak LE 4x4 Long Bed)
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