Evening star. [volume] (Washington, D.C.) 1854-1972, 1927-01-16
No. 175-Second Gears Story.

NJ. IfD-SSttUItu utdE y HSDISs
Smiths experience with low" and
particularly what he learned by driv'
ing mile in that gear combination
stimulated his interest in second gear
Here was a gear combination which
| he dashed through quite regularly
| giving ii not so much as passing
thought. Perhaps it. too, had a
| story"
| Fortunately we were at the club
when he started thinking along these
| lines That gave us an opportunity to
work out some ideas on paper which
we might have overlooked if simply
| fooing with the car itself. When we
got down to facts and figures it devel'
oped that Smith mad only the most
vague ideas about second gear.
| He had a picture of this gear com
| bination as something that compelled
the engine to run about twice as fast
as it had to when enc was using high
| gear,
That showed how badly misinformed
| he was. Gear ratios vary widely on
different makes and models of cars.
| 1t is necessary to have the facts at
hand to avoid bad blunders.
Variations Are Confusing.
Running through list of specifca.
tions. l showed him the wide varia-
ton in high as well as second gear
ratios. But | no sooner had started
than Smiths lack of knowledge be-
came quite evident. Almost immedi-
ately he asked why the high gear ra-
ito of a particular car was 40, while
the second speed gear ratio was only
LII. To make matters worse, he no
ticed in the catalogue that in another
car the second speed gear ratio was
listed as S.s5. This enormous differ
ence didn't seem logical to him.
THAT is easily explained" I told
him. Remember, first OF all, that
there are two different ways of ex-
pressing transmission gear ratios.
Let's take the conventional way first.
It's not the simplest, nor the most
logical, but 1t will help you to under
stand the whole business.
I'm high gear, the propeller shaft
just back of the transmission rotates
at exactly the same speed as the en-.
CINE shaft. This ratio then, is / to /.
That's your starting point. When you
drop back to second gear, the pro.
peller shaft runs slower than that of
the engine. due to the meshing of
gears in the transmission. Putting II
another way, the engine Is allowed to
run faster than the propeller shaft.
If 1t runs twice as fast, then the ratio
is expressed as TO 1. In low gear,
the engine runs still faster as COM
pared with the speed of the propeller
shaft. The simple ratio here might
read to /. In reverse the ratio Is
still greater, running usually about
to /.
Except the l to l ratio for high
gear the proportions are seldom as
simple as this. They are usually COM
plicated with decimal points. A typi-
cal second gear ratio would be III to
l. A typical low speed ratio would be
3.11 to /. This, however, doesn't in
any way alter the simple facts behind
the whole business.
Other Factors Present.
But there is something else to con-
slider. That is the constant reduction
at the rear axle. The propeller shaft
of every car revolves faster than the
rear axles and their wheels. The
usual ratios are from 4 to / to to /,
with extremes at either end--that is,
in the typical car the propeller shaft
runs four or five times faster than the
axles. You should see, therefore, that
II at the transmission the gears are
rearranged so that, in second. the en-
CINE is running twice as fast as the
propeller shaft, then the engine Is also