
When your car has a single-speed transmission, your engine may be
geared for acceleration (quick start-up), top end (the top speed you
could attain), or some point in between. Normally, you can't gear for
top end and acceleration at the same time, just like a seesaw can't have
both ends in the air at once. With a two-speed, however, you can cheat a
little and slightly broaden the gearing range. When you are in first
gear, your two-speed may be geared for acceleration. When you shift into
second, you can be geared more for top end.
The two-speed gives you more leeway with gearing adjustments. For
instance, you would never reach top end in track sections full of tight
turns. Those sections favor quicker acceleration. Top end gearing is
useful in those sections where you can go all out. With a single-speed
transmission, you could gear only for one section or the other, possibly
losing ground in the other sections.
By increasing or decreasing the spring tension in the two-speed's clutch
shoes, you can change the shift point from first to second gear to take
advantage of this broader gearing range at strategic points in the race.
So when you hit a high-speed section of track, the two-speed will shift
into gear for top end, then allow it to drop down again to take
advantage of quicker acceleration in the turns. Many people buy
two-speeds for this reason--to go faster.