Racing vs Street Transmissions — or Gearboxes

Dog boxes used in car racing shift lightening fast, and are basically transmissions without synchronizers.

As such, input/output shafts must have matching speeds before the shift can occur…otherwise they grind going in.

Upshifts are “self-matching” since engine speed drops while the clutch is in; however, downshifting requires a technique called double clutching.

Double Clutching

At the Skip Barber Racing School we always instructed students to think of double clutching as: “two shifts in a row, when in neutral, you try to go.”

So, after putting the clutch in, you move the shifter to neutral, and let out the clutch while quickly stepping on the gas pedal to rev the engine.  Then, within a split second, you put the clutch back in, and finish the downshift…all this is done as fast as you can move your left foot.

Dog Boxes on the Street

Motorcycles are good examples of how dog boxes can be used on the street.  However, for street cars, they’re a bit impractical since they usually “clunk” going into first gear, and they can be noisy.

Synchronizers allow the use of helical-cut gears — which run quieter — and match the speeds of input/output shafts.  But, it’s difficult to visualize how it all works…even when holding the parts.

This video animation is superb, and shows you how it all works together.

More Info

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