Miata Mailing List: October 1999, Message #95

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On Oct 1, 1999 Bill Rockoff wrote:
> assertion that a 20 hp Miata engine wouldn't be able to spin the wheels or
> move the car.  People make a lot less than a horsepower, though, and I know
> I've rotated the drivetrain assembly on my car (I've even pushed the car on
> level ground.)  So, either I have the strength of 40 men, or the drivetrain
> on a car does NOT make 15 or 20 horsepower dissappear into a black hole

The discrepancy arises over the old torque vs horsepower discussion --
the drivetrain doesn't rob hp directly, it robs torque (and thus hp
through the calculation formula).  Let's say you hook a 1-foot ratchet
to the crankshaft and put 50 pounds of force on it (I think most people
can pick up a 50 pound object with both hands) -- you'll move the car
(assuming it's in gear, brake off, etc).  Of course, since you probably
can't push it faster than about 20 rpm, you're only making about .2 hp.

I bow to the experts on the question of whether it's going to rob a
constant or variable amount of torque.

> somewhere.  Think about it - could you jack up the back of your car and
> rotate the rear wheels by hand?  Can you push your Miata along level ground?
> Not very fast, sure, but I bet you could.

Can you push it along level ground while it's in gear?  That's a lot
less likely. :)

--Ian