You've broached several different things.
Scrubbing when turning (or snow plowing if you like) is inherent with any
turning. You turn the steering wheel, which turns the front tires. Inertia
and such make the car want to go straight, so you only get a percentage of the
angle change. Ie, you turn the wheels 20 degrees, and the car only turns 19
degrees. Usually this is so small to be inperceptable because the angle of the
turn is slight. You only really feel this when you turn sharply or too fast.
Very few cars can turn their front tires as severely as a Spitfire can, so you
don't get the severe scrubbing that you do in a Spitfire.
Then there is the thing called ackerman. This has to do with the front wheels
turning at different angles. It's done on purpose because when you turn the
inside wheel turns a smaller radius circle then the outside wheel. This angle
difference between the inner and outer wheel is done by the length and position
of the arms in the steering linkage. It works fine within a small range of
motion, but gets progressively screwed up as you continue to turn the steering
wheel. In the case of a Spitifire, which can turn its wheels extremely far,
the angle is probably all screwed when cranked all the way over. There is no
alignment fix for this.
Combine the above points with rear wheel drive. In this case, the car is being
shoved from the rear (even in reverse), with the front tires thrown far over.
The front tires then have nearly as much push on them sideways as they do in
the direction of rotation, which now is across the car. Hence, scrub city!
A front wheel drive car always puts all its driving thrust in the direction of
tire rotation (talking parking lot speeds here). So even with the steering
thrown all the way over, all the torque is going in the direction of tire
rotation, so a fwd car does not scrub, geting pulled right along into the turn
instead. Hence the ability of a fwd car to turn tighter then a Spitfire when
moving above the speed of an infant crawling.
As Joe described, it's a fact of life with a Spitfire, so slow down and don't
crank the wheel over so hard. It's also darn hard on the steering components,
particularly the trunions, which are a spookily weak link in the front
suspension.
>>> "Len & Bonnie Lubbers" <lubbers@sympatico.ca> 03/21 1:14 AM >>>
Aha! I thought my alignment was out. After taking the car to The Sport Car
Factory last fall, I learned that this scrubbing is supposedly one of the
car's idiosyncrasies.
Has anyone explained this before? I also thought it was due to the front
end riding a little higher than it looks it should. (positive camber
greater than it should be.)
|