Ross MacPherson wrote:
>
> Listers,
>
> Could someone explain to me the pros and cons of "sprung" vs. "unsprung
> weight" ? I know what the terms mean but I don't understand the effects on
> performance. I would think that unsprung weight would have less effect on
> handling due to less body roll but I've heard the reverse is true. What's
> the story?
>
Tires, wheels, and suspension parts are considered unsprung weight.
Everything else is sprung weight. The ratio of sprung to unsprung weight
has an important effect on the handling of a car on bumpy surfaces, and
is a factor in automobile design. A ratio of 5 is good and a ratio of 2
is very poor.
A car with a high sprung-to-unsprung weight ratio will stick better on
bumpy roads than a car with a lower ratio. The car will also ride
better. The reason is, the heavy body of the car is not disturbed much
by the relatively light wheels and suspension parts parts bouncing up
and down. The inertia of the body resists the movement of the tires, and
thus the tire is pressed into resonably firm contact with a bumpy road
surface.
You can get this effect by ading a heavy load to your car. The ride will
usually be noticeably smoother, particularly on a washboard surface. The
cornering and acceleration or braking traction on bumps is improved too.
Up to a point, as long as the suspension doesn't begin to bottom. And
adding weight will, of course, decrease acceleration -- same power, more
mass to move.
To get better handling on bumps, it is much better to reduce unsprung
weight and keep the sprung weight as light as possible. To think of it
in another way, the lighter the car, the less sophistication is required
in the suspension to provide decent handling.
Midgets handle better than 'B's, all things being equal, because the
amount of sprung weight (the car) is a lot less while the unsprung
weight (the suspension) is nearly the same. The ratio of sprung to
unsprung weight goes up; the car seems more throwable in the corners.
With significant weight loss and just a slight decrease in horespower,
the Midget will seem as quick (and in some case is quicker) than the 'B'
roadster.
Finally, all things being equal, the B/GT may seem to be a more
comfortale tourer because it has more weight, thus again raising the
sprung-to-unsprung weight ratio, although, at the limits of handling,
and with the same horsepower, it will not perform as well.
Thus the GT may be a more comfortable tourer whereas the 'B' might be a
better sports car. And both may be out-handled by a well tuned Midget
whose driver is getting his kidneys served to him on the console.
However, the CGT sounds really cool and can kick all the little 'B' and
Midget butts and the Triumph TR6 is king of the hill because, with 4
wheel independent suspension, has the lowest unsprung weight of all.
(Sorry, couldn't resist that last part...)
Bob Allen, Kansas City, '69CGT, '75TR6
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