Ask A Scientist© Environmental Earth Science Archive

name        Dan H.
status      student
age         15

Question -  Hello, Recently my Principals of Technology teacher asked
the class a question. "Why do dragsters have big tires?" Of course
everyone answered for more traction. But according to his formula,
surface area has nothing to do with traction. And we proved that using a
block of wood and some weights. The force required to pull the block was
always the same no matter which side the block was on.
One possible answer of mine is that small tires have a limit on how fast
they can spin. Dragsters reach incredible speeds so they need big tires.
Is this answer correct? Also, could you explain why dragsters have big tires.

I have one more quick question to add to that. He also showed a
demostration using to metal sheets. There was a little bit of water
between them, and they stuck together. Why did it do this? Cohesion?
Adhesion?
PS. Could you explain in a little detail, describe why, any formulas.

This was already answered twice in the archives, just do a search and type
in "dragsters".  There are a couple different reasons for large tires
though.  The diameter is for speed and the power supplied by the dragster.
If the cars was fitted with normal cars tires the car would not be able to
go as fast at top speed, since a smaller diameter tire would have to revolve
faster than the larger diameter tire.  The diameter also allows the torque
to be balanced during the acceleration, since if the tire were smaller you
would need an even stickier tire compound to apply an equal horsepower to
the road.  The width of the tire is because of two reasons, the Centrifugal
force distorts the tire at high rotational speed and part of this thickness
becomes the sidewall, the overall width remaining in contact with the street
is only because of the wear rate.

Or look again at the block of wood test, the same force can drag the same
block no matter which side it is laying on but drag it around on the narrow
side for a year and compare it to dragging it on the wide side for a year as
well and the narrow side would wear down more, same principle applies to the
tires in the dragster as well as the brakes and clutch in any car.
Automobile engineering is really just a balance of the power involved and
what the vehicle is supposed to do, dragsters use larger clutch plates,
larger brakes or a parachute, and larger tires to handle the large size of
power involved.

This also goes for oversized brake pads, the material of 2 brake pads may be
the same, but if the 2 were stopping equal loads with all else being equal
the larger pad would not wear down as quickly.

Hope this helps, I would imagine any engineering book discussing frictional
forces would cite examples using these same examples in more finite detail,
sorry I did not discuss any equations here but equations are difficult to
cite using email.

Michael Baldwin
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