EVDL Administrator via EV wrote:
Oversize wheels are a styling gimmick. Once the wheels are big enough to clear
the brakes, making them larger has no
practical value that I can see. They only add unsprung mass and inertia.
They decrease the vehicle's efficiency, and possibly its handling and
comfort, for no real return.
Most of the fancy wheels are worse in their aerodynamic qualities, too, and
more expensive to replace if they're damaged.
From a purely functional standpoint, larger wheels do indeed increase
losses. They are heavier, and have more wind resistance. Remember that
the top of a tire is moving forward at *twice* the speed of the car
itself, which greatly magnifies the effect of its aerodynamic drag.
Larger tires can reduce rolling resistance (all other things being
equal); but that's normally only important at low speeds. The trouble
is, other things are *not* equal; larger tires tend to use wider tread
and stiffer sidewalls, which increase the othe losses.
I remember reading about the arguments Paul MacReady had with the GM
styists about the EV-1. He wanted small skinny tires for efficiency;
they wanted big "macho" tires. They wound up having Michelin develop a
special tire.
I also talked to Bob McKee (the famous race car designer). When he
designed his Sundancer (famous for a 150 mph range and 70 mph top speed
on just twelve 6v golf cart batteries), he tested tires to find the
optimum size. He found that a *small* diameter tire had the best
compromise between efficiency and handling (he paid no attention at all
to appearance).
I think the main reasons for large wide tires are, a) styling (looks
like a race car), b) sell for higher prices (more profit), c), improved
handling on smooth dry roads (like a racetrack).
Lee Hart
--
If happiness is on your mind, here's a daily list to find:
- something to do
- something to look forward to
- someone to love
- someone to take good care of
- and misbehave, just a little
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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