TYRES : Go big or go small
MOTORHUB MAGAZINE
the effect of tyre size on fuel economy
“
What’s immediately apparent from the
results is that as
the wheel-andtyre packages
get larger and
heavier, acceleration and fuel
economy suffer.
T
yres can play an important role in making
cars more fuel efficient.
Many motorists are familiar
with the concept of maintaining proper tyre pressure to
attain optimal fuel economy.
Overinflated or underinflated
tyres will not be able to maintain proper rolling resistance,
which will reduce the vehicle’s
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ISSUE #2 Jun - Sept
fuel economy. In addition to pressure, many motorists wonder whether tyre size is also a factor.
The impact tyre size can have on performance,
including fuel efficiency, was examined in the
article, titled Plus-Size Models: Testing the performance effects of upsizing wheels and tyres,
was written by Tony Quiroga. The findings in
the article were based on tests involving “nearly
identical Goodyear tyres in all five sizes, inflated
to manufacturer-recommended pressures.” In
addition, they “used the stock steel wheels for the
15-inch test and went to the aftermarket for the
larger wheels, as most owners would do.” One
sentence offers a succinct summary: “What’s immediately apparent from the results is that as the
wheel-and-tyre packages get larger and heavier,
acceleration and fuel economy suffer.” Specifically, the author cited a “10-percent drop in fuel
economy … from the 15s to the 19s.”
Changing the diameter of a vehicle’s tyre can
drastically affect every aspect of its performance,
from acceleration, to braking, to fuel economy.
From one extreme to the next, a vehicle can gain
or lose as much as 25 percent of its fuel economy,
just by changing tyre diameter.
There are two things to consider when thinking
about tyres and their effect on fuel economy;
wind and rolling resistance. When a car is driving at higher speeds, it experiences higher wind
resistance; this means lower fuel economy. Roll-
ing resistance is the impact the road has on the
tyres. If you change the features (size and width)
of your tyres, it will then influence the interaction it has with the road; thus affecting the fuel
economy. This is where tyre width can begin to
influence fuel economy.
Many people believe by changing the height of
a car’s tyres, they can increase its fuel economy.
This is not a reliable idea as speedometers are
specifically calibrated to the number of revolutions a set of tyres makes per mile while driving.
If the original set of tyres is replaced, the calibration will be off and changes in fuel economy
will be blurred. Shorter tyres calculate at higher
fuel economy because they make so many more
revolutions per mile. This negatively affects fuel
consumption because it makes the car’s engine
work at a higher rpm to achieve the same speeds.
Taller tyres do the opposite while still offering an
inaccurate reading.
Tyre width is one of the only tyre size factors that
can improve fuel economy. A narrow tyre will
have less wind resistance, rolling resistance, and
weight; thus increasing fuel economy. If choosing
a narrower tyre, be aware that they can diminish
the car’s handling characteristics. It is best to always install the proper size tyres for your particular vehicle. A mechanic will have no problem
helping you figure this out. Also, keeping