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TESTING NOTES:
(a) Tire not worn out but significant tread
wear.
(b) Tire not worn out but significant aging
(crazing, cuts)
(c) Tire worn so that casing just showing
(d) Tire worn so that casing showing extensively
(e)Tread separating from casing
(f) Ridden by one rider who felt it was worn out
at 1500 miles, then ridden 1100 more miles
before the casing started showing through tread.
All tires 23 mm marked size unless noted. F/R
refers to whether and how much the tire was used
on the front or rear wheel. Tires were
weighed on a Mettler balance accurate to 1 gm.
Thicknesses (tread and sidewall) are in
thousandths of an inch, as measured with a
micrometer accurate to 0.001". Tread
thickness was measured in the center of the
tread in at least 5 locations around the tire.
Sidewall thickness was measured in at least two
locations away from any lettering or labels.
Since rubber can be compressed, an attempt was
made to apply equal pressure (by feel) on each
measurement. Variations in pressure could
have caused thickness measurements to vary by
0.003 - 0.004". Vredesteins have softer
tread than the Michelins or Contis, making it
harder to get consistent readings.
If people are willing to send me their worn out
tires along with some key data like rider
weight, mileage, use on the front or rear, and
riding style, this data base can be updated with
results from the newest tires. If you're
interested in contributing, e-mail me for
details: irons54vortex at sbcglobal dot net.
OBSERVATIONS
Tire wear is proportional to rider power output,
which is typically proportional to rider weight.
The mechanism of tire wear (weight loss) is that
small particles of rubber are abraded from the
surface of the tire. Force per unit area
grinds off the rubber, so higher rider power and
lower contact area increase the rate of wear.
For a given amount of power dissipation, lower
speed (e.g. when climbing hills) means that the
tire will wear faster because that amount of
power is not spread over as large a total tire
area in a given period of time. Higher tire
pressure results in a smaller contact patch and
faster wear.
Because power dissipation is mostly through the
rear tire, most wear occurs on the rear tire,
far more than can be explained by F/R weight
distribution. Unless there is a LOT of
heavy front wheel braking, a front tire can lose
minimal weight due to wear, even after thousands
of miles. Front tires may thin a little
due to "cold flow" of the rubber on the casing.
Front tires "age" due to environmental exposure,
and so wear much faster if they are subsequently
mounted on the rear. If a front tire
accumulates significant mileage and is then
moved to the rear, it will show about 1/3 faster
wear than a new tire mounted on the rear.
If there is significant hard braking (e.g. lots
of steep down hills) then front tires can wear
due to power dissipation. Riders who do
lots of intervals, "stomp" rather than "spin,"
corner hard, etc. will accelerate tire wear.
Road bicycle tires are worn out (casing threads
beginning to show through the tread) when they
have lost roughly 10% of their weight.
Obviously, there are wide variations in tire
construction which can shift rubber (and weight)
to the tread or away from it, but for the
lightweight road tire this general rule applies.
There is a significant difference in
construction philosophy for different tire
brands and models. For example, with
nominally similar high performance tires, side
wall thickness has been measured between 0.020
to 0.040 inches. For tires at similar
weights, this can mean tread thickness
(including casing) ranging from 0.030 to 0.050
inches for tires targeted at the same
performance rider. The extra tread
thickness, along with rubber compound
differences, explains the significant mileage
differences seen between brands and models of
tire.
About the author:
Kerry Irons is a recently retired chemical
engineer who has been an active cyclist since
the mid-1960s. Irons began self-supported
touring with high school friends in 1965, which
led to a Michigan- Seattle-San Francisco solo
ride in 1970, and a ride around Lake Huron in
1971. Since that time, Irons’ annual
riding has averaged 7,000-12,000 miles,
including commuting to work year-round and many
roller miles in the darkness of Michigan
winters. From 1980 to 1985, Irons operated
Cyclo-Pedia, a mail order bicycle parts
business. Irons rode tubular tires for
nearly 30 years, but converted (along with his
wife) to clinchers in 1998. This
stimulated him to record tire wear data as a way
to find better tires and to understand the
issues of tire wear. Discussions with
members of
CyclingForum.com resulted in several riders
sending worn out (and not so worn out) tires to
Irons for measurement, the result of which is
the information presented here
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