The following article is reprinted from Bicycle Quarterly,
“The Magazine about the Sport We Love.”
For more information, visit www.bikequarterly.com
©Bicycle Quarterly Press
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35 kg
77 lbs.
40 kg
88 lbs.
70 kg
154 lbs.
65 kg
143 lbs.
60 kg
132 lbs.
55 kg
121 lbs.
50 kg
110 lbs.
45 kg
100 lbs.
30 kg
66 lbs.
30 psi
2.1 bar
150 psi
10.3 bar
130 psi
9.0 bar
110 psi
7.6 bar
90 psi
6.2 bar
70 psi
4.8 bar
50 psi
3.4 bar
20 mm
23 mm
25 mm
28 mm
32 mm
37 mm
Tire pressure for 15% wheel drop
Wheel load
Tire inflation for 15% wheel drop in relation to wheel load and actual tire width.
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Example: Rider and bike weight: 100 kg. Weight distribu-
tion: 45%/55%. Wheel loads: 45 kg/55 kg. Tire pressures for 20 mm tires: 125 psi/155 psi. Tire pressures for 37 mm tires: 45 psi/53
psi. For heavy riders/bikes, narrow tires require very high inflation pressures, and wide tires are a better choice.
by Jan Heine
width
tire drop
no load full load
Tire Cross-Section
Optimizing Your Tire Pressure for Your Weight
Inflating your tires to achieve 15% tire drop will optimize your
bicycle’s performance, comfort and handling. Our tests of tire
resistance have shown that tire resistance is high at very low pres-
sures. As pressures increase, tires roll faster, but the performance
levels off at a certain pressure. Beyond this point, higher inflation
brings only negligible performance improvements.
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Optimum pressures
Riding your tires at this “cut-off” pressure optimizes both comfort
and performance. At lower pressures, you roll slower. At higher
pressures your bike is no faster, but much less comfortable.
Our tests of the same tires at various pressures determined the
optimum pressure for each tire for our rider/bike combination.
How does this translate for other riders and other tire widths?
I compared our results with Frank Berto’s charts for tire drop,
and found that the “cut-off” pressure corresponds roughly to a
tire drop of 15%. Perhaps not
coincidentally, 15% is the tire
drop recommended by several
tire manufacturers.
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Tire drop
is the amount the bicycle is
lowered as the tires deform
under the load of bike and rider.
Tire drop
Measuring tire drop is not easy. Fortunately, Frank Berto already
has done it for us. The chart below shows the pressures required
for different rider/bike weights to achieve a tire drop of 15% with
tires of various widths. Berto measured this for 700C tires, but the
values apply to other tire sizes as well. Note that the weights are
wheel loads, not the weight of the entire bicycle.
Determining the wheel loads of your bicycle
Depending on your bike’s weight distribution, achieving the opti-
mal 15% tire drop may require different pressures in your front and
rear tires. To determine your weight distribution, place one wheel
of your bike on a scale, the other on a block, so that both wheels
are level. Have a helper hold your bike upright, and sit on your bike
(with any load you will carry) in your standard riding position. The
helper notes the reading of the scale. Then turn the bicycle around
and repeat for the other wheel. Use these wheel load readings to
determine your inflation pressure for each wheel.
As a first approximation, you can use the values we measured for
a variety of bicycles:
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Over- and underinflation
The table below shows that narrow tires require very high pres-
sures, otherwise the tire drop exceeds 15%. On the other hand,
wide tires do not require high pressures for optimum comfort and
speed. Inflating tires to the maximum pressure recommended by
the manufacturer tends to underinflate narrow tires and to over-
inflate wide tires.
Conclusion
Tire pressures that correspond to 15% tire drop will optimize
your bike’s performance and comfort on average road surfaces. On
very rough roads or unpaved roads, it may be useful to reduce the
pressure. On very smooth roads, increasing the pressure slightly
may improve the performance of your bike.
Notes:
This article was reviewed by Frank Berto.
1 At higher pressures, internal losses due to flexing of the casing decrease, but
suspension losses due to vibrating and bouncing of the bike increase. See Heine,
J. and M. Vande Kamp, 2006: The Performance of Tires. BQ Vol. 5, No. 1, p. 1.
2 Berto, F., 2004: Under Pressure. Australian Cyclist March/April 2004, p. 48.
3 Heine, J., M. Vande Kamp, A. Wetmore and A. Spence, 2007: Optimizing Bicycles
for Carrying Heavy Loads. Bicycle Quarterly Vol. 5, No. 3, p. 37.
4 For tires mounted on rims of appropriate width for the tire width.
Source: Frank Berto
Bike Load Weight distribution
Front Rear
Randonneur bike front 45% 55%
Racing bike - 40% 60%
City bike rear 35% 65%
