Rick’s Gentleman’s Express Blog

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Keeping Up The Pressure

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I originally wrote this for the July 2006 issue of the Humber Rider newsletter

Summer riding often means long trips on new tires. Assuming you have chosen the correct tire for your bike and the type of riding you do, your most important task becomes maintaining the correct air pressure.

It is normal for new tires to expand slightly during the initial break-in period, leading to a reduction in pressure. Checking pressure often is very important when tires are new. Once you have a few hundred kilometres on your new tires and pressures have stabilized, the question becomes what is the correct pressure?

tire_pressure_1

Most motorcycles have a tag similar to the one shown to the right somewhere on the frame. The tag lists recommended pressures for the stock tires. Some will also list a higher pressure for riding with a passenger. Unfortunately, this particular tag gives recommended pressures using kilograms per square centimetre — not the units you are likely to find on the average tire gauge or service station air pump.

North America still uses Pounds per Square Inch (PSI) as the standard for air pressure. The most common measure of air pressure in the rest of the world is KiloPascals (KPa).

Conversion is as follows:
1 PSI = 6.894757 KPa = 0.07030696 kg/cm2

tire_pressure_2

To further complicate matters, markings on the tire sidewall may seem to suggest a different pressure. In reality, the pressure on the sidewall is a maximum pressure for that particular tire at the maximum load listed.

So let’s suppose that you have non-standard size tires, are carrying a big load and a passenger and are travelling in really hot conditions at high speed. Oh, and by the way, all pressures suggested are for cold tires. What is the correct pressure?

Here is a relatively simple method for maintaining correct tire pressure that should work under almost any conditions. Using a good quality tire gauge, note the pressure in the tire when it is cold. Now go for a ride and get the tire thoroughly warmed up in conditions similar to those in which you plan ride (speed, temperature, load, etc.) and check the pressure again. If your initial cold pressure was correct, the pressure when hot should be approximately 10% higher using whatever units you prefer. For example, if you started at 30 PSI when cold, the hot pressure should be 33 PSI. If the hot pressure is more than 10% higher than the cold pressure, initial pressure was too low and the tire is flexing too much and overheating, causing a higher than normal operating temperature and pressure. If the hot pressure is less than 10% higher than the cold pressure, initial cold pressure was too high. The tire will have a smaller than normal contact patch and will be too rigid to allow the flexing that gets the tire up to operating temperature and provides maximum traction for acceleration, cornering and braking.

This method takes a little fiddling at first, but once you have your particular tires dialed in you will maximize tire life and traction while protecting your tires from overheating and possible failure.

More About Tires

Written by admin

June 20th, 2014 at 7:36 am

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