Blatherings From The Editor

Tire Pressures

(September 2004)

Last month you read the Iron Horse tech article on checking and maintaining correct tire pressure.  On the return half of our trip to the 2004 BMW MOA National in Spokane, WA, using a new Roadgear digital tire pressure gauge, I did some serious tire pressure checking.  Keeping your tires at their optimal pressure isn’t so easy.

     First you need a gauge. Per their extensive review, Motorcycle Consumer News determined that the pencil gauges readily available in just about any grocery store was as accurate as you need.  The more expensive models gave you some nice features, but no better readings, some even worse. Even so, the various pencil gauges that I have carried never seemed to give me consistent, reliable readings.

     The quality of digital/electronic gauges has improved significantly, if you can believe their manufacture’s ads, so I decided to buy a digital tire pressure gauge at the MOA National.  I got a “real deal” on a Roadgear digital gauge that fits easily into our tank bag or my jacket pocket.

     The plan was to check our tires every morning and adjust the air pressure as needed.  The first morning was at the rally site.  The tires’ pressures were high per the new gauge.  Seemed a little odd until I thought it through.  Temperatures were in the 100’s for the past few days and the last time I checked the pressure was in a cooled garage.  Interesting.  But…what would I have done if the pressures were low?  Thinking that through, if the morning check found the tires low, my plan was to ride to a gas station and add the difference to the tire(s) regardless of the pressure at the gas station.

     Just what is your tires’ “correct” pressure? Your owner’s manual is the first place to look.  Also, the tire wall on all modern motorcycle tires will have a statement saying “XX pounds maximum, cold.”  Define “cold”!  For example, the morning we left Indio, CA, “cold” at 5 am was in the 90’s.  As long as we were going to be in the desert, 90 was cool.  Then there was the morning in Fort Bragg, CA, when the morning “cold” was in the 50’s.  In the first case (morning in the 90’s) heading to the coast the tires would end up on the low side; and in the second case (morning in the 50’s) heading to the desert the tires would end up in on the high side.  The laws of physics.  Seems you also need to know what your tire pressures are when the tires are hot.  My experience was I needed to adjust tire pressure on the go, not just the first thing in the morning if I wanted to keep the tires at their optional pressure levels.

     My suggestion is to learn your tire pressure requirements at home and then extrapolate to the open road.  Check your pressures “cold” and then go for a 15 or 20 minute ride and check them again.  Per the “experts” a 10% increase in tire pressure from cold to hot is the sweet spot.  Inflate your tire too high - not enough temperature rise; too low - too much temperature rise.  Considering the importance of our tires, it’s worth the effort to find out. Deryle and Wanda, correctly inflated.