You’ve probably heard off-road riders talking about airing up an down. In case you’re wondering, They’re talking about adjusting the air pressure in their tires to improve stability and traction for different surface circumstances.

It takes high pressures to handle hard surfaces such as when on paved roads to take advantage of the side wall surfaces of your tires when cornering. Low air pressure on hard surfaces will allow the soft tire to roll in turns causing you to lose control at the most inopportune time. Low air pressure will also cause your tires to overheat at highway speeds causing premature failure including tread separation, ply failure, and in the case of knobbies, the actual throwing of knobs.

Conversely, lower pressures give you more surface area of contact to grip the softer dirt, mud, and sand that you typically ride on off-road. This results in much less squirrelling and sliding in softer material. On the other hand, if your tire pressure is too low, pinching of the tire sidewall against the rim is likely to result in flats. Higher pressure off-road will help protect against pinch damage, but you’ll sacrifice some stability and traction.

Different bikes will require different minimum pressures. For instance, on the XT225, the rear wheel is equipped with an internal rim lock. This is a wedge of rubber that is pulled down between the rim and the tire sidewall, clamping it so that the tire doesn’t slide around the

rim under toque. You can tell if your wheel has a rim lock by looking for a threaded bolt with a nut protruding from the rim nearly opposite the air valve. As a matter of fact, you’ve probably already mistook it for a second air valve. If there is no rim lock, airing down too low will cause the tire to slip around  the rim.

As an example, on the pavement the XT225 runs well with 18-22 psi in the front, and 22-25 psi in the rear. Off-road you might ride with 7-14 psi in both. If you ride fast and hard, and there are rocks and roots in the path, you’ll want to stay on the high side of the lower recommendations. If you ride like the rest of us old arts, and the trail is just dirt, sand, or loose gravel, 7 psi works well as long as you have a rim lock on the rear wheel.

WARNING! Do not fail to air up to OEM recommended tire pressures before returning to the pavement. Riding on pavement at highway speeds with improper tire pressures can result in personal injury or death.

Of course, airing down is easily accomplished when you get to the dirt, but upon return to

the pavement, airing up can be a problem if you’re not equipped. We’ve bought small lightweight 12VDC compressors at Wal-mart and even flea markets for $12-$30. Most any one will do, but we keep buying smaller and lighter versions every time we see a new one.

Install a 12VDC outlet on your bike (See another dirtly tech bulletin) and rig up wires with lighter plugs for extensions and jumper cables. It should be wired direct to the battery so it’s always on. That way you can run the compressor, GPS, trouble light, and charge your battery with the same outlet. It must be fused with a 15 to 25 amp in-line fuse to keep from starting a fire on your bike in case of a short in the wires.

The best outlet we’ve found is from Wal-mart or Pep Boys (Casco 212711C) and costs about $8. You can easily mount it on the handlebars using a couple of old reliable tie strips.

Questions? Comments? Something to add?

Call bierdo at 800-522-6257 or 407-957-5517

or eMail: danoaks (at) mac.com

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