Unless you race motorbikes you probably wouldn’t consider servicing your suspension as an important part of your motorbike’s maintenance schedule. True, it isn’t as essential as regularly changing your engine oil, but it is still and important job to keep your suspension working how it should. Your forks are constantly moving up and down as you ride and all this movement slowly causes to oil to deteriorate. Heat is generated in the oil, the springs and stanchion tubes moving together cause very fine metal filings to mix with the oil and small bits of debris work their way past the seals into the oil.
All this contamination will make the oil too thick like treacle when it’s cold causing the suspension to be too harsh and then as it heats up with riding, becomes too thin and results in little to no damping. Most motorcycle manufacturers are very vague with service intervals for fork oil but Triumph, for example, suggest every 24,000 miles. For touring bikes this interval should be fine to keep your suspension working well, but if you own a sports bike I would recommending every 12,000miles, and for track use a lot more frequently. This applies to shock absorbers as well as forks. Suspension servicing is available at James Packwood Racing for any type and make of suspension, you can find prices and descriptions.