Progressive Fork Springs? Yes or No...

[andyvh1959]

Back in the late 70s and 80s, the motorcycle magazines did great articles on modifying the damper style and cartridge style forks, which are still very common to the Vulcans. Basically the mods are greater volume of lighter oil, progressive would springs, preload spacer to reduce static sag, and in some cases adding air valves to adjust for chainging loads (like a fairing, carrying a passenger, etc). The mods details are:
1. Progressive wound springs, which start with softer rate on the bottom and get more stiff as the forks are compressed further.
2. Preload spacers, adding spacers reduce the amount of sag when you sit on the bike. Proper preload should be less than one inch. Look up "satic sag fork preload".
3. Oil volume, the factory stock volume is the LEAST amount of oil put in for the least cost to provide lube and damping control. Best practice is to remove the fork springs, fully compress the forks, oil fill the forks to within 3" from the top. Then reinstall the fork springs after the fork is extended.
4. Oil weight, go to 10wt or 15wt oil, instead of heavier oil. The bigger gain in ride quality is not heavier oil, but MORE oil. Lighter oil lets the forks react better to small bumps. More oil in the fork legs aids the forks to handle bigger bump by reducing the air volume above the oil. The reduced air volume above the oil acts like a secondary progressive spring, greatly reducing fork bottoming and dive upon braking. And adding oil volume (up to the 3" from the top of the compressed legs) will NOT blow out the fok seals.