Servicing Fox Suspensions | BUMSONTHESADDLE

TECH TUESDAY – WORKING ON FOX SUSPENSIONS

Shaun George Bike Skills, Mechanics

Your bike’s suspension basically isolates you from the terrain under your bike’s wheels. To do this two basic components are hard at work, namely, the spring and the damper.

If suspensions were simply fitted with springs, your suspension would simply bounce around for a while after a bump. Suspensions need a way to channel all the sprung up energy in the spring. That’s where the damper comes into play. The damper is a device that dissipates the stored energy from the coil and keeps the suspension from bouncing around out of control.

An oil-filled damper is the most common type of damper available on cars and motorcycle suspensions as well. When the shock absorber is compressed, a piston inside it forces oil to pass through a small hole. It takes energy to force the fluid to pass through this hole, this causes resistance. This energy is converted to heat energy in the oil. 

HOW FOX HAS EVOLVED DAMPERS ON THEIR SUSPENSIONS

Fox’s previous series of dampers, the evolution series were an impressive series of dampers for their time. They were a fairly simple design but had some problems.

The evolution series of dampers used what’s called an open-chamber system. This system allowed the oil to flow out of the damper when it expanded with heat. The oil, however, had no passage back into the damper. So, over time the responsiveness of the damper deteriorated as there was a lack of oil in it.

Another issue on the evolution series of dampers was that the damper required a lot of force to be applied for the fork travel to initiate. To ease travel, a lot of owners lowered air pressures but that resulted in the fork bottoming out on jumps. The circuit system on the evolution damper was also relatively simple resulting in a very linear and un-stable feel through the travel range.

Out with the old, In with the new – FIT GRIP

Thankfully FOX no longer uses this system. They brought in the FIT (Fox Isolated Technology) in 2016 to improve on the Evolution series experience.

FIT is Fox Isolated Technology. Basically, a sealed damper cartridge where the air and oil don’t mix and have everything contained inside the cartridge. These end up being lighter weight and have a consistent feel on most riding conditions.

Inspired from moto, the GRIP damper uses Fox’s FIT sealed cartridge technology combined with a coil-sprung, independent floating piston. GRIP allows excess oil to purge through specially designed ports at the top of the damper to maintain consistent damping, increase durability and plush and progressive travel. Rebound and small bump sensitivity were also improved in the new series.

SERVICING THESE BEAUTIES

If the oil trespasses into the damper, it will bleed itself automatically, therefore, keeping the oil level content.

FOX recommends 40ml 5wt oil in the damper side lower leg and 15wt oil in the air-spring side. While servicing this, we used Maxima full synthetic oil as it works just as well if not better.

We also noticed some extra grease that occupied some negative spring space. Greater negative volume translates to a more plush ride, better initial smoothness, small bump sensitivity, thus if grease is occupying some space it is also reducing some volume from the negative chamber. We later packed it with the correct amount of grease and added a few drops of float fluid in the negative chamber to complete the service.

Happy Rider. Happy Suspension. Happiest Mech.

Keen to have your bike suspension looked at by our expert bike mechanics?
Not in Bangalore? Not a problem – we have riders from across the country who send in their suspensions for us to work on. Connect with us and we should be able to pick up your suspension, have it worked on and shipped back to you.

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