Collapsed WP AER48 Forks

Collapsed WP AER48 forks


This page is dedicated to answer the question of why does my WP AER48 fork collapse or get stuck down.  In my work shop I have only seen a few forks with this issue and one time a dealer called me with this problem with a brand new bike right out of the crate.   It’s hard to tell how many people have had this problem and I have never seen a public report from WP.

Some WP AER48 forks are having issues of what is called collapsed or stuck down.   This is when excessive air pressure moves into the negative pressure chamber and causes the fork to become collapsed.  This phenomenon is well known in the bicycle suspension industry and is noted in many bicycle suspension owner’s manuals under cautions.

The WP AER48 has taken the idea of the air negative spring chamber air bypass channel that is explained in a patent #6,135,434 by another suspension company (that I worked for) and is a brilliant move by WP since the patent only covers rear shocks. It’a very simple way to create a negative air spring and is user friendly.



Drawing for patent # 6,135,435  Channel port ID#66


The use of negative springs in motocross suspension systems is not exactly new and was explored in the 70’s by Steve Simmons and Bob Fox.

Many things can make an air fork collapse and the most common are seal defects, debris under the seal lip and “DITHER MODE”- a Neezer coined term circa 1997″

In my early years of bicycle air spring testing I discovered the issues with NBR seals in cold weather.   I clearly remember the day I discovered the cold weather problem and showing this discovery to the engineering team.

Cold weather riding was causing the seal to fail.  At that time I was calling it “DITHER MODE” .  The cold temperatures would cause the seal material to lose it’s elasticity and with side loads the air pressure would by-pass around the seal causing the air spring to collapse.  The rubber seal lip needs to be flexible and resilient in order to remain in contact with the air piston cylinder bore at all times.  You can test elasticity of an O-ring yourself. Flex an O-ring into a figure eight at room temperature and see how it snaps back.   Now put the O-ring in the freezer for about 15 minutes and do the same test again. That O-ring will be very slow to snap back to its original shape….. un-less you are testing a cold weather rated 0-ring material…. and yes that’s a partial clue to the solution.

Do you remember the space shuttle challenger accident 1986?  The Challenger failure was caused by the failure of O-ring seals used in the joint that were not designed to handle the unusually cold conditions that existed at the time of launch.

Here are a few ways to get fork back to ride height before taking the air side cartridge apart to service.

Caution ! :  Procedures may be used to Un-collapse the WP AER48 fork.  Use at your your own risk.  Riding dirt bikes are dangerous and put you at risk of death or serious harm.  


Follow WP fork service manual and procedures to service the WP AER 48 fork.


Pump the fork up to 250-300 PSI and try to pull the fork up to ride height by holding front wheel down and having your buddies pull up on handle bars.  If this method work’s make sure to re-set your fork air pressure.


Use a hydraulic jack or scissor jack between tire and the fender. With jack slowing apply lift pressure.  Make sure to control Jack so it will not slip out!

This will bring air piston back by the air bypass channel and at that point the air will transfer back to the positive spring chamber.

We suggest that you always have the fork inspected / serviced by qualified technician as soon as possible.