What is an Inverted Shaft Strut?

An inverted shaft KW strut on Dai Yoshihara’s S13.  Drifting is probably the second hardest motorsport on struts behind rally and the stiffness and strength of the inverted shaft really help the cars handling and ability to take hits.

So an inverted shaft strut has the following advantages, it is much stronger, it is much stiffer for better handling, the internals of the shock like the piston bushing, strut shaft, and upper packing last much longer.  There is less internal bind due to the strut shaft sideload.

The disadvantages are that an inverted shaft costs more to make, is because the OD of the shock body has to be closely controlled with centerless grinding, the finish of the body must be something like hard chrome, and a case with bushings and a seal must be included in the cost. An inverted shaft strut weighs a little more. There is less sticking in the design due to reduced binding but the extra set of seals and bushings add some stiction.  Finally, the inverted shaft strut must be periodically taken apart cleaned and greased for long life although this isn’t too big of a deal.

Performance-wise, an inverted shaft strut’s advantages outweigh the disadvantages. Although many excellent struts are of the conventional design, the inverted shaft is still a great advantage to consider when looking for a performance suspension for your high-performance car.