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Another recent thread mentioned the problem of friction in shocks due to the side loading imparted on the shock when a coil over spring buckles under compression. I have been curious about how big of an effect this is (I would like to see some numbers). The main problem that I see with quantifying this is that I don’t know what would happen to a damper dyno if you tried to run it with a spring mounted WITH the shock – maybe people do it all the time. I know a lot of racecar teams are spending a lot of R&D $$$ to try and reduce all forms of suspension friction (shocks included) and I assume this is even why some F1 teams have gone to a torsion bar setup.
I believe that this friction can and does significantly affect the performance of the suspension, but I would like to see some numbers.
I can’t quote numbers directly, but in the early stages of a production vehicle module design, the measured side loads were in the 1000 - 2000 N range.
A product of interest to the race car side of the industry might be the Hyperco/ICP Hydraulic Coupling Device:
This devise allows the spring seat to pivot to reduce the side-load of the spring.
There is an article on this system in the April/May 2003 issue of Racetech Magazine (www.racetechmag.com).
Additionally, The following SAE International (www.sae.org) technical papers all include information on the phenomenon of side-load in springs:
2002-01-0317: The Effect of Rubber Seats on Coil Spring Force Line
2001-01-0496: Modeling of Coil Springs Using Parallel Mechanisms
2001-01-0497: Development of L-Shape Coil Spring to Reduce a Friction on the McPherson Strut Suspension System
2000-01-0101: Optimization of Force Action Line With New Spring Design on the McPherson Strut Suspension for Riding Comfort
2000-01-0727: System Modeling of a Damper Module
970100: Optimization on Mac Pherson Suspension With a Spring
960730: Approaches to Minimizing Side Force of Helical Coil Springs for Riding Comfort
940862: Side Load Springs as a Solution to Minimize Adverse Side Loads Acting on the Mcpherson Strut
For automotive damper struts, the springs can be intentionally designed to produce side-loads to minimize system friction. For damper modules, the side-load needs to be minimized.