Simple terminology question -- strut
Simple terminology question -- strut
(OP)
I know what a macpherson strut is, but is there a strut that is not a macpherson strut? On some automotive forums I see "coilover" and "strut" used interchangeably and I think that is incorrect.





RE: Simple terminology question -- strut
Cheers
Greg Locock
RE: Simple terminology question -- strut
It actually happens all the time in the US and Europe. In fact, the Germans call a strut a federbein (literally spring leg) but they also seem to call a "high content" spring/damper module the same. Many people call anything that performs both the springing and damping functions in a one assemble-able unit a strut. Witness that many (semi-)active actuator units are called struts even though they do not perform any kinematic function.
Best regards,
Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Simple terminology question -- strut
I think "coil over" refers to any spring mounted to a shock such that the spring AND damping forces are applied thru the upper and lower shock mounts. This is in strict contrast to having a separate spring seat on the chassis and/or control arm. The coil-over shock >COULD< have rubber bushings or pivots top and bottom, thus preventing it from making any significant contribution to wheel location, as in the rear suspension of just about every twin shock motorcycle ever made. Of course Macpherson and Chapman struts would also qualify as coil-overs, even though they >DO< provide wheel location.
http://www.off-road.com/ford/news/2004_03/rancho_triple.html
www.spiritowners.f9.co.uk/ mods.htm
www.howeracing.com/Chassis/ Index-Front-Nascar.htm
www.roberts.ezpublishing.com/croberts/susp.htm
RE: Simple terminology question -- strut
We call ours a strut, it mounts to the lower arm via a rubber bush. The hub mounts to the lower arm via a spherical joint. I'm not saying we're right, that's just the way it is.
Cheers
Greg Locock
RE: Simple terminology question -- strut
Best regards,
Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Simple terminology question -- strut
What has happened since is that the aftermarket has stepped up with concentric shock/spring replacements for the OE shocks and springs (which in these cases actually returns the arrangement to be closer to what Mr. MacPherson originally envisioned) that bolt on in place of what was originally only the shock. The OE springs are then discarded.
Norm
RE: Simple terminology question -- strut
Lots of people (non engineers) differentiate the two types of setups by calling the front coilover shock/spring a "strut" just because it's all one unit. I figured this wasn't right but I wanted clarification from the pros first.
RE: Simple terminology question -- strut
Strut:
A strut MUST locate the wheel. Meaning that if you remove the shock/spring assembly, the suspension will NOT retain it's basic geometric integrity. So this means a strut must act lick a kingpin, controlling the verticle displacement axis and the rotaional center of the suspension. The opposite would be a double wishbone setup, where the shock and spring typically only control verticle motion. We use MacPherson strut design in our front suspensions, while we use a multi-link suspension in the rear which has a shock/spring assembly which we refer to as a shock absorber, because it does not add geomtric constraints to the system. Typically if the assembly has a sperical bushing at the top of the assembly, and a hard point mounting flange(to the knuckle) at the bottom, I would call it a Strut. So in short, if the shock absorber sees a moment force, caster/camber regidity, I would call it a strut.
Coilovers:
As someone else pointed out... this term I believe started in the racing world. I have 9 years of dirt late model racing experience, and we always called the Spring/shock assembly a coilover, but the front suspension is a double wishbone. To me, when I hear the term coilover, it means a threaded shock body with an adjustable springseat. This technology has found it's way into the aftermaket on-road vehicle applications.
I think it is just a matter of racers/enthusisists starting aftermarket suspension companies and car specific forum users talking about suspensions without a strong engineering background like most of us on this forum. So it is easy to see how theese terms would be interchanged. It is not correct to interchange the terms most of the time, but most people understand what you are talking about. Even though we use a "Shock absorber" in the rear of our cars, I sometimes refer to them as a strut because they are a spring/shock assembly,even though I am wrong.
RE: Simple terminology question -- strut
This may reinforce the belief that a strut provides geometric rigidity as well as damping.
Brian
RE: Simple terminology question -- strut
RE: Simple terminology question -- strut
A strut is a compression member in any linkage or structure. It doesn't have to locate the wheel at all or even be part of a suspension system. It therefore could apply to any suspension member which is continuously in compression, including almost every 'spring unit'.
Auto engineers use it as a shorthand for "MacPherson strut", probably because they can't spell MacPherson. Earle S. MacPherson rarely got it wrong when he worked for Ford in Dagenham, England.
A coilover is a shorthand word for a coaxial coil spring and damper combination, and is therefore common on many suspensions.
At least one car I worked on had a MacPherson Strut front suspension, where the strut located the wheel and provided damping, but the spring worked on a rocker arm elsewhere (was it a Rover 2000?). There's another which uses a torsion bar as the spring, the torsion bar crank as the lower arm, and the damper in a MacP strut. I would suggest that the MacP term describes the geometry, whether the spring and damping are effected on the strut or elsewhere.
So MacPherson strut geometry often features coilovers but not necessarily, and coilovers are often found on MacPherson struts (but not necessarily).
Cheers - John
RE: Simple terminology question -- strut
If you remove a strut from your vehicle, the wheel will fall off. MacPherson Struts turn WITH the steering mechanisms because they are attached to the steering and the wheel assembly
SHOCK ABSORBERS work like this:
If you remove a shock absorber from your vehicle, you can drive it as normal, but you lose the dampening effect.
RE: Simple terminology question -- strut
A strut is defined as one that is also a load bearing member.
A coil over unit that does not act as a load bearer.
I hope this shed some light on the subject