Simple terminology question -- strut

[robinhood4x4]

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.

 

[GregLocock]

Yes, that is common terminology. I get the impression that coilover is an Americanism, and comes from the racers, I have never heard a strut being referred to as a coilover in the production world (not saying it doesn't happen, just I haven't heard it)

Cheers

Greg Locock

 

[mloew]

Greg,

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.

 

[Tmoose]

I'm pretty confident saying (Macperson) struts are coil-overs, but not all coil-overs are struts.

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

http://www.spiritowners.f9.co.uk/

mods.htm

http://www.howeracing.com/Chassis/

Index-Front-Nascar.htm

http://www.roberts.ezpublishing.com/croberts/susp.htm

 

[GregLocock]

OK, I get it. You are saying that to be a strut the hub has to mount directly to the coilover?

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

 

[mloew]

Not quite. MB had used a strut with no spring on it a few years back. A strut is a suspension devise that provides a damping function and a wheel locating function; springing is typical, but not strictly required.

Best regards,

Matthew Ian Loew
&quot;Luck is the residue of design.&quot;
Branch Rickey

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[NormPeterson]

I suspect that robinhood4x4's confusion may be based on browsing Fox/SN95 Mustang and/or possibly 3rd generation Camaro/Firebird boards. Those cars come OE-equipped with modified MacPherson strut arrangements, where the damper portion is still firmly clamped to the steering knuckle and must still perform the wheel location functions in addition to providing the damping. But the spring is entirely separate and sits midway out on the control arm as is common practice with SLA designs.

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

 

[robinhood4x4]

Well, I was thinking more in the off road scene, toyotas specifically. The Tacomas and newer 4runners have an upper and lower A-arm with a concentric shock/spring (a coilover) attached to the lower A-arm and a shock tower. The shock does not locate the wheel like a macpherson strut. This is in contrast to the rear suspension which uses a seperate shock and coil spring setup attached to a solid axle.

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.

 

[SusTestEng]

Here's my take on the subject.

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.

 

[bubb375]

I was just passing through, but I thought I would add that in aviation, a strut is typically a part of the landing gear assembly. But Boeing also calls the engine support a strut. Most other manufacturers call it a pylon.

This may reinforce the belief that a strut provides geometric rigidity as well as damping.

Brian

 

[ZoRG]

A strut is known as a shock absorber, a coilover is generally a term used for a height adjustable system(Strut and coilspring), it does this by having the strut(Shock absorber) body threaded and having two rings that screw on there, (one for adjusting the hight, the other one simply to lock it in place), whith shorter than usual springs, now you can lower the car by up to 4" and retain good ride comfort. They perform really well too as most of the high end models have up to 36 way adjustability.

 

[harrisj]

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

 

[blackraven]

MAC PHERSON STRUTS work like this:

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.

 

[Dysus]

A MacPherson strut is one that has an integral stub axel, a strut without an integral stub axel is known as a semi-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