Why are shock absorbers so long?

[Peter7307]

Conventional shock absorbers are typically 4 to 5 times longer than the springs they are intended to control.

My own car for example has shock absorbers around 20 inches long where the spring height is about 5 inches.

Any thoughts?

Cheers , Pete.

 

[GregLocock]

Well, I think you only talking about struts. They are that long to get from the bottom of the spring down to the lower suspension arm.

Rule of thumb is that the minimum extended length of a shock is around 2*stroke +6 inches, overall, ie 16 inches in your case.


If you draw the shock in the extended and compressed position you'll see why.


Cheers

Greg Locock

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

 

[Peter7307]

Greg,
Thanks for the reply.

Re reading my original post it is not as clear as I had intended so if I may try again here.

The car is my Holden VY (2003) Acclaim sedan.

The rear springs are about 5 inches or so high and are conical shape and sit well below the boot floor level.

The conventional shock absorbers fitted extend well up into the wheel arch and into the boot behind the rear seat.

This is what prompted the question. The total wheel travel is about about six inches or so (I am guessing and have not measured it) but the fitted length of the shock is well over double this distance.

Cheers , Pete.

 

[GregLocock]

No, you have to include the rebound travel in the stroke in that equation.

Typical total travel for a suspension in Oz is 7-8 inches, so the shock will need to be 20 inches long.

In practice you often can't fit that in, so we lean the shock over or move the wheelend mounting pt inboard to reduce its motion ratio.

Cheers

Greg Locock

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

 

[Peter7307]

Aha , got it now.
Thanks for the explanation.

Cheers , Pete.