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Old 04-12-2010, 08:51 AM
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Theoretical Q - how much force on shock mounts?

I was fabricating some new shock mounts and got to thinking about the amount of force exerted on the mounts. Here's two theories I came up with...toss in more as you see fit.

Theory 1 - The force on the shock mounts is never more than the force required to compress or expand a shock...something you can do fairly easily with just muscle power. Thus, most shock mounts are way over built.

Theory 2 - The force on the shock mounts is multiplied many times over when the suspension encounters a bump or pothole and the axle and nearly equals the force on the springs themselves. Thus, most shock mounts may be way under built.

I would imagine somewhere on the web an engineer has laid this all out...but I was too lazy to try to dig it out. More fun to just get some discussion here.

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Old 04-12-2010, 09:35 AM
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Good question, but looking back at the way some OEM shocks are mounted leads me to believe it's like the first example you laid out. Most upper shock mounts are in body sheet metal with just a sheet metal doubler at the attachment point.

Vince
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Old 04-12-2010, 12:28 PM
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Quote:
Originally Posted by 302 Z28
...looking back at the way some OEM shocks are mounted leads me to believe it's like the first example you laid out.
As I've mulled this over, I'm wondering if some folks utilize their shocks as a suspension limit strap...and therefore feel a stout bracket is called for to hold the axles to the frame in the event of severe axle travel.
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Old 04-12-2010, 12:57 PM
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This is a general concept here, as the actual calculations are pretty busy.
The load that is transmitted to attach points on any given shock will be velocity dependent. ie if you try to compress it quickly the load will be higher than if done slowly. Make your mounts stout for the banzai runs over speed bumps.
(damn wheres my book on differential equations )
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Old 04-12-2010, 01:48 PM
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Quote:
Originally Posted by merlinsoars
The load that is transmitted to attach points on any given shock will be velocity dependent.
Ah, so a little bit of Theory 1 AND a whole lot of Theory 2? The force on the brackets is multiplied and it is multiplied the faster you are going (the higher the velocity of the bump impact.)? I'd be interested in a tad more of the theory/equations if you have them handy. Particularly what causes the shock to create more resistance (or in the alternative - provide less "give") when the force on it occurs quickly rather than slowly. I would suppose this has to do with the total number of square inches the oil in the shock is able to move through...i.e a quart could move through the holes/spaces if the force was applied over 5 minutes but only a squirt can move through those same holes/spaces if an equal force was applied over 5 nano-seconds. Or something like that.

It's making a bit more sense now why folks make their shock mounts pretty beefy.
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Old 04-12-2010, 02:03 PM
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Quote:
Originally Posted by cboy
As I've mulled this over, I'm wondering if some folks utilize their shocks as a suspension limit strap...and therefore feel a stout bracket is called for to hold the axles to the frame in the event of severe axle travel.
In the event of, say, a spring/spring bracket failure, the shock/shock mounts will be all there is between the sprung weight of that corner of the vehicle and the tire, so you have to make them able to withstand this (admittedly and hopefully rare!) instance.

There are rubber bump stops that might come into play before the shock limits travel in the front suspension of most vehicles, less so out back.
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