Shock Length

[DA_cookie_monstA]

Hi, I was reading through the online GT3 manual, and they had shock lengths on it.

What is the length required for the 7-7 club please, or a starter anyways.

And those shocks are nice to build too.

[James_Stewart]

The 7-7 Manual shows a length of 63mm front and rear.

They do build nicely, but make sure you have the pistons up the right way, you should have the smaller hole at the top and the larger one at the bottom.

[DA_cookie_monstA]

This is going to sound like a daft question, but.... WHY?

The oil will only flow through the pison as fast as the smallest hole allows, no matter which way up it is..???

I think I might of struggled to get an overall length of 63mm, is that from top of the shock, to the bottom of the ball joint?

[James_Stewart]

A bit of blatent plagiarism from the 'old' Lab site reveals:


Bernoulli's laws show that the flow of fluid through an orifice (a hole!) is affected by the characteristics (shape, face transition and linearity) of that hole. The shapes of the edges in particular of the hole will alter the flow performance (speed) of the fluid through the hole, in some cases in a dramatic way.

The oil holes in the pistons on the 7-6.0 Pro have a special shape that will affect the damping characteristics of the shocks. A careful look at the shock pistons will show that these pistons are carefully moulded to have a rounded face on one side, with a tapering of the oil hole down to a very sharp edge on the other face. The side with the two mould bosses has the rounded edge, if you are having difficulty in identifying this.

These "edges" will result in a damping action that is reactive to the compression speed of the suspension, but different in both directions. The sharp entry into the hole will cause an exponential and rapid increase in turbulence in the oil flow while the reverse taper (in this direction) causes the oil to de-pressure as it passes through the piston, smoothing out the downstream flow - this results in a progressively stiffer damper effect. While the rounded edge face will allow a smooth unimpeded flow through the hole that increases more linearly in proportion to the speed of flow due to the taper.

When building the shocks make sure you get all 4 pistons the same way up and to fit the pistons to the shock shaft with the rounded hole side downwards - smooth piston faces upwards, mould bosses downwards.

Feel free to remove this Mike, if you want to explain it differently

[DA_cookie_monstA]

Right, apart from now having to go rebuild the shocks to make sure I got the pistons up the right way on all four shocks (doubt it!!!), I can only seem to get the shocks down to 66mm, looks like I will HAVE to run some tubing on the shock shaft then!!

[MikeS]

As long as the shocks are the same length, on the same axle, the actual length isn't that important.
You want full compression, and the Droop screws will control the down stroke extension.

[DA_cookie_monstA]

Thats ok then Mike, thanks.