aerosam
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| posted on 15/4/09 at 07:11 PM |
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How do you calculate shock absorber length?
Hi Guys,
I need to buy the rear shocks for my bmwcost but how do i work out what length shocks I need to give me a useable range of ride height?
For those who don't know, I'm using a +4 chassis with the BMW E34 axle carrier and semi trailing arms. The shockers are going to be
mounted between the trailing arms and normal mounting points on the chassis.
I haven't yet welded on the mounting brackets for the shocks so all figures below are innacurate but fairly close, I just need to know how to
work it out.
With a trailing arm at it's lowest point of travel the distance between mounting hole centres is 17" at it's highest point
it's 10" ( but i'm not sure I want the wheel to travel that far)
Help! This is the stuff I simply don't understand.
Thanks,
Sam
Had enough of this dictatorship known as LCB. Gone elsewhere, not coming back. Kiss my ass ChrisW.
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MikeCapon
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| posted on 15/4/09 at 08:36 PM |
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Simples! Drop the wheels down to the lowest point you want (maximum droop) and measure between mounting points. This is your open length.
Then lift the wheels to the highest point you want (maximum bump) and measure again between mounting points. Full droop measurement minus full bump
measurement equals stroke.
Most locosts seem to have a total wheel movement of around 4" or 100mm. What have you got at the front?
If you need more help then I'll be back on tomorrow.
Cheers,
Mike
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aerosam
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| posted on 15/4/09 at 09:44 PM |
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Hi Mike,
The only thing that worries me is might I be at risk of bottoming out the rear suspension if the trailing arms have more movement than the shocks will
allow?
the front is Haynes Roadster so I'll be using the same shocks it uses. The wishbone mounting points are almost identical the the locost (3mm
further apart on the lower wishbone i think).
Thanks!
Sam
Had enough of this dictatorship known as LCB. Gone elsewhere, not coming back. Kiss my ass ChrisW.
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procomp
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| posted on 16/4/09 at 07:14 AM |
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Hi
Regarding your trailing arms. They will have quite a lot of travel due to there not being any joints that can lock out / run out of travel. But in
reality as a guide virtually all cars running rear trailing arms run with a 13" open length. This generally gives 3.5" of travel which is
more than enough.
At the rear put some packers under the car to get the desired ride height you wish to attain with driver on board with the wheels/tyres on the
ground.
Then raise the chassis 1.5" and measure this as Mike says ^^. This gives you the open length. This is the dimension that the damper suppliers
are quoting when referring to the length of a damper.
Cheers Matt
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