Spring set up for coil-overs

rdc

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Okay I want people's opinion on this. Why would you run a small 4 to 6" primary coil with a very low rate on a dual rate coil-over system vs. two almost equal length coils with a good primary rate for ride quality and a heavy rate secondary to catch the big hits.

Tony
 

vwguy

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part of the reason for a small coil is for preload
 

rdc

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You can preload with the nut treaded on the shock body.

Tony
 

Jack

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With a longer lite coil it will have a lot of turns, and will "stack or coil bind" and you will not get the full travel of shock, you only need a long enough lite coil to hold the wieght of the vehicle at hide hight plus about 10% of your travel (for small bumps smooth ride) then you want the higher rate to take over as soon as posable (use the spinners on the shock body to set the tranition) and that coil being stifer will have less turns and therfore more travel for full shock compresion without any coil bind.
 

FABRICATOR

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Tigger,

To put it in non-scientific terms, it's just a simple method of creating an acceptable spring rate. Multiple or progressively wound springs are a way of making the spring position sensitive. A good comparison is the often overlooked motocross motorcycle rear suspension, of the type with linkage. Many of these do not have multiple or even dual-rate-single springs. If there is a dual rate spring on this application, it is often for extreme fine tuning for a particular rider. Many are just a single, straight rate coil spring and work fantastically. The real tuning has already been done within the corresponding linkage. This is not a straight rate of movement however, but is what is known as a rising rate movement. That is (simplified) the farther the rear wheel goes up at a given speed, the faster the compression of the shock absorber and spring. It is this rising rate of movement which makes the spring and shock absorber position sensitive. It is perhaps just good luck for us that the spring and shock can share the same modified rates advantageously together.

A secret that evades most all fabricators and designers is that the spring and shock absorber are both highly position sensitive, not just the shock alone. This is being addressed unknowingly but somewhat effectively with multiple rate coils and bypass tubes. Proper linkage, or leverage, is why bypass shocks and fancy springs are not necessary on a motocross bike. On a bypass shock, the external tubes only purpose is to make the shock position sensitive. And no, the weight of the vehicle has nothing to do with the need for bypass technology. This is one reason why bypass shocks won't be around forever. Bypass shocks work great, but they are hell on the chassis and A-arms. And I'm not talking about the big rocker arm setup in Walker Evans old Chevy either. But that is another story.

Another example is the torsion bar. If properly used, it is argueably the most reliable and efficient spring there is. The problem is that preload is the only adjustment, and fine tuning is either grinding down of the diameter or adding additional torsion bars or other springs. In most race cars, there is never quite enough room for a properly sized bar, so what is installed ends up being overworked or too complicated. And a torsion bar cannot protect itself with coil-bind. There are motocross bikes without linkage (KTM, etc) and even Trophy Trucks or buggys with single, straight rate coil spring setups that work just fine. There is no magic in these cases. It is just a matter of finding (or stumbling across) a spring that has a near perfect rate for the application.



<P ID="edit"><FONT SIZE=-1>Edited by FABRICATOR on 04/17/01 11:27 PM (server time).</FONT></P>
 
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