Locked Swing Arm

[RW57]

On a locked Swing Arm that does not rotate is the spring rate basically cut in half like a rotating swing arm Also does anyone know where I can get the formula to figure the rates besides the Dirt Forum tool box I can not get it to work it worked for a while but has stopped working again..

[1Blacksheep]

Measure the total length of the Arm . Lets say its 17". Then measure to the spring mount . Lets say that is 14". Divide 14 by 17. Take the .82 x the spring rate . lets say its 300#. 300 X .82 = 246# New spring rate .

[HEAVY DUTY]

There is one more step to the formula. You have to square the .82 motion ratio. .82x.82 =.67 300 x .62= 186
On most 17" swingarms that have the spring moved forward far enough for the spring to clear ( about 5") have a motion ratio at about 49% which is why they run 350 or 400 springs. If you have a 15" arm it will need about a 450 or 500

[RW57]

Thanks that is what I was looking for right now it has 375 on left rear which when formula worked came out to a 260 which is now not right as I took off the 19 in swing arm and put a 15 on it to get more rear steer it has a 20 in arm on right with a 250 on top of housing on rr which I think is too stiff and am going to go with a 200 for an open practice session at a nearby track this week Thaks again,

[1Blacksheep]

Ooops . Yep , thanks Heavy D I wrote that in a hurry and forgot the Square .

[HEAVY DUTY]

I figured you did Blacksheep. They don't show it on the dirt forum toolbox either. They figure just like a lower a arm motion ratio. Another thing to consider is that they are a degressive rate also, because the front of the swingarm is dropping as the chassis rolls, which is unloading the spring while the wheel movement (compression) is trying to load the spring.