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Author Topic:   swing arm calculator
irace74
Dirt Forum Racer

Total posts: 80
posted July 05, 2005 06:07 PM  
Hey Jammin: I went to the swing arm spring rate calculator and found a descrepency between the tool box calculated values and those as presented by Mark Bush in the Racewise workshops. I used to believe that the swing arm rate was the length to the spring / total length of the swing arm but, Mark showed me that the actual calculation is the
(length to the spring / overall bar length)^2
After examining the situation I think that he is right. The tool box calculation will result in spring rates on the arm which are substantially lower then the desired values (i.e. tool box spring factor-(10.25/14.5)=.71, racewise spring factor-(10.25/14.5)^2=.50).

For a desired 200# spring rate at the wheel the tool box would say that you need a 285# spring while the Racewise method would require a 400# spring to achieve the 200#rate.

joeltjen
Dirt Maniac

Total posts: 182
posted July 05, 2005 10:44 PM  
i've been using the tool box one but i've been assuming this is giving me the spring rate not at the wheel but rather at the mounting point on the birdcage. then i've been using these rates and calculating the distance to the wheel patches as you would to figure wheel rate if the springs where just simply setting on top of the rearend. not sure if thats right but it seemed right to me. john

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