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Motion ratios for FB/FC/FD?

Old 05-27-05, 03:45 PM
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Motion ratios for FB/FC/FD?

Looking to compile a fairly complete listing of motion ratio's for popular performance cars.

I know someone here must have this info--

Thanks,
Steve
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Old 05-27-05, 08:50 PM
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Bueller?
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Old 05-28-05, 05:52 AM
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The FD ratios are about 1.6 front and 1.4 rear, IIRC.

-Max
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Old 05-29-05, 12:38 AM
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what is a motion ratio?
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Old 05-29-05, 02:08 AM
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http://www.google.com/search?hl=en&l...on&btnG=Search

Basically, the motion ratio is the lever effect the suspension has on the shock/spring. For instance, if you have a suspension arm that is 24" long and the shock/spring connects 16" from the chassis side, the motion ratio is 24/16 = 1.5. When the suspension moves, the wheel moves 1.5 times as far as the lower spring/shock attachment point moves. If you had a 500 lbs/in spring, the wheel rate would be 500 / 1.5 = 333 lbs/in.

-Max
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Old 05-29-05, 11:37 AM
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By definition the Motion Ratio for a MacPherson Strut (ie fb, fc front suspension) is allways 1.
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Old 06-04-05, 04:44 PM
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Originally Posted by maxcooper
http://www.google.com/search?hl=en&l...on&btnG=Search

Basically, the motion ratio is the lever effect the suspension has on the shock/spring. For instance, if you have a suspension arm that is 24" long and the shock/spring connects 16" from the chassis side, the motion ratio is 24/16 = 1.5. When the suspension moves, the wheel moves 1.5 times as far as the lower spring/shock attachment point moves. If you had a 500 lbs/in spring, the wheel rate would be 500 / 1.5 = 333 lbs/in.

-Max
Wheel rate is the spring rate divided by the motion ratio squared. In your example the 500 lb/in spring is 222.2 lbs/in of wheel travel. I have seen the motion ratio calculation listed as the length between the suspension pivot to spindle mounting divided by the length between the suspension pivot moutning and the spring mount squared. This simply takes the square function out of the wheel rate calculation and moves it into the motion ratio calulation. Sorry to say, but you didn't do either.
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Old 06-05-05, 03:23 AM
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D'oh!

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