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Post by flipflopoo1oo on Sept 21, 2014 8:00:39 GMT -6
Not finding good info on spring rates for new swing arm change! Any input would be helpful!
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hd
Pit Crew
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Post by hd on Oct 4, 2014 14:29:34 GMT -6
figure the motion ratio just like you would a lower a frame. Don't forget to square it. If you had a 17" swing arm, with the spring at 5" from rear heim (about the least you can get by with on a 5" spring) you would divide 12" ( 17" minus 5") by 17" = .705. then you would multiply .705 by itself ( .705 x .705 = 49.7% ) 400 lb spring x 49.7% = 199 lbs at the axle tube if spring was straight up with no angle.
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Post by flipflopoo1oo on Oct 4, 2014 16:03:32 GMT -6
Yeah but yeah and then the transfer rates in the splits with thrust angles and compressed factors kicking my brain in to under drive with added rear percentages! A good guess at a 25lb split then becomes most tricky in unloading the right!
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hd
Pit Crew
Posts: 6
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Post by hd on Oct 26, 2014 20:35:57 GMT -6
With the swing arm on the RR, the spring rate is somewhat digressive I think, because the front of the swing arm is dropping as the chassis rolls which is unloading the spring at the front, as it is loading the spring from the rear from chassis roll. I have seen LM cars run 6 or 700 lb springs on the RR with success. It is probably better to run the spring somewhere besides on the arm on the RR, so you have a 1 to 1 ratio or a progressive rate. JMO Thrust angles are different according to the swing arm and trailing arm lengths. If you have a short swingarm, and a long rear bar, the thrust angle will get greater as the chassis lifts, but if they are the same length, the thrust angle will be the same at ride height as when it is lifted, because the front bar will gain angle at the same rate as the back bar loses its angle.
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Post by flipflopoo1oo on Oct 27, 2014 23:49:07 GMT -6
Just trying to help a guy out with some info my self! His rules says both spring locations have to be the same and chassis not equipped for easy change! I see your point in decline during roll messing with pounds and I always want mine on top! We never needed extra movement but have ran left side with great success with a 50 percent split in spring pounds! Trying to get it to unload with two is too much trouble or to radical to be the same each time! It took a spring change of a 150 split and a few tries adjusting but got it do-able with one pound of left rear! His driver was happy with it the last I heard! This was not hiking the left and running more angle on the right than left with my old school set-up not moving the left rear corner by adding weight there to hold and never loose left rear but gain right! The factors you spoke of gave the 25lb split in spring pounds by loosing right rear to gain left when lifting and letting it nose to turn with left drag! It turned and rolled quickly adding right rear for the drive off the corner and he said he couldn't spin the tires! Hooked up, drivable and held the corners at higher speeds! Seems like his left bar was a bit shorter but both were long! I never liked short bars loosing and gaining so much, not needed if not hiking! Running the right higher for effect is diminished by having a shorter left! Finding the correct preload on the right to change at movement with two swing arms and different lengths can be temper-mental! Thanks for the input!
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