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Post by derbydad on Mar 27, 2011 16:34:09 GMT -6
We built a rail rider and raced it last week. From the start to 3/4 of the race it was in first place. Then it developed a significant wobble/ shimmy in the rear end of the car. Every race was the same.
Any thoughts?
As an aside, this is the first year any on my son's have not finished first, through districts. This is due to your help here on the board. Thank you for all your help and advise.
Derby Dad
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Post by rocketpine21 on Mar 27, 2011 18:07:27 GMT -6
I am not certainly a pro....but it sounds to me like an axle had moved or rotated to start the rear end fighting each other? Some say the rear wheel behind the DFW is pretty important with alignment, maybe roll check that wheel and see if it is perfect toe? Good luck.
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Post by cycrunner on Mar 27, 2011 23:31:30 GMT -6
I run my cars on my track and see this often with my rail riders if the COM is too far aft - that is, too close in front of the rear axel. Have you checked to see the balance point? This is the COM. If my COM is closer than 0.6 inches I can get wobbles. This usually develops right after the curve transition to the flat portion of the track because the center of mass moves aft as the car moves from a steep angle to a horizontal position. The further aft the COM gets the more likely you will get a wobble. A very safe COM (center of mass) is between .75 and 1.0 inches. Shoot for .75 and see if you get a steady run. You will need a track to test this. Good luck!
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Post by RacerX on Mar 28, 2011 8:40:14 GMT -6
a few questions first:
what kind of track and do you know the length?
how much steer did you tune the car with?
how much camber in the rear?
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Post by cycrunner on Mar 30, 2011 18:26:52 GMT -6
I should have adder that increasing the drift on your car will often solve the wobble problem with a rail rider.
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rocket21
Newbie
"In it to win it"
Posts: 5 
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Post by rocket21 on Mar 17, 2012 11:13:08 GMT -6
Usually the issue here is the rear axles are not perfectly true. The Toe is off and they are fighting eachother which results in the wobble. Inceasing the drift can fix the problem but it will result in slower times. The rears MUST be drilled perfectly straight for a gentle drift, fast speeds and no wobble. On another note, if you shaved more than 1/16th of wood off the DFW side, this can cause rear troubles as well.
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