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Color0's Micro RC Blog -- A technical brain dump from the mind of yours truly...
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The Penny Drop (or Quarter/Dime/Spur...)

Posted 01-15-2012 at 03:02 PM by color0
Today, a quick and simple test for tweak brought to you originally by the 1/12 pan car crowd: the penny drop test. Basically, it's a really easy way to see if your chassis is places equal weight on the rear tires, so long as your front end is already guaranteed even.

Why that last sentence is so: The penny drop test can only tell you if the car is overall tweaked -- it cannot tell you which part. So if your front end is tweaked but your rear end is fine, or your front end is fine but your rear end is tweaked, this test returns the same result. For most of us Mini-Z owners (barring those with double A-arm suspension), the front ends are only adjustable with shims, so once you get that visually even, the front end is "just about" even and we're going to assume it's no longer tweaked. And under that assumption, we can use the penny drop test to figure out the rear. So, here's the setup:

I use spur gears because I have spurs but not pocket change. Anyways, lay your spurs across the front tires, not flat, since you actually want them to roll off the wheel the instant the tire leaves the ground. Then you stick a sharp object underneath the car at its centerline and lift up the front end like so:

And if you see that, it means your rear left wheel is pushing down harder than the rear right, causing the front right wheel to lift first. A quick adjustment with shims (if you run disk damper) or spring collar (if you run tri-shock) and you should get the two spurs falling simultaneously on your next try:

There you go! No more tweak. Again though, this is only going to tell you if the chassis alone is mechanically sound -- once you've got this test out of the way, if your car is still driving like it's tweaked, then you need to start looking at the other possibilities: tire issues, body issues, drivetrain/bearing issues, etc. etc. Sometimes the way the track is will make the car feel tweaked as well, and in those cases, you just gotta use your best judgment and perhaps even deviate from what was perfect on the bench. I often purposely tweak a little to the right for clockwise tracks, and vice-versa. Whatever works, is whatever works. Have fun!


Next week: I've solved the Super GT wall handling problem! An aerodynamic solution that will give you more front downforce while allowing you to run +3N front wheels on your GT500 GT-R/HSV body AND protecting its fragile front end at the same time!
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