In response to Alan Sheidler's request to post the answers we give to
the list, here's what I told Dave...
Byron Short wrote:
> Hey Dave,
>
> The sawblade pattern is usually caused by you, but often the car
> contributes to it as well by virtue of a "lateral bounce" in the
> chassis. Because of the initial peak to 3/4 g followed by the drop
> back to 1/4 g, I would conclude that you entered the turn with too
> much steer input. After the rapid left turn you snapped the car into
> the right, and essentially "over-snapped" it, and then had to turn
> back. This allows the body to set up a natural frequency as it
> "bounces" laterally on the chassis. As the body bounces out, the car
> is essentially taking an oversteer set, so the driver tends to counter
> steer, which helps make the body bounce back in to a more understeer
> set, whereupon the driver again steers in more to stay on line, which
> perpetuates the cycle.
>
> Another clue that make me think this is what is happening is the
> g-levels. The car won't do this at full lateral g's because the
> chassis is saturated. But at relatively low g levels (like 1/4-3/4
> g's) the tires can produce the high-low sawtooth force to bounce the
> car back and forth on the chassis.
> So the solution is, get into the turn hard enough to saturate the
> chassis so it can't produce the return bounce. Or barring that, slow
> down your hand inputs to dampen out the bounce of the chassis. I
> wouldn't necessarily attempt to try to change the car to eliminate
> this "feature", because it's this same snappiness that makes the car
> quick in transitions when you need it, such as slaloms.
>
> Let me conclude by stealing the line made famous by Dennis Miller:
> "That's just my opinion. I could be wrong."
>
> --Byron
>
> Dave Vasko wrote:
>
>> I pulled an interesting lateral G graph off my G-Cube on Sunday's
>> autox and I
>> was hoping someone could help me interpret it. The pattern is so
>> regular it
>> would seem to mean something.
>>
>>
>>
>>
>http://www.imagestation.com/picture/sraid81/pe98cb65e29491d88efea0018658531ea
>>
>> /fb014039.jpg
>>
>>
>>
>> The trace in question is the last right hand turn on this graph. The
>> turn is
>> entered in 3rd gear at 66 MPH and exited at 69 MPH and last 3.5
>> seconds. (Yes
>> it was a very fast course) Each of the peaks is about 600 ms apart.
>>
>>
>>
>> The car is an ES Miata on Hoosiers.
>>
>>
>>
>> The peaks seem too regular and a little too fast to be driver input.
>> Has
>> anyone seen this before in DAS or Geez graphs? Any ideas what may be
>> causing
>> this?
>>
>>
>>
>> Dave
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