Try running an experiment:
Run a strip of reflectorized tape down the side of each rocker panel and see
if it become completely invisable to the timing system. <g>
--- Rick Brown
> -----Original Message-----
> From: owner-ba-autox@autox.team.net
> [mailto:owner-ba-autox@autox.team.net]On Behalf Of Kevin Stevens
> Sent: Friday, May 28, 2004 1:34 PM
> To: Autox List (E-mail)
> Subject: Fwd: How accurate are our timers?
>
>
> On May 28, 2004, at 12:03, Richard Urschel wrote:
>
> > How accurate are our timers?
> >
> > Having made no changes to my car for the past 18 months, and having
> > concentrated exclusively on driving during that period, I have finally
> > developed a consistent ability to duplicate runs within a tenth.
> > However, it still seems that in at least 1 out of every 25 runs the
> > time is inexplicably faster or slower than expected by 3 tenths or
> > more.
> >
> > Unless our timing software confirms a trip on both the front and rear
> > wheels the perceived time discrepancy may be due to intermittent
> > failures of the timers to consistently trip. There would be no other
> > indication of this unless the timer failed to trip on both the front
> > and rear wheels at either the start or finish. A 1 in 50 intermittent
> > failure rate would only cause this once in every 1250 runs, but would
> > fail to trip on the front wheels only at either the start or finish in
> > 1 out of 26 runs.
>
> I frequently misunderstand you, Rich, so let me check my understanding:
>
> - Your premise is that in about 1 of 25 runs, either the start sensor
> or finish sensor fails to pick up the front wheel and gets the rear
> wheel instead, causing a time variance of "3 tenths or more"
>
> - We're not talking about precision here, we're talking accuracy - in
> other words, how the run time compares to reality, not whether the
> timer system is inherently precise to +/- .001 or not.
>
> If that is all correct, I have the following observations, if not,
> please disregard and clarify:
>
> > So, does anyone know if our timing systems confirm a double trip at
> > the start and finish or do they just accept what they get while
> > rejecting any additional trips for a half second or so afterwards? Are
> > the lights even capable of resetting and retripping in two tenths of a
> > second?
>
> Dunno, ask Boris to check the manual. I note an assumption here,
> though, that the lights are triggering on the wheels. I don't know
> that to be the case for low-riding cars, are you sure it's true for
> yours? I would think it more likely for it to generally trigger on the
> nose of your car, and sometimes miss that and get the front wheel, than
> for it to miss one wheel but get the other.
>
> I have seen/heard of problems with reflectors missing highly-polished
> chrome wheels on occasion, BTW. I avoid that by letting mine get all
> gooked up with brake dust.
>
> Let's do a little math:
>
> I'm using 8' for your wheelbase, that's 96", adjust as necessary.
>
> x = 8' / .3 sec = 26.67 ft/sec, which converts to 18 mi/hr
>
> It's my impression that most finishes run somewhat faster than that,
> but I could be wrong. It might be more characteristic of the start
> light. Note that if your wheelbase is shorter, or the time difference
> is greater, that speed would be lower.
>
> Finally, it seems very odd to me that for all runs you typically
> maintain times within .1. Even with perfectly consistent driving, I'd
> expect greater changes than that from tire heating. Do you have a
> breakdown of how many of these anomalies are faster vs slower, and on
> which run of the event they occur?
>
> KeS
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