Andy Levy <andy.levy@gmail.com> wrote:
: On 10/20/05, jon@dakota-truck.net <jon@dakota-truck.net> wrote:
:>
:> david.clement@verizon.net wrote:
:> : Aaron,
:>
:> : You have to remember the speedo's up near the top of the scale have huge errors
:> : and they are optomistic so you were not going any where near the indicated
:> : speeds. Plus, just to go from 115 to 130 with your 2.5 would require almost
:> : doubling the horsepower.
:>
:>
:> Yep, for us "non professionals", using a GPS is probably the best/cheapest
:> way of getting an accurate speed reading.
: Except a GPS has its own range of error-inducing factors too. The
: only really good way to get an accurate speed reading (without, say, a
: calibrated radar gun) is timing a trip across a measured distance.
(Note that I used the qualifier: "non professionals") :-)
True, there will be some error involved in anything, but the GPS is
going to be a heck of a lot more accurate than your average speedometer.
As far as timing across a measured distance, that'll work but then you
introduce error due to trying to synchronize with a stopwatch. You can
eliminate that by going to electronic equipment, but then you're looking
at some considerable expense, and that'd fall into the "professionals"
category - not what I was addressing. (Maybe you could mount a video
camera on the dash referenced to known points and count the frames later.
You'd need a high speed camera though since the standard video camera's
30fps means that at 100mph, each frame is about 5 feet apart, which is
potentially enough time to miss your landmark, to say nothing of the focus.)
The "known distance" is also problematic - how do you measure it? I'm
guessing your answer isn't going to be via GPS. :-) An odometer would
just re-introduce the speedometer error which we are trying to eliminate.
I suppose if you had a lot of time on your hands, you could use a tape
measure or a wheel. IMHO though, the main drawback to the measured
distance is that you need to get up to your top speed before you get to
the start point and you need to hold your speed until you get over the
end point. If you accelerate/decelerate at all during the measured
distance, the result is not your true top speed. Also, this is bound
to be more dangerous than something which is going to give you an
instant reading like a GPS would - especially in something like our
trucks which have all the aerodynamics of a brick. (Actually many GPS
units will record a track so you could probably just toss it on the
dash, concentrate on your driving, and then play it back later and
find out what your top speed was.) For $50-100, a GPS is a pretty
cheap and easy way to get a speed reading that is going to be more
than adequate for whatever we would need it for. (If you need a more
accurate speed reading than what a GPS will give you, then you're
probably ready to move up to a fifth wheel, electronic timing
equipment, etc. which takes you out of the realm of curiosity and
plunks you solidly in the "professional" category.) So anyhoo, I'll
stick with my original statement; the above is my opinion, worth what
y'all paid for it. ;-)
Why does it feel like there should be a little caption at the
bottom of this post that says "Professional driver, closed course"? :-)
Ok, the professional driver doesn't apply to most of us, but if anyone
is actually contemplating any of the above, please do be sure to
observe the "closed course" part. :-)
--
-Jon-
.-- Jon Steiger --- jon@dakota-truck.net or jon@jonsteiger.com --.
| '70 Barracuda, '90 Dakota Convertible, '92 Ram 4x4, '96 Dakota |
| '96 Intruder, '96 Kolb FireFly, '99 Cherokee, '01 Ram 3500 |
`----------------------------------- http://www.jonsteiger.com --'
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