speedo's are always off exponentially. They are usually figured by %.
Hence, if you go with a tire that's 5% taller, you speedo will be 5% off,
reading slower than actual speed. So at 50 you'll actually be goin' 52.5.
etc. Used that lecture to defend my arse in court =) Flatfoot got me for 61
in a 55... back when I had 225/75's on my dak. Now I've got 235/60's on
there and my speedo is closer to correct. No speedo is absolutely
correct, unless it is controled by a computer..or something =)
-mike d.
>>> Sam Parthemer <srp@home.com> 03/29/99 09:32pm >>>
Confused by the statements below, but the 275/40/17 is a shorter tire
than
both
the 195/75, and 215/75... so much that in either configuration your
speedometer
would read anywhere between 3-9 mph HIGHER than actual 'ground
speed'.
What RPM was your truck running when you were above 115??? The
reason
I ask.. stock speedometers are not accurate, nor are intended to be,
about
85 mph
in a majority of vehicles. Even Porsche VDO gauges are optimistic with
195
mph
indicated, with an actual speed of 179 mph in a recent magazine test.
RPMS
will
tell the real story, as will a good GPS, and radar, and a highway
patrolman,
and....
Sam '99 RT x 2
>
> The truck was calibrated for p195/75/15's. My truck was born a work
special
> before it became a Vipertruck, so it came with the michelin LT215/75/15
which
> were a little more than an inch larger in diameter. Now I have
275/40/zr17's
> in the rear which are the right size. Now the speedo is calibrated
properlt
> and it cuts me off @ 155...damn!!
>
> > Oh ,and is yours an R/T ?
>
> Nah, I wish!! Just a plain ole Dakota WS with a ton of mods.....and
currently
> saving up for a supercharger....let ya know when I got the $3500 (grin)
>
> -Austin
> Vipertruck
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