Fordnatics List Archive

This read-only message was archived from a public mail list.
Mail From: Shel Belinkoff <(email redacted)>


While the mile marker is a good idea, it's limited in its ability. First,
the markers are not always accurate, although they are "close enough for
Government work." More importantly, a speedo shop will give you a readout
over a range of speeds. On my truck I got a readout at 10-mph increments
from 20-mph to 70-mph. Shops will sometimes go to higher speeds as well,
depending on a number of factors.

What is interesting is that the vehicle speedometor's accuracy changes at
different speeds. My last check showed 100% accuracy at 60-mph, but at
lower speeds the speedo read higher than the actual mph, gradually getting
closer to the true speed as the speed increased. This should hold true in
all situations, for as the speed of the vehicle increases, most tires will
change their rolling diameter to some degree.

Just for the heck of it, I'll post my readings:

ACTUAL: 20 30 40 50 60 70
SPEEDO: 23 33 42 51 60 69

Shel Belinkoff
(email redacted)
_________________

On Fri, 7 Apr 1995, Robert Kirk wrote:

> >Why don't you first go to a speedometer shop and check your speedo for
> >accuracy?

> Rather than a speedo shop, just go onto any freeway with mile posts.

This read-only message was archived from a public mail list.
Mail From: (email redacted) (Robert Kirk)

At 09:01 AM 4/7/95 -0700, Shel Belinkoff wrote:
>
>While the mile marker is a good idea, it's limited in its ability. First,
>the markers are not always accurate, although they are "close enough for
>Government work." More importantly, a speedo shop will give you a readout
>over a range of speeds. On my truck I got a readout at 10-mph increments
>from 20-mph to 70-mph. Shops will sometimes go to higher speeds as well,
>depending on a number of factors.

Shel...

This read-only message was archived from a public mail list.
Mail From: Shel Belinkoff <(email redacted)>

I'd rather enjoy the scenery than concentrate on mile posts <g>.

Since there's a minimum legal speed on freeways and highways, it
might be very difficult to piddle along at 20, 30, or even 40-mph to
calibrate your speedo. That means you have a relatively narrow window
with which you can (legally) test the accuracy of your calculations.

Of course, there's also the safety factor to consider. If you're in the
car by yourself it is unwise to be reading a stop watch and watching your
speedometer while trying to concentrate on your driving.

BTW, I should also mention that when the speedometer shop calibrates your
speedometer, they also calibrate your odometer. The two do not work with
an exact 1:1 relationship, although my personal experience shows the
odometer to be more accurate than the speedometer over the entire range.

Shel Belinkoff
(email redacted)
_________________

On Fri, 7 Apr 1995, Robert Kirk wrote:

> Amazing what you start thinking about on the internet if you let your
> mind wander. To get back to Fords, I've clocked many mileposts in
> my Galaxie :-)
>
> Also, if you want to calibrate a range of speeds, you just time the mileposts
> at whatever steady speed from 20 to 70 and calculate the true speed.

This read-only message was archived from a public mail list.
Mail From: John Stewart/PicTel

That's all well and good, but does anyone know how to CORRECT the problem. I
went out at lunch and did the mile marker calibration. As far as I can tell,
my speedometer is 4 MPH off. Not a big deal, but I'd like the mileage to be
somewhat accurate for oil changes, maintenance, etc.

John Stewart (stewartj @ pictel.com)
PictureTel Corp.
222 Rosewood Drive
Danvers, MA 01923
(508) 762-5858 - voice
(508) 762-5102 - fax


I'd rather enjoy the scenery than concentrate on mile posts <g>.

Since there's a minimum legal speed on freeways and highways, it
might be very difficult to piddle along at 20, 30, or even 40-mph to
calibrate your speedo. That means you have a relatively narrow window
with which you can (legally) test the accuracy of your calculations.

Of course, there's also the safety factor to consider. If you're in the
car by yourself it is unwise to be reading a stop watch and watching your
speedometer while trying to concentrate on your driving.

BTW, I should also mention that when the speedometer shop calibrates your
speedometer, they also calibrate your odometer. The two do not work with
an exact 1:1 relationship, although my personal experience shows the
odometer to be more accurate than the speedometer over the entire range.

Shel Belinkoff
(email redacted)
_________________

On Fri, 7 Apr 1995, Robert Kirk wrote:

> Amazing what you start thinking about on the internet if you let your
> mind wander. To get back to Fords, I've clocked many mileposts in
> my Galaxie :-)
>
> Also, if you want to calibrate a range of speeds, you just time the mileposts
> at whatever steady speed from 20 to 70 and calculate the true speed.

This read-only message was archived from a public mail list.
Mail From: Shel Belinkoff <(email redacted)>

The speedometer and the odometer can be calibrated separately. Go to a
shop and have them theck the accuracy of the gauges and make the
appropriate corrections. You don't know how accurate your spedometer or
odometer is by using the mile marker method. There are too many variables.
If accuracy is important to you, get the work done accurately. It cost me
less than a tank of gas to get my speed/odometer checked.

Assuming that you were dead on in your assessment of how inaccurate your
speedometer is, that's only 6.6%. Over a period of 3,000 miles you will
be off by less than 200 miles, which is bubkis in relation to oil change
intervals. IAC, I bet your odometer isn't off as much as the speedometer
should everything on your vehicle be stock.

Shel Belinkoff
(email redacted)
_________________

On 7 Apr 1995, John Stewart/PicTel wrote:

> That's all well and good, but does anyone know how to CORRECT the problem
> went out at lunch and did the mile marker calibration. As far as I can tell,
> my speedometer is 4 MPH off. Not a big deal, but I'd like the mileage to be
> somewhat accurate for oil changes, maintenance, etc.