Speedo Correction For Different-Sized Tires?

My speedo is set for fat tires: 2090 mm for one complete rotation.

Today I did a ride that the speedo said was 46 miles - but on slicks that
measure only 1965 mm for one complete rotation.

The diff is 125. 125/2090 = approx 6%.

Can I just use this as a straight-line correction factor for both milage and
speed?

e.g. Today's nominal 46 miles actually = 46 * .94 = 43.2?

or 20 mph nominal actually = 20 * .94 = 18.8 mph?


Obviously not a religious issue - but might be useful when comparing pedaling
effort between tires, or navigating to precise directions.
--
PeteCresswell

"(Pete Cresswell)" wrote in
:
The diff is 125. 125/2090 = approx 6%.

Can I just use this as a straight-line correction factor for both milage
and speed?

Yes. The speedometer is just counting revolutions.

"(Pete Cresswell)" wrote in
:
The diff is 125. 125/2090 = approx 6%.

Can I just use this as a straight-line correction factor for both milage
and speed?

Yes. The speedometer is just counting revolutions.

On Tue, 12 Oct 2004 23:19:49 GMT, "(Pete Cresswell)"
wrote:

My speedo is set for fat tires: 2090 mm for one complete rotation.

Today I did a ride that the speedo said was 46 miles - but on slicks that
measure only 1965 mm for one complete rotation.

The diff is 125. 125/2090 = approx 6%.

Can I just use this as a straight-line correction factor for both milage and
speed?

e.g. Today's nominal 46 miles actually = 46 * .94 = 43.2?

or 20 mph nominal actually = 20 * .94 = 18.8 mph?


Obviously not a religious issue - but might be useful when comparing pedaling
effort between tires, or navigating to precise directions.

Dear Pete,

If you can live with such vague approximations of such
crucial figures (and do them in your head in time to avoid
almost certain death), then your shameful scheme should
work.

After all, it's pretty much what the speedometer does
anyway. Every time the magnet whips by the sensor, the
computer yawns and checks to see how many miles or
kilometers per hour that many clicks in that many seconds
should be. It trusts you to tell the truth.

In 1968, I spent a fearfully noisy and uncomfortable few
hours as a little boy in the cramped jump seat of a doctor's
poorly muffled Aston Martin, bored witless and watching the
speedometer needle sitting on the 100 mph mark as we headed
dead east out US 50 to the Kansas border.

Pawing through the glove box at one stop, I found (of all
things) a copy of the doctor's will and was intrigued to see
that it covered what to do if he died first, if his wife
died first, or if no one could tell who died first.

His wife wasn't with us, so I lost interest and kept
looking.

Even more intriguing was a handwritten table of corrections
from some garage that had been paid to calibrate the Aston
Martin's speedometer. I felt much better knowing that
although the doctor kept the needle right on 100 mph, we
were doing only 94 mph.

Hope you feel better at 18.8 mph.

Carl Fogel

On Tue, 12 Oct 2004 23:19:49 GMT, "(Pete Cresswell)"
wrote:

My speedo is set for fat tires: 2090 mm for one complete rotation.

Today I did a ride that the speedo said was 46 miles - but on slicks that
measure only 1965 mm for one complete rotation.

The diff is 125. 125/2090 = approx 6%.

Can I just use this as a straight-line correction factor for both milage and
speed?

e.g. Today's nominal 46 miles actually = 46 * .94 = 43.2?

or 20 mph nominal actually = 20 * .94 = 18.8 mph?


Obviously not a religious issue - but might be useful when comparing pedaling
effort between tires, or navigating to precise directions.

Dear Pete,

If you can live with such vague approximations of such
crucial figures (and do them in your head in time to avoid
almost certain death), then your shameful scheme should
work.

After all, it's pretty much what the speedometer does
anyway. Every time the magnet whips by the sensor, the
computer yawns and checks to see how many miles or
kilometers per hour that many clicks in that many seconds
should be. It trusts you to tell the truth.

In 1968, I spent a fearfully noisy and uncomfortable few
hours as a little boy in the cramped jump seat of a doctor's
poorly muffled Aston Martin, bored witless and watching the
speedometer needle sitting on the 100 mph mark as we headed
dead east out US 50 to the Kansas border.

Pawing through the glove box at one stop, I found (of all
things) a copy of the doctor's will and was intrigued to see
that it covered what to do if he died first, if his wife
died first, or if no one could tell who died first.

His wife wasn't with us, so I lost interest and kept
looking.

Even more intriguing was a handwritten table of corrections
from some garage that had been paid to calibrate the Aston
Martin's speedometer. I felt much better knowing that
although the doctor kept the needle right on 100 mph, we
were doing only 94 mph.

Hope you feel better at 18.8 mph.

Carl Fogel

wrote in message . ..
On Tue, 12 Oct 2004 23:19:49 GMT, "(Pete Cresswell)"
wrote:

My speedo is set for fat tires: 2090 mm for one complete rotation.

Today I did a ride that the speedo said was 46 miles - but on slicks that
measure only 1965 mm for one complete rotation.

The diff is 125. 125/2090 = approx 6%.

Can I just use this as a straight-line correction factor for both milage and
speed?

e.g. Today's nominal 46 miles actually = 46 * .94 = 43.2?

or 20 mph nominal actually = 20 * .94 = 18.8 mph?


Obviously not a religious issue - but might be useful when comparing pedaling
effort between tires, or navigating to precise directions.

Dear Pete,

If you can live with such vague approximations of such
crucial figures (and do them in your head in time to avoid
almost certain death), then your shameful scheme should
work.

After all, it's pretty much what the speedometer does
anyway. Every time the magnet whips by the sensor, the
computer yawns and checks to see how many miles or
kilometers per hour that many clicks in that many seconds
should be. It trusts you to tell the truth.

In 1968, I spent a fearfully noisy and uncomfortable few
hours as a little boy in the cramped jump seat of a doctor's
poorly muffled Aston Martin, bored witless and watching the
speedometer needle sitting on the 100 mph mark as we headed
dead east out US 50 to the Kansas border.

Pawing through the glove box at one stop, I found (of all
things) a copy of the doctor's will and was intrigued to see
that it covered what to do if he died first, if his wife
died first, or if no one could tell who died first.

His wife wasn't with us, so I lost interest and kept
looking.

Even more intriguing was a handwritten table of corrections
from some garage that had been paid to calibrate the Aston
Martin's speedometer. I felt much better knowing that
although the doctor kept the needle right on 100 mph, we
were doing only 94 mph.

Hope you feel better at 18.8 mph.

Carl Fogel

*********************************************

Hi, Carl, I love your story.

You're WAY ahead of your time. :-)

Lewis.

*************************

wrote in message . ..
On Tue, 12 Oct 2004 23:19:49 GMT, "(Pete Cresswell)"
wrote:

My speedo is set for fat tires: 2090 mm for one complete rotation.

Today I did a ride that the speedo said was 46 miles - but on slicks that
measure only 1965 mm for one complete rotation.

The diff is 125. 125/2090 = approx 6%.

Can I just use this as a straight-line correction factor for both milage and
speed?

e.g. Today's nominal 46 miles actually = 46 * .94 = 43.2?

or 20 mph nominal actually = 20 * .94 = 18.8 mph?


Obviously not a religious issue - but might be useful when comparing pedaling
effort between tires, or navigating to precise directions.

Dear Pete,

If you can live with such vague approximations of such
crucial figures (and do them in your head in time to avoid
almost certain death), then your shameful scheme should
work.

After all, it's pretty much what the speedometer does
anyway. Every time the magnet whips by the sensor, the
computer yawns and checks to see how many miles or
kilometers per hour that many clicks in that many seconds
should be. It trusts you to tell the truth.

In 1968, I spent a fearfully noisy and uncomfortable few
hours as a little boy in the cramped jump seat of a doctor's
poorly muffled Aston Martin, bored witless and watching the
speedometer needle sitting on the 100 mph mark as we headed
dead east out US 50 to the Kansas border.

Pawing through the glove box at one stop, I found (of all
things) a copy of the doctor's will and was intrigued to see
that it covered what to do if he died first, if his wife
died first, or if no one could tell who died first.

His wife wasn't with us, so I lost interest and kept
looking.

Even more intriguing was a handwritten table of corrections
from some garage that had been paid to calibrate the Aston
Martin's speedometer. I felt much better knowing that
although the doctor kept the needle right on 100 mph, we
were doing only 94 mph.

Hope you feel better at 18.8 mph.

Carl Fogel

*********************************************

Hi, Carl, I love your story.

You're WAY ahead of your time. :-)

Lewis.

*************************

RE/
Dear Pete,

Another good laugh from Carl...Thanks!...
--
PeteCresswell

RE/
Dear Pete,

Another good laugh from Carl...Thanks!...
--
PeteCresswell

Even more intriguing was a handwritten table of corrections
from some garage that had been paid to calibrate the Aston
Martin's speedometer. I felt much better knowing that
although the doctor kept the needle right on 100 mph, we
were doing only 94 mph.

Might've been cheaper, too, had he gotten a ticket, so it's a double-whammy.

--
Phil, Squid-in-Training