I think I know the answer already, but why not.

I have a 1982 Yamaha DT80 enduro bike that has a speedometer from a
DT100. The DT100 had a larger wheel diameter than the DT80 does, so the
reading isn't correct. Is there any adjustment to compensate for this,
or do I need to get a bigger wheel?

Jack Hunt wrote:
> On Tue, 01 Mar 2005 19:54:44 -0600, Mark Olson <(E-Mail Removed)>
> wrote:
>
>
>>I can think of three possibilities besides a bigger wheel.
>
>
> How about:
>
> Are you sure it isn't correct? The ratio for the speedometer is
> usually in the sending unit, not in the speedo itself.
>
> 4. Get a speedo sending unit from a DT80
>
> or
>
> Calculate the margin of error. If your speedometer is reading about
> 10% optimistic:
>
> 4b. They all do that, sir.
>
>
> --
> Jack

The sending unit is the original DT80 one. When you say they are about
10% optimistic, would that mean the trip odometer would be 10%
"optimistic" as well?

Jack Hunt wrote:
> On Tue, 01 Mar 2005 19:54:44 -0600, Mark Olson <(E-Mail Removed)>
> wrote:
>
>
>>I can think of three possibilities besides a bigger wheel.
>
>
> How about:
>
> Are you sure it isn't correct? The ratio for the speedometer is
> usually in the sending unit, not in the speedo itself.
>
> 4. Get a speedo sending unit from a DT80
>
> or
>
> Calculate the margin of error. If your speedometer is reading about
> 10% optimistic:
>
> 4b. They all do that, sir.
>
>
> --
> Jack

I'm not positive it is not accurate - it just "feels" wrong. Especially
the odometer seems off.

Masospaghetti wrote:
> I think I know the answer already, but why not.
>
> I have a 1982 Yamaha DT80 enduro bike that has a speedometer from a
> DT100. The DT100 had a larger wheel diameter than the DT80 does, so
the
> reading isn't correct. Is there any adjustment to compensate for
this,
> or do I need to get a bigger wheel?

http://home.jtan.com/~joe/speedo.htm

Calibrating speedometers for fun with a rusty spike and big
ugly hammer.

http://www.ibmwr.org/otech/speedo.html

Slightly more elegant solution involves fiddling with spring
tension.

Not so sure you really want to try any of these experiments though.