Speedometer Accuracy

[Averyman]

I was out cruising today and the speedometer read 40MPH at a nice cruise and I could top out at 50MPH.  It SEEMED like I may have been going 50MPH but I had no way of telling if I actually was.  Does one have to do an adjustment to the indicated reading or is the speedometer indicating the actual speed?  I don't see anything in my Operators Manual about this.
Clarence

[Swamp Dawg]

Nice way to double check your speedo is with a GPS. 

[Cranman]

If your spedo is original I believe they read double until late 1953 when the model change was made and a different gear was found for the newer type speedo.

[grfishmaker]

 OK, Here's a question. I have a 1953 machine, it now has a Ford 300 6cyl. and a 3/4 ton differential installed. I has its original speedometer on the bash with no speedometer cable hooked up to it.  What kind of cable will I have to install and will it be accurate without changing the dash indicator? Is there some sort of gear reducer/increaser that has to be changed to match the sproket speed with the dash speedometer indicator?
 I have used a gps, but it would be nice to have an operating speedometer for convenience sake. If I had an external antenna for my gps it would also make my life easier.
 Thanks for any suggestions anyone may have.

[Averyman]

Cranman -  Spedo is origional and your answer makes sense, 25 MPH is likely closer to top speed.

Grfishmaker - Good question and sorry I have no idea of the answer. If that engine/diff was actually origionally used in a Bombardier then perhaps someone like Dan Shaver could help. His Phone # is 204 467 2605

[the old trucker]

OK, Here's a question. I have a 1953 machine, it now has a Ford 300 6cyl. and a 3/4 ton differential installed. I has its original speedometer on the bash with no speedometer cable hooked up to it.  What kind of cable will I have to install and will it be accurate without changing the dash indicator? Is there some sort of gear reducer/increaser that has to be changed to match the sproket speed with the dash speedometer indicator?
 I have used a gps, but it would be nice to have an operating speedometer for convenience sake. If I had an external antenna for my gps it would also make my life easier.
 Thanks for any suggestions anyone may have.

   Grfishmaker I was told that you could get a cable made with different ends attached for different applications. That's the way taxis had their meters hooked up. Ask around the taxi companies for a place that does it, it may help.....

                                                                       OT.

[fisher]

Speedometer measures rpms of the sprocket not the track. Changed tire diameter on my little nissan truck one time and it messed up everything. Speedo in a bomber would only be close to accurate on a packed road and the one I did see working said you were going twice as fast as you actually were

[the old trucker]

  I know there is some kind of formula used to figure it out though. I know because when I ordered a new truck I was asked about what trans, gears in the diff, & tire size. They could tell me how fast, in what gear, & what the RPM. would be.. OT. must start snooping around again... 

[fisher]

You could really get into a brain twister here. Count the cleats you have on the track and the length of the track. Sprocket would move ? amount of cleats per minute. Then you could figure out how many times the track goes around per minute. With solid road you could come close.  Or get a gps.

[the old trucker]

  Here's an answer I got back from a site that I look at.

  Sprocket diameter in inches X 3.1415 finds inches per revolution of the axle. Divide by 12 gives feet per rev. Divide 5280 by this number gives you turns per mile. Multiply by rear end ratio-3.91-gives you engine turns per mile, which is RPM at 60 MPH. Half that is RPM at 30 MPH.
Note that the "sprocket diameter" is the effective measurement, which is the diameter of the circle made by the track drive slats in the grooves between the teeth. It will be slightly less than the OD of the sprockets.
Nice Bombardier, by the way! Most Bombardiers I have been in were turning up about 3000 RPM at 30 MPH. Your Ford six can stand more RPM than that.

  Here's another place to go look at,

                               http://www.google.ca/webhp?sourceid=...w=1536&bih=670