rear gears vs. odometer

[waldo786]

I took a trip last weekend and looked at my odometer and it was 109 miles and the mapquest directions said it'd take around 145. I have 3.73 gears in the rear instead of the 3.42s. I know that will cause problems but is that the way it should be in that the odometer said I traveled less than I should have, or is there something else I should check?

 

[TurboDave]

Rear gears wont have any affect on the odometer, they will affect the cruise rpm required for a given speed. What will have the greatest affect on odometer accuracey would be the overall diameter of the drive wheels/tires.

 

[turbo2nr]

Hold on now. I have plentyof experience with that. Yes, the rear gears do have a direct affect on the odo.

Maybe you have one of my old cars.

I add a reducer from a Monty Carlo SS in-line with the two piece speedo cable to my cars when I change gears. You can flip the gears to add/subtract around 15% of the cable RPMs.

It's a little metal box. Goes by the firewall.

The odo goes hand in hand with the speedo, why would it not? They get the same signal from the same spinning cable, unless you have digital dash, then I have no experience with tat.?

I have messed around with gears, tires, speedo stuff for a while.

Change tires and/or rear gears, and the speedo and odo will change.

 

[waldo786]

Hold on now. I have plentyof experience with that. Yes, the rear gears do have a direct affect on the odo.
Maybe you have one of my old cars.
I add a reducer from a Monty Carlo SS in-line with the two piece speedo cable to my cars when I change gears. You can flip the gears to add/subtract around 15% of the cable RPMs.
It's a little metal box. Goes by the firewall.
The odo goes hand in hand with the speedo, why would it not? They get the same signal from the same spinning cable, unless you have digital dash, then I have no experience with tat.?
I have messed around with gears, tires, speedo stuff for a while.
Change tires and/or rear gears, and the speedo and odo will change.

Thanks for the info. Thats very useful. I do have a regular non digital guage. The funny thing is though the speedo seems to be accurate. It is upgraded to a 145 mph one so could that have been adjusted while the odometer isn't? The tires I have are 25" and as far as I know that is the stock size or is it larger? Thanks!

 

[TurboDave]

Hold on now. I have plentyof experience with that. Yes, the rear gears do have a direct affect on the odo.

Maybe you have one of my old cars.

I add a reducer from a Monty Carlo SS in-line with the two piece speedo cable to my cars when I change gears. You can flip the gears to add/subtract around 15% of the cable RPMs.

It's a little metal box. Goes by the firewall.

The odo goes hand in hand with the speedo, why would it not? They get the same signal from the same spinning cable, unless you have digital dash, then I have no experience with tat.?

I have messed around with gears, tires, speedo stuff for a while.

Change tires and/or rear gears, and the speedo and odo will change.

Sorry, I wasn't awake yet. changing the rear gears spins the tranny tail shaft faster/slower, thereby affecting the odo/speedo

 

[Ormand]

The stock tires are 26", not 25". And the speedo can be recalibrated by changing the spring in the speedo head, and if that is done, the odometer will not read correctly.

 

[turbo2nr]

Sounds good to me..

 

[wagon]

Thanks for the info. Thats very useful. I do have a regular non digital guage. The funny thing is though the speedo seems to be accurate. It is upgraded to a 145 mph one so could that have been adjusted while the odometer isn't? The tires I have are 25" and as far as I know that is the stock size or is it larger? Thanks!

Your speedo was upgraded to the 145, but it was probably done with the reducer, hence the reduced mileage on your odo, while your speedo is still correct. Also, if you had a correct speedo, and all you did was change to 3.73s, then it would read higher miles, not lower.

 

[waldo786]

Thanks again for the info. Is the reducer the piece from the Monte Carlo that was previously mentioned?

 

[jurassic five 7]

mapquest isnt always correct on length of trip.

 

[turbo2nr]

Thanks again for the info. Is the reducer the piece from the Monte Carlo that was previously mentioned?

I doubt it. Most likely it is a different gear in the head of the speedo unit.