Tire change and speed increase

[paladin06]

So my question is, my 69 road runner has a speedo gear for 14 tires I'm sure. So with 20 inch tires on the rear what is the speedo difference in the speedo? Example, if my speedo reads 45mph how fast am I traveling?

 

[hawkeye]

http://tire-size-conversion.com/speedometer-calibration/

 

[AMX364]

Well if the outside diameter of the 14 inch tire is 25 inches and with the 20 inch tire is 25 inches then the speedometer should read 45 mph.

 

[coronet340]

Well if the outside diameter of the 14 inch tire is 25 inches and with the 20 inch tire is 25 inches then the speedometer should read 45 mph.

what if you are going uphill though?

 

[sleepar]

Don't forget to change your air every month!!! So it doesn't get stale and rot you're tires.

 

[sleepar]

There are shops that calibrate spedos it involves replacing the gears in the transmission tailstock where the spedo cable goes. Some transmission shops do it but Mopars are notorious for bad spedos at the gauge Bob's speedometer will recognition you're cluster for about $400 if it's just basics

 

[paladin06]

Speedometer Calibration Calculator

Indicates it reads 4.93 mph high.

 

[PlumcrazyRR]

Speedometer Calibration Calculator

Indicates it reads 4.93 mph high.

I would probably verify that with a gps that shows your actual speed. That would be the easiest and most accurate way of doing it.

 

[eric383]

Isn't there a place that makes speedometer corrector that installs in line between the speedometer and speedometer cable behind the instrument cluster? I think you just give them the rear tire diameter and they make up the corrector for your application. I just don't remember the name of the place. It's hell getting old. Maybe these folks. http://www.texasindustrialelectric.com/speedo.asp

 

[68bigblock]

Keisler has a speed analyzer just pick auto or std, tire size and gear ratio. as long as you have a tach you should be able to figure out your speed

http://keislerauto.com/speedanalyzer.html

 

[Meep-Meep]

A very basic rule of thumb for the MoPars is 2.5 MPH per tooth. If you are slow by 10 MPH and have a 35T gear then you need to turn the gear faster, so 4 teeth less would be about 10 MPH.

 

[paladin06]

Well I'm about 5 to 6 mph fast.

 

[Meep-Meep]

Then add about two teeth.