blackimpala

Got a 96 2500 automatic. I am going from stock 16" tires to stock, off a 2012, 17" tire, I think my speedometer will be off some. Can any one suggest a speedometer gear that might get me close to an accurate reading?

Thanks

Floyd

oliver foster

It is not the rim size that changes the speedo, but the actual tire size.
Unless you are changing it a lot, say 30 inch stocker to a 35 inch tire, the amount off will be pretty minimal.

blackimpala

I understand that it's the od of the tire that changes speedometer reading. When I said stock, I meant the stock wheel size. Sorry for the misunderstanding.

oliver foster

How much bigger is a stock '12 tire to a stock '96 tire. An inch maybe?
What do the two tires look like next to each other on the floor? Is one a lot taller? I doubt there is much difference.

u2slow

On most Dodges I've owned the speedo reads high in the first place. Going up a tire size makes it more accurate.

patdaly

Just for grins, i went from the stock 245-75-16 to a 235-80-16, gained about 1-1/2" taller, at 60 MPH the change was slightly less than 2 MPH, so indicated 60 is actually 62.

You would have to really get different for it to matter much.

oliver foster

Like I said unless it is a big change in tire size it is not worth a speedo gear change.

blackimpala

Thanks for all the reply's. Sounds like there will be no need to adjust for the different tire size.

04ctd

I have ~31's on my 2nd gen, and the MPH is off by ~7mph,

do I just take it to a tranny shop & have them try different gears, or buy gears & do it myself (in other words, will pulling the speedo gear/cable drain out a ton of tranny fluid out?)

Ronco95

As I recall these trucks have electronic speed sensors so a gear isn't used anyway.

Look up new vs old tire diameters and see what the difference is.

I also went to 235/85 tires and my speedometer is more accurate on my "95.

u2slow

On the 94-95 tcases I have... the 'widget' (lets call it) coverts the mechanical gear speed into a electrical signal.

On truly electric speedo tcases, the pickup is aimed directly at the output shaft (not tangential as with mechanical) to read the toothed reluctor ring.

I believe later trucks dropped the tcase speedo completely... sharing the ABS signal off the rear axle.

patdaly

On your 2006 it it all programming, dealership should be able to accommodate you or I know some programmers do have the ability to adjust, but which specific models are able to I don't know.