This combination isn't an easy one. 4.10 gear, 295-45-18 tire and a 727 auto. The speedo hasn't worked in quite a while, and I cant remember which one I had before. It wasn't very accurate. Anyone have a clue here?

Tire is 28.4 tall, pinion should be a 38 or a 39 tooth 39 is speced for a 28 inch tall tire..

Thanks! Hey, when is the San Joaquin Mopar show?

Their website shows Oct 9th..

Mopar Speedometer Pinion Numbers
AXLE RATIO 24" 26" 28" 30" Tire

2.76 2538930 2538928 2538926 2538924
2.94 2538932 2538930 2538928 2538926
3.21 2538935 2538933 2838931 2838929
3.55 2538939 2538936 2538933 2538931
3.91 2538943 2538940 2538937 2538935
4.10 2538945 2538942 2538939 2538936
4.30 2538944 2538941 2538938
4.56 2538945 2538943 2538940

I put a piece of flat stock on top of a rear tire and measured underneath it to ground for my EXACT dia which might be slightly different from the tire mfr's listed dia and if your're in the middle could nudge you up or down to the correct whole number. W that figure and the gear ratio the simple chart in the archives worked dead on for me and made my odo be correct measured at the mile markers on the interstate. passed each one in exactly 60 seconds at 60 mph THEN at a road sign digital MPH sign my speedo was also correct which the odo can be correct (& the correct pinion will gaurantee that) but the magnetic speedo gismo can still be off (& the speedo head needs to come out and take n to a specialy speedo shop) but the correct pinion as you know needs to be selected 1st. BUT I was chastized (on here!) for not using rollout to get an absolute figure since under load the tire is not a perfect circle which will then take more math as opposed to just using the dia on the chart.