MGB Smiths Speedometers Reference

The variety of speedometers fitted to the MGB is a common source of confusion, especially in relation to the fairly common practise of swapping O/D and fully synchronized transmissions into MGBs that didn't originally have them. This will consequently cause the speedometer and odometer to read too high or too low, not an ideal situation.

"Revs" in the table below referrs to the turns-per-mile (TPM) the speedo expects to receive from the transmission via the speedometer cable. The TPM of your speedo should be printed somewhere on the face, along with a serial number.

Any variation in tire size from original specifications will of course also have an effect on the accuracy of your speedometer. See the discussion on tires and tire sizes in the Service section of the Tech Library on this website for more information on this topic.

The NAMGBR also has a cross reference table from car numbers to speedometer serial numbers by Orin Harding. [Ed. Note- this link seems to have gone MIA, so I've duplicated the table below.]

KMR reports that if you have a setup that doesn't correlate to any existing speedometer type, Nisonger can put a new faceplate on your speedometer, and recalibrate that way. Check the Directory section of this website to find a list of companies that provide Smiths and Jaeger instrument servicing.

Tooth count (transmission):

• Overdrive - 21
• Normal - 27

Thanks to Bruce Mills for scanning and submitting in this chart - it's a lot more complete than the chart I was building!

MGB Smiths Speedometer Range and Turns-per-mile (Revs) Reference Chart

MGB Speedometer Cross Reference Chart

by Orin Harding, NAMGBR

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