Which speedometer have I got?

The identifying mark on the face: SNT 6209/22 1504

The calculations

Series Land Rover have a 4.7 : 1 reduction differential and a 2.2 : 1 speedometer drive gear reduction from propshaft to speedometer. 4.7 divided by 2.2 = 2.136 which means a 1 : 2.136 step up from rear wheels to speedometer. For every revolution described by the wheels we get 2.136 revolutions in the speedometer. This is a constant relationship (K) that can be use in every speedometer calculation.

Here are the calculations for my Imperial speedometer marked 1504 turns per mile.

turns per mile divided by K gives the number of turns of the wheels per mile

1504 divided by 2.136 = 704

My Lightweight will do 704 turns of the wheels for every mile clocked up on the speedometer.

A mile is, 5280 feet, divide this by 704 wheel turns gives 7.5 feet of travel per wheel turn

that is a wheel circumference of 7.5 feet or 90 inches.

Dividing this by 3.14 (close enough to Pi) gives the diameter of wheel.

90 inches divided by 3.14 = 28.6 inches.

Hence, it is calibrated for 6.50 x 16 Tyres.

The identifying mark on the face: SNT 6209/22 1504

The calculations

Series Land Rover have a 4.7 : 1 reduction differential and a 2.2 : 1 speedometer drive gear reduction from propshaft to speedometer. 4.7 divided by 2.2 = 2.136 which means a 1 : 2.136 step up from rear wheels to speedometer. For every revolution described by the wheels we get 2.136 revolutions in the speedometer. This is a constant relationship (K) that can be use in every speedometer calculation.

Here are the calculations for my Imperial speedometer marked 1504 turns per mile.

turns per mile divided by K gives the number of turns of the wheels per mile

1504 divided by 2.136 = 704

My Lightweight will do 704 turns of the wheels for every mile clocked up on the speedometer.

A mile is, 5280 feet, divide this by 704 wheel turns gives 7.5 feet of travel per wheel turn

that is a wheel circumference of 7.5 feet or 90 inches.

Dividing this by 3.14 (close enough to Pi) gives the diameter of wheel.

90 inches divided by 3.14 = 28.6 inches.

Hence, it is calibrated for 6.50 x 16 Tyres.

LWB speedowill have the figures 1408

SWB ones are 1536 or close.

Some are 1376 if intended for bigger tyres.

These figures are speedo revs per mile.

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