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J D O Instrument Engrs
Classic Car Instrument Repairs ( Est 1963 )
Tele: (UK) 01535 672125 Mobile / SMS: 07831 886545
Fixed price repairs for most British & European Classic Instruments
48 hr service available... Why pay more & wait longer ! no vat
48 hr service available... Why pay more & wait longer ! no vat
‘Good luck with your project’... Enjoy your classic motoring...
Fixed price repairs are based on the assumption that unit/s received
are ‘original & complete’... a surcharge may be applied to cover
missing parts etc... If in doubt send in the unit for inspection
Fixed price repairs are based on the assumption that unit/s received
are ‘original & complete’... a surcharge may be applied to cover
missing parts etc... If in doubt send in the unit for inspection
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press F11 again to revert to normal view contact the webmaster
Jaguar XK 120 ( 1948 / 54 )
708.1M
Payment options
Speedo Calibration... Calculation page
To calculate the calibration required ( wheel turn method ) use the following formula
( 6336 ÷ A ) x B = TPM ( cable turns per mile )
A = Circumference of a fitted tyre in inches* ( Cross-ply ) for Radial multiply A x 0.98
B = number of speedo cable turns for 20 turns of one wheel ( 10 turns for LSD )
Typical example :
A = 80 for Cross-ply or 78.4 for Radial B = 14.5 speedo cable turns
( 6336 ÷ 78.4 ) x 14.5 = 1172 TPM ( Radial ) or ( 6336 ÷ 80 ) x 14.5 = 1148 TPM ( Cross-ply )
If using the road test method the following formula applies ...
( A ÷ B ) x the present calibration = TPM where A = your indicated distance & B = true distance
Typical example : A = 9 miles & B = 10 miles.. if the present calibration is say 1000 TPM
the required calibration would be ( 9 ÷ 10 ) x 1000 = 900 TPM
For TPKM ( cable turns per kilometre ) multiply TPM x 0.621
*Centimetres x 0.393 = inches Continued on next page
To calculate the calibration required ( wheel turn method ) use the following formula
( 6336 ÷ A ) x B = TPM ( cable turns per mile )
A = Circumference of a fitted tyre in inches* ( Cross-
B = number of speedo cable turns for 20 turns of one wheel ( 10 turns for LSD )
Typical example :
A = 80 for Cross-
If using the road test method the following formula applies ...
( A ÷ B ) x the present calibration = TPM where A = your indicated distance & B = true distance
Typical example : A = 9 miles & B = 10 miles.. if the present calibration is say 1000 TPM
the required calibration would be ( 9 ÷ 10 ) x 1000 = 900 TPM
For TPKM ( cable turns per kilometre ) multiply TPM x 0.621
*Centimetres x 0.393 = inches Continued on next page
Scimitar GTE
Re-Calibration surcharge