The gearing of the speedometer is fixed at the gearbox but it is "geared" for a specific differential ratio (and a standard set of tyres on a standard set of wheels). Change the size of the wheels and you'll change the output seen at the needle on the gauge.

Change the differential - which is essentially what I'm doing as far as the gearbox is concerned - and you'll see a much bigger change than swapping tyre sizes. [Unless you've put a 5 ft lift on the suspension and a set of tractor wheels!]

The five speed gearbox expects to "see" a 3.64 differential. I have a 3.46 fitted which is correct for the 4 speed.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!