I moved this to "Group 1 - Electrical" because that is where gauges go in the FSM.

Here's an answer that I was given on the classicopels site:

Subject: Fwd: Re: [Opel] speedo help

--- In

[email protected],

[email protected] wrote:

This has been explained in an earlier e-mail by Uwe Klippert:

Very easily the correctness of the speedometer is to be checked. On the speedometer is the so-called "Wegdrehzahl= way [road] number of revolutions: W=... " indicated.

This number is the number of revolutions of the speedometer cable, if the vehicle moves exactly 1000 m [KM]. The " way number of revolutions " at your car can checked, if you know:

- the dynamic free length (U) of the tire, [circumference]

- the reduction in the rear axle (ia) and

- the gear reduction in the transmission (it) .

- The reductions in the transmission are

red: 7/18,

yellow: 7/19 and

blue:7/20

Typical values for U are about 1795 mm for 185/70 13R an for Ia:

3.67,

3.44,

3,18

So finally:

W = (1000 * ia * it)/U

Example:

W = (1000 * 3.44 * 7) / (1,795 * 20) = 671

The theoretically correct way number of revolutions W in the speedometer should be 671.

So you should change the coloured driven gear in the transmission to reduce the deviation.

Uwe

Of course we are using miles here, so the correct equation for your case is:

W = (1609 * 3.18 * 7) / (1.795 * 20) = 998

This is assuming you have a blue cog wheel in the speedo pick-up. Thomas 72 Rallye