Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Speedometer Adjustment?

Afternoon all,

I am (still) looking into replacement tyres for my Plus 4.

There doesnt seem to be a tyre i'm keen on in 195/60 R15. But there is options available in 195/65 R15. However the speedometer would under read with that size.

Is it possible to change the revolutions per mile on the gauge?

Hope all are well, thanks in advance

I have 195/65 R15’s and I am always impressed how accurate my speedo is when I drive by one of those roadside speed detectors with the big digital displays. The slightly larger rolling diameter appears to have made the speedo more accurate, more so than my regular car. I've never changed the speedo settings.

If it’s a digital VDO speedo it is possible.

and likely with any speedo as the tolerance the manufacturers have to work to is 0 to 10% + 6.25mph over read. A true 40mph could legally display as 50.25mph on the speedo therefore, however unlikely.

The 60/65 change in ratio equates to about 3.2%, so I agree, it probably makes your speedo even more accurate. I would carry on and fit your tyres of choice and then check speed against a gps or sat-nav. IF perchance the inaccuracy is too great, it is an easy job to recalibrate an electronic speedo. A simple search on this site will give guidance as it has been discussed in the past.

thanks for the replies gents. I have tested my speedo against a GPS a found that it matches the GPS readout exactly. I will have to try another search of the archive

May be quicker to visit the GoMoG workshop manual, (www.gomog.com) look up instruments and gauges from the index, and then section 6 of that deals with speedos. There is a very good manufacturers manual included for modern electronic instruments where you will find a simple way to nudge it up or down, though they recommend its done on a rolling road. (that may only be for safety or maybe because you would have something to calibrate against, but as we know, a gps is fine and if there’s two of you, one driving and one fiddling, that should overcome the safety issue.

Check out Gambalunga's post for 12/11/2016 tells you how to recalibrate.

I agree with all the commentators in what they say. Perhaps two more things in addition. One, you also gain the advantage of slightly better ground clearance. Second, just in case it's of interest to you, it changes not only the displayed speed, but also the measured distance. I have adjusted my measuring device in such a way that the counted distance is correct and the speed display is slightly ahead.

Whether you can adjust the speed display and the counted distance independently, I think on my gauge in the 4/4 from 2014, it is not the case. But I do not want to be a bean counter.

I think your speedo will Caerbont, check thier website, there's a procedure on there somewhere for calibrating the speedo