Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Re-calibrating Speedo

According to the speed fuction on my Garmin, my Mog speedo is a touch inaccurate (speedo 30mph, Garmin 31 or 32mph). Is it worth trying to re-calibrate (taking advice from the Go Mog site) or should I just drive at an indicated 27? Gerry.

Not sure what accuracy of a GPS speedo is, although uncorrected, I believe they read just a touch low as they are measuring the speed between a group of fixed points and roads are curved. I'd suspect there is some correction built into the GPS unit, so no idea what the result is.

Try having a word with the trading standards people or a local traffic officer. Good chance there is a measured mile very close to you and it would make sense to check with this as well.

For anyone who has not tried to check a speedo on the "measured mile" at 30 mph one mile takes 2 minutes. There are two issues to check. One is that the speed indication is correct and the other is that the distance measured is correct. Best to do it in two runs, one for distance (so that you can start and stop at the posts to check the odometer) and the other to time the run at a constant speed. Best done with a passenger armed with a stopwatch.

It is not easy to keep a constant speed over a mile.

Dual carriageways and motorways should have numbered marker posts every 100m in the central reservation. Sometimes one might be missing due to bridges etc, hence the numbers on them are useful. 16 of these is a mile.

Richard

If you are reading a couple of mph over at 30 I'd be tempted to leave it be...a nice safely margin!

Edit: Or do I mean under?....you know what I mean!

Edit number 2: Whoops...misread it. Neilda is right!! Ignore me!!!

As your speedo is fractionally underestimating your true speed, I'd see if it can be tweaked back. The scameras could catch you out - my wife was done at 34 in a 30.

Normally it's the other way around - in that the cars speedometer overestimates your speed - which is a useful safety margin. My Range Rover is doing 76 at 80 indicated (for example).

Of course, you only noticed this whilst on a trip to Europe?

Bud
_________
2003 - 4/4
Stanley

In NZ there are specific stretches of road accurately marked for odometer (not speedo) calibration. The speedo reading and odometer accuracy are NOT necessarily linked so using the 100m markers in UK is not going to help unless you also use an accurate stopwatch. An under-reading speedo is a liability for many reasons.

I understand most of the current trads can have the speedo calibrated by the user (there is some sort of menu that can be accessed by a button press though I don't have the details) - someone on here will know how.

Ja.

A fellow Hopmogger had to change his speedo recently, and whilst out testing the calibration by chance he came across a traffic cop with a hand held speed gun. He pulled over and the obliging copper agreed to carry out the test with his gun. He turned round then drove back past the copper at 30 MPH, and the calibration was OK. I wonder what would have happened had the calibration been off and he was actually speeding. Would the cop have booked him?