Tyre size and wheel circumference configuration.

[mjsroofing]

Long old story, but short one first, using ids i changed my tyre size years ago to 195/75/16 instead on 15's.
Ive always thought the speed was still out , so today I checked to see if I had done it correctly, and noticed it said the credit tyre size but then it said rolling tyre circumference 1980. Which im sure is wrong. Should I change this ?

[tranmx2]

195/75/16 rolling circumference about 2,196 mm about 86 "
rolling tyre circumference 1980 - could/not matter in the settings.
Could check the speedo by driving where there are the speed indicators at the roadside - usually seen in built up areas.
Tyre charts on the internet.
The tyre circumference when the tyre is inflated without load shall be different to its inflated pressure with load.
When the tyre is inflated and loaded - has weight on it - it'll be bulbous round at the top and bulbous flattish at the bottom. The inflation pressure shall change the shape of the wieghted tyre at the bottom.

[mjsroofing]

195/75/16 rolling circumference about 2,196 mm about 86 "
rolling tyre circumference 1980 - could/not matter in the settings.
Could check the speedo by driving where there are the speed indicators at the roadside - usually seen in built up areas.
Tyre charts on the internet.
The tyre circumference when the tyre is inflated without load shall be different to its inflated pressure with load.
When the tyre is inflated and loaded - has weight on it - it'll be bulbous round at the top and bulbous flattish at the bottom. The inflation pressure shall change the shape of the wieghted tyre at the bottom.

The speedo is slight over. Which i thought it was for a long time. Since I changed the tyres from 15 to 16.
I suspect that changing ghe tyre size on ids made no difference and that I have to change rolling tyre circumference to channge speedometer readings.
But , I changed it to the collest one available and my abs, traction control and brake warning lights ckme kn while driving, ive now changed it back to 1980 and lights are off again.

[mjsroofing]

I worked my way down to 2040mm kn the list and that seems to work.