Speedo is miles out

[bmcecosse]

Since Jack is comparing two radial tyres - I doubt any of that is significant - neither is a 0.8% difference !

[IslipMinor]

The starting point is not a standard Minor size, so the speedo will be a bit out to begin with.

Ultimately the speedos listed from eBay will give you an accuracy that is at least as good as most modern cars have!