I used Speedy Cables for the Smiths speedo calibration in my Lotus seven. They asked me to measure the distance the rear tyres rolled and how many times the speedo cable at the back of the speedo rotated in that length. I then sent the Smiths gauge off to them with the information and got it back within the week. Once fitted I had the calibration checked on a rolling road as part of test I had to have and it was spot on. No problems for me with Speed Cables.

 

My Mk2 problem was cable routing which also damaged the angle drive at the gearbox