Anyone tried this speedo correction unit?
 

Wondered if anyone who had altered their wheel/tire sizes and noticed the speedo optimism increase (e.g. rolling diameter of 255/40/17's is 4.3% lower than stock 16" tires according to the calculator on the Miata web site) had tried one of these?

http://www.blackrobotics.com/index.htm

Looks like a well-thought out unit, I'll likely try it. Maybe Wayne could stock them if there's enough interest?

Give it a try; it does look interesting. For $110, how wrong can you go?
When can we expect the test report?
Pat

Looks like a piece of cake, except it assumes that the frequency error remains consistent across the speed range. Probably a pretty good assumption and if its not and you set it so its spot on at X MPH you probably wont notice an error at X +- Y anyway :)

Still, its basically a track day in cost...

-Michael

The person who answers their "email support" doesn't seem to have a clue. Here are two responses that I've received so far.

"The Porsche 911 uses a unique speed system that is not compatible with the 2-wire Yellow Box. Sorry."

After explaining to her that their own website claim compatibility with ALL PORSCHE CARS and that my 911 is a '78 and giving her the benefit of the doubt that she thought I had some whiz-bang 997 "unique speed system" she replied...

"Your '78 model 911 will have a cable driven speedometer, a thick black mechanical bowden cable going to the back of the speedo."

I've replied that my VDO gauge is in fact electronic. I haven't heard back.