I have a 87 se model with standard rims and tires. When I'm going 70mph the speedo says 80mph? Anyway to fix that?

 

How do you know how fast you are actually going?? If it is the speedo problem, I think you can get it re-calibrated, you need to take it to a shop I think, maybe someone else can elaborate because Im not too sure how that works.

 

You could possibly swap out speedo cables

 

I had my wife drive another car which was going 70, but the rx-7 said 80.

 

My 91 is off by 5 mph, based on the same technique that you used.

 

they are probably both off by 5

every car speedo is off by a bit. that's why cops normaly give you the 10mph over or so range before giving tickets.