how hard is it to calibrate speedometer?

[Losiracer2]

I recently got a GPS system on black friday and it tells me my MPH. when i'm going 70 on the GPS, my car's speedo reads 72mph. I do have 17 in wheels with 215/45r17 tires. SO i think that's why its off by a little. How much do people charge to calibrate the speedo's? b/c then my mileage is going to be off and my trip meter also. Anyone had this done after getting wheels/tires?

[The G-Man]

You cannot change it.
Just figure out what the difference is in overall wheel diameter.

It is not large enough to matter.

Besides 70 vs. 72 is within margin of error on the GPS side.
http://www.miata.net/garage/tirecalcold.html

[NAiL05]

Some cars you can calibrate the speedo by changine the gear on the speedo gear. I know you can do this with mustangs and some american cars. Another thing is some american cars you can calibrate speedo to tire size by the diagnostic tool. Personally I havent seen an import do it yet.

[The G-Man]

Yeah, but you cannot on the CB7 VSS. Unless there is something new out.

[NAiL05]

Yeah, but you cannot on the CB7 VSS. Unless there is something new out.

Ya thats why I added my last statement. Ive done it on a few domestics lol thats why I know you can do for that. I dunno about imports I havent seen anyone do that. Most people just ignore it anyway from what I have seen. Really not a big thing to worry about.

[preludeman92]

2MPH is within error of both the gauge and the GPS. Most of the GPS units are +/- 3mph, but some of the better ones are +/-1mph. The gauge is around +/-2mph. A 215/40/17 tire will throw the gauge a little, but not much. A 215/45 will throw it more and you will notice it at 70mph like you are.

[GreenMadness]

Those GPS are pretty damn acurate, my friend has one in a Cobalt SS and it reads the same as the gauge 99% of the time....and it holds 2 decimal places. so your gauge is around 33 and the GPS will say you are going 32.55mph....

[preludeman92]

But, he said it's a black friday GPS. Those are the super cheap ones. I've got a good sensor and streets&trips for my laptop. My GPS was seeing 9 satelites and my buddies factory GPS in an 03 accord saw 4. The laptop said 35mph, the gauge said 34ish, and the factory unit said 37. It's even wired to the car's speed sensor. I don't know, this is beside the point. To the original question, you cannot calibrate a factory gauge on a honda.