tire size, speedo and emmisions test

Sorta simple question, but probably more to it than I can figure out:
Big meats make speedo show 10% low. When I have it sniff tested, they run the truck at 20 or 25 mph on a treadmill/roller thing. (It will really be running a couple mph higher than indicated by the speedo)

Since it is actually reving higher than the speedo shows, does it stand to reason that my emissions will also be higher?

The real question is, will changing the speedo gear to the correct one reduce my emissions on the test?

Depending on where their speed is measured from... I wouldn't imagine that they rely on your speedo, but if they do, then correcting the speedo will likely have little effect anyway

The larger tires will put a higher load on the engine for the same RPM as before, but by the same amount the engine will be turning slower... Emissions should be quantified by concentration (parts per million and/or milligrams per liter) so the speed of the engine is not so much of an issue as the loading (possibly shifting into a different area of the computer's mapping.

It's not revving higher, it's revving lower. Dunno how they test where you are, but the dyno test here in Connecticut has the operator at the station run up the engine on a rear wheel chassis dyno. He has a monitor in front of him that tells him when to run it up, and shows him what speed it's turning. He has to keep the speed bar between an upper and lower limit. He never even looks at the speedo, so the test is conducted at a corrected speed. That means bigger tires will make the engine run slower than stock for the test.

The O2 sensor should adjust the mixture irrespective of the wheel speed and engine RPM, so the short answer to your question is "No."

That's the same test as here in Ohio.
I won't bother with the speedo gear change.

Thanks. That's what I wanted to know.