Thanks for asking for me. I have the stock rims and stock size tires on it, so it should be right. But my speedo is off by about 20mph at 60 anyway. Like my car is doing 60mph (gps speed), but it only shows 40mph on the speedo. I don't think any size tire I could fit on there would make it be off by 20mph, haha.
But I understand all about speedo gears and gear ratios. I have a lifted Jeep wrangler that I swapped the axle gears out of with lower ones, and even with the deep gears and big tires, the speedo was still only off by 15mph. A new speedo gear with a different tooth count fixed that though.
I'm starting to think mine is faulty at the actual speedometer, like maybe the needle is worn out or something. With yours, have you tried reaching under the dash and wiggling some wires around while driving? I've seen a few threads where the solder starts to break down and cause a intermittently working speedo.
96 Golf GL, 5-speed, 2.0L