yah my was only off by about 10. that seems alittle rediculous lol. I just chanted to the 23 tooth gear and its almost exact. I tested it with a gps so im guessing it accurate
it would be off by a percentage buddy...if you are off by 25-30 miles per hour you are driving hella fast...slow down...should at highway speeds be off by about 5 but yeah just go to a shop and tell them you need a speedo gear change...quick easy and cheap in most cases..
How much your speedo is off depends on what your original gears were. The lower the stock gears your car had, the smaller your speedo gear would have been to compensate for them. Now that he moved up to 3.73s, his speedo gear is WAY too small while everyone else with larger stock gears had larger speedo gears so their cars were already halfway compensated. So while yours is only off maybe 15 MPH his is off 25-30 MPH. See how that works? I went from 2.73s to 4.10s in my auto and I was off by about 30mph when going the speed limit on the freeway. I was going 65 and reading 95.
By the way, I have 3.73s now and and a 23 tooth speedo gear and my speedometer is still about 10 off at 55-65 MPH. Some may suggest that you can also change the transmission gear along with the speedo gear and also get it accurate. That may be true but who wants to be messing with what all goes into doing that?? Even if it is cheaper. A Speedcal is only $85 and it is easily changable if need be.
That being the case, the only accurate, consistent and simple way to guarantee an accurate speedometer is to buy a Speedcal or a device that works like it.