Quote:
Originally Posted by viperguy
Since the original VX tires were 165/70/13 and I now have 175/70/13 on, does that mean i'm getting more milage than what my odometer is reading. If my odometer is showing that i'm getting 50MPG, will the 175/70/13 get more or less mpg than 50mpg? Thanks

So for the math...
STOCK SIZE (Civic VX)
165/7013 would leave a 165*.70=115.5mm sidewall. Wheel diameter is 13in or 330.2mm. Total tire diameter would be 115.5*2+330.2=561.2mm.
NEW TIRE SIZE (on VX wheels)
175/7013 would leave a 175*.70=122.5mm sidewall. Total tire diameter would be 122.5*2+330.2=575.2mm.
That is a difference of 575.2/561.21=2.49%
So at a speedometer reading of 70mph your car will actually be going 70*1.0249=71.74mph.
This also means that for every 100 miles traveled, the odometer will only read (100/1.0249) 97.57 of those miles, effectively decreasing your MPG calculations if you do not account for the difference.
That said, more than likely the odometer was still not 100% accurate to begin with as it would change with tire wear, etc. so as cems70 mentioned, a GPS might be your best bet for trying to figure off how much you are actually off.