Howdy all, I am seeking some knowledge on fixing my speedometer. So for starters, the car is a mostly stock 92 LX 2.3 with an A4LD. I did change from the stock 14 rims to some 15 rims off another foxbody. Beyond that everything is stock. So of course the speed was off from the rim swap so I changed my speedometer gear. When testing the speed though, I found that it was off by different amounts at different speeds. When going 25, the speedometer was reading 26. Likewise when going 35 it was reading about 36. When going 60 though it read 56. I was testing my speed while pacing a car with a good speedometer. I was wondering if anybody knew what could be causing the speed to be off variably like I described. The speedometer isn't very jumpy (bounces up and down by 1 MPH at worse) so it seems to me like the cable would be good, which would leave the VSS and the actual speedometer itself. I noticed this problem when I had the stock rims on too. Any help would be appreciated, thanks!

 

When something like wheel diameter is changed, it will have a multiplier effect on the speedometer reading. It's not always just going to be 1mph off. It's going to be off by a % of your actual speed. As speed rises, the amount it's off will increase.

 

Ok thanks! I was kinda wondering if it was something like that

 

So I have actually found a new problem with my speedometer. So along with the speedometer still being off (from an incorrect tire size) I have found that it is reading differently in the morning when I leave for work vs. when I come home from work. I have been using a GPS speedometer app on my phone to track my speed (it is surprisingly very accurate). I have found that in the morning that when I go 45 my speedometer is reading 51. When traveling at 60 it read right at 61. When I come home from work, when going 45 my speedometer reads at 44 and when going 60 it reads 56. It has been very consistent with being off by the same amounts in the morning and in the afternoon (meaning that when traveling 45 in the morning it always reads 51 and in the afternoon it always reads 44). Could of changing the speedometer of gear caused this this, or am I looking at another problem?