Speedometer error correction......

[duffy]

I have an 89' B2 with auto (A4LD), 4x4 (electric shift), 3.73 gears (according to the door tag) 205-75-15 tires, and a white speedo gear (17 tooth). My speedo reads high at all speeds. It reads 10 mph high at GPS indicated 60mph (reads 70mph). Internet cruising indicates that I need to get a higher tooth gear. Around a 3.5 tooth increase which should be a 20-21 tooth. Anyone have any input about which gear might be closest to accurate?

 

[tw205]

This should get you what you need. https://www.therangerstation.com/tech_library/Speedogear.shtml

 

[duffy]

I found an older formula that I used back when I was working on a 77' F250......I got a 20 tooth (black) and installed it. Reads 1 mph high at 25 and 2 high at 60......good enough for me.

 

[wildbill23c]

Mine is 5mph off, so my speedometer says I'm doing 55mph for example and I'm actually only doing 50mph...that's with the 205/75-R15's I'm assuming the speedo gear that's in mine is probably for the 235/75-R15's that it had on when I bought the B2 about 4 years ago. Which I think when I get new tires I'll go back to the 235's as its a little easier to find tires for that size than 205's, at least in a tire tread that'll handle some snow/ice conditions.

 

[McWillies]

I have the same year and spec BII and my speedo is about 7% slow. Are you on stock size tires, stock speedo, and stock gears? I'm asking because I'm trying to figure out what gear is in my truck, without having to pull the sensor out (call me lazy).