How to recalibrate your speedometer after changing tire sizes or gears

[machoheadgames]

Reading faster on the GPS than the speedo after I replaced the part.

So going 65 on the dash, 70 on the GPS?

If that’s the case, you need a 29 tooth gear.

65 * 31 / 70 = 28.8

I never recommend anybody buy their gear based on a chart or nominal tire size. Math is always the best way to get it accurate. Too many incorrect charts out there and too many fluctuations in real world tire diameters.

 

[Viking Jeeper]

Or, just buy the electronic solution and be done with it.............https://www.12oclocklabs.com

 

[AWTJ2000]

So going 65 on the dash, 70 on the GPS?

If that’s the case, you need a 29 tooth gear.

65 * 31 / 70 = 28.8

I never recommend anybody buy their gear based on a chart or nominal tire size. Math is always the best way to get it accurate. Too many incorrect charts out there and too many fluctuations in real world tire diameters.

Thanks so much for the response!

We actually had it flipped- 65 on speedometer, and 62 on the GPS.

 

[AWTJ2000]

So going 65 on the dash, 70 on the GPS?

If that’s the case, you need a 29 tooth gear.

65 * 3 / 70 = 28.8

I never recommend anybody buy their gear based on a chart or nominal tire size. Math is always the best way to get it accurate. Too many incorrect charts out there and too many fluctuations in real world tire diameters.

 

[MoonShadowTJ]

So I replaced the speedometer gear with a 31 tooth gear, per the graph (3.73 gears and 33x12.50/15 tires). Originally my speedometer was 10% slow against my GPS Speed App. Now, however, I am 3 mph fast at all speeds, 20, 40, 50??? This doesn’t make any sense? Any suggestions?

 

[Viking Jeeper]

https://wranglertjforum.com/threads...-changing-tire-sizes-or-gears.83/post-1187100

 

[machoheadgames]

If it’s off by a flat 3 mph, then you have a speedo problem and no amount of calibration will change that.

 

[AWTJ2000]

I replaced my speedo gear with a 35 tooth, and it runs fairly close to the GPS UNTIL i get up to 60+ MPH, then it’s like 5 MPH low now on the speedometer.

 

[Hopper]

I'm confused. I have 99, 4.0, 3 speed auto and 33s 4:10 gears. What speedo gear do I need?

 

[machoheadgames]

I'm confused. I have 99, 4.0, 3 speed auto and 33s 4:10 gears. What speedo gear do I need?

Usually 35 or 36. What tooth do you have now and how much are you off by at a set speed?

 

[Hopper]

Usually 35 or 36. What tooth do you have now and how much are you off by at a set speed?

Thanks. I'll have to check it's original for 3:07 gears and 32rh. I'm off like 15-20 mph. Been like that for a couple years since my regear. Really should get around to correcting it.

 

[Accelerometer]

Nice work on this!