How to recalibrate your speedometer after changing tire sizes or gears

machoheadgames

LED turn signal club
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Jan 21, 2021
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Dallas, TX
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.
 

AWTJ2000

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Jun 3, 2021
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Las Vegas, NV
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

New Member
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Jun 3, 2021
Messages
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Location
Las Vegas, NV
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.
 
Last edited:

MoonShadowTJ

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Sep 19, 2022
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Lake Wales FL
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?
 

AWTJ2000

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Jun 3, 2021
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Las Vegas, NV
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

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Dec 28, 2018
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Georgia
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.