How to recalibrate your speedometer after changing tire sizes or gears

machoheadgames

LED turn signal club
Supporting Member
Joined
Jan 21, 2021
Messages
1,315
Location
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

New Member
Joined
Jun 3, 2021
Messages
23
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 * 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
Joined
Jun 3, 2021
Messages
23
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.
 
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