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Speedometer Caibration

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Hey Guys, 

New guy question that I am sure is covered on the forum, but I am getting myself turned around: What is the best way to calibrate the speedometer/speed sensor on the 280z?

Swapping out the stock wheels (195/70R14) for a larger set of rims on a lower profile tire (225/45R15). Change in tires/rims will result in about a 7% differential (83mph/90mph). Want to see if there is a good way to correct for this. 

Also, is there any difference in speedometer readings when swapping from a 4 speed to 5 speed (both out of late 70s 280z) assuming both were built to work with the same R200. 

Links are welcome! 

 

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Transmission difference is irrelevant as the speedometer pinion is taken off the output shaft in every instance. Because of that the only variables are tire circumference and differential ratio. Nissan builds speedometer pinion gears with different tooth numbers to use with different differential gear ratios (because they are assuming you stick close to the stock tire size). I'm dyslexic when it comes to which gear count to use - I don't know if you should go "up a tooth" or "down a tooth" - but some here will know as they're lots smarter than I am. There are many discussions on speedometer pinion gears you can also refer to. IIRC the the 3.54 differential uses a black pinion gear - that would be stock in a manual trans 280Z.

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14 hours ago, cgsheen1 said:

There are many discussions on speedometer pinion gears you can also refer to. 

Awesome, will use that as a search term. Thanks!

 

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Here a calculator that can help you see how each veritable can effect the actual speed of the car. Knowing your transmission gear ratios  and final drive ratio is imperative. By hanging tire height  you can see the difference in final speed. 

https://www.tremec.com/calculadora.php

 

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