Speedometer wrong?
Thread Starter
Instructor
Joined: Apr 2001
Posts: 140
Likes: 0
From: Las Vegas NV
Speedometer wrong?
Howdy!
Finally got within visible distance of my wife today, and determined that at highway speeds, my speedo is ~10mph slow!! :chevy
It is a '74 auto, 454. The tires are 225/70R15's front and back, stock rims. I can't find what the stock tire sizes are in today's measurements. But, is there a way to fix this, or am I stuck with wrong mileage, and a ~10mph reading? Or, is buying new tires the only option?
I really don't want to buy new tires for it, I just spent a bunch of $$ on the motor rebuild, MSD ignition, etc, and want some more $$ for interior work, and don't have that many brownie points left with the wife! :eek:
Thanks,
David
Finally got within visible distance of my wife today, and determined that at highway speeds, my speedo is ~10mph slow!! :chevy
It is a '74 auto, 454. The tires are 225/70R15's front and back, stock rims. I can't find what the stock tire sizes are in today's measurements. But, is there a way to fix this, or am I stuck with wrong mileage, and a ~10mph reading? Or, is buying new tires the only option?
I really don't want to buy new tires for it, I just spent a bunch of $$ on the motor rebuild, MSD ignition, etc, and want some more $$ for interior work, and don't have that many brownie points left with the wife! :eek:
Thanks,
David
Le Mans Master
Joined: Nov 2000
Posts: 8,220
Likes: 208
Re: Speedometer wrong? (djlangford)
You can calibrate your tranny with new gears. Use this link to calculate you tire diameter:
http://www.smokemup.com/auto_math/tire_diameter.php
http://www.smokemup.com/auto_math/tire_diameter.php
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: Speedometer wrong? (djlangford)
225/70/15's are almost identical in diameter to the original. 27.4".. The above post is correct, you can get different gears for the speedo drive. That's at the transmissin end of the cable and is very easy to change. You do need to know how many teeth yours has so you can get one to replace it.
[Modified by silvervetteman, 6:36 AM 4/16/2003]
[Modified by silvervetteman, 6:36 AM 4/16/2003]
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Re: Speedometer wrong? (Schmucker)
Each gear tooth is approx 3MPH. So you need to use 3teeth as the guide. To make the speedo go FASTER lose three teeth and Obviously if you want it to go slower, add three. :lurk:
