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MPG and Tires
https://slantsix.org/forum/viewtopic.php?t=15927
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Author:  Super 170 [ Fri Jan 27, 2006 5:33 pm ]
Post subject:  MPG and Tires

HI Everyone
I have a 66 val as a daily driver, 170 with super six conversion, 3 on the tree and a 7 1/4 rear. I have had the about 6 months and love it.
I bought tires from BJ's and they had very few choices but a good price and I really needed to get something on the car as the ones I bought it with were dry rotted.
When I drive thru a radar display at 40 it shows 37 but that is just an estimated speed.
Can someone tell me how my Tiger Paws , P175-70 R13 are affecting my odometer and my MPG caculations and can I change speedometer gears to correct it.
Thanks Steve

Author:  emsvitil [ Fri Jan 27, 2006 9:27 pm ]
Post subject: 

Original tire diameter was 24.65" or a 185/80 13

A 175/70 13 is 22.65"

So your odometer/speedometer will read at least 9% high. Go with 10% for easy math............


So you'll need a speedometer gear that has 90-91% of the teeth than whatever is in there.......

Author:  Super 170 [ Sat Jan 28, 2006 5:43 pm ]
Post subject:  10%

Thanks ED So if I am driving at 50 mph it is actually 45 mph and if I think I am getting 20 mpg it is actually 18 mpg?
Steve

Author:  emsvitil [ Sat Jan 28, 2006 5:49 pm ]
Post subject: 

Yep..........

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