Tire Size / Odometer
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Junior User
Joined: Dec 2004
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From: Denver, Colorado
Tire Size / Odometer
Does anyone know what size tires came stock on the '68 F250 4x4? I installed a "new" spedometer cable this afternoon, but I am running on 33" tires, so the speedo / odometer will always be a little off. I am trying to keep track of my gas mileage as I perform upgrades and mods, so knowing the difference in stock tires and my 33's would help me develop a conversion factor...
Thanks.
-Craig
Thanks.
-Craig
Thread Starter
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Junior User
Joined: Dec 2004
Posts: 70
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From: Denver, Colorado
So...
Since the circumference of a circle = Pi(D)
The 29" tire has a circumference of approximately 91"
The 33" tire has a circumference of approximately 103.5"
13.7% increase in tire circumference / tread length per rotation
If my odometer reads a distance of 100 miles, then my actual distance traveled is 113.7 miles. Does this sound correct?
-Craig
Since the circumference of a circle = Pi(D)
The 29" tire has a circumference of approximately 91"
The 33" tire has a circumference of approximately 103.5"
13.7% increase in tire circumference / tread length per rotation
If my odometer reads a distance of 100 miles, then my actual distance traveled is 113.7 miles. Does this sound correct?
-Craig
Cargo Master
Joined: Sep 2004
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You are correct sir. You could have come to the same percentage increase by just comparing the diameters of the tires. If you really wanted to be super accurate you'd put on the original tires, put a mark on the tire where it touches the ground and also a mark on the ground. Then roll it one rev and measure the distance traveled. This would be your circumference. Then do the same with the 33s. The only reason this is more accurate is because not all 33s are the same.
Cross-Country
Joined: Dec 2004
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On average a "33" is technically 32.5 inches tall. All of you high flotation sizes: 30, 31, 32, 33, 35 etc are technically 1/2 in smaller than what is read on the sidewall. Also tread design and tread height has an effect on this measurement.
Freshman User
Joined: Aug 2004
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The measuring part is OK but there is an easy way:
<>Get on an interstate and take an odometer reading at a mile marker, reset your trip odometer if you have one.
<>Drive several miles and note the difference between odometer reading and mile marker reading.
<>If Odometer reading is less that Mile marker reading: divide odo into mile marker and use the result to multiply times odo readings .
<>If Odometer reading is more than mile marker reading: divide mile marker into odo, again using the result to multiply times odo readings.
I have done this with a machine that had larger-than-factory tires.
<>Get on an interstate and take an odometer reading at a mile marker, reset your trip odometer if you have one.
<>Drive several miles and note the difference between odometer reading and mile marker reading.
<>If Odometer reading is less that Mile marker reading: divide odo into mile marker and use the result to multiply times odo readings .
<>If Odometer reading is more than mile marker reading: divide mile marker into odo, again using the result to multiply times odo readings.
I have done this with a machine that had larger-than-factory tires.
