Tire size/speedo reading
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Elder User
Joined: Dec 2010
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From: Arkansas
Tire size/speedo reading
My '94 is running the stock size tires & says 13.1 or 13.2 miles from my house to work.
My '85 has 215/85r16 on the drive axle & 235/85r16 on the steer axle. The sticker on the door jamb does not list a tire size. The other night it showed 18.xx miles to work. A solid 5 mile difference.
I know going to a taller tire will slow down a speedo & smaller speed it up. I used the calculator here. According to it, the speedo reads ~2.5mph fast.
Ive had a brain fart for the last hour trying to figure up if swapping the 235s to the drive axle will correct it. Cant find a calculator online to figure it up or come up with something on paper.
3.54 is (should be) the axle ratio. It seems fairly tall geared & the cover hasnt been removed in years so Im pretty sure I have 3.54.
Any help figuring this out would be greatly appreciated.
My '85 has 215/85r16 on the drive axle & 235/85r16 on the steer axle. The sticker on the door jamb does not list a tire size. The other night it showed 18.xx miles to work. A solid 5 mile difference.
I know going to a taller tire will slow down a speedo & smaller speed it up. I used the calculator here. According to it, the speedo reads ~2.5mph fast.
Ive had a brain fart for the last hour trying to figure up if swapping the 235s to the drive axle will correct it. Cant find a calculator online to figure it up or come up with something on paper.
3.54 is (should be) the axle ratio. It seems fairly tall geared & the cover hasnt been removed in years so Im pretty sure I have 3.54.
Any help figuring this out would be greatly appreciated.
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Does anything here help?
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Cargo Master
Joined: Apr 2010
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From: Acworth, GA
What about going from 215's to 31x10.50's?
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A 215/85R16 is 30.4" in diameter.
A 235/85R16 is 31.7" in diameter.
Assuming a 31x10.50 is 31" in diameter (I assume that is what the "31" means) it would actually correct your spedo/odometer LESS than the 235/85R16.
To get your odometer reading from 18 miles (with the 215/85R16) down to 13 you would need a tire that is 42.1" in diameter! You are not going to get there with a tire change. You are going to have to change speedo gears to correct it.
A 235/85R16 is 31.7" in diameter.
Assuming a 31x10.50 is 31" in diameter (I assume that is what the "31" means) it would actually correct your spedo/odometer LESS than the 235/85R16.
To get your odometer reading from 18 miles (with the 215/85R16) down to 13 you would need a tire that is 42.1" in diameter! You are not going to get there with a tire change. You are going to have to change speedo gears to correct it.
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