New Shoes
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Fleet Mechanic
Joined: Oct 2012
Posts: 1,943
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New Shoes
So I got some new tires for my 1988 E250. Stock size is listed as 215/85r16 on the door tag.
The old tires were 225/75r16
Up sized the new tires to 235/85r16 (the size listed for the e350)
I will have to change my speedo gear. According to GPS the odometer is now off by 10%. Drops my rpm at hwy speeds. The rpms at 70mph are what they used to be at 65mph. Lower cabin noise and maybe a little more mileage.
The old tires were 225/75r16
Up sized the new tires to 235/85r16 (the size listed for the e350)
I will have to change my speedo gear. According to GPS the odometer is now off by 10%. Drops my rpm at hwy speeds. The rpms at 70mph are what they used to be at 65mph. Lower cabin noise and maybe a little more mileage.
Posting Guru
Joined: Apr 2014
Posts: 2,196
Likes: 5
From: N Ca.
You might get worse mileage due to the increased weight and size.
They are harder to turn.
Did you have the weight of the old vs. new tires?
https://tiresize.com/calculator/
Looks like you are going up less than 2 inches in circumference. Nowhere near 10%
Let us know how it works out.
They are harder to turn.
Did you have the weight of the old vs. new tires?
https://tiresize.com/calculator/
Looks like you are going up less than 2 inches in circumference. Nowhere near 10%
Let us know how it works out.
Thread Starter
|
Fleet Mechanic
Joined: Oct 2012
Posts: 1,943
Likes: 21
You might get worse mileage due to the increased weight and size.
They are harder to turn.
Did you have the weight of the old vs. new tires?
https://tiresize.com/calculator/
Looks like you are going up less than 2 inches in circumference. Nowhere near 10%
Let us know how it works out.
They are harder to turn.
Did you have the weight of the old vs. new tires?
https://tiresize.com/calculator/
Looks like you are going up less than 2 inches in circumference. Nowhere near 10%
Let us know how it works out.
I did a little bit longer distance comparison of my odometer vs GPS instead of just watching it for a mile and comparing it to the tenth wheel on the speedo. The way to work this morning. GPS said 19.8 miles. Odometer said 18.3.....so a 7.6% difference. Ran it through an online calculator and cam up with 8.2% so there is a slight variance in numbers assuming that my old setup was dead on. GPS comparison showed the old setup as very close, but a mechanical odometer from 1988 may not be calibrated 100% correctly.
I will be interested to see how the mileage is affected? Watching my EGT gauge it doesn't appear to be running any higher. If fuel delivery per RPM has stayed really close and the RPMs have dropped, then in theory I should use less fuel over time.........but we all know there is often a disconnect between theory and reality.
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