Swapping 20's for 18's with 3.55 - Ford Powerstroke Diesel Forum
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post #1 of 10 Old 09-21-2012, 07:41 AM Thread Starter
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Swapping 20's for 18's with 3.55

Like the title says I am looking at going down to 18's from my 20" wheels. I just like the look of 18's better than 20's. Will I sacrifice mpg by doing so? Will I need to get the speedo recalibrated?

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post #2 of 10 Old 09-21-2012, 10:50 AM
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Originally Posted by chongo View Post
Like the title says I am looking at going down to 18's from my 20" wheels. I just like the look of 18's better than 20's. Will I sacrifice mpg by doing so? Will I need to get the speedo recalibrated?

Thanks
Doesn't matter wheel size for speedometer recalibration. What matters is whole wheel and tire diameter.

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post #3 of 10 Old 09-21-2012, 10:54 AM Thread Starter
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So if I go with a 285/75/18 (34.8") tire I should be fine?

Any issues or concerns with that much sidewall?


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post #4 of 10 Old 09-21-2012, 12:39 PM
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My truck came with 18''s. I just put on 305/70r18's and now my speedo is almost right. When my speedo says 55 and I pass a laser speed sign it will say 56.

The 305/70r18 is 34.8" tall.
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post #5 of 10 Old 09-21-2012, 08:30 PM
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Quote:
Originally Posted by chongo View Post
So if I go with a 285/75/18 (34.8") tire I should be fine?

Any issues or concerns with that much sidewall?


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What size diameter is on your truck? If these new wheels and tires are bigger then your original ones. Your actual speed will be faster then your what your speedometer says.

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post #6 of 10 Old 09-21-2012, 08:39 PM Thread Starter
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I currently have 275/60/20

34.1 or 34.8 -whatever comes factory.

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post #7 of 10 Old 09-21-2012, 09:17 PM
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Quote:
Originally Posted by coryz71 View Post
My truck came with 18''s. I just put on 305/70r18's and now my speedo is almost right. When my speedo says 55 and I pass a laser speed sign it will say 56.

The 305/70r18 is 34.8" tall.
For the 305's did you change the rim width size to be more than the stock 8?

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post #8 of 10 Old 09-21-2012, 11:03 PM
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the oem 20's are 20 x 8 " the tire is a 275/65/20 275 MM wide by 65 % for sidewall hight

so do 275mm divided by .65 = actual sidewall height. convert to inches 25.4 mm = 1 inch

or convert the 20" wheel to MM

Take the wheel dia plus add the sidewall height x 2 and thats the over all rolling diameter

take the overall rolling dia and subtract that from the overall diameter on the 18" wheel/ tire combo. You then have your answer

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post #9 of 10 Old 09-22-2012, 10:26 AM
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Quote:
Originally Posted by Adventure Rider View Post
For the 305's did you change the rim width size to be more than the stock 8?
No, stock wheels.
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post #10 of 10 Old 09-22-2012, 05:50 PM
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Where r u located I want 20s and I have 18s

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