Wheels Difference
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Junior User
Joined: Aug 2006
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From: Chicago Burbs
Wheels Difference
My '04 FX4 Scab came with 17" rims. According to Tire Rack, original tire size is 255/70-17.
Orignal for the 18" rims is 275/65-18.
I'm just curious if there's any major difference done to a truck that has 17" wheels as opposed to the optional 18" wheels? I mean are they completely interchangeable? I would like to upgrade to the 18's.
Orignal for the 18" rims is 275/65-18.
I'm just curious if there's any major difference done to a truck that has 17" wheels as opposed to the optional 18" wheels? I mean are they completely interchangeable? I would like to upgrade to the 18's.
Laughing Gas
Joined: Mar 2007
Posts: 1,063
Likes: 329
From: Ontario
The 17 inch has a 31 inch diameter and the 18 inch has a 32 inch diameter. There would be a small difference in the speedometer reading but nothing worth worrying about.
Punch both sizes into this calculator and check out the results:
http://www.discounttire.com/dtcs/infoTireMath.dos
Punch both sizes into this calculator and check out the results:
http://www.discounttire.com/dtcs/infoTireMath.dos
MMNC (SS)(Ret)
Joined: Mar 2004
Posts: 11,594
Likes: 144
From: SE Georgia
go for it. since both are OEM, you WILL NOT have problems with them
as said though, you might see about 1 mph difference if you get the 18" rims. they are 31.8" tall, vs the 31" tall tires.
as said though, you might see about 1 mph difference if you get the 18" rims. they are 31.8" tall, vs the 31" tall tires.
Senior User
Joined: Feb 2005
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From: Mobile Alabama
I have a 04 FX4 SCAB. It came with 17"s. The trucks with 17"s have 3.55 gears the trucks with 18"s have 3.73 gears. I put 18"s on my truck. I had my mph checked it was off by 3 mph at 70.....
Senior User
Joined: Dec 2004
Posts: 201
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From: Boise, ID
My 04 FX4 also came with 17s and 3.73s. Tire size had nothing to do with gear choice, at least in 04 and 05.
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Laughing Gas
Joined: Mar 2007
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From: Ontario
Yep, my 05 XLT has 17's and 373's, but the 373's are something that comes along with the trailer tow package from my understanding.
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Junior User
Joined: Aug 2006
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From: Chicago Burbs
I never really dug too deep to see what gearing my truck had. I do have the tow package, is there a tag on the diff or a stamp or something I can use to verify?
Again a n00b question I'm sure. I think I remember some of the older cars having aluminum tags stamped with the original gearing on it.
Again a n00b question I'm sure. I think I remember some of the older cars having aluminum tags stamped with the original gearing on it.
Laughing Gas
Joined: Mar 2007
Posts: 1,063
Likes: 329
From: Ontario
To the best of my recollection, under "axle code" as indicated on the door sticker, if you have a "B6" code, you have 373's.
Also, at 120 kmh, or roughly 75 mph, your tachometer should be reading close to 2200 rpm.
Also, at 120 kmh, or roughly 75 mph, your tachometer should be reading close to 2200 rpm.
Laughing Gas
Joined: Mar 2007
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From: Ontario
Originally Posted by last5oh_302
Also, at 120 kmh, or roughly 75 mph, your tachometer should be reading close to 2200 rpm.
Laughing Gas
Joined: Mar 2007
Posts: 1,063
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From: Ontario
Originally Posted by HomerWinzlow
Mine has 3.55 and trailer tow package.... came with 235/75 17s and I changed to 265/60 18s. I recalibrated odometer.
.I'm thinking perhaps that with the 5.4 and trailer tow package, the truck comes with 373's? I'm certain I heard or was told this somewhere. Could be wrong though. Wouldn't be the first time.
Logistics Pro
Joined: Jul 2003
Posts: 3,595
Likes: 52
From: Lawton, Oklahoma
That may be a requirement for the 5.4. I have a 4.6. Or 5.4 may be a requirement for 3.73. You know how Ford loves to make you buy a different package to upgrade one item.
Last edited by HomerWinzlow; Apr 12, 2007 at 07:01 AM.
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Junior User
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From: Chicago Burbs
Well, I checked my sticker and my axle code is H9, which from what I can find, means it's a LS 3.55 diff. I have the tow package on my FX4 with 17's, so it's not an automatic 3.73's for the tow package.
In a way I'm glad they are the 3.55's. I read somewhere else that if you do a minimal gear upgrade of .25, that the gain is minimal for all the effort and cost. Now that i know I have 3.55's, moving up to the 4.10's would be a nice jump. Although that will happen quite a ways down the line.
My main focus now is getting the 18's and a bigger tire to make it just look fatter and meaner. I would like to go a little bigger than the stock 18 size, but not too much. It won't have THAT much of an effect on the rear would it?
In a way I'm glad they are the 3.55's. I read somewhere else that if you do a minimal gear upgrade of .25, that the gain is minimal for all the effort and cost. Now that i know I have 3.55's, moving up to the 4.10's would be a nice jump. Although that will happen quite a ways down the line.
My main focus now is getting the 18's and a bigger tire to make it just look fatter and meaner. I would like to go a little bigger than the stock 18 size, but not too much. It won't have THAT much of an effect on the rear would it?