Factory Wheel Specs? 17", 18" & 20" rims
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Senior Member
Joined: Nov 2007
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From: Calgary, Alberta
Factory Wheel Specs? 17", 18" & 20" rims
Being a complete idiot, and not knowing a damn thing about GVWR, GCWR, etc. etc. etc., I bought my F-150 to tow an rv with.
As it turns out... a loaded SuperCrew Lariat doesn't tow nearly as much as the (er... optimistic) 10,000lbs maximum capacity Ford talks about. So now I need an expensive ultra-light trailer to sleep 5. Oh well. I love my truck anyway.
Along with a hundred lbs of window-motors, sunroof-motors and seat motors, one of the things that eats into your towing capacity is the optional 20" wheel package. I'm really not sure why that is since, I think, the rolling height of the various wheel/tire combos is approximately the same.
anyone?
Anyway... researching the wheel thing, I didn't understand what offset or backspace were (and it seems important if you don't want to alter the handling of the truck) so I did my best to coble together a diagram from the sparse (and often conflicting) info on the net.
Anybody who knows could tell me if this drawing is correct. Oh... the one dash line is the center line of the wheel.
As it turns out... a loaded SuperCrew Lariat doesn't tow nearly as much as the (er... optimistic) 10,000lbs maximum capacity Ford talks about. So now I need an expensive ultra-light trailer to sleep 5. Oh well. I love my truck anyway.
Along with a hundred lbs of window-motors, sunroof-motors and seat motors, one of the things that eats into your towing capacity is the optional 20" wheel package. I'm really not sure why that is since, I think, the rolling height of the various wheel/tire combos is approximately the same.
anyone?Anyway... researching the wheel thing, I didn't understand what offset or backspace were (and it seems important if you don't want to alter the handling of the truck) so I did my best to coble together a diagram from the sparse (and often conflicting) info on the net.
Anybody who knows could tell me if this drawing is correct. Oh... the one dash line is the center line of the wheel.
Thread Starter
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Senior Member
Joined: Nov 2007
Posts: 119
Likes: 1
From: Calgary, Alberta
My bad...
The tire size on the various wheels does end up significantly different.
According to these calculations (no warranty expressed or implied) the tire size on the 20" rims is very nearly 2" taller than on the 17" rims.
So... the driveline has to roll a bigger wheel; which takes away some mechanical advantage and lowers the towing capacity.
The tire size on the various wheels does end up significantly different.
According to these calculations (no warranty expressed or implied) the tire size on the 20" rims is very nearly 2" taller than on the 17" rims.
So... the driveline has to roll a bigger wheel; which takes away some mechanical advantage and lowers the towing capacity.
Thread Starter
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Senior Member
Joined: Nov 2007
Posts: 119
Likes: 1
From: Calgary, Alberta
Originally Posted by wandell
I'm not sure about the 20's. I was under the impression the oem 20's were 8.5 inches wide with 5.5 inches of bs.
Offset = Backspace - (Rim Width / 2)
So, for the 17" and 18" rims:Offset = 5.5" - (7.5"/2)
Offset = 5.5" - 3.75", which equals 1.75" (essentially 44mm)
44mm is the offset number I keep seeing for (all) these rims. Offset = 5.5" - 3.75", which equals 1.75" (essentially 44mm)
If the 20" rim is 8.5" w/ 5.5" backspace then:
Offset = 5.5" - (8.5"/2) = 1.25" (32mm)
So, long story short, if the 20" rim is 8.5" with 5.5" backspace... is its offset 32mm?
