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Backspacing conversion to Offset to determine correct wheel size
Brand new to the forum and yes I searched first & read the Tire and Wheel Fitment Guide - 2009 and newer and the one about leveling and have decided to go with the Bilstein 2.25” level kit. (Not installed yet on the attached pic) Now I've seen a lot of 2wd trucks on this forum that have used 22 x 9.5" wheels but I haven't seen any that mention what their back spacing is. Once in awhile they may mention their offset. And NON of them had fender flares which may allow for a wider tire and may or may not create an additional rubbing problem.
The wheel & tire overview says that stock 17" and 18" wheels are 7.5 inches wide with 5.5 inches of backspacing. Now when you go to buy after market wheels everyone rates them with Offset NOT backspacing. So I went to a online conversion chart and it says that a 9.5” wide wheel with backspacing of 5.5" is 6.00 offset. Is that right?
The reason I'm asking this is I want to keep the offset as close to stock as possible to keep from unnecessary wear on the ball joints.
My truck does have fender flares (see attached pic). So does that allow me to go with a wider/bigger wheel & tire and still keep—the outside edge of the tires within the flare—and also not rub anywhere? I don't offload, but I do carry around a lot of camera gear & clients so I want to put a nice street tire on that runs smooth & quiet too.
It's a little confusing to get all these sizes right as I've seen many others have the same problem figuring out.
2015, F150 XLT, 2wd, 2.7Eco
Currently have: Stock 18” Chrome PVD Rims, Tires are 265/60R18
Last edited by mydreamtruck; 05-03-2016 at 10:59 AM.
Back spacing is the distance from the inside edge of the wheel (closest to the suspension) to the centerline of the wheel. So, a 9.5" wheel with 5.5" backspace would have the mounting surface of the wheel (inside edge of the hub mounting surface) 4" from the front. That is 0.75" from the center toward the outside of the wheel.
Offset is the distance of the mounting surface off the centerline, typically expressed in mm. A 0 offset wheel at 9.5" wide would have the mounting surface 4.75" from the front and back edges of the wheel. a +25mm offset wheel would have the mounting surface 1" toward the outside of the wheel, effectively moving the wheel 1" in toward the suspension. Conversely, a -25mm offset would have the mounting surface 1" toward the inside edge of the wheel, effectively pushing the wheel out away from the suspension by 1".
Where it gets a bit muddy is that backspace is measured from the outside edge of the wheel, and offset is measured from the edge of where the tire sites, at the bead of the rim, from all that I have gathered.
So, not taking into account that roughly 1/4" from the bead to the lip, a 9.5" wide wheel with 5.5" back spacing would have the mounting surface 0.75" off the centerline toward the outside edge of the wheel. This would equate to approximately +14mm offset.
I hope that made sense. I may have had a couple of glasses of whiskey already, lol.
05-03-2016, 10:54 AM
Backspacing conversion to Offset to determine correct wheel size
