Need Help with Wheel Conversion Chart

I am going to be shopping for some 20" rims & tires for my 1996 Explorer Limited and I am trying to figure out what size rims and tire will fit to match the factory wheels so they are not sticking out past the fender. I currently have the stock 15x7 Limited rims on now with 245/70/15 tires and I am trying to use the conversion chart to get close to the same look with 20" wheels. Can anyone explain or tell me if this conversion chart is correct - https://www.rsracing.com/tech-wheel.html#backspace. I am confused because if you look at a 7" rim it says that 0 offset is 4", but on an 8" rim, 0 Offset is 4.25". How is this possible, wouldn't 0 offset on an 8" rim be 4"? Is this chart correct? I am pretty sure my 15x7 stock rims are 4.5" bs, so I am trying to figure out what 20" rim measurements with either a 20x8 or 20x8.5" rim will work so they fit like stock and not stick out of the fenders. thanks for the help

 

[SR77]

Anyone with some knowledge on this?????

 

[Dan Whitaker]

No because the back spacing is different for an 8" wide.
Offset is how far the lip of the the wheel is from the center of the wheel.

If the wheel center is exactly in the middle you have 0 offset.
If the wheel center is <---- (outer rim) you have possitive offset.
If the wheel center is ----> (outer rim) you have negative offset.

 

[SR77]

thanks for the reply.

But if you have an 8" wide wheel, if the offset is 0 wouldn't the backspace be 4" or vice versa? Thats where the chart gets confusing because it states differently.

 

[JohnnyO]

But if you have an 8" wide wheel, if the offset is 0 wouldn't the backspace be 4" or vice versa?

Actually a wee bit less because of the thickness of the wheel center, but basically yes.

 

[BryanB]

thanks for the reply.

But if you have an 8" wide wheel, if the offset is 0 wouldn't the backspace be 4" or vice versa? Thats where the chart gets confusing because it states differently.

NO! Wheel widths are measured from one wheel bead to the other ON THE INSIDE Backspacing is measured from the mounting surface to the OUTSIDE OF THE WEIGHT LIP A 16x8 wheel with 0 offset has a 4 1/2" backspacing. The extra 1/2' is the thickness of the wheel...assuming it is aluminum.

 

[SR77]

BryanB, thats for the explaination. makes sense now. I will have to measure the stock wheel myself to be sure, but I am pretty sure I read somewhere on here that the stock Ford Limited wheel on my Explorer is 15x7 with 4.5"bs, so basically by reading the chart this wheel would have 12 offset, so to keep the same measure/look with a 20" wheel I would need either a 20x8 with 5"bs or 20x8.5 with 5.25"bs. Is this what most people on here run with 20 wheels?thanks again

 

[CDW6212R]

The stock wheel offset is just under 20mm from doing the math. I have had 8" wide wheels with a 30-32mm offset, and added 1/4" spacers later. Currently I have 8.5" wide wheels with 35mm offsets, and the 1/4" spacer(front only). The factory trucks have the wheels inboard some from the fender edges. Most people want the wheel to stick out some. I prefer the wheel to be close to flush with the fender.

I wish people would stop wasting time mixing apples and oranges. The term and measurement of wheel offset is the universal measurement defined with all wheels now. Almost all wheels now have the offset stamped into the back of them(44ET is 44mm(factory 2002+ Explorer)). You can, if you insist, determine backspacing or all other measurments from the width and offset.

 

[SR77]

cdw6212r,
thanks for the reply. I think people use BS alot because it is easier to work with and calculate with the rim width then offset is. I also took off my stock wheels and they are 12mm offset or 4.5 bs. I have 245/70/15 on my truck now and the width of these tires and my stock wheels are very close to being flush with the fender lip and thats why i am trying to use them are a starting point to decide what to go with in 20". You 8.5" wheel and 35mm offset and also 1/4 spacers just doesn't make sense to me how it still does not stick out past the fender. Shopping for rims and tires is more difficult that I though, I just want to make the right choice the first time and get the look I want if i am gonna spend that kind of money. thanks

 

[CDW6212R]

My Cobra wheels fit very well with 1/4" spacers, so my best fit of 8" rims is about a 24mm offset. My spacers reduce the offset by 1/4", or 6.35mm, so my 18's have 29mm offsets, and they are 8.5" wide, so they locate at about the same point of the fender. The ball joint is what you must worry about clearing, and the right side caster bolts. That control arm has a cross bar in it with bolts that can be touched by the right tire, if they set inboard too far.

Check out this link for light forged wheels. The offset is only 12mm, so they will sit outboard 1/2" more than mine, but it's an option. Good luck,