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Backspacing and Offset calculated!

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playbak

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Discussion starter · #1 ·
I've been researching for the past month whether the aftermarket rims/tire combo I wanted would fit without modification. So many of you have helped in giving me valuable information. But since no one has the exact setup I'm looking at it has been very hard to determine.

I know there has been confusion between offset and backspacing numbers. I'm not talking about the difference of what they represent, just some people are used to offset (measured in mm) and some back spacing (measured in inches).
I stumbled upon this page and wanted to share it.

The formula I found is directly off the Yokohama Tire website:

http://www.yokohamatire.com/utcustom.asp

I'll ask for peoples opinion on my setup in a moment, but first the calculation:

offset = backspacing - (Rim width ÷ 2)

therefor

backspacing = offset + ( rim width ÷ 2)

Common Setups:
(remember to keep units the same whether using inches or mm)

17" patriot limited rims: offset is +40mm, rim width is 6.5" (or 165mm)
BS? = 40mm + (165mm ÷ 2)
BS = 122.54mm = 4.8"

16" Moabs: backspacing is 5", rim width is 8"
Offset = 5" - (8" ÷ 2)
Offset = 1" = 25mm

The wheel setup I want to run is a 17x8 rim with 255/60/17.
overall diameter = 29"
overall width = 10.3"
Offset = 10mm
Back Spacing = 4.4"

This means I will have 0.6" more inside space than the Moabs. I figure this should compensate for the extra width of a 255 series tire. However consequently the tires are pushed out the same amount and cause a greater tire arc.

Anyone knowledgeable please give me your opinion on if this setup can work with no mods. If you feel modification may be needed please elaborate.

Thanks in advance.
 
#3 ·
They likely will hit inside on the rear. I am running 235/50/18's on Enkie's with 42mm backspacing. I have 11 mm between the tire and shock. Your setup would eat up 8 of that. In theory it would fit, but with the dynamics of a rolling vehicle I wouldn't try it.
 
#5 ·
nanrurt said:
I am not good with wheel sizing... Would I be able to bolt on a 16x8, on5x4.5, 13mm offset wearing 235/70R16 ATs to my '08 4x4 Sport without rubbing? If so, would they be pushed out or in line with the body of my Pat?
Click to expand...

is that "13mm" positive or negative offset? big difference....:)
 
Discussion starter · #7 ·
At +13mm you're safer than my +10mm offset.
They would also be pushed out (away from the vehicle). Mine would be pushed out slightly more than yours.

I'm confident mine will fit but my tires 235/60/17 will have a 28" overall diameter (OD). The tires you're considering will have 29". This means there is less space between your tire and the wheel well. Which is fine if you are running stock offset +25 to +40. But as you push your wheels away from the car your turning radius changes and you can lose space quickly under sharp turning.

I was considering a tire setup with 29" OD tires (255/60/17), but decided against it for now. I may test fit the size to see if they will fit. Pending the cooperation of the garage. I'm not looking at getting the wheels till April.

I know you 235 series tire width is definitely safe.
 
#12 ·
looking for the right wheel

tskm2, I have purchased 225/75/16 tires and am now looking to order wheels. I know that the 4" backspacing will work but dont know if the set up will stick out a little to far. I hope someone might have a suggestion as to the best backspacing for this tire size for the best overall look and function. My main concern is the set up sticking out to far and with the lack of fender flares, loosing some paint. Any wheel sizing suggestions? Thanks in advance!
 
#14 ·
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#16 ·
Scotty, here is my unlifted FDI next to a stock FDII.

Image

Image


If you want a badass look, I would recommend it. If you want more of your wheel tucked under the fender, then I advise against the 4" backspace. Whatever floats your boat.
 
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#17 ·
Most of you shouldn't have a problem using older wheels on a Patriot. Most older wheels have the bolt mount, or back spacing, nearer to the center of the rim. That kicks the wheel out beyond the body and makes big fat tires less likely to rub on turns. The patriot stock wheel has, what, 5+" of back spacing?
 
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#18 ·
5 1/4 inches I believe

I believe the stock wheels have a backspacing of around 5 1/4 inches. I was wondering if a 4 1/2 inch backspacing might be perfect for my application? Not so much sticking out beyound the fenders but still no major rub with the wider tire. Copper those pics are great really puts your wheels and tires into perspective, looking forward to seeing pics of your rig with the lift installed.
 
#19 ·
cool tool

found this cool wheel offset calculator tool and thought i'd share :banana:

(side note) thinking of slapping on some 18 x 8 wheels with an offset of 19mm. it'll push out the tires by 1.7" and increase the backspace to 5.25". would this cause any rubbing issues? oh, tires i'm thinking off are 235-50-18.
 
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