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S10 wheel Backspacing and Offset Revisited

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Old 11-12-2009, 10:16 PM   #1
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S10 wheel Backspacing and Offset Revisited

Ok Since the first backspacing thread I made years ago is getting a little long and little confusing with all the edits and questions in it, I'll just start fresh here. Here goes..
First thing, the Bolt pattern on an S10 is: 5 x 4 3/4"
OR
if you measure it out in metric the pattern is: 5 x 120.65mm.
Alot of people ask if a 5 x 120mm wheel will fit.. if ya wanna be picky, no its not the correct size, but yes they do physically fit on the vehicle. **DO not hold me personally nor S10forum.com responsible if your wheel studs break from running a wheel with this 5 x 120mm pattern to them.. saw it first hand happen to a buddy of mine while driving 70mph down the highway**

Measuring a 5 lug wheel is different then 4, 6, or 8 lug wheels. For the 5 lug you measure from the far side of the one lug hole, to the center of the 3rd hole.



Now on to the offset and backspacing info. To make this as simple as possible, offset and backspace values can be interchangeable... if that makes any sense to ya, if not read on.

Offset is the distance of the mounting flange to the center of the rim. The offset of a wheel is measured with the following formula:
Offset = Backspace - (Rim Width)/2
(after you get your number it will have to be converted to millimeters)

tip..To convert from inches to mm multiply by 25.4
To convert from mm to inches divide by 25.4


Backspace is the distance from the mounting flange to the inside back edge of the rim.

If you only have the rim width to go by, you can calculate either one, given the other. The easiest way to measure backspacing is to carefully lay the wheel face down, then lay a board or something flat across the back of the rim. Last measure down to the mounting flange, this will give you your backspacing number.




Theres 3 different types of offset a wheel can have,

First is a Positive offset: This is where mounting flange is positioned toward the front side of the wheel. This style wheel will have a large backspacing and is typical to the style of rim on most FWD cars. These WILL NOT fit a 2wd s10 unless you run adapter to space the wheels out correctly.

Next is a Zero offset: This is where the mounting flange is positioned evenly with the center line of the rim. This is the style wheel a 2wd S10 requires for a stock fitment.

Lastly is the Negative offset: This style rim has the mounting flange shifted towards the back side of the rim towards the brakes. This wheel has a small backspacing and so on a 2wd S10 will push the wheels out of the wheel well further. On bagged or lowered trucks ya have to be careful as theres a good chance the wheels wont tuck up inside the fenders.


when tightening the wheels down, make sure you finger tighten the lugs enough to center the wheel on the lugs, then go around and tighten them down in a criss cross pattern this will center the wheel on the lug nuts without undue stress and or unwanted vibrations



Now finally to the part everyone really cares about. What fits! As I mentioned before since the amount of backspacing and offset required to correctly tuck inside the fenders and fit the truck changes with the size and width of the rim, you have to pay attention especially with smaller rims.



As you can see with the chart the wider the wheel the larger the amount of backspacing you need in order to maintain close to a Zero offset.


Now keep in mind you can vary outside these numbers, this is only a suggested guideline. With extreme drops, bags, and or a bodydrop these measurements can be changed to better fit if need be.


On smaller rims 14" - 17" you wont want to go much more positive offset then these numbers up front as you can run into rubbing issues on the outer tierod on the spindle steering knuckle.

7" wide - -12mm up to a +10mm offset
8" wide - -6mm up to a +10mm offset
8.5" wide - 0mm up to +6mm

On 18" and up rim sizes you can increase the positive offset a little more since the inner lip of the rim will now clear the steering knuckle of the spindle.

7" wide - -12mm up to +6mm
8" wide - -6mm up to +15mm
8.5" wide - 0mm up to +15mm
9" wide - -6mm up to +15mm


Hope this helps and isnt too confusing. If anyone has any questions feel free to post in here or pm me. Also i dont claim to know everything about wheels, so if you see something you dont agree with mention it.

Last edited by 98layinframe; 11-12-2009 at 10:21 PM.
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