espi

My stock 2013 Sport 17s also had offset of 44.45 stamped into the back of the wheel. Either the older wheels had a different offset or people just miscalculated the back space.


ResQGrnRubi, Are you going to a larger size tire?

I posted this in another forum but may help you.

A lot of people throw around you need at least 4.5" Back space to run larger tires. It all depends on wheel width and tire width as to what back space you really need. If you look at wheel manufacturer specs they unusually list the offset as that is a better guide based on wheel width.

Just for reference AEV wheels are 17x8.5 with +10mm (5.1" to 5.2" back space) which they claim can run up to a 37" tire

I ran both 285/70r17 and 315/70r17 with 17x8.5 and +12mm offset (5.2" back space) wheels.

The 285/70r17 was on a stock suspension and then on a AEV 2.5" lift and the 315/70r17 was with the AEV 2.5"

The 285/70r17 was just inside the edge of the fenders and the 315/70r17 is right at the edge. Note that the Duratracs are wider than 12.5" and depending on your wheel width will determine how much bulge there is.

One downside I have seen from 5.2" back space wheels is long rear sway bar links will contact your tire, but you could drop the sway bar itself down. Ohh ya and you hit the plastic air dam, but that can be removed or trimmed.

Here is a list of wheel sizes and backspace required to run 315/70r17 or 35x12.5r17 and have as much clearance as stock.

Stock wheels are 17x7.5 with 44.45mm offset which is 6" back space not the 6.25 that is always thrown around. You can find the stamping on the back of the wheel.

17x7.5 with +44.45mm Offset (Stock wheels) will require 1.5" spacers which equals 4.5" back space

17x8 : +12mm Offset or 5" back space
17x8.5 : (close to AEV wheels) +12mm Offset or 5.2" back space
17x9 : +12mm Offset or 5.5" back space
17x9.5 : +12mm Offset or 5.7" back space
17x10 : +12mm Offset or 5.9" back space

If you notice the pattern. The back spacing changes but the offset does not.

Now a few things to consider when choosing new wheels.

If you like the really wide stance go ahead and get a wheel with less wheel offset then listed above

If you are concerned about aftermarket suspension clearance or plan to go wider than a 315 or 12.5" wide tire you should get wheels with less offset.

If you want to stick with 4.5" back space here is a list and how much further is sticks out vs the values above.

17x8 with 0mm offset will stick out 0.5" more.
17x8.5 with -6mm offset will stick out 0.7" more.
17x9 with -12mm offset will stick out 1" more.
17x9.5 with -18mm offset will stick out 1.2" more.
17x10 with -25mm offset will stick out 1.5" more.

14Sport

Great post, espi. I always read 6.25" backspacing all day long on the forum. And up until now I believed it with just the Rubis being 6". Good info!

And a lot of people believe that wheel width includes the flanges. Wheel width is measured bead seat to bead seat which is why you have to add .5" (standard U.S. flange width) to the result of the backspacing calculation or add 1" to rim width before starting the calculation.

espi

I researched for a long time about back space and offset because I didn't want my tires to stick past the fenders. I am an electronics engineer but I am mechanically inclined and a tinker since I was a little child. I worked on my cars for the last 12 years and even did a few honda motor swaps, but reading jeep forums and researching has taught me a lot about automotive engineering.

I think the one of the biggest mistakes people make is confusing backspace and offset. They think a certain back spacing will position the wheel in the same location regardless of wheel width when really the same offset on different wheel widths will position the wheel in the same location.

nthinuf

It's all about ease of use. The majority of people will see offset and have absolutely no clue, even after they spend time reading about it. Then they see backspace and it is an easy subtraction. 6.25" (or 6.00") stock minus 1.5" spacer = xx". Or going from stock 6.00 rim to 4.50 bs aftermarket rim = xx".

It is what it is. Offset may be more accurate, but we all know which most people are going to continue to use...



I had read a post a while back saying that some stock rims were 6.00 bs instead of 6.25, but had not seen that thread before. Good to know. Though one guy was saying his stock rims were 5.75.

14Sport

I don't bother to do the math. I just use an online calculator to convert. You enter rim width and offset and then hit calculate. Much easier even though I do know how to do the math.

CCW - Complete Custom Wheel // Technical - Offset Backspacing Converter

espi

Nice easy app.

I like this site because it helps you compare different tire and wheel configurations

http://www.rimsntires.com/specspro.jsp

14Sport

Nice. Bookmarked that.

This is the one I use for comparisons...

265/70-R17 vs 255/75-R17 Tire Comparison - Tire Size Calculator