Wheel Backspacing and Offset Info

bump

maybe someone can tell me the difference in poke between these two rims and stock:

17x8 0 offset

and

18x9 -6 offset

thanks for any help guys, i just don't want to make the wrong decision on such a pricey purchase. thanks again!

 

took me forever and a million button strikes on the calculator to realize that wheel size isn't the same as rim width. A wheel that is labeled 16x8 is really 9" wide (usually)
Meaning a 8" rim with 0 offset isn't 4" backspacing.

examples

Size: 20x9
<li id="frontOffset137" style="display: block;">Offset: 1mm<li id="frontBackSpacing137" style="display: block;">Backspacing: 5.039"Bolt Pattern: 6-139
Rec. Tire Size: 265/50-20
Weight: 34.65lbs.
Finish: Black w/Spot Milling
<li id="frontConstruction137" style="display: block;">Construction: 1pc. Gravity Cast<li id="frontFinishWar137" style="display: block;">Finish Warranty: 1 Year<li id="frontManufactured137" style="display: block;">Manufactured in China
and

Front and Rear

• Size: 16x8
• Offset: 00mm
• Backspacing: 4.45"
• Bolt Pattern: 6-139
• Rec. Tire Size: 245/75-16
• Weight: 24.2lbs.
• Finish: Teflon Coated
• Construction: 1pc. Gravity Cast
• Finish Warranty: 2 Years
• Manufactured in China

 

usually (there are exceptions which is why you cant just do the math yourself)

17x8 is 9" wide.
Divide 9" in half. This is dead center of the wheel. 4.5.
Add the offset +(0)
Back spacing = 4.5

18x9 is 10" wide
divide 10 in half =5
add the offset -10mm (.39")
back spacing = 4.61

 

I have looked at so many threads over the last few days my eyes hurt but I believe I finally got the info straight. I plan to install the Complete Old Man Emu Suspension System with NitroCharger Sport Shocks which I believe will give me about 3" of lift.

If I go with a 17X9 wheel -12 offset (stick out 1/2" ish) and 4.5 BS I can mount 285/70-17 tires. Is that correct?

That said, what will I need to do/trim/remove to not have rubbing issues?

I would appreciate any info anyone could provide related to my questions.

Thank You,
Bob

 

thank you teamcurtis! i believe that cleared up some of my confusion.

i'm pretty sure i have also decided on a 17x9 -12offset wheel. although i think i will have less than 3" of lift so i'm also curious to the answer to this. but from the research, it sounds like you might need to chop the cab mounts for the 285, or you might not have to. lol it seems like some people need to, and some don't. i may play it safe and just go with a smaller tire than the 285. i'd rather not chop cab mounts, but i don't have a problem removing mudflaps or a little minor trimming of fender flares. information overload!

 

Have the same wheel numbers with 285's...minor trimming. no CMC...

 

awesome thank you!

 

so does a negative or a positive offset make the wheel stick out of the fender? i'm looking at 15 inch wheels with a +38mm offset, and am wondering if i will need wheel spacers to get the aggressive 4x4 stance...

 

Negative moves the tire outboard

 

+38 will move your wheel in 1.5", which may cause contact with the suspension. Also, 15" wheels won't fit on a 2nd gen Tacoma, most 16" wheels do.

 

what is the width?

 

Well i have the base model, 5-lug tacoma and was wondering because i like the look of the tires when they are slightly out of the wheel wells

 

This chart above and this formula:

backspacing=(wheel width)/2 + offset+(about 0.25 inches)

do not agree.

For example: 10" wheel/2 + zero offset + .25" =5.25". The chart shows 5.5".

Another example: 8" wheel with a 19mm offsit: first 19mm offsit/25.4 =.748 inches. 8" wheel/2 + offsit of .75 + .25 = 5". The chart shows 5.25".

I made an Excel table to run all the calculations. All the measurement are .25 inches off.

In the formula should the "about .25 inches" be changed to "about .5 inches" or is the chart off by one column?

 

Pro Comp 7031's, will the 15x8's fit on the 5-lug tacoma? 3.75 backspacing and -19mm offset

 

Did you account for the rim width vs the actual wheel width?
a 17x8.5 wheel is really 9.5 wide. (inner rim lip for tire vs outer most part of the wheel for clearance)

 

Yeah, This ^^^^^

Drew up some diagrams for guys like me and you. Posted 'em earlier in this thread. Link Below
Visual Backspace Explaination - Simple Drawings of 3 wheels w/ different backspacing
Now has 5 different wheels
Needed to grasp the concept myself and this was the best way for me.
Wheel width is measured INSIDE the rim's bead flanges.
Lay wheel flat on back and it measures 1" more to the top than rated width.
8" Wheel is measurement inside flanges, but it 9" from outside to outside of flanges.
Confused yet? Look at the Pics, should clear it up for ya

EDIT: Offset measured from center of width to mounting surface
Backspacing measured from mounting surface to outer edge of back (vehicle side) flange
Though they are related, they are two different measurements,
with the mounting surface, being the only common denominator.
FWIW

EDIT EDIT: When you get the spreadsheet straightened out, maybe you could post it for the rest of us.
Or for just me . I for one would be interested is seeing it.

Good Luck


CC

 

Nevermind
Just went to the thread I linked for you and noticed you were the 6th post in it. (2012/04/21)
Guess you've seen it.



CC

 

how do you find out what your back spacing is on some stock 17'' sport wheels cause im wanting to put some 285 70 17 on them but not sure if i need wheel spacers or just get new wheels and tires.

cause i really like my stock sport wheels but not sure about wheel spacers

 

http://www.tacomaworld.com/forum/wheels-tires/30754-wheel-specs.html

 

I have a 09 TRD offroad accesscab with stock TRD OR wheels which have a 5.25" backspacing if I'm not mistaken. I am putting on 255/85/r16 toyo open country MT/s which is a 33.5" tall and 10.2" wide tire. I will be installing my full OME lift with 886 (planning on bumpers and armor down the road) struts up front and dakars in the rear. I will be doing Camburg Uniball UCA's at the same time which require a maximum wheel backspacing of 4.75".

So I imagine I'm going to have an issue somewhere due to the wheel backspacing of the stock TRD OR wheel. Where am I going to rub? Would spidertrax wheel spacers alleviate this problem? Is my wheel going to rub on the camburg UCA's? I'm just hoping it will go together fine as I don't have much more money at this time to spend on aftermarket wheels/wheel spacers.