Sponsored

Backspace and Offset | How do they relate?

Discount Tire

Well-Known Member
Peak Sponsor (Level 2)
Joined
Feb 27, 2019
Threads
34
Messages
974
Reaction score
1,045
Location
Arizona, USA
Website
discountti.re
Vehicle(s)
All Things JEEP
Occupation
Tire & Wheel Specialists
We've had a few questions come up recently regarding this topic so we'd thought this may be useful.

Offset and backspace are essentially two different ways of looking at the same thing. They determine the location of the wheel and tire assembly when bolted to the vehicles hub.

Offset is the measured distance between the hub mounting surface and the wheels center line.

With X being the determined offset, the hub mounting surface on positive offset wheels is X amount forward from the wheel center line. The hub mounting surface on negative offset wheels is X amount backwards from the wheel center line. The hub mounting surface on 0 offset wheels is the wheel center line.

Backspacing
is the measurement from the hub mounting surface to the back edge of the wheel.

backspace_offset.jpg


***Typically speaking, the higher the offset/backspace, the more the wheel will tuck inwards towards the suspension or away from the fender. The lower the offset/backspace, the more the wheel will push out away from the suspension or towards the fender.

For Example:

*If the offset on a 9" wide wheel is +12mm, the hub mounting surface will be 12mm forward from the wheels center line. Measuring from the hub mounting surface to the back edge of the wheel, the backspacing is 5.5"

*If the offset on a 9" wide wheel is -12mm, the hub mounting surface would be 12mm towards the back of the wheel from the wheels center line. Measuring from the hub mounting surface to the back edge of the wheel, the backspacing is 4.5"

Here's how to calculate the backspacing using the rim width and offset:

First - add 1" to the rim width and then divide by 2 to find the wheels center line (you have to account for the wheel flange which is why you add 1" to the rim width) . Second - convert the offset which is in millimeters into inches. There is 25.4mm in 1 inch so divide the offset by 25.4. Lastly - add the converted offset to the wheels center line if the offset is positive for the correct backspacing. Subtract the converted offset to the wheels center line if the offset is negative for the correct backspacing.

For Example:

17x9 +12mm offset

*9" rim width + 1" = 10"
*10"/2 = 5" (wheels center line)
*+12mm offset/25.4 = 0.47" (0.50" rounded up)
*0.50" + 5" = 5.50" Backspace


17x9 -12mm offset

*9" rim width + 1" = 10"
*10"/2 = 5" (wheels center line)
*-12mm offset/25.4 = 0.47" (0.50" rounded up)
*0.50" - 5" = 4.50" Backspace

***Please note that the wheels center line is the backspacing for 0 offset wheels.

Check out our TIPS & GUIDES Section at discounttire.com for more helpful write-ups!
Sponsored

 

blnewt

Well-Known Member
First Name
Brad
Joined
Oct 8, 2018
Threads
96
Messages
9,876
Reaction score
23,794
Location
New Mexico
Vehicle(s)
2019 Jeep JL V6 SportS, (Retired 74 CJ-5, 80 CJ-7)
Occupation
Just ask @cosine he knows!
Nominate this for a sticky thread, asked about enough that it's warranted and nice job w/ the details!
 

Hayseed_JLUR

Well-Known Member
Joined
Apr 12, 2019
Threads
29
Messages
708
Reaction score
854
Location
Midwest
Vehicle(s)
2019 JLUR, 2015 JKU
Nominate this for a sticky thread, asked about enough that it's warranted and nice job w/ the details!
I second that nomination on sticking that one and also nominate that your clown avatar be banned.
 

blnewt

Well-Known Member
First Name
Brad
Joined
Oct 8, 2018
Threads
96
Messages
9,876
Reaction score
23,794
Location
New Mexico
Vehicle(s)
2019 Jeep JL V6 SportS, (Retired 74 CJ-5, 80 CJ-7)
Occupation
Just ask @cosine he knows!
 



Top