RCCrawler Forums - Offset & Backspace Tutorial

We frequently get questions about how to determine offset & backspace for our wheels vs. "whatever wheels you currently have on your vehicle".
:mrgreen:

This post is our attempt to help you guys figure that out. We will update this post with relevant info and pictures as we build upon it. Your input is always welcome!
***For all of these measurements, we are going to assume you have beadlock rings installed on both the front and back of the wheel and that both rings are the same thickness.
If you don't have a beadlock, that is OK. Just measure form the outermost and innermost edges of the wheel.

Basics
So we are all talking apples to apples here is how we use the terms:
Backspacing: The distance from the wheel mount face (where your wheel hex goes) to the inner most part of the wheel.
Offset: The distance from the wheel mount face to the center line of the wheel.
Positive Offset: When the wheel mount face is closer to the outer bead on the wheel
Zero Offset: When the wheel mount face is even with the center line of the wheel
Negative Offset: When the wheel mount face is closer to the inner bead on the wheel
Comparison Number: This is a term/calculation we use to help determine your offset change when switching between wheel types.
http://www.lockeduprc.net/19wheels/backspace_offset.jpg

For each wheel type we will help you calculate your backspacing, width, offset and your Comparison Number.

How to measure a standard hex wheel (LURC 8L, Axial SCX10, etc)
To figure out your offset, our formula (yes, math outside of school .... we know) is:
Offset = B - (W/2)
B= Backspacing
W= Width
Start by pulling a backspace measurement like we do for our 8L wheels:
http://www.lockeduprc.net/19wheels/8lbackspace.jpg

Call that measurement "B" and for our example lets say it's B=18mm.

Now measure the entire width of the wheel (with the rings).
Call that "W" and for our example W=30mm.

So we have Offset = 18 - (30/2)
Or 18 - (15) = 3
So the example wheel has a positive offset of 3
(Yours could be negative)

For an 8L wheel your offset equals your comparison number so it's easy!

How to measure a Vanquish SLW style wheel
To figure out your offset, our formula again is:
Offset = B - (W/2)
B= Backspacing
W= Width

So, pull a backspace measurement like we do for our SLW style wheels:
http://www.lockeduprc.net/19wheels/slwbackspace.jpg

Call that measurement "B" and for example lets say B=14.75mm.

Now measure the entire width of the wheel (with the rings).
Call that "W" and for this example W=34mm.

That makes your formula look like this:
Offset = B - (W/2)
Offset = 14.75 - (34/2)
Offset = -2.25

To get a Comparison Number you need:
CN= O - HM

O is offset
HM is Hub Measurement .

The VP .225 has about 2.15mm of meat between where your wheel hex touches the hub and where the hub touches the wheel face:
http://www.lockeduprc.net/19wheels/225thickness.jpg
That 2.15 becomes your HM number....
.185 HM: 1.2mm
.225 HM: 2.15mm
.350 HM: 5.33mm
.475 HM: 8.5mm
.600 HM: 11.68mm

So then we have
CN= O - HM
CN= -2.25-2.15
CN= -4.4

For the example wheel with an offset of -2.25 you get the following Comparison Number with various SLW hubs:
.185: -3.45mm
.225: -4.4mm
.350: -7.58
.475: -10.75
.600: -13.93

How to measure for an AO8 wheel
To figure out your offset, our formula one more time is:
Offset = B - (W/2)
B= Backspacing
W= Width

So we pull a backspace measurement like we do for all our AO8 style wheels:
http://www.lockeduprc.net/19wheels/ao8backspace.jpg

Call that measurement "B" and for example lets say B=12.15mm.

Now measure the entire width of the wheel (with the rings).
Call that "W" and for this example W=27mm.
That makes your formula look like this:
Offset = B - (W/2)
Offset = 13 - (27/2)
Offset = -.5

Now to get the Comparison Number we need:
CN= O + FM - WH
FM is Flange Measurement.
WH is Wheel Hex (that you are removing).

The AO8 285 flange has 2.85mm of meat between where your pin touches the flange and where the flange touches the wheel face:
http://www.lockeduprc.net/19wheels/285thickness.jpg
That 2.85 becomes you FM number:
285 FM= 2.85mm
485 FM= 4.85mm
685 FM= 6.85mm
885 FM= 8.85mm

Most narrow wheel hexes have 2.85mm of material between the pin and wheel face.
Most thicker one have about 4mm.
The 2mm or 4mm is your "WH" number.

Lets say you are going to a 285 FM and had a narrow wheel hex.

So:
CN= O - FM + WH
CN= -.5 - 2.85 + 2.5mm
CN= -.85
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Now, let's put this to the test with an example...
You are moving from an 8L wheel to an AO8 with a 285 flange. You were also running a standard Axial wheel hex.

The 8L has a backspacing measurement of 13mm and width of 27mm.
Offset= B-(W/2)
Offset= 13 - (27/2)
Offset= -0.50mm
O= CN= -0.50mm

The AO8 has a backspacing of 13, a width of 27mm and you will use a 285 Flange.
Offset= B - (W/2)
Offset= 13 -(27/2)
Offset = -5
CN= O + FM - WH
CN= -.5 - 2.85 + 4mm
CN= .65

So we compare the -.5 (8L) to the .65 (AO8 ) and you have a +1.15mm change in the Comparison Number.
This means with the AO8 wheel setup your offset will change by +1.15mm, sucking your wheel in by 1.15mm compared to the 8L setup and the thick wheel hex.

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If you look at the numbers you can really hurt your brain ... so one way we've made it easy for you is this:

1.9:
An AO8 with a 285 will give you the same stance as a stock SCX10, or one of our 8L wheels, or one of our SLW wheels with a .185 hub.

http://www.lockeduprc.net/19wheels/a...compare285.jpg
In other words, we measure the stock SCX10 wheel (with our beadlock rings) to be 27mm wide with a backspace of 13mm, giving you an offset (and Comparison Number) of -0.50mm.

For every size up AO8 you get 2mm wider.
http://www.lockeduprc.net/19wheels/a...compare485.jpg

http://www.lockeduprc.net/19wheels/a...compare685.jpg

http://www.lockeduprc.net/19wheels/a...compare885.jpg

2.2:
We measure a stock Wraith wheel to be 41mm wide, with a backspace of 26mm.
That makes the offset (and Comparison Number) a +5.5.

Our 2.2 SLW with a .185 and our 8L will both offer a similar stance to the Wraith wheel but because they are narrower you have less backspacing ... so more knuckle/link clearance.

Our 2.2 AO8 has width of 30.5 and backspacing of 18mm, for an offset of +2.75mm.
Assuming a 285 flange and that you removed a narrow wheel hex you get a Comparison Number of 2.65.

http://www.lockeduprc.net/19wheels/a...pare285-22.jpg
As you can see, our A08 with a 285 has an offset that is 2.65mm less (pokes out more) than a Wraith wheel, our 8L and our SLW.

And again, for every size up AO8 you get 2mm wider.
http://www.lockeduprc.net/19wheels/a...pare485-22.jpg

http://www.lockeduprc.net/19wheels/a...pare685-22.jpg

http://www.lockeduprc.net/19wheels/a...pare885-22.jpg

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