lol this is like wheel fitment 101.
from a forum i frequent, VipStyleCars.com
from a forum i frequent, VipStyleCars.com
bOosty.ViP;183610 said:Do not give me credit for this. Got this from OG-MADE, hopefully this will contribute to our other members. Hopefully we can get this stickied
If you look at a wheel along its barrel (width wise), zero (0) offset would be the imaginary line that is dead center between barrel end to end. The imaginary line is determined by where the backpad of the wheel sits. Keep in mind that this tutorial is based on MULTIPIECE WHEELS (which is what my previous how to determine lip post was referring to). Cast wheels follow the same idea, but the drawings I made are for multipiece wheels (since it shows lip size changing). If the backpad moves towards the outside of the wheel, then the offsets increase in positive numbers (in increments of mm). If the backpad moves towards the inside of the wheel, the the offsets increase in negative numbers (in increments of mm).
Rule of thumb: the lower the offset, the further the wheel moved OUTWARD of the fender, and vice versa. As you can see, the orange line demonstrates the fender position, and the blue line demonstrates the hub/rotor where the wheel mounts to. For general purposes, let’s say this wheel is a 18×9.5+0 (images are not drawn to scale). As you can see, the outer position is “flush” (even) with the outer fender imaginary line (shown in orange). Also take note of the size of the outer lip of the wheel. Let see what happens if we raise the offset of the wheel…
So instead of a 18×9.5+0, let’s try to run a 18×9.5+22 and see what happens. As you can see, if you change the offset of a wheel from a +0 to a +22, the overall position of the wheel is going to move INWARD 22mm. As you can see by the area shown in green, that is the 22mm that the wheel backpad moved between the two sizes. Since the wheels shown are multipiece, the face of the wheel moves inside the barrel to change offsets, rather than adding more material to the wheel backpad. In addition, notice that the lip size decreased when the offset increase. Generally speaking, one can assume that the lip size decreases when the offset increases, but sometimes it might not be the case (depending on face design, but that’s gonna get confusing).
- Lowering the offset: the more it moves outward from the fender (”more flush”
- Raising the offset: the more it moves inward inside the fender (”more sunk”
How to Read a Wheel Sizing Chart
1. “Free Range” Offsets: These are sizing charts that allow you to choose from a “range” of offsets, rather than a preset number. Before all that though, you read the chart like any other table. As demonstrated by the purple arrow, this wheel is offered in an 18 inch (diameter) by 10 inch (width). If you look at the top of the chart, there are the following column headings: Taper Low Disk / Flat Low Disk / Flat High Disk. Each brand has a different name for its face choices, but for the most part, it will either go lowest to highest, or vice versa (obviously if it has “low” in the name, then you know it has LESS brake clearance in comparison to a “high” disk). Brake clearance and face choice is a whole other blog though. Let’s just take “Taper Low Disk,” which usually will be a rear wheel. As shown by the green arrow, you can get any offset -13 through +53. This means you can get any whole number offset, i.e -12, -11, +0, +1, and so on. The circled lip size I will be referring to is in light blue, i.e 77mm. Also, PCD = bolt pattern.
Lazy reader notes:
- Purple arrow: Wheel size - diameter (18″by width (10″
- Green arrow: Face choice + respective columns of available offsets
- Magenta square: PCD = bolt pattern of wheel
- Blue circle: “77″ is the wheel lip size in mm that is associated to +53 offset
- Taper Low Disk = least brake clearance (ideal for rear)
- Flat Low Disk = standard brake clearance (will clear most standard size front calipers)
- Flat High Disk = maximum brake clearance (ideal for BBK or big caliper)
2. “Preset” Offsets: These are sizing charts that allow you to choose from a “preset” offset, given to you by the sizing chart for that specific wheel. In this case, the 18×11.5 is offered in +5, -8, -16, and so on down the row. Each column represents the wheel faces that are offered, i.e “SL, NR, MD, HP.” Their respective meanings are color coded and shown below the chart. Again, it (SL, NR, MD, HP) goes from least amount of brake clearance (Super Low Disk) to maximum amount of brake clearance (Hyper Disk). At the top of the column, the 135mm refers to the lip size, and is the lip size for the 4 columns below it (i.e +5, -8, -16, and -26 all have 135mm lip size). Lip size is easy with presets, since you just figure out what diameter x width x offset you are running, and look at the column above. For example, an 18×11.5-26 (HP Face) has a 135mm lip, as well as an 18×11-14 (NR Face). An 18×12-1 (SL) has a 148mm lip, etc. Got it?
Lazy reader notes:
- Navy Blue square: Wheel size - diameter (18″
- Orange square: Lip sizing in mm, refers to the 4 columns of offset choices listed below it
- Magenta square: “HP” refers to the wheel face choice (i.e determines level of brake clearance), and offsets for that face choice are listed below it
- Lime green square: Usually where special notes are, in this case there are different color choices (which also can mean different prices). PCD = bolt pattern of wheel, and in this case, there are more bolt patterns possible, i.e you might be able to do a 5×120, 5×112, etc
- SL, NR, MD, HP: listed in order from least to most brake clearance
3. How to calculate lip size: First of all, you have to figure out what size wheel you want to go with. So if you take a look at the top most chart, let’s say you want a 18×10 with a +15 offset with a Taper Low Disk for your rear wheel. I had circled the number “77″ in blue, which is the lip size for an 18×10+53 Taper Low Disk wheel (this does not go for all 18×10 multipiece wheels, lip size is specific to EACH brand and model of wheel, so check the sizing chart always). So a +53 gives you 77mm of lip, which tells you that if you go to a +15, you will be getting MORE LIP (rule of thumb: lower the offset, the more the wheel sticks outward from the fender, and bigger the lip gets). So a (+53) minus (+15) = 38mm. Add 77mm + 38mm and you get 115mm, which is the lip size of a 18×10+15 Taper Low Disk.
