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Discussion Starter · #1 ·
I as well as other gets emails all the time and i figured i would post some info if a mod could STICKY the thread it would helps as well.

Im not going to say everything in here is exact or even in the right terms but to my know how it is i did not do much research further into this rather this is everything off my head and hope it helps put things into perspective and will guide others in the right direction.




PCD

The term PCD stands for (pitch circle diameter) and is the diameter of a circle drawn through the center of your wheels bolt holes. PCD is measured in millimeters and also indicates the number of studs or bolts the wheel will have.


OFFSET

Every car requires a unique offset. This is where the outside of the wheel needs to be in relation to the body-line of the vehicle, realistically you can go 5-7mm outside these recommendations, but always check with vehicle and wheel manufacturer' if you are unsure, as there are often other factors that need to be considered.


One thing to remember for wheel offset is everything is in MM So if you had a wheel width of 8 Inches you would multiply it by 25.4 for the Inch to Millimeter Conversion

So i will use this next picture to explain it as simple as i can. I will use a default size.

Default Wheel Specs:
Wheel Diameter= 18 inch
Wheel Width= 8 inch aka 203.2mm (8 x 25.4)
Offset= +30mm

So center line of the wheel is found by dividing the wheel width by two which would be 8/2 having center-line at 4" inward.

Center-line is also Zero offset. So if your wheel was 8 Inches wide and had a Zero offset you would have a 4 Inch lip or 4 Inches of concave.

That being said your wheel of 8 Inches wide with a +30mm offset would be looked at as the following.

203.2mm (8 Inches)
101.6mm (Center-line 8/2 = 4" Center-line 4x25.4)

Now that you know Center-line known on this wheel as 101.6mm you can take your +30 which is 30mm added to the center-line going towards the outside of the wheel away from the brake. A negative offset would pull towards the brake side.

+30mm lets you know that your hub is sitting at 30mm plus of the center-line of the wheel.

so knowing your center is 4" that converts to 101.6 add the 30mm it would be 131.6mm.

203.2mm - 131.6mm = 71.6mm which converts back to 2.8.. inches of lip/concave.

131.6 is your back spacing which converts to 5.18... inches.

5.18..." + 2.8..." = 7.98.." as shown above 8 Inch wide wheel.

Sum it up again:
203.2 is overall width in MM
101.6 is the center line of the wheel in MM
+30mm is the Offset of the wheel.

Add the offset and centerline to get the 131.6 which is your back spacing. Take the overall width in mm and minus the backspacing you will have your offset or inset as shown above.




Measuring for Backspacing.



Thanks,
PhillyB aka Gary aka Phillie
 

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Discussion Starter · #2 ·
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Wow, great info and write up G ~

We need more committed/dedicated members like you on this board!!
 

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Discussion Starter · #7 ·
well i can go more in depth but true people will be more confused yet they will know the difference between +30mm and +22mm offsets i hope.
 

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I thought this was well put together. Coming from a beginner, (me) I was able to comprehend this and it made perfect sense. After all it's really not rocket science just takes a lil time to let everything sink in a bit. For a newb, numbers and diagrams like this will take more time to adjust in their brain but soon enough it will start to click.
 
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Discussion Starter · #10 ·
The game is not to get as close to center-line yet know what center-line stands for your goal is to get the wheel lip as close to the fender as possible for a flush fit. You can go a few mm outside of the fender and stretch the tire. Yet there is going to be talk back and forth. If you do have a question post it up or PM me and im more then happy to help you out further.

Gary
 
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Discussion Starter · #12 · (Edited)
**Disclaimer spacers are to be used at your own risk. Do not purchase a cheap set of spacers and if i may recommend use the bolt on spacers which give you new stud mounting points rather then using slip on spacers

Bolt on spacers shown below.

With that being said Lets talk offset with spacer applications:

Im going to use one of my friends Twestman's car as an example.

Twestman's setup.

His setup is as follows:
Enkei RPF1 18x9+35, 18x10+38

Yet to reach the fitment he wanted he leaned towards spacers.

The way a spacer works is it adds to the offset of the wheel. Does not physically change any properties of the wheel yet does add to the backspacing.

Example of an 18 inch Diameter wheel with a 9 inch width and a +35mm offset.


Now with the application of the spacer you have moved Outer Position of the wheel 10mm out and now have earned yourself 10mm of Inner Clearance.

***Shown in the picture is a 15mm spacer yet same theory.


With the addition of the spacer you can see how it pushed the wheel outward by using a spacer to achieve a 18x9 +25.




An example of how this works:

Remeber that 25.4mm is equal to 1 full inch.

You have a 18x8 with a +50mm offset if you were to add the following size spacers you would end up with:

10mm spacer: 18x8 +40
15mm spacer: 18x8 +35
20mm spacer: 18x8 +30
25mm spacer: 18x8 +25

Again your not changing anything physical about the wheel so the face, lip , and concave will remain the same. Yet it will push the wheel out away from the hub to reach the fitment desired.
 

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Discussion Starter · #13 ·
Many people will worry about brake clearance and still want to run aggressive fitments. Going with a wider wheel will have you lose the inner clearance yet if you were to run a smaller wheel you can go with a even lower offset and be safe on both counts.

18x9 +25 will fit the same fender wise as:

18x8.5 +19 With 12mm more inner clearance
18x8 +12 With 26mm more inner clearance

That being said you have the same aggressive fitment that a 18x9+25 would give you yet you made more clearance for the suspension components. I would make visual drawings if this is needed. If so please send me a pm and i can make it happen. Yet i'm sure that if you use the info given previously you can do the math and see for yourself how it adds up.
 

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Many people will worry about brake clearance and still want to run aggressive fitments. Going with a wider wheel will have you lose the inner clearance yet if you were to run a smaller wheel you can go with a even lower offset and be safe on both counts.

18x9 +25 will fit the same fender wise as:

18x8.5 +19 With 12mm more inner clearance
18x8 +12 With 26mm more inner clearance

That being said you have the same aggressive fitment that a 18x9+25 would give you yet you made more clearance for the suspension components. I would make visual drawings if this is needed. If so please send me a pm and i can make it happen. Yet i'm sure that if you use the info given previously you can do the math and see for yourself how it adds up.
The only problem with doing that is you need a much smaller tire. Twestman is running a 215 on a 9, so you'd need something like a 195 on an 8 in order to have the same tire to fender clearance. Or a 205 on an 8.5.
 

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Discussion Starter · #15 ·
true. Yet that is a whole other subject haha. Just showing the options of what can be done. Im still working on some more. These are really quick write ups you can tell by reading over it haha.

I used his as an example cause a +25 with a 18x9 is a perfect fitment for the front of the IS300.

Maybe i should have just showed other 9" wheels with a spacer to use as an example rather then smaller widths.
 

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Nice write-up. +reppage
 

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true. Yet that is a whole other subject haha. Just showing the options of what can be done. Im still working on some more. These are really quick write ups you can tell by reading over it haha.

I used his as an example cause a +25 with a 18x9 is a perfect fitment for the front of the IS300.

Maybe i should have just showed other 9" wheels with a spacer to use as an example rather then smaller widths.
No I understand what you're saying. I think what you did is fine. I've done similar posts through out the fitment threads, but it's way better have them all in one spot. I don't think it will eliminate the problems with the influx of threads, but it SHOULD help.

I do think there should be a copy in the Wheels and Tires sections though.
 

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I'd like to throw in my $0.02 if I may

My front wheel setup consists of 18x9+35 with 235/40 with a big brake kit, (soon to go to you Philly) and coilovers, and have no fitment issues. the stock brakes had more clearance then my big brake kit does, the suspension I can't answer for since I did everything at the same time.
 

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Discussion Starter · #20 ·
thats another factor to come into play. concave and lip to brake clearance with hub selection.

Still waiting for reply on price on the brakes. :)
 
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