Getting a handle on wheel sizing & offsets – A Preliminary Guide
02-11-13, 03:12 PM
#1
Getting a handle on wheel sizing & offsets – A Preliminary Guide [UPDATED 4/15/13]
Hey everyone!
I’m sure most of us (myself included) have wrestled with visualizing wheel fitments of aftermarket wheels. The overwhelming question that everyone asks is: “will these wheels with X-width and Y-Offset fit?!?!” and the most accurate answer to that question, although useless, is it depends! Is your car lowered? how low is it? do you have a camber kit installed? are the fenders rolled/shaved? Etc.
Since answering this question is inherently difficult (even if you know the answers to all of the questions above, it’s still hard to put it into perspective with your own setup), we instead reserve to browsing countless pictures of similar setups and trying to make an informed decision on the wheel fitments.
So here is my take on it, even though it’s somewhat primitive. I was doing some research on this issue and I stumbled on an interesting post on FlushStance: http://www.flushstance.com/wheel-measurements/ It basically describes how a wheel is measured and how offsets get into the picture. So I took the liberty of applying those simple equations listed to our OEM wheels. My main interest was to understand how much a certain wheel would “stick out” given its width & offset compared to my OEM setup.
Applying these simple equations in an Excel spreadsheet, I was able to develop the tables below which are specific to our wheels (2008-2009 wheels). The calculated values are in millimeters and they represent the difference between where the OEM wheel would sit compared to an aftermarket wheel for a given size combinations.
Let me give you a quick example of how this works: say you are running a stock setup and want to know if a 19x11 55offset wheel would "fit" your car in the rear.
1) Look up on the value on the charts above (the bottom chart), and there it shows that the new wheel will "stick out" about 25mm (the intersection of 11 & 55)
2) Use the method described in this short video to measure the gap between your current wheel and the edge of fender: http://www.trakplus.com/measure
4) Compare the two numbers and see if the new wheel will fit!
Again, in my case, I actually owned a set of 9X11 +55offset wheels, and from the pictures below I can confidently say the measurement came pretty close to actual!
ALTERNATIVE METHOD:
Another way to use this table: Say you already have the 19x9.5 40offset wheels in the rear, and you want to upgrade to 19x10.5 45offset wheels. Now all you have to do is compare the two numbers (21mm for the first, and 29mm for the second) and this automatically tells you that the new setup will stick out another 9mm from your current setup, almost the same as using a 10mm spacer on the 19x9.5 wheel.
Points of caution:
1) These calculations are based on 2008-2009 wheels (19X8 +45offset FRONT, 19X9 +55offset REAR). I believe newer wheels are a bit wider… I can generate those tables if there is enough interest.
2) Depending on the aftermarket tires that you purchase, you may gain/lose a few mms based on how wide your new tires are (stretched vs. beefy sidewalls)
3) This method doesn't tell you anything about clearing BBKs. Be sure to check with the wheel manufacture before making a purchase.
4) This only holds true if you make NO adjustments to your car suspension.
I’m sure most of us (myself included) have wrestled with visualizing wheel fitments of aftermarket wheels. The overwhelming question that everyone asks is: “will these wheels with X-width and Y-Offset fit?!?!” and the most accurate answer to that question, although useless, is it depends! Is your car lowered? how low is it? do you have a camber kit installed? are the fenders rolled/shaved? Etc.
Since answering this question is inherently difficult (even if you know the answers to all of the questions above, it’s still hard to put it into perspective with your own setup), we instead reserve to browsing countless pictures of similar setups and trying to make an informed decision on the wheel fitments.
So here is my take on it, even though it’s somewhat primitive. I was doing some research on this issue and I stumbled on an interesting post on FlushStance: http://www.flushstance.com/wheel-measurements/ It basically describes how a wheel is measured and how offsets get into the picture. So I took the liberty of applying those simple equations listed to our OEM wheels. My main interest was to understand how much a certain wheel would “stick out” given its width & offset compared to my OEM setup.
Applying these simple equations in an Excel spreadsheet, I was able to develop the tables below which are specific to our wheels (2008-2009 wheels). The calculated values are in millimeters and they represent the difference between where the OEM wheel would sit compared to an aftermarket wheel for a given size combinations.
Let me give you a quick example of how this works: say you are running a stock setup and want to know if a 19x11 55offset wheel would "fit" your car in the rear.
1) Look up on the value on the charts above (the bottom chart), and there it shows that the new wheel will "stick out" about 25mm (the intersection of 11 & 55)
2) Use the method described in this short video to measure the gap between your current wheel and the edge of fender: http://www.trakplus.com/measure
4) Compare the two numbers and see if the new wheel will fit!
Again, in my case, I actually owned a set of 9X11 +55offset wheels, and from the pictures below I can confidently say the measurement came pretty close to actual!
ALTERNATIVE METHOD:
Another way to use this table: Say you already have the 19x9.5 40offset wheels in the rear, and you want to upgrade to 19x10.5 45offset wheels. Now all you have to do is compare the two numbers (21mm for the first, and 29mm for the second) and this automatically tells you that the new setup will stick out another 9mm from your current setup, almost the same as using a 10mm spacer on the 19x9.5 wheel.
Points of caution:
1) These calculations are based on 2008-2009 wheels (19X8 +45offset FRONT, 19X9 +55offset REAR). I believe newer wheels are a bit wider… I can generate those tables if there is enough interest.
2) Depending on the aftermarket tires that you purchase, you may gain/lose a few mms based on how wide your new tires are (stretched vs. beefy sidewalls)
3) This method doesn't tell you anything about clearing BBKs. Be sure to check with the wheel manufacture before making a purchase.
4) This only holds true if you make NO adjustments to your car suspension.
Last edited by DS2k; 04-15-13 at 08:33 AM.
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02-12-13, 05:05 PM
#9
Let me give you a quick example of how this works: say you are running a stock setup and want to know if a 19x9.5 40offset wheel would "fit" your car in the rear.
- First, you look at the chart above (the second one), and there will see that the new wheel will "stick out" about 21mm (the intersection of 9.5 & 40)
- Second, you take a ruler (preferable one with a wide edge) and you place it perpendicular to your wheel (kinda like what this guy is doing)
- Third, you measure the distance between the edge of your wheel an the INNER edge of your fender. That would be your wheel clearance for your given setup.
- Last, you compare the two numbers and see if the new wheel will fit!
Another way to use this table: Say you already have the 19x9.5 40offset wheels in the rear, and you want to upgrade to 19x10.5 45offset wheels. Now all you have to do is compare the two numbers (21mm for the first, and 29mm for the second) and will see that this new setup will push out 9mm further than the old one, almost as if you used a 10mm spacer on the 19x9.5 wheel.
I hope this helps explaining it a little better. I will update the original post later with step-by-step instructions and most graphics that illustrate the math.
Last edited by DS2k; 02-12-13 at 05:10 PM.
02-21-13, 05:45 PM
#10
Lexus Test Driver
Sorry guys im trying to grasp the whole offest thing. According to the link it says that we should be able to fit a 9.5" +20 ?
Trying to see if these offsets would fit on our cars or not, and how would they look?
Fronts: 19x8.5 +20
Rears: 19x9.5 +20
Tires: Unknown
Car: 2012 ISF dropped on Swift Sport Springs.
A buddy of mine is letting go of his wheels for cheap and I just want to change up the look on my car without breaking the pockets. Ultimately I dont want to waste each others times. I appreciate the help in advance guys!
-Art
Trying to see if these offsets would fit on our cars or not, and how would they look?
Fronts: 19x8.5 +20
Rears: 19x9.5 +20
Tires: Unknown
Car: 2012 ISF dropped on Swift Sport Springs.
A buddy of mine is letting go of his wheels for cheap and I just want to change up the look on my car without breaking the pockets. Ultimately I dont want to waste each others times. I appreciate the help in advance guys!
-Art
02-21-13, 07:33 PM
#11
You might not be breaking your wallet with the wheels themselves, but you will most defniitely have to spend some more for fender rolling/cutting. the 8.5's and 9.5's +20 pushes the wheel and tire out about an inch and a half for front and rear. I haven't heard of anyone putting +20s on either fronts or rears, but the most aggressive I've heard was +32. Anything can technically fit with fender modification and/or other components, but it's a matter of how much you're willing to go. Best of luck to you if you get those wheels!
02-22-13, 11:20 AM
#14
No problem, my friend! I'm still learning more about wheels and offsets, and the chart the OP put together is a nice visual for members here. Thankfully, other members who have chosen aftermarket wheels were kind enough to shed light on what modifications they've done to achieve the look and fitment they wanted on their rides. I've seen a bunch of my friends guesstimate what they think are conservative offsets for their cars- only to find out that the wheels don't fit at all. It definitely pays to do the research beforehand and find offsets that work for our cars, even if it means paying a little more for them.