Offset/backspacing converter for wheels and measuring lug bolt length.
Thread Starter
MBWorld Fanatic!
Joined: Feb 2009
Posts: 5,054
Likes: 11
From: fort worth, tx
06 C230 SS 6spd
Offset/backspacing converter for wheels and measuring lug bolt length.
Ok everyone. Since offset and wheel fitment has become a big topic lately here's a offset/backspacing converter from CCW that will let you input the width of the wheel and the offset and it'll calculate the backspacing. If you dont know what backspacing is, its the measurement from the inner edge of the wheel to the hub mounting surface. Also known as rear spacing. Just remember to switch the conversion to "offset to backspacing". From there you can get your base backspacing of your OEM wheels, then you can enter the offset and width of your new wheels and see what the backspacing is. Youll want to get it pretty close to what your OEM one is or less. ***REMEMBER the higher the number the backspacing is the more the inner wheel will be to the suspension*** This will give you an idea if the wheels will clear our brakes and suspension.
So if you're OEM wheel is 7.5 +38 the backspacing is 5.75" and say you want to go with 8.5, you'll want around a +26 offset making it 5.77" of backspacing keeping your backspacing close to the OEM backspacing. Now you can get a different offset if you dont want the +26. My general rule of thumb is that I don't want to go more than 0.5" from the OEM backspacing, so the max backspacing in this situation would be 6.25" which would be a +38 offset. This will all depend on if you have sport/amg calipers and upgraded suspension since in some cases it will effect the backspacing.
I'm not saying this will work on ALL wheels, but this is just a reference tool to help with making wheel choices and their offsets. Each wheel manf. designs their wheels differently so use this tool at your convenience and risk as I am not responsible for what you decide to order. This is just a reference tool.
Hope this helps many members. Also remember to get the correct lug bolt length when getting new wheels. From beginning of threading the lug to tightening it it should be 6 full rotations. I'll post how to get the measurement for the correct lug bolt length below.
OFFSET/BACKSPACING CONVERTER TOOL
So as you can see from the diagram that if you get a high offset the further way the inner wheel edge is to the mounting surface since its further way from the the centerline (0 offset) and vice versa when you go with a lower offset it'll be closer to the centerline and the distance will be less to the inner wheel edge.
Another diagram to help
So if you're OEM wheel is 7.5 +38 the backspacing is 5.75" and say you want to go with 8.5, you'll want around a +26 offset making it 5.77" of backspacing keeping your backspacing close to the OEM backspacing. Now you can get a different offset if you dont want the +26. My general rule of thumb is that I don't want to go more than 0.5" from the OEM backspacing, so the max backspacing in this situation would be 6.25" which would be a +38 offset. This will all depend on if you have sport/amg calipers and upgraded suspension since in some cases it will effect the backspacing.
I'm not saying this will work on ALL wheels, but this is just a reference tool to help with making wheel choices and their offsets. Each wheel manf. designs their wheels differently so use this tool at your convenience and risk as I am not responsible for what you decide to order. This is just a reference tool.
Hope this helps many members. Also remember to get the correct lug bolt length when getting new wheels. From beginning of threading the lug to tightening it it should be 6 full rotations. I'll post how to get the measurement for the correct lug bolt length below.
OFFSET/BACKSPACING CONVERTER TOOL
So as you can see from the diagram that if you get a high offset the further way the inner wheel edge is to the mounting surface since its further way from the the centerline (0 offset) and vice versa when you go with a lower offset it'll be closer to the centerline and the distance will be less to the inner wheel edge.
Another diagram to help
Last edited by phister; Feb 4, 2012 at 08:50 AM.
Thread Starter
MBWorld Fanatic!
Joined: Feb 2009
Posts: 5,054
Likes: 11
From: fort worth, tx
06 C230 SS 6spd
Measuring lug bolt shaft lengths.
Here's a little DIY on how to get the proper length lug bolt for your car.
1. Remove the OEM wheel and lug bolt.
2. Place the lug bolt in the OEM whell and push it all the way in till it makes contact with the wheel (like its tightened down)
3. Measure how much bolt is sticking out from the back of the wheel. (measure in mm since all our lug bolts are in mm). WRITE IT DOWN.
4. Now grab your new wheel and the OEM bolt.
5. Place the OEM bolt in the new wheel and push it all the way in like in the previous step.
6. Measure how much is sticking out and WRITE IT DOWN.
7. Now that you have the two numbers you can calculate the difference. Might need more shaft length or might need less.
8. Now that you have the difference you can add/subtract it from the OEM shaft length which is 39.9mm for the w203. Shaft lengths will be in whole numbers so say our OEM is 40mm
9. You should now be able to get the proper length bolt. If you are adding a spacer to it, just add the width of the spacer to the length you need. So you if you need a 45mm shaft length and you have a 5mm spacer you'll want to get a 50mm shaft length to accommodate the extra 5mm spacer.
HOPE THIS HELPS EVERYONE! and SAFE DRIVING!
Here's a little DIY on how to get the proper length lug bolt for your car.
1. Remove the OEM wheel and lug bolt.
2. Place the lug bolt in the OEM whell and push it all the way in till it makes contact with the wheel (like its tightened down)
3. Measure how much bolt is sticking out from the back of the wheel. (measure in mm since all our lug bolts are in mm). WRITE IT DOWN.
4. Now grab your new wheel and the OEM bolt.
5. Place the OEM bolt in the new wheel and push it all the way in like in the previous step.
6. Measure how much is sticking out and WRITE IT DOWN.
7. Now that you have the two numbers you can calculate the difference. Might need more shaft length or might need less.
8. Now that you have the difference you can add/subtract it from the OEM shaft length which is 39.9mm for the w203. Shaft lengths will be in whole numbers so say our OEM is 40mm
9. You should now be able to get the proper length bolt. If you are adding a spacer to it, just add the width of the spacer to the length you need. So you if you need a 45mm shaft length and you have a 5mm spacer you'll want to get a 50mm shaft length to accommodate the extra 5mm spacer.
HOPE THIS HELPS EVERYONE! and SAFE DRIVING!
Last edited by phister; Feb 4, 2012 at 08:52 AM.
