Maximamike
06-22-2008, 05:51 PM
http://i124.photobucket.com/albums/p11/mjcnismo/DSC02150.jpg
So you're interested or already bought a set of wheels but you seem to be missing these? Here is a quick and easy way to tell offsets/backspacing so you can be sure they'll fit your ride.
http://i124.photobucket.com/albums/p11/mjcnismo/DSC02151.jpg
First thing you need to do is gather all your equipment. What I have missing here is a roll of tape, a piece of paper and a pen. I also hit my head on a moving ceiling fan while taking this picture. :doh: Shown is two larger yardsticks and a smaller ruler. You only need one ruler, thats at least the width of the wheel, the others will be used as shown. I'm lazy and didn't feel like finding my straight edge.
http://i124.photobucket.com/albums/p11/mjcnismo/DSC02152.jpg
First thing is first, find the height of the wheel. With the wheel laying on a level surface, measure the height from the base to the other straight edge. As you can see here my 9" wheel measures 10" from top to bottom. You can also measure from bead to bead, but I find this way quicker and easier. Write down this measurement and divide it by two. What that will leave you with is the wheel centerline. This will help you determine whether or not the wheel has a positive or a negative offset. A positive offset will have the backpad of the wheel with a higher distance than the centerline that you just found, a negative will be the opposite.
http://i124.photobucket.com/albums/p11/mjcnismo/DSC02153.jpg
Next, secure the smaller straight edge to the backpad of the wheel. Make sure there is nothing on the backpad that would tilt or make this not flat. Flip the wheel back over so the face of the wheel is up again.
http://i124.photobucket.com/albums/p11/mjcnismo/DSC02154.jpg
Lastly, measure the distance from the base to the bottom of the backpad. Remember to make sure the other straight edge did not sag from the bottom of the backpad and that you take your measurement from the correct side of the straight edge. Write down this measurement.
Lastly, its math time. The only two measurements you have taken are the wheel height and the backpad height.
First, take all the measurements and convert them from inches into millemeteres. The conversion factor is 1" = 25.4 mm. For example, these are my measurements. Because of the thickness of the smaller ruler my measurements vary by 1/8" or around 3 mm.
Wheel height:
10" x 25.4 mm = 254 mm
Centerline:
254 mm / 2 = 127 mm
Backpad Height:
5.875" x 25.4 mm = 149.2 mm
or
5.75" x 25.4 mm = 146.05 mm
Offset calculation:
149.2 mm - 127 mm = ~ +22 mm
or
146.05 mm - 127mm = ~ +19 mm.
So the offsets of my front wheels are anywhere from + 22 mm to + 19 mm. You can further narrow it down by using a very thin straight edge on the backpad of the wheel. Any questions?
So you're interested or already bought a set of wheels but you seem to be missing these? Here is a quick and easy way to tell offsets/backspacing so you can be sure they'll fit your ride.
http://i124.photobucket.com/albums/p11/mjcnismo/DSC02151.jpg
First thing you need to do is gather all your equipment. What I have missing here is a roll of tape, a piece of paper and a pen. I also hit my head on a moving ceiling fan while taking this picture. :doh: Shown is two larger yardsticks and a smaller ruler. You only need one ruler, thats at least the width of the wheel, the others will be used as shown. I'm lazy and didn't feel like finding my straight edge.
http://i124.photobucket.com/albums/p11/mjcnismo/DSC02152.jpg
First thing is first, find the height of the wheel. With the wheel laying on a level surface, measure the height from the base to the other straight edge. As you can see here my 9" wheel measures 10" from top to bottom. You can also measure from bead to bead, but I find this way quicker and easier. Write down this measurement and divide it by two. What that will leave you with is the wheel centerline. This will help you determine whether or not the wheel has a positive or a negative offset. A positive offset will have the backpad of the wheel with a higher distance than the centerline that you just found, a negative will be the opposite.
http://i124.photobucket.com/albums/p11/mjcnismo/DSC02153.jpg
Next, secure the smaller straight edge to the backpad of the wheel. Make sure there is nothing on the backpad that would tilt or make this not flat. Flip the wheel back over so the face of the wheel is up again.
http://i124.photobucket.com/albums/p11/mjcnismo/DSC02154.jpg
Lastly, measure the distance from the base to the bottom of the backpad. Remember to make sure the other straight edge did not sag from the bottom of the backpad and that you take your measurement from the correct side of the straight edge. Write down this measurement.
Lastly, its math time. The only two measurements you have taken are the wheel height and the backpad height.
First, take all the measurements and convert them from inches into millemeteres. The conversion factor is 1" = 25.4 mm. For example, these are my measurements. Because of the thickness of the smaller ruler my measurements vary by 1/8" or around 3 mm.
Wheel height:
10" x 25.4 mm = 254 mm
Centerline:
254 mm / 2 = 127 mm
Backpad Height:
5.875" x 25.4 mm = 149.2 mm
or
5.75" x 25.4 mm = 146.05 mm
Offset calculation:
149.2 mm - 127 mm = ~ +22 mm
or
146.05 mm - 127mm = ~ +19 mm.
So the offsets of my front wheels are anywhere from + 22 mm to + 19 mm. You can further narrow it down by using a very thin straight edge on the backpad of the wheel. Any questions?