How To Measure A Wheel

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In order to help us, HELP YOU THE CUSTOMER, get the correct wheel for your machine or application, we need to get the correct information from you about the wheel you require.   Follow these steps to accurately measure your wheel!

Step 1 - Do you have the Original Equipment Manufacturer's or the wheel manufacturer's part number for the wheel?

If you have any of those numbers, call our customer service staff to see if we may be able to cross reference the information in the database of part numbers we already have. If we don't have it in our database already, we will want to add it with the other information collected. If none of these numbers are available, proceed to step 2.

Step 2 - What is the specific tire size you are using?

The tire size will tell us the proper rim diameter and width required. The size of the tire may also help us determine the correct rim profile to use. In certain cases it won't and we will need you to help us identify the profile from the rims shown in our catalog. An extensive table is located in the back of our Agricultural catalog for locating the tire size and the proper rim size. In most cases, steps 1 and 2 will give us the information we need to make sure we are providing you with the correct wheel for your machine.

Step 3 - How many bolt holes are there?

Simply count the number of holes in the disc for the wheel studs. We also need to know if the holes are equally spaced or not. If in doubt, just measure the distance between a few of the holes to see.

Step 4 - What is the Bolt Circle size?

How you correctly measure the Bolt Circle depends on how many holes are in the disc. If the disc has an even number of holes and they are equally spaced, the following illustration shows you how to measure the dimensions easily. Use a tape measure or a straight edge and measure the holes as shown in the illustration.

When measuring the Bolt Circle, you want to measure from the top edge of the hole at one end to the top edge of the hole on the other end. You want to be as exact as possible in your measurements. Odd numbered bolt holes are the only real difficult bolt patterns to measure because they require four separate measurements and a little math.

Reference the illustration for the 5 hole pattern, measure dimension A, B, C and D. Plug those numbers into the formula A+B+C+D = Bolt Circle, and you have the correct dimension for the odd numbered bolt holes. Note: This only works when the holes are equally spaced. If the bolt holes are grouped (ie. 2 holes, a space, 2 more holes, a space, this will require that you send the wheel to one of our facilities to be measured by our technical staff to make sure we have the correct pattern information. Measure the Inside Diameter (ID) of the Pilot Hole.

Remember that for hubs with flat-based wheel nuts, the Pilot Hole should have a plus tolerance of a few tenths of a mm. The Pilot hole should both support the wheel and guide it correctly onto the hub. If the gap between the hub and the disc is too large, the disc will not center on the hub and the vehicle will rock while in motion, greatly increasing the risk of the wheel nuts coming loose.

For applications with tapered or rounded wheel nuts, the plus tolerance of the Pilot Hole can vary between one or two mm. Countersinks in the bolt holes should fit the nuts shape correctly, as the nuts are supposed to center the disc. Incorrect countersinks may cause wheel nuts to come loose.

Step 5 - Are the bolt holes chamfered or are they straight?

If the bolt holes are straight, that means you are using a “flange wheel nut” to secure the wheel to the hub. If the bolt holes have a chamfer, we need to know if it is spherical or conical. We also need to know if the chamfer is only on one side or both.  lf the holes are chamfered, you could give us the nut information and we can translate that into the correct chamfer information. lf you don't have the nut information, you will have to measure the chamfer widths and depths.   If necessary, you can send us a wheel nut to make sure we get it exact.

Step 6 - What is the wheel offset?

You will need to take a measurement for the “Back Spacing” which we will translate into the correct offset for the wheel. Reference the illustration below for measuring the back spacing. You need to take the wheel and lay it down so the machine side of the wheel is facing up. The Back Spacing dimension is the distance from the extreme back edge of the rim, not the bead seat, to the mounting pad of the disc. Lay a straight edge across the back edge of the rim and measure down to the mounting pad. Nearly all custom wheels use this measurement method to indicate the location of the mounting pad in relation to the rim. We can use this dimension to calculate the actual Inset or Outset measurement for the wheel.

Step 7 - What kind of disc is being used in the wheel?

The disc can be either a flat plate or formed disc. A formed disc is usually pushed into the center of the rim with a press and then welded in place. The disc usually has a leg width greater than the disc thickness. This leg provides greater support and disperses the load stress over a wider area of the rim center than would a flate plate disc welded in the center. Several of the possible disc profiles are pictured in the illustrations above. Discs can come in several different thicknesses and diameters for the different rim sizes that are used. You should be able to easily identify the disc type in the wheel you have from the illustrations above. Just let your customer service person know which one you require.