Fitment Guide
How to Measure a Wheel
Seven quick checks tell you exactly which wheel and lug nuts fit your trailer. Step through them at your own pace, then match your numbers to the specs on any wheel listing.
- You'll Need
- Tape measure
- Straightedge
- Caliper
- Thread pitch gauge (optional)
Step 1 of 7Diameter
Side view, cut away
Step 1 of 7
Measure the Diameter
Diameter is the first number in a wheel size, like the 10 in a 10 x 6 wheel. It's the size your tire is built for, so it has to match the tire exactly.
How to Measure
- Check the tire first. The last number in the tire size is the wheel diameter it needs: a 4.80-12 tire fits a 12 in. wheel, and an ST175/80R13 fits a 13 in. wheel.
- To measure the wheel itself, take the tire off and lay a tape measure across the face of the wheel, straight through the center.
- Read from the bead seat on one side to the bead seat on the other. The bead seats are the flat ledges just inside each flange where the tire beads sit.
- Round to the nearest whole inch. Most trailer wheels come in whole sizes such as 8, 10, 12, 13, 14, 15 and 16 in.
Why It Matters
A tire only seals and seats on the diameter it was made for. A wheel that's even half an inch off won't hold the beads, so this number has to match exactly.
Get It Right: Skip the outer lip. Measuring lip to lip reads an inch or more bigger than the wheel's true size.
Step 2 of 7
Measure the Width
Width is the second number in a wheel size, like the 6 in a 10 x 6. It decides which tire widths the wheel can safely carry.
How to Measure
- With the tire off, stand the wheel on its edge.
- Measure across the inside of the rim, from the inner face of one flange to the inner face of the other, right at the bead seats. That's the wheel's stated width.
- Now measure across the outside edges of both flanges. That's the overall width, usually about 1 in. more. Write both numbers down.
Why It Matters
Every tire lists a range of approved rim widths. On a rim that's too narrow or too wide, the sidewalls flex the wrong way, which wears the tire faster and makes the trailer handle worse under load.
Get It Right: Keep the overall width handy. You'll use it in step 6 to work out the offset.
Step 3 of 7
Find the Bolt Pattern
The bolt pattern is the number of lug holes plus the size of the circle they sit on, written like 5 on 4.5. It has to match your hub exactly.
How to Measure
- Count the lug holes.
- Pick any hole. Skip the hole next to it and find either of the two holes across the wheel.
- Measure from the center of your first hole to the outside edge of that far hole. No hole sits straight across on a 5 lug wheel, and this reading gives you the bolt circle.
- Write it as holes on circle: 5 holes on a 4.5 in. circle is 5 on 4.5.
- Count the lug holes.
- Pick any hole and find the one directly across from it.
- Measure from the center of the first hole to the center of the opposite hole. That's the bolt circle.
- Write it as holes on circle: 4 holes on a 4 in. circle is 4 on 4. 6 and 8 lug wheels measure the same way.
Why It Matters
A wheel with the wrong bolt pattern can't center on the hub or seat its lug nuts. Close isn't good enough: 5 on 4.5 and 5 on 4.75 look almost the same and don't swap.
Get It Right: A caliper gives the cleanest reading. You can measure the studs on your hub the same way to double check.
Step 4 of 7
Measure the Center Bore
The center bore is the large hole in the middle of the wheel. Our wheel listings call it the center hole.
How to Measure
- Measure straight across the center hole, edge to edge through the middle.
- On the trailer, measure across the center of the hub that the wheel slides over, where the grease cap sits.
- The wheel's bore should be the same size as that hub measurement or a little larger.
Why It Matters
If the bore is smaller than the hub, the wheel can't sit flat against it, and the lug nuts can't clamp it the way they should.
Get It Right: A slightly larger bore is normal on trailer wheels. The cone-shaped lug nuts center the wheel on the studs.
Step 5 of 7
Measure the Backspacing
Backspacing is the distance from the mounting surface to the back edge of the wheel. It sets how far the wheel reaches in toward the springs and frame.
How to Measure
- Lay the wheel face down on a flat floor or bench.
- Set a straightedge across the back flange so it spans the whole wheel.
- Measure straight down from the straightedge to the mounting surface, the flat face around the lug holes that bolts against the hub.
- Take the reading at two or three spots around the wheel and use the average if they differ a little.
Why It Matters
Too much backspacing pulls the tire in toward the springs or frame. Too little pushes it out toward the fender. Matching your old wheel keeps the tire right where it was.
Get It Right: Our wheel listings show this as backspacing or backside spacing. Both mean the same thing.
Step 6 of 7
Work Out the Offset
Offset is the distance from the wheel's centerline to the mounting surface. It's another way to describe where the wheel sits, and some listings give it instead of backspacing.
Try three example wheels
Backspacing − (overall width ÷ 2)
3.5 − (7 ÷ 2) = 0 in.
The mounting surface sits right on the centerline. That's the setup on our Premium Service trailer wheels.
4.5 − (7 ÷ 2) = +1 in.
The mounting surface sits toward the face of the wheel, about +25 mm.
2.5 − (7 ÷ 2) = −1 in.
The mounting surface sits toward the back of the wheel, about −25 mm.
How to Work It Out
- Take the overall width from step 2 and divide it by 2. That puts you at the centerline.
- Subtract that number from the backspacing you measured in step 5.
- A plus result is positive offset, zero means the mounting surface sits right on the centerline, and a minus result is negative offset.
Why It Matters
Two wheels with the same size and bolt pattern can still sit in different spots. Matching the offset or backspacing keeps your track width and clearances the same.
Get It Right: Some listings give offset in millimeters. Multiply inches by 25.4 to compare.
Step 7 of 7
Match the Lug Nuts
Your lug nuts have to fit the studs on your hub and match the seats in your wheel. Check three things: thread size, seat type and hex size.
How to Measure
- Thread diameter. Measure across the threads of a stud with a caliper, from peak to peak. 1/2 in. is common on trailers.
- Thread pitch. Count the threads in 1 in. of stud, or use a thread pitch gauge. A 1/2 in. stud with 20 threads per inch is written 1/2-20. Metric studs give the gap between threads in millimeters, like M12 x 1.5.
- Seat type. Look at the end of the nut that touches the wheel. Most steel trailer wheels take a 60° cone seat, and some heavier wheels use 90°. Ball (radius), flat and mag seats are shaped differently and don't swap with a cone.
- Hex size. This is the wrench or socket size across the flats of the nut, like 3/4 in. or 13/16 in.
Why It Matters
The seat is what holds the wheel tight against the hub. A nut with the wrong thread or the wrong seat can work loose even when it's torqued.
Get It Right: Torque the nuts to your axle maker's spec in a crisscross pattern, then check them again after the first 10, 25 and 50 miles.
All 7 Steps Done
Your Wheel in One Line
Put your numbers together and any wheel listing reads at a glance. Here's how the example wheel reads.
10 x 6, 5 on 4.5
Diameter x width, then lug holes on bolt circle
- Diameter
- 10 in.
- Width
- 6 in. (7 in. overall)
- Bolt Pattern
- 5 on 4.5
- Center Bore
- 2.82 in.
- Backspacing
- 3.5 in.
- Offset
- 0 in.
- Lug Nuts
- 1/2-20, 60° cone, 13/16 in. hex
Example readings from a Premium Service 10 x 6, 5 on 4.5 trailer wheel on a hub with 1/2-20 studs. Your numbers may differ.
Match Your Numbers
Our wheel listings show the size, bolt pattern, center hole, backspacing and offset, and our lug nut listings show the thread, seat and hex size, so you can check the fit before you order.