How To Measure A Trailer Wheel Bolt Pattern

What is the bolt pattern on your trailer wheels?  For the most part it does not matter because we rarely change trailer wheels, yet when it does matter, it really matters.  If you need replacement wheels, or a spare that fits, here is the info to measure and calculate just what that trailer wheel bolt pattern is.

There are a bunch of different hole combinations for connecting the wheels on cars, trucks and trailers.  The set of holes for the fasteners attaching the wheel to the hub is the “Bolt Pattern”.  While it is not usually a concern, it is important when buying new wheels.  If the pattern is wrong, then of course, the wheel won’t fit.

As another detail, if you ever wonder about load capacity of an axle, the bolt pattern can give a clue.  It is not exact, and it is not a rating by itself, but in combination with other information, it can help identify the axle capacity.

Terms For A Trailer Wheel Bolt Pattern

Before we dive into the trailer wheel bolt patterns, we need to define some of the terms so our discussion is not confusing.  Here are some important terms and phrases to know, along with an image to reference.

• Bolts, Studs, Lug Nuts, and Lugs – These are the fasteners that hold the wheel to the axle hub.  Some hubs have threaded studs that stick out for the wheel to slide over.  Some have threaded holes that bolts go into.  In casual language, people often use “lug” for the studs, nuts, or wheel holes.  (We use “lug” interchangeably with those in this article.)
• Bolt Pattern – The set of holes, or more exactly, the combination of holes and locations for the bolts attaching the wheel to the axle hub.  For example, 5 on 4.5″ means 5 lugs on a 4.5″ bolt circle diameter.
• BCD, or Bolt Circle Diameter – The diameter of an imaginary circle that passes through the center of each bolt hole.  Some call this PCD, or Pitch Circle Diameter.  For trailer wheels, BCD is a dimension required to define the bolt pattern.
• Bolt Size – The size of the fasteners (bolts or studs) that pass through the bolt holes in the trailer wheel.  The holes will be a little larger than the actual bolt diameter.
• Hub Diameter – The diameter of the portion of the axle hub that must pass through the center hole of the wheel.  It is usually measured at the point where the wheel fits in operation.
• Center Hole Diameter – Size of the large hole in the center of the wheel.  This is also called the hub bore or pilot hole, and it must be large enough to fit over the axle hub diameter.  In some wheel and hub combinations, it also helps locate the wheel.
• Distance Between Bolts – (distance between adjacent bolts) – The center-to-center distance from one bolt to the next bolt beside it.  We use this adjacent bolt spacing to calculate the bolt circle diameter when direct measurement is difficult.

While there are a lot more terms to describe a wheel, we covered many of them in our Wheels and Tires article.   That is a good one to read as well for more information.  However, in this article we will focus on the bolt pattern.

Common Trailer Wheel Bolt Patterns

A very common way to refer to the various bolt patterns is “the number of bolts” on a “bolt circle diameter”.  Something like 5 on 4.5″ – meaning 5 bolts on a 4.5″ diameter circle (bolt circle).  It is a short-hand reference, but it does the job in communication.

The different patterns generally fit different sizes and capacities of trailers.  Lighter applications have fewer studs and a smaller bolt circle because the hubs, bearings, wheels, and loads are smaller.  Heavy-duty applications need larger bearings, therefore larger hubs, for higher load capacity, so the bolt circle diameter is larger.  For strength and load distribution, the number of bolts also increases.

Here are some common trailer wheel bolt patterns.  This chart is not every possibility, but it does include the most common patterns.

Trailer Wheel Bolt Pattern Chart

* NOTE:  The capacity ranges in the list are typical axle ratings where we often see a trailer wheel bolt pattern appear, NOT a rating for the bolt pattern itself.  Always verify the axle, hub, stud size, center hole diameter, and wheel rating before choosing wheels.

What Do Trailer Wheel Bolt Patterns Look Like?

Use the bolt pattern names in the table above when shopping for wheels.  It helps to know the terms.  Here are some visual examples.

In general, heavier trailer hubs use larger bearings, more bolts, and a larger center hole.  That is why the center hole often gets larger as the bolt count and bolt circle get larger.  However, the bolt pattern does not guarantee the center hole diameter, so always measure to be sure.

Though it is not part of the name, for most bolt patterns, the size of the bolts (aka “studs”) is also important.  Many common trailer wheel studs are 1/2″-20 threads, but heavier axles often use larger studs like 9/16″-18 or 5/8″-18.  Always check the stud size before ordering wheels or lug nuts.

Here is another article with more info about trailer wheel lug nuts and lug bolts.

How To Measure A Trailer Wheel Bolt Pattern

How do we measure a bolt pattern?  Start by counting the number of bolts, then find the bolt circle diameter, or BCD.  The bolt pattern is the number of lugs combined with the BCD, like 5 on 4.5″ or 6 on 5.5″.

Measuring the BCD for wheels with an even number of lugs – like 4, 6, or 8 – is often easiest with a direct measurement.  Measure straight across the wheel from the center of one stud or hole to the center of the opposite stud or hole.  That is the bolt circle diameter.

That seems easy enough, but what if the wheel is mounted and the hub is in the way?  Or, what if the trailer wheel has 5 lugs where there is no opposite stud?

For odd-numbered bolt patterns, or when the hub is in the way, we can get the BCD by measuring any 2 adjacent bolts.  Measure the distance, center-to-center, from one stud to the next one beside it.  With the adjacent lug spacing, we can calculate the bolt circle diameter.  Here is the equation.  DBB is the measured distance, center-to-center between adjacent bolts.  (Hole to hole works too.)

Since measurements are not always perfect, simply do the calculation and round a little to find the bolt pattern that makes the most sense.  For instance, a 5 bolt pattern is not likely to be 5 on 4.467″, but we know that a common trailer wheel bolt pattern is 5 on 4.5″, so we round a little, then have the answer.

If you don’t want to calculate, use this wheel lug spacing table.  Here are a few of the common patterns and the theoretical perfect distance between the bolts.

What About Ford Or Chevy 5 Lug Bolt Pattern?

Some people talk about wheels by vehicle brand names like “5 lug Chevy bolt pattern” or a “5 lug Ford bolt pattern,” but trailer wheel fitment is not that convenient.  Every automotive brand has several wheel sizes, so to identify the right wheel, we must measure the actual bolt pattern.

Some automotive 5-lug patterns overlap with trailer patterns, but many do not.

To play this up, going old-school (because I began in that era), the wheel size we called the “Ford 5-bolt wheel” is the small Ford pattern, which is 5 on 4.5″.  The wheel size we called the “Chevy 5-bolt wheel” is the small GM pattern, which is 5 on 4.75″.  That was simple, but often misleading, because Ford and Chevy both used more than one 5-lug bolt pattern.

If you hear that old nomenclature, now you know what it probably means.  Now, you also know that it is not the best way to reference a trailer wheel bolt pattern.

Bolt Pattern Is Only One Wheel Specification

Getting the trailer wheel bolt pattern right is important, but it is only one part of wheel fitment.  A wheel can have the correct bolt pattern and still be wrong for the trailer.

To get the full picture, we must also include Wheel Diameter, Rim Width, Offset, Wheel Load Rating, Center Hole Diameter, Stud Size, and Lug Seat Style.  We cover a lot more about trailer wheels in Trailer Wheels and Tires.  That article also talks about matching tires with wheels for the trailer.

So, use the trailer wheel bolt pattern to identify the correct lug layout, then verify the rest of the wheel specifications so they will fit your trailer, and your loads.

More Trailer Wheel And Tire Information

For odd bolt patterns – like 5 bolts – for trailer wheel sizes, there is a cheat method that mostly works.  As an engineer, I like the direct methods above, but this measuring trick is worth knowing.  It is not exact, but it gets close – well, for these specific circumstances.

We have a few more articles on the subject of Axles, Wheels, and Tires.  First, the Trailer Axles 101 article is a great overview of axles in general.

Next, the article reference above for Trailer Wheels and Tires – which is about combining wheel and tire specifications.  (They have to work together.)  Add the above information for the trailer wheel bolt pattern to the specs for your wheels and you will have the full set.

Finally, we also have an article about when it is time to replace trailer tires.

Thank you for joining us for the read.  Have a Wonderful Day.