As many of you know, I’ve been involved with aftermarket wheels and hardcore fitment problems for most of my career. This has exposed me to a lifetime of diagnosing drivability complaints and fitment issues that most people rarely, if ever, experience.
Still, there’s always that one time when something unique and out of the ordinary happens. That can make for a miserable day, or worse, a miserable year.
Starting this month, the subject matter of my Performance column will move toward issues that you have already faced or probably will at some point, especially when installing aftermarket wheels and non-OE tires.
This first of two parts on installation will cover items of which you may not be aware. Many of these topics are derived from onsite training courses that I have provided for more than a decade.
Primary Considerations
First, when you are selling and installing aftermarket wheels, always consider the following components:
• Bolt pattern
• Lug-hole/lug-nut seat style
• How far lug bolts extend past the mounting pad
• Length of stud
• Offset (backside setting)
• Caliper clearance (x-factor)
• Overall width
• Centerbore
• Center cap clearance and fit
• Valve-stem clearance
• Valve-stem angle for TPMS
• Drop-center position
• Obstructions on the vehicle
Knowing about how each of these can play a vital role in installing aftermarket wheels will make your shop more profitable and lessen the possibility for a problem to arise.
Matching the bolt pattern of the wheel to the vehicle seems obvious, but there are several SAE/metric bolt patterns that are very close. That means you might substitute them without even knowing it.
There are three sets of bolt patterns that are very close: 5×4.5/5x115mm, 5×4.75/5x120mm and 6×4.5/6x115mm. Some wheel manufacturers don’t spend the money to drill a 5×115 bolt pattern, which is common on GM mid-sized cars since 1988 and not much else. Instead, they will stock heavily with 5×4.5 bolt pattern wheels (the most common) and offer them as a ‘fit’ for the 5×115. If you work the math, 4.5 inches = 114.3 mm.
Now, 0.7 mm doesn’t seem like a lot of distance, and in most cases, you can get away with it without any problems. However, the two most obvious questions in your mind right now should be: “What is my liability?” and “Will the customer complain of vibration?”
Years ago, I was called to help diagnose a problem with a late-1980s Cadillac that had broken two studs on the same hub within a few weeks. One stud breaking doesn’t usually cause me much alarm, but two on the same hub got me thinking. It turned out that the wheels were 5×4.5.
What happened? Well, when the first lug nut was tightened (probably with an impact gun) it drew the wheel off center, and by the time the last two lug nuts were hammered on, they were forcing the two opposite studs to give slightly, so that the lug nut seated into the wheel. I surmised that the studs were developing stress fractures, which led to failure.
Another example is the Cadillac SRX. When this new platform arrived a couple of years ago, it brought with it another new bolt pattern: 6×115. Many people were quick to offer a 6×4.5, which was drilled for the Dodge Dakota/Durango for nearly a decade. I spoke to a wheel importer who was drilling blanks regarding this matter, and the naÏve salesman told me that the 6×4.5 would “fit” the vehicle. While biting my tongue, I gently explained that a local dealer had mistakenly drilled a 6×4.5 for this vehicle, causing it to shake profusely.
Watch Lug Seats
The lug-hole seat style of most wheels is a 60-degree conical or acorn style. The other styles are ball-seat lug bolts (stud and lug built into one piece), which are common on European vehicles; mag shank, used on vintage-style wheels; tuner (socket) and spline drive lugs used on a wide array of wheels with smaller lug holes.
Conical-seat lugs are fairly straightforward, but ball-seat lug bolts require much more attention. Case in point: A Mercedes-Benz comes with a lug bolt that could be any of five lengths, from the bottom of the ball seat to the tip of the bolt (see Diagram 1).
The bolt pattern for M-B is common in many VW and Audi vehicles, as well. Installing this wheel requires measuring the length of the threads that extend pass the mounting pad on the OE wheel and matching this length up with a aftermarket lug bolt to provide the same length and thread engagement. The lug holes in the aftermarket wheel may be drilled to a different depth, or the wheel may simply have a mounting pad with a different thickness than the OE wheel.
As you can see from the diagram, using the OE lug bolts in the aftermarket wheel would not be safe. Conversely, if the depth of the lug hole in the aftermarket wheel is deeper than that of the OE, then using the OE lug bolt would cause the lug bolt to protrude further into the rotor. This can cause the lug bolt to interfere with the internal brake assembly and cause damage. This typically occurs on the rear with the parking brake assembly.
Related to this subject is the length of the lug stud on the vehicle. Some vehicles have longer studs on the rear than on the front. Based on what we just learned regarding the depth of lug holes, it is possible that a standard-length, closed-end lug nut could ‘bottom out’ before applying the proper amount of torque to the wheel.
The best way to determine if the lugs are bottoming out is to paint the inside of the lug nut cap with a felt marker and secure the wheel to the vehicle. Then, remove the lug nut and inspect the cap for scoring. Long studs were a big problem when tuner lugs came out because the installation key had to fit inside the lug nut. Long studs, like those on the rear of a Mustang, would drive the key out and prevent proper torque from being applied. The spline drive lugs corrected this, but you may still have to order duplex length in some cases.
Offset Headaches
The next critical dimension is the offset. Small variances such as ±3 to 5 mm aren’t going to affect anything in most cases, but when the variance is ± 8 to 10 mm or more, you may be asking for trouble. A good case is the Dodge Magnum/Charger and Chrysler 300C siblings. These cars have a 5×115 mm bolt pattern coupled with a medium offset. To attain the medium offset, most wheel manufacturers thicken the mounting pad. The fun part is when someone tries to sell you a 5×115 bolt pattern, which is correct, but the offset is more positive, like the wheels that fit the GM cars that we mentioned earlier.
Again, some wheel companies try to limit their inventory costs and fit both of these vehicles at the same time. Large-diameter wheels in 20 to 22 inches will fit both in most cases, but there are very few 17- and 18-inch wheels that are still built with a medium offset. This means that the high offset wheels built for the GM cars may not have a thick enough mounting pad or caliper clearance for the Dodge/Chrysler cars and will hit the calipers. Diagram 2 illustrates this point.
Next month, we’ll discuss how a problem that went unchecked for nearly a year was finally solved.
