The Next Gen Wheel

On Wednesday, NASCAR levied two NextGen wheel-related penalties incurred during the Daytona 500. NASCAR suspended the crew chief and two crew members (a tire changer and jackman) on the #31 and the #50 for the next four races. NASCAR did not, however, penalize Roush Fenway Keselowski or Penske, despite having confiscated wheels from both prior to the race.

Let’s break down these penalties. And, while we’re at it, the non-penalties, too.

Why Were Wheels Confiscated?

A NASCAR official observed the teams modifying the wheels. Roger Penske and Brad Keselowski each said that their teams had found inconsistencies in the drive pin holes and notified NASCAR. Neither heard anything back, so they opened up the drive pin holes to the specifications.

A photo of the NextGen wheel, highlighting the drive pin holes

What Are Drive Pin Holes?

2022 marks the first appearance of the single-lug NextGen wheel in NASCAR. But single-lug wheels pose a problem: how do you ensure that the wheel doesn’t turn relative to the lug?

The answer: drive pins.

To the right, I’ve annotated a photo Larry McReynolds posted on Twitter, highlighting the 18 drive-pin holes on the rear side of the NextGen wheel.

To understand how those holes work, we need to see the part to which the wheel mates. Thanks (again) to Larry Mac, we can.

The NextGen Wheel’s Mounting Bell Sub-Assembly

A photo of the NextGen rotor and mounting bell sub-assembly showing the drive pins to which the NextGen wheel mates.

The photo at left shows the NextGen rotor and mounting bell sub-assembly. The mounting bell bolts to the inside of the brake rotor.

The photo also shows how the wheel nut threads onto the hub to secure the wheel. But, as mentioned above, using just the wheel nut might allow the wheel to rotate with respect to the hub.

That’s why the mounting bell sub-assembly also sports six drive pins. The drive pins mate with six of the eighteen drive-pin holes in the wheel. The drive pins are tapered (the same way the five lugs on the previous car were tapered) to help position the wheel.

Successfully changing a tire requires two distinct actions: You have to slip the main hole over the lug AND mate the drive pins with one set of drive-pin holes.

Why 6 Drive Pins and 18 Drive Pin Holes?

If you only need six holes, why go to the trouble of making eighteen of them? Three reasons:

  • Wheels must be balanced, which requires cylindrical symmetry. In the first of the two pictures above, you can see a silver strip crimped on the bottom. Goodyear adds weights when needed to ensure that the tire is balanced.
  • Removing aluminum for 18 holes instead of just 6 makes the wheels lighter. The 18-inch aluminum wheels and tire weigh 48 pounds. The 15-inch steel wheels (with tire but without inner liner) weigh 57 pounds.
  • Eighteen drive pin holes gives you three sets to engage. The most a tire changer should have to rotate a wheel is ten degrees. Imagine how much harder it would be for the tire changer to seat the tire with only one set of drive holes — which he or she can’t see while positioning the tire.

What Did the Ford Teams Change?

NASCAR specifies a tolerance for each dimension of each part the same way they specify inspection measurements. For example, the front tread width is specified as 73.81″ (-0.50/+1.21), which means that the front tread width is legal if it is between 73.31″ and 75.02″. Similarly, BBS, the NextGen wheel provider, must ensure every wheel sold to a team is within the NASCAR’s tolerances.

Race teams ensure that every bit of their car is on the most advantageous side of its allowed tolerances. When it comes to wheels, larger diameter drive-pin holes make it easier to seat the wheel, and thus speeds up pit stops.

The new rules push teams to investigate every possible way of finding advantages. I guarantee you that some poor junior engineer or mechanic at Penske and RFK measured every drive pin hole in every wheel the company bought. At 12 sets of wheels per car and 18 drive pin holes per wheel, that’s 864 measurements per car, plus another 48 measurements of the main lug.

When teams were responsible for their own parts, they made or modified the parts to maximize their advantage. And the rules do say that “Holes, stud, and pin locations may be tapped and/or reamed to return them to their original nominal size.” This seems to be what Roger Penske described.

“We had contacted NASCAR a week before and said that the wheels we were getting were not all the same, and we felt we needed to modify the holes where the drive pins go. We didn’t really get any feedback, and at that point we went ahead and opened the holes up. … I just think there was so much going on and trying to get the communication back and forth — we certainly talked about it with them.”

Roger Penske

If the teams whose wheels NASCAR confiscated had enlarged the holes beyond the maximum values, there would have been penalties.

So There’s Really No Problem with NextGen Wheels?

What teams say publicly is often not the whole story, so let’s look at another aspect.

Different manufacturers make the NextGen hubs and the NextGen wheels, each to NASCAR-mandated tolerances. If you get the case where your hub’s outside diameter is as large as allowed, and the inside main lug hold is as small as allowed, you will have a harder time getting the wheel on. The same goes for the drive pin holes.

Since it’s easier to enlarge holes than shave lugs and pins, modifying the NextGen wheels is the simplest fix. No doubt, that’s what NASCAR and their suppliers will talk about when they revisit the issue. Until then, NASCAR is allowing a little more tolerance on wheel holes for Fontana.

Shouldn’t NASCAR Have Known This Was a Problem?

It’s not like the tolerances are such that the hub can be larger than the wheel’s hole. We’re talking about making it easier or harder to get a wheel on quickly. Having AutoCad-ed my share of parts, I know that something working perfectly on paper sometimes hits a snag in real life. Given the tolerances, the problem would only pop up in a small subset of lug/wheel combinations.

Isn’t This a Safety Problem?

So There Are No Problems with the Next Gen Wheel?

Well, not exactly no problems. The NextGen wheel is a different animal and requires different handling. In an ‘Overtime‘ video, Metrology Engineer Matt Faulkner suggests that this isn’t a tolerance problem: it’s a ‘feel’ problem.

As Faulkner notes, NASCAR has always had loose wheel problems. Loose wheels vibrate. So far, same as the old wheel. But the consequences are different for the NextGen wheel because the wheel is aluminum and the hub and locknut are steel. A lose NextGen wheel can bend and, Faulkner says, bond to the nut. Martin Truex, Jr.’s team had a pit stop where they couldn’t get the wheel OFF the car, as did Ryan Blaney. Pit crews will have to be more rigorous ensuring they’ve got the wheels on tight because there’s a greater penalty.

A closeup photo from the lug onto which the NextGen wheel fits.

I’m also hearing that it’s pretty easy to damage the hub threads if a tire changer just slams the nut onto the hub and cranks down. NextGen wheels require a finesse the old wheels didn’t. Increasing tolerances doesn’t solve that problem. Tire changers will have to break some long-held habits.

Should NASCAR Have Penalized the Other Teams?

Some assert that the #31 and the #50 shouldn’t have been penalized because the wheel is to blame. That’s a hard argument to support when you examine the numbers.

Pit crews changed about 567 tires during the Daytona 500. Two came off: That’s 0.35% of all wheel/tire changes. A major wheel issue would produce a Charlotte or Indy-scale catastrophe.

The #31 (Kaulig Racing/Driver Justin Haley) and the #50 (The Money Team Racing/Driver Kaz Grala) penalties refer to safety section 10.5.2.6: the “loss or separation of an improperly installed tire/wheel from the vehicle.”

The tire changer’s number one responsibility is to not let the car leave its pit box without its tires securely attached — even if that means taking a few extra seconds to ensure that the tire is securely fastened.

The penalty is predetermined. It’s severe because a loose tire can kill or injure people on track or in the stands.

3 Comments

  1. Thank you. Have a much better understanding of the situation. Have some additional questions.

    Do you have any idea how many wheels were confiscated from each team?

    Did differential expansion rates between the two materials used in the wheel assembly contribute to the issues?

    Was there any truth to the reports I heard that as a result of issues experienced, teams chose to do gas only pit stops rather than attempt additional tire changes?

    Also, were there any wheels used at Daytona that after use the wheels were damaged or worn beyond tolerances? What is their status?

    The new rules released after Daytona now allow reaming and tapping. Can you explain those processes and their differences.

    Likewise, “NASCAR made small adjustments to increase the upper tolerance on pin and pilot bores for Fontana”. So I take it that these small adjustments are allowed to be made by the teams without penalty? So will this mean that NSCSR will be making similar inspections of all wheels being used by all teams as you describe in your article

    Does these new tolerances extend to the manufacturers for products made after the technical bulletin date?

    Thanks again for your comprehensive

    • Hi David:

      Lots of questions, only some of which (unfortunately) I know reliable answers to.

      I don’t know how many wheels were confiscated. I would assume that the teams made the holes the largest they could be, so NASCAR would learn little from seizing a lot of them other than proving they had been changed — and the teams weren’t denying that.

      I don’t think differential expansion is a factor here, but I can’t say for sure because I haven’t been able to find the allowed tolerances on the wheel holes.

      I will get back to you about the pitstops. I can look to see how many each team made and how many tires they changed.

      I’ve not heard anything about wheels being damaged during the race. This is complicated by the fact that so many cars are damaged during the race. We’ll get a better idea this weekend.

      Reaming is enlarging a hole. Tapping is re-creating screw threads on the inside of a hole. If you’ve got a threaded hole that’s been gunked up, you can re-tap the hole to make sure that it’s still the right same. Reaming is just making the hole bigger. The nice thing about reaming is that there’s less change of getting a tool stuck in the hole! I do not like thinking about all the taps I broke in grad school.

      I suspect NASCAR may pull a few random wheels from different teams and check sizes. I also expect that every team at California will have reamed out their lug and drive-pin holes to the maximum allowed values!

      One NASCAR establishes a permanent upper limit for the drive-pin and lug holes, it will apply to all wheels, regardless of manufacture date.

      On the positive side, this is a relatively easy issue to fix and the teams can do it themselves. Imagine the problem they’d have if the hole were too big and the wheels couldn’t be securely fastened. It’s easier to make holes bigger than smaller!

      Thanks for the questions and I wish I had better answers for you. I will get back to you about the pit stops.

      Dr. D.

  2. Thanks for your reply. Much appreciated.

    Thank you for the explanation on reaming and tapping. I wanted to make sure that my understanding was consistent with its use in the rules. Where would tapping be used with these wheels?

    If a hole had been reamed out in excess of tolerances, I can see where the hole would be tapped to put an insert in to bring it back into tolerance (if that’s even allowable), but there are no threads in the pin holes or on the drive pins or the center hole is there? So where would tapping be used?

    Are wheels removed from vehicles that are now towed in after being high centered from flats still useable or do they continue to have enough roll to prevent damage to the rims?

    Interesting challenge. Be interesting to see the solution.

    Thanks again.

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