This is mid-November. The last Supercars round for 2023 is in Adelaide. Formula One will be in Las Vegas. The TCR and Trans-Am2 seasons have already drawn to a close. The NASCAR seasons have also already drawn to a close. Collectively the off-season as far as motorsport fans are concerned, is when you look back into the archives, mining the past for dreams which never existed. Or maybe mining the past for things which you didn't see the first time because the interconnectedness of all things via those series of pipes we call the internets, wasn't a thing.
As was my wont, I decided to look back through the 1992 NASCAR Season. This was the one where Allan Kulwicki won the championship by 10 points, at the very end of the season, at the last race of the season, and due to tactics which only developed in the context of that last race of the season; where he'd worked out while inside the car, that if he closed out the number of laps led to 109, then it wouldn't matter if Bill Elliot won the race or not. There are lots of things that could be said about that particular season but they thing that I want to explain for the benefit of a select few readers (you know who who are) is to do with the alleged fragility of the rear toe-links on the NASCAR Gen-7 Cup cars. The reason why I watched 1992 in particular, is that there are sufficiently enough complete races that people put on videotape and now on YouTube, that a good enough comparison can be made.
What I found was that there are no appreciable differences in the amount of rear toe-link failures between the current 2023 Gen-7 Cup cars and then then 1992 Gen-4 Cup cars.
Shock! Horror! Lock all the doors. Batten down the hatches. Sell your kids for cheese and your mothers-in-law to the circus. Rub my nose in the dirt and call me "stinky".
No, really. 1992 was not particularly all that much different in terms of the number of rear toe-link failures and the cars that retired from races as a result of those rear toe-link failures. Actually, when you bother to think about this for more than 15 seconds, that should be the case. The case are not markedly different. They still are 3300 pound rectangles moving about a mile-and-a-half of concrete at 190mph. The function is identical. The form is very very close. The componentry in this area has not changed. Of course this begs the question...
What's a toe-link?
The toe-links, pull or push the tops of the wheel-hub mounts, relative to dead vertical camber. Camber is the amount that tyres lean inwards (negative) or outwards (positive) relative to dead vertical. On normal road cars, camber is likely to be either dead reckoned to vertical or very slightly negative. This has to do with setting up the geometry of the car to chase better handling, or better wear on the tyres since they are the only point of contact on the road. Tyres that engage the road better make for better road holding.
You can get a better idea of what the toe-link does, by looking at one out in the wild. These photos are looking at the rear suspension setup of a VE Commodore:
We should expect that if the banking is different at different tracks, and eve different at different places on those tracks, then relative to the face of the tyre meeting the road, that the banking will be different can the camber should be different on the two-sides of the car. NASCAR is mostly not a technology battle, nor specifically an equipment battle but a specific engineering battle to see who can come up with the best suite of geometry settings in terms of camber, stagger, rear wedge adjustment and tyre pressure. To a far far far lesser extent, the toe-in/toe-out of the front tyres and how much bite that the steering can take out of a corner.
Granted that some minor adjustments can be made in terms of numbers of turns on a worm gear to pull or push the tops of the wheel-hub mounts, relative to dead vertical camber, but it isn't particularly all that much. Mostly that is baked in before a session; based upon the physical length of the toe-link.
Very obviously, when you have a side impact which is going to bend a piece of steel, it is not going to unbend in a hurry. Steel tends to be strong in compression but not all that strong in tension. Having a 3300 pound car strike flush against a concrete wall (also bearing in mind that kinetic energy has a velocity squared component in the equation), will compress directly through the centre of a toe-link but if the micro forces are not perfectly balanced (which we can assume that they never are), then the point of failure and bending will happen where some part of that toe-link is in tension. All of this is a fancy way of saying that an random force, bends metal.
The thing is that I do not think that there is a sensible way to stop the issue. You could simply attach the hub with hinges to the top and bottom of the A-Arms in the suspension, and then have the rear axles pass through a hole and have universal joints at the bearings; but the adjustability of the suspension is gone. I note that Supercars use an even cruder system by having a solid dead rear axle and suspension setup, with a crown-wheel acting as a single spool drive. This is almost certainly not an option on a NASCAR Cup car, given that they regularly go on banked tracks.
The real answer would be to stop hitting the walls as much and change the culture such that drivers act far less pugilistic with 3300 pound machines. I would even go so far as to ban pushing as a tactic because that creates all kinds of longitudinal forces through the yaw axis which nobody and guess much less control.
Specifically with regards toe-link failures, well they have not markedly changed. I suspect that the reason they appear to be so common has to do with perception. People think that toe-link failures are more likely to happen; so tend to notice them more when they do happen because they are primed to notice toe-link failures when they do happen. I am sure that this is similar to the phenomenon of why you notice more cars on the road that look like yours, or why I am on the lookout for shopping trolleys in the wild.
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