Overthinking Vibration Math (or how I learned to stop worrying and buy tires?)

I've got an old pickup. It has some vibes I find particularly annoying/offputting at freeway speed. It's not massive, just annoying and makes the truck feel... crappy and lame. Moreso than it is.

I finally got an app on my phone to pretty solidly give me a frequency of said vibes, and I was bummed to find that it was probably pretty close to 2x wheel speed.

So my next thought, given that that's not fast enough for driveshaft, is that it's probably something about either a tire or tires, or wheel or wheels, which is misshapen in some way which results in two cycles per rotation. Oval or egg-shaped, or bent across the center so its running onto the outer edge on one side and inner edge 180 degrees later (no tread wear to suggest this, however).

The other thought I have is that while it's conceivable that it's a chunk of rubber, spring, or other aspect of the truck that just happens to resonate in the ~21-23Hz range at IIRC ~58-65mph even if the exciter isn't right at that frequency (245/75-16 giving 661 revs/mile and conveniently ~11Hz at 60mph), the wheels/tires are still the likeliest culprits, and at a certain point you've got to stop trying to diagnose a 27-year-old truck's peculiarities with a calculator.

Anyhow, I've picked up a set of non-mismatched wheels off a later E-series and am basically waiting for a good spot in my schedule to buy some tires that aren't 9-year-old Sailuns.

Just curious about what random thoughts people have about at what point they feel like they've pondered sufficiently before throwing money at tires or whatever direction this sort of diagnosis takes folks.

Find a place that does "Roadforce" balancing, or its equivalent?  Get them to tell you what is wrong instead of buying stuff?

I've fixed that exact issue with a rebalance. I recall my weights were off diagonally on one tire.

When I had them rebalanced about four years ago, finding a Roadforce balancer was probably the right option (I just defaulted to my then-favorite tire shop; it didn't affect the vibration).

With nine year old tires and mismatched wheels that can't be rotated front to rear, I don't see spending any more time or money on these tires making sense. But I didn't get to all of that in the summary.

To answer the hanging question, I found a better and Motorsport-oriented tire shop; I didn't abandon the old one out of a terrible experience or anything.

I average a few hundred miles a year in this truck, most of it around town, to answer the other obvious question of "how did you live with it/yourself so long!?" Tracking down this thing's loose ends is a fourth-tier hobby.