@MrT
There are many forces involved, but for simplicity I’ll walk through the “why” which physics/math explains readily.
These 3 formulae all apply to what impact larger rims/tires (wheel assemblies) have on various components of our drivetrain.
Torque= Length x Force (note: our stock 10R Ford Raptor transmission has nominal TQ rating of 590lb/ft)
Moment of Inertia (amount of torque required): Inertia=angular momentum/angular velocity
Rotational inertia (resistance to changing rotation)=mass x radius2
1. Increasing the length of the lever (ie the diameter), raises torque applied significantly.
2. Larger diameter tires also have more rotational inertia placed further from the hub (acceleration/deceleration). A larger diameter tire of the same/similar weight to a OEM diameter tire has more rotational inertia. This requires more work by drivetrain components.
3. Larger diameter tire increases amount of torque required by engine/transmission/drivetrain to turn the larger tires (and/or larger wheels).
4. This impacts the transmission by placing additional strain/load on the internal clutches. This increases internal heat, friction, wear from the increased load. Over time, this is not beneficial to a transmission—or any part of the drivetrain.
NOTE1: A heavier standard diameter tire does impact the suspension, but the larger diameter tire has a greater effect mathematically. This is why Jeep owners “regear” their differentials when going with a bigger rim and/or tire setup. Even after regearing, the problems aren’t fully solved—but it is a step in the correct direction.
NOTE2: Also remember that the further the weight is from the hub center—the greater the multiplication effect. This means—two wheels (and/or tires) can weigh the same, but if one wheel/tire has more weight further from the hub—the greater the forces impacting rotation, torque, etc.
NOTE3: I’m confident that Gen 3 Raptor w/37”s will take this factor into consideration using whatever proprietary approach the engineers choose to implement vs. the standard those on the Raptor running the standard 315/70R 17s.
NOTE4: OEM diameter for Gen 2 Raptor is 315/70R 17. As long as you go with the factory size, you are in safe harbor even if you are a few pounds heavier per tire (as that has far less impact than diameter). Of note—the OEM Ford forged beadlocks are heavier than the OEM Ford cast wheels—but the diameter is the same, thus minimal impact.
In closing, if your truck isn’t under warranty—no big deal. If your truck is under warranty and you don’t intend to keep it long enough for something to break—no big deal. If the transmission has an issue under warranty—I can state with 100% certainty—my OEM wouldn’t cover it at all (factory bumper to bumper, factory extended, or aftermarket warranty).
Ultimately, we are all adults and can do with our vehicles what we wish—while also accepting the consequences of our actions in an ethical manner.