what are you doing to compensate for the tongue weight? Have you reinforced your hitch? Perhaps you have added a leaf spring?
I have a fabricated bumper that includes a hitch and moves it a couple inches forward. I also cut down the ball mount and re-drilled it to move it a couple more inches forward. Every inch helps, how much I'm unsure. Front still starts getting unacceptably light in the low 600lb range which impacts steering but more importantly braking. An ex-cab could probably eek out a couple hundred more pounds.
I also installed longer, softer bump stops (from a mid 00s Town and Country) that engage about an inch and a half earlier but are tons softer.
Springs are stock. I don't want to suffer through a terrible ride for all the miles I'm not towing.
what is the limiting factor in a ranger that makes 400-500 pounds the maximum tongue weight capacity on any of the hitches you can buy for any of the original 1983-2012 ford rangers?
You're pushing a whole lot of things to the edge of their comfort zone around 5-600lb tongue weight and the resultant 5-6k of trailer that you get for that tongue weight is pushing a bunch of other things as well. There's no one weak link that you can address at that point in order to get a ton more capacity.
The hitch itself can likely take far more but you gotta throw more rear spring (airbags probably the best option TBH) at the vehicle to keep it from hammering the axle/frame to oblivion over every bump, that still doesn't add more weight to the front though. So you slap on a big honkin winch bumper or some other weight. The vehicle is probably pushing 4000lb now, call it 4500 for an ex-cab. You've still got brakes, engine and trans on the small side for all this. At some point the juice stops being worth the squeeze and you're better off going to a weight distributing hitch (which people with fullsize trucks also start reccomending at around the same tow weights relative to the tow vehicle. Still, even with proper equipment towing 2-3x your vehicle weight with a vehicle that wasn't specifically built to do so gracefully isn't fun or comfortable.
I would definitely say that 400-500lb is a "good safe number, but not one that leaves too much performance on the table" from the POV of the hitch manufacturer. It also correlates to ~10% of what these trucks are rated to tow. At 5k in tow you're definitely into "you must seriously consider all the details if you want it to go well" territory at that point.
I would implore anyone seeking to tow these kinds of weights with these small trucks to work their way up to it both in terms of weight and in terms of speed and setting/conditions. Don't just park a 4000lb vehicle on a car hauler without a care for positioning, drop it on the wrong height hitch ball that's too long to begin with and take off down the highway without a care in the world for speed or traffic conditions.
