It all comes down the chassis.
For instance my class C with a E-450 chassis weighs about 12,500 loaded. My GCVW (gross combined vehicle weight) is 22,000lbs. So if I subtract the RV weight from the GCVW I could tow 9,500lbs. Now I have a limit on the hitch of 8,000lbs so my max towing is 8,000lbs.
Now same scenario but if I had a E-350 chassis instead of a E-450. RV weight of 12,500. GVCW of a E-350 chassis (new one) is 18,500. So if I take 18,500 and minus the RV weight of 12,500 that leaves me with a 6,000lb difference so even if I had a 8,000lb hitch I can only tow 6,000lbs.
Now the other thing with the hitches is the tongue weight. Rule of thumb is 10% of the weight of a trailer is suppose to be on the tongue pushing down on the RV hitch. I know mine can tow 8,000lbs but the tongue weight is only 500lbs. I tow 7,000lbs of boat so I had to adjust my boat trailer from about 800lbs on the hitch to 450lbs. What this causes is the trailer will not trailer as well and is more liable to swing around more. That said I do it anyway. Even in a high cross wind my boat doesn't swing around at all. I notice it a bit behind my F250 but not the RV and I thought it would have been the other way around.
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