Often, someone will suggest that a vehicle’s published tow rating should be 80% of the published towing capacity to provide a safe towing capacity margin. Apparently, some are teaching this rule at various RV safety seminars too.
Is the 80% rule enough? Is it too much? Will this simple formula keep someone within the manufacturer’s weight safety ratings?
Unfortunately, this simple rule does not consider every family’s size and additional cargo that may be carried (or attached equipment) in the tow vehicle. The weight of a tow-ready vehicle directly affects the realistic vehicle towing capacity (RVTC).
Let’s look at two scenarios to show how this simple rule will not keep a tow vehicle from exceeding the weight safety ratings. This example shows the same vehicle with two different families.
2017 Ford F250, Crew Cab, 4X2, Diesel, LWB
Published 5th Wheel Towing=16,800
5th Wheel/Gooseneck Hitch Combo Weight=250
Two persons weighing 335 pounds
Additional cargo=100 pounds
Four persons weighing 565 pounds
Additional cargo=150 pounds
Using the simple rule of reducing the published tow rating by 20%, the alleged safe towing capacity margin is 13,440 pounds (16,800 X .8 = 13,440).
Now, let’s consider the family size and the gross vehicle weight (GVW). To accomplish this, the app found at RVtowCheck.com was used to develop the RVTC for a 5th wheel trailer having a 20% pin weight.
Family A: The RVTC is 11,055 pounds. (Difference: 2,385 pounds—80% margin not nearly enough)
Family B: The RVTC is 9,655 pounds. (Difference: 3,785 pounds—80% margin not nearly enough)
As you see above, the 80% rule fails badly. Even if the pin weight were calculated at 17% for family A and 15% for family B, the rule would have failed. These simple rules that have been freely tossed around do not always work. In fact, this rule could put a family at risk. It is possible that rules like this are part of the reason that 60% of all tow vehicles exceed their published weight safety ratings.
If a 2017 Ford F350 Crew Cab, 4X2, SRW, Diesel, SWB was used, the alleged 80% safe towing capacity margin is 16,800 pounds (21,000 X .8 = 16,800), then the RVTC would be as follows:
Family A: The RVTC is 17,910 pounds. (Difference: 1,110 pounds—80% margin too much)
Family B: The RVTC is 16,510 pounds. (Difference: 290 pounds—Pretty close to 80% margin)
Another RVer provided this version of an 80% rule. They suggested "80% of the GCWR". Sorry, this version will fail too because there is no difference in the results between the two rules.
Friends, anytime someone suggest simple rules like these, don't just walk away, RUN! If a simple rule is not correct 100% of the time, it is worthless and may place you in a situation you may regret.
Rather than sharing the unreliable and potentially unsafe 80% rule, you could recommend them to use RV Tow Check to obtain a true realistic vehicle towing capacity (RVTC).