Throughout the trailer, hitch, and tow vehicle industry a recommendation of 10% tongue weight for a tow-behind trailer and 15% for a 5th wheel trailer seem universal. They have even been changed to 10%-15% and 15%-25% recently.

Where did they come from? How were they determined? Was it to keep the trailer on the ball in all conditions? If so, a weight-distribution hitch dramatically increases the forces on the ball but there is no recommendation for lower tongue weights with a weight distributing hitch.

With all the GVWR, GAWR, and GCWR numbers are thrown about, the only one with a standard seems to be GCWR with the relatively recent (last 10 years) SAE J2807 standard. And that standard has been widely criticized as not accounting for basic factors such as steering ratio and wheelbase when specs talk about steering wheel angle.

So, where did the 10% recommendation come from?

  • $\begingroup$ All towing vehicles have a max allowable load that can be applied to the tow hitch, this should not be exceeded and that 10% is limited to that maximum. $\endgroup$ – Solar Mike Sep 5 '19 at 11:15
  • $\begingroup$ Yes, but I also see toy-hauler trailers with hitch to axle:axle to rear trailer bumper ratios of 2:1, To get the desired 10% would require that 3/4 of the load be behind the axle. $\endgroup$ – Sherwood Botsford Sep 5 '19 at 13:08
  • $\begingroup$ The 10% is a minimum. It is to ensure sway stability. The hitch and wheelbase geometry can demand additional restrictions. Coordinated trailer braking needs to take the weights and geometry into account as well. Really bad aerodynamics, such as on some small cheap rental trailers, can require more than 10% at highway speeds. That's why many had "Max tow speed 45 mph" plastered all over them. A related issue is how vehicle mfgs arrive at their CGWR and GVWR ratings. BOTH of these have to be within limits, and that tends to limit the trailer tongue weight to arround 10% so as not to exceed GVWR. $\endgroup$ – Phil Sweet Sep 5 '19 at 20:57

If you get the CG of the trailer too far back the combination will be unstable, with the trailer fishtailing. This fishtailing can be to the point of causing a crash.

If you put too much tongue weight on the pull vehicle it'll be too heavily loaded -- so a really light trailer pulled by a heavy truck can have a far-forward CG. Think of those hitch-mounted bicycle carriers as a super-extreme example of this.

This video: https://www.youtube.com/watch?v=4jk9H5AB4lM (and yes, I know, link rot, etc. -- search on "trailer stability video" and you'll get something).

  • $\begingroup$ There is also another example on this link. It's a bit too late at my place for a detailed answer, but this would give some easy piece of information for digesting $\endgroup$ – ComradeH Sep 5 '19 at 16:20

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