Towbar Loads With Bike Carriers (Strada DL3)

[dr_gn]

(also posted in caravans section).

I've got an old Civic fitted with a towbar. Handbook defines a 50kg vertical load limit.

I want to buy a towbar-mounted bike rack (Strada DL3), total weight with bikes almost exactly 50kg.

Simple questions:

1) Even though the vertical load is still 50kg, it'll be located about 400mm behind the vertical axis of the towbar, giving a significant moment (lever effect). Is the max. vertical load figure primarily due to strength limitations of the towbar-body mountings, or suspension compression? If it's the latter, surely the vertical load limit should be de-rated to compensate for the lever effect of something rigidly clamped to the ball?

2) Are tow hitches designed to take this moment loading? Obviously, the're spherical to avoid this kind of load, and provide articulation.

I can't find any information on this on the carrier specs.

Thanks.

[dr_gn]

gazza285 said:

Don't confuse static nose weight limits with carrying capacity, your bike rack will be fine.

I think it will indeed be fine, but it seems strange that in theory you could weld a scaffolding pole horizontally to to towball like a massive lever, load it on the end (fully compressing the rear suspension), yet still comply with the vertical load and towing capacity limits. All I'm saying is that the loads imparted by a fixed bike carrier are totally different from towing, so do the limits apply?

[dr_gn]

Thanks guys,

There are towing limits and vertical load limits, so I just wondered if there was a cantilever case which I'd missed somewhere. As stated, it puts bending directly into the ball stem which, due to the spherical bearing being locked, would not be the case with a trailer (ignoring frction, again as stated py a previous poster).

I'll be ordering either a DL3 or M3 tomorrow.

[dr_gn]

Watchman said:

Kawasicki said:

The only moment on a tow ball from a trailer will be due to friction on the ball itself.

I wouldn't worry about your bike rack...engineers will have considered that normal usage.

I understand why you'd think this but if you think of the rearward force a caravan exerts on the hook, it approximates the momentary downward force a bike carrier exerts.

The bike carrier is locked to the ball, so there's a constant moment applied to it (the ball itself), as well as bending loads. If you drew free-body diagrams for the bike carrier and trailer loadcases, they'd be different.