Exceeding maximum weight on towbar when using cycle rack

[TeeEmCee]

It doesn't matter how much flex there is in the rack, all the loads are still reacted through the tow bar. In fact a very flexible rack boinging up and down undamped would make matters worse, not better.

Right. Following that logic, a block of steel is better than a collapsible/flexible crumple zone, a girder is better than a spring and strut and planes would have rigid wings.

F = m*a. Less a => less F, as the mass m is accelerated less than it would if it had a more rigid connection
T = F*r. (assuming a 90 deg. application of force) Less F => less T

Less T => less torque on the bolts holding the tow bar assembly, so lower shear torque on the bolts and less deforming action on the fastening points.

So no, it's not worse.

 

[mknox]

Here is a shot of the instructions right on the hitch receiver. Some of the "limitation" may be due to the way the Bosal receiver attaches to the bar on the car. You will also note there is very little latitude on the length, rise and drop (none) allowed when towing a trailer.

I have heard of others who tow close to capacity having issues with this hitch system. Some trailer towing companies will recommend replacing the Tesla hitch with a unified hitch (non-removable tow bar). This does leave the square receiver opening showing below the bumper all the time, but is a sturdier overall solution.

 

[Peteski]

Right. Following that logic, a block of steel is better than a collapsible/flexible crumple zone, a girder is better than a spring and strut and planes would have rigid wings.

F = m*a. Less a => less F, as the mass m is accelerated less than it would if it had a more rigid connection
T = F*r. (assuming a 90 deg. application of force) Less F => less T

Less T => less torque on the bolts holding the tow bar assembly, so lower shear torque on the bolts and less deforming action on the fastening points.

So no, it's not worse.

Yeah, yeah, but this is not the same kind of application. What we have here is a flexible mass (loaded bike rack) attached rigidly to a tow hitch at a single point. So if that flexible mass is banging up and down undamped then it will increase the "a" in F = ma, not reduce it.

Try jumping up and down on a bathroom weight scale to get the idea.

Flexibility in the bike rack only increases the force/torque transmitted through the hitch because of the mass accelerating up and down as it flexes. The more flexible the bike rack is, the more it will bounce up and down. So personally I would want the bike rack to be as rigid as possible, without being excessively heavy of course.

 

[wycolo]

With that goofy X hitch just re-weld a new 2x2 receiver into the hitch crossmember, and cut holes in bumper skin too. Then you will have a nice high mounted hitch like every other tow vehicle on the road and be done with it.
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[Mtnrunner]

I realise that the maximum towbar vertical (nose) weight is only 120 lbs (54 kg) when using a cycle rack. I've just bought a very nice 4-bike rack that weighs 44 lbs (20 kg) and I've just added up the weight of our 2 adult carbon mountain bikes and 2 small lightweight kids' bikes and the grand total (including the rack itself) surprisingly comes out at 137 lbs (62 kg)...

Many thanks for any info.

Have you had any experience yet doing this? I’m in a similar situation with a 50lb Thule tray rack and two Specialized Turbo Levo eMTBs weighing ~40+lbs each putting me about 20lbs over the limit. I expect to be on smooth roads most of the time and hope to load the bikes up next wknd but would like to avoid any possible catastrophe!

I suppose one thing I can do is remove the batteries from the eMTBs and I’d be within spec but pita

 

[gustesta]

I’ve carrier a motorcycle Behind my S on a bike rack with no issues. 50lb bike rack and 220 lbs dirt bike. Keep the heaviest bike closesest to the hitch and lightest on the outboard side.

Please what rack are you using? Also can you put another bike on it besides the dirt bike? Thanks

 

[RedXowner]

This has been a very interesting thread to explain to me the difference between the trailer tongue weight (500 lbs) and the vertical load rating (120 lbs). Didn't make sense without this conversation. But as you've all stated, 120 lbs is not actually the capacity in all situations. it depends on, as you have stated, the torque from the actual application. It would be great, like flar stated, for those who find themselves exceeding the 120 lbs "rule of thumb" rating, to be able to calculate the weight and torque of the application in question and compare it to the actual capacity of the tow hitch vertical load capacity. I suspect there might be a legal liability issue with the manufacturer publishing anything other than a flat rate that requires the customer to do arithmetic.

 

[Xenoilphobe]

Please what rack are you using? Also can you put another bike on it besides the dirt bike? Thanks

Yes both fit.

and here is the one I use for my dirt bike

https://www.ebay.com/itm/380525494367

 

[gustesta]

Yes both fit.

and here is the one I use for my dirt bike

https://www.ebay.com/itm/380525494367

Thank you! I think the link is not working. Do you have the rack model name (that you use for the dirt bike)? Can you put anything else with the dirt bike?