Going beyond the weight capacity of a Tow Bar Bike Rack

[Buggbairn]

What's everyone's thought on slightly breaching the load capacity on a tow bar bike rack?

I have a Thule Easyfold XT3 carrier which has a load capacity of 60Kg

Our 3 Emtbs have a combined weight of approx 65Kg

Give we cannot lose any weight due to internal batteries would we be pushing things too far beyond the capacity?
Their must be some kind of undocumented tolerance that would be in place to cope with downward forces such as dips in roads.

 

[Growmac]

You might also want to check the load limit on your towbar. It's often only 60-80 kg or so, and the rack is 23 kg, so you may be well far over the limit for the bar before you start taking into account the rack limits.

 

[Buggbairn]

You might also want to check the load limit on your towbar. It's often only 60-80 kg or so, and the rack is 23 kg, so you may be well far over the limit for the bar before you start taking into account the rack limits.

I believe the "s-value" is 80kg. Therefore I'd be slightly over on that side too.

 

[lindbeckb]

I would think you can get the weight down by putting the batteries in the boot but if you say it is internal non removable that that’s out the window.


Safety margins are normally 2:1 or 3:1 Thule is a reputable brand and it would be reasonable to assume going less than 10% over the weight limit, functionally you can get away with it. How the insurance man will see it though, is you knowingly over loaded the carrier and proceeded to make an unsafe journey, therefore voiding any claim and (regardless of fault) putting your wallet on the line should the other party pursue damages.

Worst case scenario but should your bike fall off I doubt you would have any recourse to get it repaired or the car that ran over it repaired via insurance.

 

[steve_sordy]

In the event of any claim at all, the insurer may seize on the overload as evidence that the car was not being driven in a safe condition. There may be more at stake than just your bike.

I'm sure that if Thule thought they could justify a safe working load of 65 kg instead of the 60kg they are claiming, then they would for sure!

I carry just the one bike on my Thule, although it is designed for two, max 60kg. When I hit a speed bump or drive over something, the whole thing doesn't half move about! Although some of that may be bike suspension, still looks alarming.

 

[Pdoz]

I believe the "s-value" is 80kg. Therefore I'd be slightly over on that side too.

I'm not sure how it's measured in your country, but the down force is amplified if you have the weight at the end of a long lever ( like a horizontal thule rack) - so, eg, if you pack 60+ kg of bikes onto that rack, the down force on the hitch could easily be twice that if the rack extends beyond where the towball originally was.

We have a rack designed to cope with 5x 25 kg bikes, so only about 100 kg total when fully loaded, but because it extends back from the vehicle it has more effect on the handling than, eg, my boat trailer with a 250 kg ball load. ( 2tonne total )

 

[RustyIron]

Safety margins are normally 2:1 or 3:1 Thule is a reputable brand

Safety factors vary depending upon the accepted standards for that particular device... and it's all found in the books. If there are any mechanical engineers among us, they could probably tell use the number off the top of their head. Just don't ask the engineers that designed the 2022 Giant Reign.

My knowledge is limited to only a couple things that I care about. Climbing gear is rated for the maximum load that the part can withstand. For instance, if a nut is rated at 6 kN, you can assume that it will break at 6.1kN. Climbing gear ratings are no joke. Ratings for cast iron flywheels use a safety factor of 10. If I recall correctly, the force on the rotating wheel increases as the square of the speed. You you can expect the flywheel to explode at the (rated speed)(10^(-2)).

I'm sure that the accepted safety of a bike rack falls somewhere in between those two extremes. Since Thule is a legit brand, I expect that the rack would hold up as the manufacturer claims, unlike those no-name products that come from that country that makes cheap junk. If it was me and there were no other options, I'd probably put the bikes on the rack and drive gently. Don't load it up and then go flying down a washboard road. Keep a close eye to make sure that rack don't crack. Materials fatigue and break over time. More load and more time equals a greater probability of breaking.

 

[Mcharza]

What's everyone's thought on slightly breaching the load capacity on a tow bar bike rack?

I have a Thule Easyfold XT3 carrier which has a load capacity of 60Kg

Our 3 Emtbs have a combined weight of approx 65Kg

Give we cannot lose any weight due to internal batteries would we be pushing things too far beyond the capacity?
Their must be some kind of undocumented tolerance that would be in place to cope with downward forces such as dips in roads.

I have the same bike rack. On one trip, we had three electric bikes with a total weight of about 75 kg. It worked well, but it was noticed that the rack was moving downwards during the trip. However, 3000 km was driven and everything went well. We lifted back horizontally a couple of times. Note that the SUV was also driven in real terrain.

 

[steve_sordy]

The clamping force on the towbar ball is a user variable. So........

Why not back off the clamping force a bit, then if you hit a big hole in the road, the clamp will slip on the ball and nothing will break.

Provided you get the clamping force correct of course, otherwise you will be dragging the rack along the road; you will notice that!

 

[Gary]

Why are you even asking?
I personally couldn't care less if you damage your precious bikes or your car but that's not the point is it? By risking it you're putting other innocent road users safety at risk.

If your car's towbar has a high enough load rating buy an appropriately rated carrier for the load.
Or get a van

 

[Daev]

Passengers on the rack, bikes in the car, everytime

 

[Daev]

Batteries can't be removed?
Could probaly read the whole thread to find out but far too lazy.

Yup, no

 

[Buggbairn]

I've decided not to risk 3 Brand new Ebikes, one will go in the boot and 2 on the rack

 

[Akiwi]

All the bikes I transport have removable batteries, so I am close to, or below the limit. Just for safety, I add a strap from my roof rack rails to help support things. In the worst case of a breakage it would mean we drag the rack behind us minimising the risk of other parties being involved.