Maths / Bike Carrier / Extension / Load?
Discussion
Jim1064 said:
A 10 kg weight 10cm behind the tow ball remains a 10 kg weight one metre behind it, it doesn't become 100 kg 
This is NOT a fulcrum as suggested above
This. 10kg is 10kg.This is NOT a fulcrum as suggested above
The distance will generate a moment at the interface between the tow bar and car, so it'll need to be able to react both the 10kg downward force and bending moment.
As an aside, apologies if I'm misreading this but I suspect the 100kg limit isn't a vertical limit but horizontal?
EmailAddress said:
I think you two are saying the same thing as earlier in the thread but in a more direct manner?
I don't believe anyone is suggesting that the actual weight changes as such. But that the total 'force' ('moment', bending) ((I don't know the correct word)) will put more stress on the extension the further from point A it is extended.
Like, I don't think an orange at the end of a ruler weighs more. But it will 'make a more heavy weighty forcy-worcy down thing than if it was balanced near where you are holding it!
That's right no?
Plus flex of extension must exentuate that stress.
They usually recommend not using extensions with RVs (campervans) because the hitch/towball is already extended to reach out past the overhang.
I just don't know the right words to use to say that concept properly.
I'm most definitely not saying the same thing as earlier in the thread. Someone said 1kg ends up being 6kg or something. That's not the same thing as a bending moment. I'm not being an arse BTW.I don't believe anyone is suggesting that the actual weight changes as such. But that the total 'force' ('moment', bending) ((I don't know the correct word)) will put more stress on the extension the further from point A it is extended.
Like, I don't think an orange at the end of a ruler weighs more. But it will 'make a more heavy weighty forcy-worcy down thing than if it was balanced near where you are holding it!
That's right no?
Plus flex of extension must exentuate that stress.
They usually recommend not using extensions with RVs (campervans) because the hitch/towball is already extended to reach out past the overhang.
I just don't know the right words to use to say that concept properly.
It's probably an idea to upload a sketch so I get it right. But you're correct in saying that the distance will generate a bending moment and the stresses are different. The equation for a moment, M = F x L, where F = the mass x g (Newtons) and L = length/distance (metres).
Whether your hitch cat take it is another matter but it should be able to take some element of bending. I'm assuming the 100kg limit is a horizontal load i.e. pulling a trailer or similar. Driving around will definitely put some vertical load on the hitch but you'd have to check how much.
10kg over a 50cm distance will generate a bending moment of ~50Nm.
Don't tow hitch bike racks do a similar thing?
Edited by Zero Fuchs on Sunday 6th August 23:10
Ah ok.
It may sound pedantic but there is no 'effective weight' just varying amounts of bending moment. Ultimately the less the better.
But I think I know what you're trying to work out
If your tow bar is 10cm long and can take a vertical load of 100kg, it'll generate a bending moment of 100 9.81 x 0.1 = 98.1Nm.
If your bikes are 10kg then the maximum length is: 98.1/(10 x 9.81) = 1m. Any further out and the moment will exceed the 100kg rating.
It's late so someone should double check but think that's right.
It may sound pedantic but there is no 'effective weight' just varying amounts of bending moment. Ultimately the less the better.
But I think I know what you're trying to work out
If your tow bar is 10cm long and can take a vertical load of 100kg, it'll generate a bending moment of 100 9.81 x 0.1 = 98.1Nm.
If your bikes are 10kg then the maximum length is: 98.1/(10 x 9.81) = 1m. Any further out and the moment will exceed the 100kg rating.
It's late so someone should double check but think that's right.
Edited by Zero Fuchs on Sunday 6th August 23:09
EmailAddress said:
Now drive at 60mph down a meandering elevation and camber of potholed British A-road.
How does the end get whapped about with that 10kg on the end now. Versus bringing it back inboard to be above the toeball
As I've mentioned before about bike racks... it doesn't matter too much anyway, because it won't be my problem when the resonant frequency hits. It will be the person behinds problem
That would be a slightly different problem How does the end get whapped about with that 10kg on the end now. Versus bringing it back inboard to be above the toeball
As I've mentioned before about bike racks... it doesn't matter too much anyway, because it won't be my problem when the resonant frequency hits. It will be the person behinds problem
You'd be pretty foolish to drive around like that so assumed anyone with that type of setup would extend the rack purely for loading and offloading. Anyone with any sense would fold it as close to the car as possible during transit.
Regarding resonant frequencies, I doubt it would be a factor when driving around
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