Question for engineers - leverage and mass/work

[dazzler]

Howdy

One for the mechanically, physic's'ee, engineery types.

Scoping out building a single wheel pull behind motorcycle trailer for my R1200GSA for my wife and I to go touring.

In the States they have a unit called the Eaglemate;

eaglematetrailers.com

and there is this one;

Uni-Go Motorcycle Trailers (http://www.uni-go.com)

The question I have is about leverage and weight.

Using the attached drawings can anyone answer the following;

If we have say 50kgs of luggage on the bike and we transfer that luggage to the box on the trailer what is the change in weight over the rear tyre?

For ease the 50kg of luggage is exactly in the middle of the trailer.

I thought it would work out at 50% or 25kg over the rear wheel but then my electrical engineer son suggested the angle may change it but seeing as there are no wires he couldnt help much further. LOL

many thanks in advance.

dazza


PS: I am not asking anyones opinion on whether or not motorcycles should tow trailers. Kind of get a bit tired of it on the bike forums. :) :roll:

[justonething]

I'll bite. I have to go back nearly 40 years since I last worked on one of these problems.
You will get two components on your load at the point it is attached to the trailer.
The vertical component is a downward force of http://latex.codecogs.com/gif.latex?w%5Cleft%20%28%200.5%20cos%20%5E%7B2%7D%5Ctheta%20+%20sin%5E%7B2%7D%5Ctheta%20%5Cright%20%29 and a horizontal pulling force of http://latex.codecogs.com/gif.latex?0.5%20w%20cos%5Ctheta%20sin%5Ctheta, where w is the weight and http://latex.codecogs.com/gif.latex?%5Ctheta is the angle of inclination, assuming the load is situated exactly half way in the middle.
Using your info w is 50 Kg and http://latex.codecogs.com/gif.latex?%5Ctheta is 15.4 deg, the downward force is 26.7 Kg and the pull force is 6.4 Kg.
You could have persisted with your son. Any way I could wrong, It's been a very long time.

[dazzler]

I'll bite. I have to go back nearly 40 years since I last worked on one of these problems.
You will get two components on your load at the point it is attached to the trailer.
The vertical component is a downward force of http://latex.codecogs.com/gif.latex?w%5Cleft%20%28%200.5%20cos%20%5E%7B2%7D%5Ctheta%20+%20sin%5E%7B2%7D%5Ctheta%20%5Cright%20%29 and a horizontal pulling force of http://latex.codecogs.com/gif.latex?0.5%20w%20cos%5Ctheta%20sin%5Ctheta, where w is the weight and http://latex.codecogs.com/gif.latex?%5Ctheta is the angle of inclination, assuming the load is situated exactly half way in the middle.
Using your info w is 50 Kg and http://latex.codecogs.com/gif.latex?%5Ctheta is 15.4 deg, the downward force is 26.7 Kg and the pull force is 6.4 Kg.
You could have persisted with your son. Any way I could wrong, It's been a very long time.

Hey thanks heaps.

Funny timing he just sent me his working out.

Will look at both when near a computer. Thanks again! http://uploads.tapatalk-cdn.com/20161031/b6ea56c3e5f88c74a2451e1ffe3da1ad.jpg


Sent from my iPhone using Tapatalk

[justonething]

Sorry can't read the pic.
Anyway I want to add that the figures would be only when the bike is stationary on a level ground. Not sure what you want it for though! But it would not be the design load for towing.
When you are going uphill, downhill, with acceleration or deceleration, together with wind load especially coming from the side while you're turning would exert far force more than those numbers on your luggage rack.

[ian]

Howdy

One for the mechanically, physic's'ee, engineery types.

Scoping out building a single wheel pull behind motorcycle trailer for my R1200GSA for my wife and I to go touring.

The question I have is about leverage and weight.

Using the attached drawings can anyone answer the following;

If we have say 50kgs of luggage on the bike and we transfer that luggage to the box on the trailer what is the change in weight over the rear tyre?

For ease the 50kg of luggage is exactly in the middle of the trailer.

I thought it would work out at 50% or 25kg over the rear wheel but then my electrical engineer son suggested the angle may change it but seeing as there are no wires he couldnt help much further. LOLHi dazza

like justonething it's been a very long time since I've done those sorts of calculations.
In broad terms, in your diagram the load on the bike's rear tyre will be about 1/2 the weight transferred from the panniers PLUS some proportion of the trailer's weight. If the transferred weight is over the trailer's axle, then there will be less load on the bike itself.

BUT
over here I only see trailers behind Honda Goldwings, big Harley's and BMWs, and the hitch is always mounted low enough that the draw bar is horizontal, which takes out the angle you have sketched, but requires a fairly strong motorcycle frame plus a suitable tow hitch.

I also note that the Uni-go trailers you linked to have a tow bar weight of about 27kg when carrying 50kg, to which you would be adding the mass of the hitch itself.

SO, as a first approximation, transferring 50 kg from panniers to a trailer will likely only reduce the weight on the rear wheel of your bike by about 10 or 12 kg.

Then there's the usual yadda yadda about braking, GVM, etc.

[joe greiner]

The angle doesn't matter. But the proper span is from wheel-to-wheel, not the length of the trailer. Load distribution is inverse of the span ratio: at mid-span, 50% to each wheel; farther back, more to the trailer wheel; farther forward, more to the bike wheel.

"Load" includes the weight of the trailer, and location is the c.g. of the assembly - mid-point of the trailer in your example.

Your hitch should include provision against twisting/rolling of the trailer, not a simple ball hitch.

Cheers,
Joe

[dazzler]

Thanks for an interesting conversation. I think the main thing I want to make sure of is that any load from the trailer is not more than that being taken off.

When you see some of these adventure bikes loaded up you wonder how the frame takes it.



EG;

http://uploads.tapatalk-cdn.com/20161031/beaeaebbdd5d1e5721820f0bd8a9e55a.jpg

http://uploads.tapatalk-cdn.com/20161031/fb317e8b79498303fb048b45061f7bb0.jpg

Cheers.



Sent from my iPhone using Tapatalk

[Pearo]

Thanks for an interesting conversation. I think the main thing I want to make sure of is that any load from the trailer is not more than that being taken off.

When you see some of these adventure bikes loaded up you wonder how the frame takes it.


This is me for 3 months on the road and after that trip I vowed to replace the overweight top heavy top box (that was only filled with clothes and laptop) with a bag. The swag will also be ditched in favour of a lightweight hiking tent that I already own.

https://lh3.googleusercontent.com/-VkTK5ki1K_M/Vjm4N9T-9xI/AAAAAAAACCE/tDkHrd2O2Mg/s640-Ic42/20151019_103753.jpg

Mind you, that was being totally self sufficient and I only stopped in paid accommodation when I need to do washing!

EDIT: Side view:

https://lh3.googleusercontent.com/-WITePLAEUUY/Vjm4NHc8oAI/AAAAAAAACB8/C9OCtfCX_28/s640-Ic42/20151014_054743.jpg