The physics of towing/carrying

[1cyl]

Evening all.

Last week I got a flange type towbar fitted to wife's 04 shiteoen C3 1.4 hdi hatchback.
So I can hook up my little bike trailer and haul the KTM to Wales when we next go to visit my father Inlaw. Without having to take the van which she cannot drive.

However. I've also got one of these https://item.mobileweb.ebay.co.uk/viewitem?itemId=150574405149 ive used on the van to ferry about small off road pits (60kg) when the kangoo is to full to squeeze it inside.
Used it twice : Great success!

Swapped it to the C3 today and proceeded to transport 83kgs of road legal cr70 pit bike. For reasons that called for it. No probs.

Thought nothing of it till I sat on the pan after, then it dawned on me I might have been pushing the laws of physics!

Searched and phoned:

Internet says 36kg max laden on tobar.
Garage Who fitted It says 48kg max laden.
Supplier of bike rack says 150kg max capacity of rack. But this is irrelevant.

Had a look underneath and everything looks fine. No sign of buckling/warping/cracking.

Debating doing it again. Would you do it again? Have you done worse?

The cars suspension was a bit low, but nowhere near bottoming out. The max laden trailer is 900kg or something. So what if all that load is at the front of the trailer (on tow hitch).
____________________
Chase my Witch up, Catch my Snitch up.
The SMC | The Pit | Stable

[G]

The 900kg will be fairly evenly distributed.

The 'nose weight' of the trailer is seperate and not many cars go as far as 83kg - a good few are rated for around 75, but I suspect yours is more likely the 36 you listed.

The issue is likely with the weight that far back lifting the front of the car up, meaning steering and braking are less effective.

[Lord Percy]

Depends mainly on three things I think:

What the towbar is made of or, more likely, how it is fitted;
How hard your suspension is;
And how you drive.

Towbar material and fitting will decide whether the thing is happy to deal with the stress of the load.
Soft suspension will help absorb the the changes in weight as you go over bumps etc.
Your driving style - eg racing over speedbumps - will greatly effect the force the towbar feels.

No idea how you can really do any checks on it though, other than to check it after each journey until you're confident it's not getting worse each time.

Edit:

Wait I'm confused. I thought you feared for breaking this new towbar or something. But after reading G's post, I have no idea if I was on about the right thing or not

[G]

I think he was and I should have elaborated that there is a separate legal issue which could see you get in to various problems ending up in court if exceeding the limits set for the vehicle.

[1cyl]

[G]

The nasty situation is something along the lines of someone pulling in front of you and you hitting them.

Police decide it's your fault because you couldn't brake/steer as well and aggressively pursue you.

Worst case and not very likely.

[1cyl]

[Nexus Icon]

Exceeding the weight limit of a trailer or rack by just 15% may incur a £200 fine. Exceed it by 30% or more and a court summons is feasible.

I don't think I'd risk it. £200 would buy a pretty decent, fit-for-purpose bike trailer.
____________________
Greetings from Shitsville!

[sabian92]

Risking sounding like a cock here, but the limits are there for a reason. It isn't just about the car, it's about if you can stop if little Johnny runs into the street. Plowing into him with a C3 with 150kg of bikes behind you probably won't end well for him. And you might decapitate your rear passengers with two bikes coming through your rear windscreen

By all means do it if you think it's alright but you are breaking the law (they might even do you for an unsafe load as well, not sure on the laws of it).

I personally wouldn't tow anything over the limit but that's just me, and I wouldn't be towing 150kg of shit when the limit is 36kg through the tow bar. I drive a C4 Picasso and I wouldn't tow anything behind it - it's a complete wank box anyway.

[DrSnoosnoo]

[Aff]

[GrantT]

You need to be careful on your max towing weights with the trailer. Just becasue the trailer is rated to 900kg doesn't mean your car is.

A quick google:

Max towing weight - braked 950 kg
Max towing weight - unbraked 570 kg

Is your bike trailer braked? If not then you're limited to 570kg which is the weight of the trailer and bike combined.

With regards to tow head weight, when the father in law used to tow a caravan with his old sierra he didn't get the concept of balancing the weight inside resulting in the dog with worms bum drag and lots of bottoming out. I recommend loading up the trailer, and putting a set of bathroom scales under the front jockey wheel. Try and get this down to 36kg by shifting the load back to keep you nice and legal

[Matt B]

[1cyl]

My trailer is a two wheel unbraked. I have no concerns with it weighing more than 570kg with ktm on. It's well balanced to the point that I can lift hitch and wheel it around by hand with bike on.

I would not dream of using carry rack and trailer at same time.

It's just the carry rack and the pit bike I'm pondering.

The pros are:
Less overall mass for c3 to haul (than a trailer with pit bike on) so better mpg.
Easier manourvering for wife.
No trailer toll charges.
When we reach a destination, and I go off on bike. The rack fits in boot so she's not stuck with trailer.

The cons:
100ish kgs of weight on tow hitch.(my biggest concern)
Lighter steering.
Breaking laws.


I'm not sure about how brakes would be affected as the car dives under braking quite severely so if anything it might just even it out.
Unless I was cornering hard, in which case It would spin like a top.

Regardless of trailer or carry rack I wouldn't be driving like a plonker.
____________________
Chase my Witch up, Catch my Snitch up.
The SMC | The Pit | Stable

[Aff]

Maybe you should conduct some braking and swerve tests, would be interesting to see.
____________________
Current Bikes:Honda 929RR Fireblade, Honda CD200 Benly (Project), Stomp Z2 140
Electric Bike Project

[Bezzer]

You've obviously talked yourself into using it no matter what but doubling the noseweight on the tow bar is foolhardy to say the least. Most decent sized saloon/estate motors that tow have a 75kg noseweight limit on a towbar still not good enough for your intended use and you want to use a smaller motor that obviously has construction/strength reasons why it's limit is so much lower, otherwise they would rate it higher, you're asking for trouble.
I tow a caravan regularly and can tell by the car's handling and braking whether something has slipped forward on the journey and increased the 80kg noseweight it should have once it's over 100ishkg let alone double.
____________________
I used to be indecisive but now I'm not quite so sure.

[1cyl]

[Bezzer]