Bike Racks

Malcolm

I assume that all 4WD tow bar tongues are essentially the same a length of RHS (hollow square tube) which slides in to a slightly larger piece or RHS (the housing) attached to the vehicle. You slide a pin through holes that line up in both pieces of RHS to lock it in place. Now my undestanding is that you want the tongue of you towbar to sit out further than it does so that the bike rack that attaches to it will clear the spare tyre. Assuming I am correct so far, the easiest way to do this would be to drill a new hole in the RHS tongue where it slides in to the housing, so that you don' have to slide the tongue so far in to the housing as you currently do for the holes to line up so that you can slide the pin through. Assuming we are both still on the same track, there are two main stress's/forces that come in to play here, particularly when towing heavy loads.

The first is shear when you take off from standstill, this is the force that wants to pull the tounge out of the housing, but is stopped by the locking pin. As long as the locking pin is atleast 2 diameters back from the edge of the tongue RHS that slides in to the housing, this force won't cause the locking pin to tear through the tube.

The second main force is from the tow ball loading, ie where you have a trailer load that is distributed too far forward, putting excessive downward loading on you towbar. Now without knowing the exact dimensions of your tow set-up, the loads you are going to be towing and where, I can not say with 100% certainty exactly how much of the tongue needs to be in the housing. So on this one I would say, to only bring the tongue as far as required and no futher.

Malcolm

A picture is worth a thousand words, using the picture throughtfully provided below in the thread. If the hole you want to drill for the pin is 10mm (I am not sure exactly what size the pin is off the top of my head), then the closest edge of the hole you drill should be atleast 20mm from the edge of the tongue that slides in to the housing. So when marking it up to drill the hole, you should mark the centre of the hole 25mm (1/2 of 10mm + 20mm) from the end of the tongue that slides in to the housing. Also use a square edge (T-square) to make sure you get the new holes level with the existing one, so that the hole on tongue and the hole on the housing line up vertically when you slide the tongue in. Take some time and make sure you get the marking up right, you can't undrill a hole. Also when drilling it clamp it in a vice, a decent steel drill bit in a plug-in power drill (not a battery drill) should be fine, also use a bit of oil (proper cutting oil is best but even engine ore gear oil will help) on the tip of the drill bit. Safety tip; make sure you wear some form of eye protection, even if it is just some sunglasses. Finally if you are still a bit unsure take it to any engineering/machine workshop, tell them what you want and they should be able to do this for you in less than ten minutes on a drill-press, the nice ones probably wouldn't even bother charging you for it.

Regards

Snowy

well that certainly worked well!!!