I'm building a towable bandsaw mill, which is in effect a long thin trailer. The bandsaw head runs on inverted Vee rails which sit on top of the main 100x50x3 mm RHS chassis rails. So the "trailer" frame width is set by my saw head track width. This means I've got 950 mm outside dimensions for the trailer frame width. The mill is 6.5 m long (5 m rails plus a 1.5 m drawbar). The "trailer" parts including the main frame will weigh ~290 kg. The saw head will weigh 260 kg. The plan is to register the trailer for an ATM of 1000 kg, leaving 450 kg of payload (cut timber or a log). The trailer will have mechanical over-ride disc brakes. The springs are 5 leaf, 45mm, slipper springs (rated for 1000kg)

The frame width of 950mm, and a standard 50 mm gap from frame to inside of tyre, is dictating an axle length of 1340 mm or 53 inches. For comparison, a small 6x4 box trailer uses an ~ 1650 mm or 65 inch axle. So I'm 150 mm, 6 inches narrower on each side than a 6x4 box trailer.

My question is will this narrower width lead to stability issues when towing at freeway speeds? A moderate proportion of the weight; trailer main frame, cross members, timber load, etc. is low down right on top of the springs. The saw head has a 45 kg engine and heavy bandwheels that will sit about 600 mm above the trailer frame. Most of the time I'd be towing it without any timber loaded, so the weight would be ~550 kg.

Any thoughts on stability? Should I be looking at welding sister frames outside the main frames to increase the axle width?


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