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Moving cars around is rarely fun, and usually a pain, so anything to make that less of a pain is good, especially if doing it often.

I've been seriously thinking about this for about 4 years, so I figure it's time to start making a shopping list.

First up, which type? Hydraulic or air bagged or some sort of manual winch/ratchet system.

Air has the following advantages:

1. Off the shelf parts easily available
2. Spring and lowering device are one unit
3. Compressed air available for non-suspension things

So it'll probably end up being air-bagged.

The following list is what I (probably) still have available to me, and included so you know what not to suggest:

• MIG welder
• MIG wire
• Grinders
• Disks for grinders
• Good condition 6-stud steel wheels
• Maybe some axle parts?
• Plenty of wire
• Plenty of cable ties

And this is what I think I need to get to achieve this:

• Braked trailer coupling 100-400nzd
• Box section steel for chassis - no idea?
• Other assorted steel for suspension - ditto.
• Alloy or steel tread-plate for deck - ditto.
• Fasteners if using alloy for deck - ditto.
• Bottle of argoshield or similar welding gas - not sure if buying. ~90nzd + ~20nzd/month rent on big one.
• Air compressor of some sort - could be anywhere from 20 to 500 nzd depending on patience and reliability etc.
• 4 air bags ~1000nzd total
• 4 shocks ~200 to 400nzd
• 4 commercial tyres 200 - 1000nzd
• Some sort of control mechanism - who knows?
• Air valving, independent pressure control and/or self leveling - no idea.
• Lights as required by relevant laws - no idea?
• Maybe more suitable wire + trailer plug(s)
• Removable skid plates, thin - cheap.
• Brake line material and fittings - no idea.
• Galvanising service - no idea.

What's likely not needed:

• Jockey wheel at front (unless legally required?)
• Air tank - use the frame 17+ - 57+ litres depending upon construction
• Winch - trailer will sit so flat it'll be straight forward to roll into on flat ground. However, thinking more, ground isn't always flat... certainly not compulsory anyway. Good excuse to keep cars running ;-)

Dimensions and features:

• Deck width 2000mm
• Deck length 4000-5000mm 5000 will hold a maximal b2000 ute without overhang, 4300 holds an FC RX7, 4000 holds most stuff with a bit of overhang, etc.
• Box height 50mm, and width 50, 75, 100, or 150mm
• Wall 3mm, enough? 4mm and 5mm also available, but much heavier. This is calculable if someone wants to help.
• Multiple tie ins to main two rails from front A section
• Tapered initial 500 - 1000mm down to 15 - 25mm thickness for built in ramp functionality. Dual rails in this thinner section
• Removable/installable sides, front, back
• Some sort of wheel locking/jamming mechanism, eg movable/lockable wedges

A similar design is here: http://www.facebook.com/AirbaggedTrailers

Comments welcome, will update this post from time to time.

Fred.

Using 3mm steel checker plate = 205.2kg alone for 4m long, and 256.5kg for 5m, that's too much IMO.

((3mm x 7.85kg/mm) + 2.1kg) * 5m * 2m = mass

Could go hybrid and use plywood on the top and steel for the entry (to get low enough).

Alloy would be about 1/3 the weight for the same thickness plate, but might require a bit of extra reinforcement underneath.

EDIT: Next post moved here to make way for a budget post.

http://www.trademe.co.nz/business-farmi ... 739048.htm

* 4 = 600nzd

Dimensions best @ 4880mm deck length or a fraction less.

Maybe a hair less width in the deck too, then could use the offcuts as guards without tigging together.

2mm too, so lighter, but would for sure need some reinforcement.

Or double the price to 1200nzd for 4mm.

Costings/budget:

Tools/supplies:

• 717+gst = 824.55 5m^2 MIG gas bottle inc. fill
• 45 - Thicker MIG wire

Cost range checked:

• 600-1200 - Alloy deck plate
• 550-1000 - SS-7 air bags
• 10-100 - Rivets for deck
• 135-270 - Shock absorbers (2 or 4)
• 100-400 - Braked coupling

Unknown costs:

• Box section steel for chassis/draw bar
• Other assorted steel for suspension
• Air compressor of some sort
• Wheel/tyre package (5)
• Hubs/brakes
• Some sort of control mechanism
• Air valving, independent pressure control and/or self leveling
• Lights as required by relevant laws
• Maybe more suitable wire + trailer plug(s)
• Removable skid plates, thin
• Brake line material and fittings
• Galvanising service
• Electric winch

A quick poke around shows that the air bags will be getting imported from the US in pairs @ 50 - 100usd each. I'll need to actually design the arms and think about travel and bumps and slamming it and so forth to know what size, how much load carrying, how much travel, etc.

Common ones are:

1. SS-5 and bigger friends from Slam Specialists - well regarded and inexpensive
2. D2500 Dominator and bigger friends from Air Lift - poorly regarded
3. Firestones - not well regarded, just like the tyres...
4. Contitechs - expensive

Some info here: http://www.slamspecialties.com/compare.html

A couple of threads on a truck forum had a lot of agreement that the Air Lift ones balloon, not good for a trailer... So probably SS-6 or SS-7 or something like that, then. Ref: http://www.streetsource.com/Forums/9/To ... 97/?z=&P=1

Edit, interesting tech data here: http://tesairsprings.com.au/fileadmin/f ... -20_CI.pdf

Fred.

Spent some time drawing up the frame design last night. It needs to have certain characteristics:

• The entire thing should be light, not too light, just heavy enough to not be too weak, just strong enough to survive 500kg steady state, or 1000kg under impact going over a bump, for each corner
• Outer main fore-aft rails must be strong enough to withstand all twisting loads fully loaded with side mounted suspension
• There must be strong cross beams that tie into the inside of the outer rails keeping them from twisting, there should be one of these close to each suspension point
• The draw bar A frame at the front should come directly, and uninterruptedly, back to the front one of these two main cross members and tie into the main side rails too
• The floor needs to be well supported where ever the wheels go, and reasonably everywhere else, which varies, see further down for a list of wheel bases and widths
• Carried car doors should clear fully raised trailer wheels/guards; typical range of 1200-1400 from front of car with longer cars putting doors closer to the front, shorter more central.

So, because I think 4.8m or 4.88m is a good length, the obvious thing to do is put two cross beams at the 1/4 and 3/4 marks, IE, 2.4m apart. It turns out that this is almost good:

Wheelbases:

• 2036 mm Mini normal car body
• 2400 mm standard VW beetle
• 2400 mm AE86
• 2426 mm FD RX7
• 2431 mm FC RX7
• 2615 mm R32 skyline
• 2665 mm R34 skyline
• 2720 mm R33 skyline
• 2720 mm Stagea
• 2761 mm SWB to...
• 3000 mm LWB B2000 series truck like mine (unsure of wheelbase of mine is 3000mm)

The difference from smallest to largest, excluding the mini which weighs nothing, and the LWB ute, which is an exception is only 361mm. With this difference divided by two we've got 180mm of range for centres at each axle. I estimate the fore-aft tyre contact patch size to be in the 100mm to 200mm range, so if we centre the cross rails at 2400 + 90 + 90 = 2580 we should properly support almost everything during towing. But not while loading...

Widths, assuming tyres to outer edge of vehicle:

• 1397 mm Mini
• 1539 mm VW beetle, standard
• 1630 mm AE86
• 1689 mm FC RX7
• 1695 mm R32 skyline
• 1704 mm B2000
• 1720 mm R33 skyline
• 1725 mm R34 skyline
• 1750 mm FD RX7
• 1755 mm Stagea

So again, we've got a range of about 350mm with the tyres extending significantly in lower than that in most cases. So perhaps 300 difference from min outer to max outer, and on the inner:

1200 to 1400 or something like this.

So the longitudinal reinforcements should begin 150 inside the edge, at the earliest, and end 450mm from the edge, at latest.

If we place 50x25mm wide channel from 200 to 250 and from 350 - 400 then a narrow tyre that is worst case of 100mm situated exactly between them will be well supported by sheer loads. Any other tyre/track will be over at least one and likely both of the rails.

Use of 100mm wide channel in the centre would make for 250mm gaps if we insert one more on each side equidistantly for GP support.

Putting two strips can stop where the front most axle is likely to stop, ie, 1500mm from the centre, or where ever is convenient past that.

If I figure out how to use QCAD again, I'll draw it all up.

Fred.

Current plan after lots of thinking and sketching is this: 4600mm x 2000mm deck with LOA @ 6300mm

This maintains strong tie-ins to the sides at appropriate points, while keeping the draw bar short, the wheels centred on the deck, and a suitable shallow ramp for driving into.

I've come up with a good air bag arm design that will allow car doors to be fully opened with the trailer jacked right up, too. This is superior to another design I've been taking some inspiration from.

The deck will have full box sections in the following places:

• dead centre
• 1000mm each side of centre
• 1500mm each side of centre
• double height across the front over the draw bars to tie the front of the frame together and provide up/down strength

Combined with fore-aft steel supports at ~200mm spacing, 50mm wide, this gives these benefits:

• Any wheel/tyre will be close to 2 or over 1 or 2 supports, regardless of track width
• Either side of the centre will be well enough supported for rolling on during load.
• Between 1000mm and 1500mm will be twice as stiff (half the span) for appropriate towing deck strength, and could be reinforced if required.
• Behind the rear 1500 offset cross members will be an 800mm ramp consisting of lighter deck support material
• In front of the forward 1500 offset cross members will be 800mm of flat deck with lighter deck support material
• Vehicles with wheel bases in the range 2000 to 3000mm will all be properly supported while towing.
• Vehicles with an outer tread width of 1600 will be very well supported, and 1700 to 1300 will be well supported.

Some trailers that I know of have the following specs:

• 3540 x 1710 - single axle, braked, borderline too narrow for my use, lots of overhang for my use (Cam's)
• 4000 x 1900 - tandem, braked, tipping, big enough, heavy steel sides, heavy ply deck, heavy general construction (Chris')
• 4100 x 1900 - random trailer on internet that I mostly like the look of.
• 3900 x 1880 - hire trailer I used to move the ute before, pictured below
• 4080 x 2000 - for sale recently, single axle, tilt, no flat deck
• 5000 x 2060 - for sale recently, single axle, tilt, full steel flat deck, heavy, huge, bad.
• 4350 x 2040 - for sale recently, tandem, tilt, 2/3 steel flat deck, heavyish.
• 4600 x 2040 - http://www.trademe.co.nz/motors/trailer ... 695505.htm + http://stuff.fredcooke.com/trademe.tilt.trailer/ HEAVY, but I like it in other ways

If my suspension plans work out well, I could go as narrow as 1800 without drama. This would reduce the length of the draw bar, improve turning, and save weight.

If it's 2000 wide, the tyres will be necessarily narrow to not exceed 2.5m overall max width:

"The maximum width for a light simple trailer (including its load) is 2.5 metres (excluding side marker lights and direction indicators and the bulge towards the bottom of the tyre). An additional 25mm is allowed on each side of the vehicle for ropes, lashings, straps, chains, connectors and tensioning devices that are neither permanently nor rigidly fixed to the vehicle; or J-hooks (to secure stock crates or bins)."

Dropping to 1800 would give ample room for tyres/wheels, 1900 would be comfortable too, but 250mm allowed by a 2000 deck is OK regardless.

Tyre diameter should probably be closer to 650mm than 700mm to reduce required range for maximum jack to clear the deck enough for door opening AND still be able to lay flat or close to it.

Fred.

Pictured below, nearly forgot:





Clearly no one is reading ;-)

Fred.

Just called an old friend in the states who has some experience with bagging various things and the universal consensus seems to be that SS-X airbags are the ONLY way to roll for this task. He uses firestones on his setup, and has had them in there for a decade with no issues, but recommends the Slam Specialties units for this heavy duty task.

Now, given my requirements and cunning design, I pretty much need a bag that will push 1000kg under normal circumstances.

The SS-7 units hold 2262 lb @ max stroke of 9.3 inches with a base height of 2.7 inches. Wait, let me fix that...
The SS-7 units hold 1026 kg @ max stroke of 236.32 mm with a base height of 68.58 mm. Ahh, that's better! :-)

The SS-6 unit only holds 712 kg @ max stroke, so isn't suitable for my design.

The SS-7 unit is 177.8 mm in diameter which is plenty small enough. The SS-8 unit is 203.2mm in diameter (still plenty small enough) and only offers an extra ~250kg of load and 25mm of extra stroke.

Price goes up with size, unsurprisingly.

Bed time, Fred.

Childish and naughty idea:

Fit my HUGE air horn to the thing, and run a relay feed from the tow vehicle to it, such that if the tow vehicle honks, it honks with passion :-)

I never had an air supply suitable for that before.

Fred.

I can see it now: Fred getting pissed, driving down the road, leaning on the airhorn. Then suddenly the trailer starts dragging because the compressor couldn't keep up with the horn and he lost pressure to the airbags