Thread: car trailer questions?

Welcome aboard Matt.

Good choice of length for the trailer as 4 sheets of 2400 x 1200 will cover the entire floor minimal cutting and waste, or 2 sheets cut in half lengthwise will give you two 600mm wide tracks up the side with no waste at all.

I like to run a 75 X 50 rear cross rail as well as the two chassis rails. It just adds a bit of strength across the back, as there is nothing else. Also, you have to buy two 8.0M lengths of 75 X 50 to get your 4700mm chassis rails (plus 50mm rear cross & 50mm front cross = 4800mm), so the off cuts can be the front & rear rails. 75 x 50 x 3mm would be borderline for the drawbar, so I'd suggest 75 x 50 x 4 or 5mm or go up to 100 x 50 x 3mm.

I would not run it without suspension, as it put alot more stress on the chassis of the trailer (will well and truly test your welds) and the axles. 4" drop axles will get the same result height wise (around 350mm). The way aroud the drawbar height would be to stitch two 500mm pieces of 50 x 50 x 3mm on top of the end of the drawbar and then attach the coupling plate on top of this.

Something like this...



Butting the brawbar straight up to the front cross rail is a big no-no and I've seen then come apart with catastrophic results.

My only other comment would be the tyres. 215's aren't that much narrower than standard 235mm guards, so you might have to space the guards off the chassis by about 25mm to cover the tyres as you need a minimum of 40mm between the chassis and the tyres.

Another thought with going as low as you can with the suspension and axles is that the tyre diameter doesn't change. Therefore your guard height is restricted by this tyre height, and the lower you go with the chassis, the greater the distance between the floor of the trailer and the guards, making it difficult to open the doors on the car being towed (especially a lowered car).

If you want to make the trailer so its easy to load low or long cars with terrible ramp angles make it with a provision to tilt, not much tilt is needed you will still need ramps but they can be made a shorter length(easier to manhandle about)and of lesser strength(even easier again to manhandle).
Also make sure that you install a winch strap of decent length a good 3m longer than the trailer. Dont use a cable!

Sorry for taking so long to reply, i've been doing a lot of research and have still yet to start!

The main problems i am having is the running gear, im thinking 45mm square axles for a bit more strength, using commodore wheels, should you use ford bearings and will they fit? I want the trailer to be able to be towed on more than one car so i cant have the electric brake wired up. I dont have a clue who makes the best gear and am stuck on what type of brakes to use/ benefits and limitations of each.

I dont think i want to make it a tilt trailer and i would prefer the trailer to cover the length of the car.

Also what type of chassis supporting rails is the strongest? i've only seen cross rails before but am wondering if they are the best option?

Yonnee What is it that you mean by 235mm standard guards?

Cheers matt.

The outer diameter of the bearing cups for Holden & Ford are the same, it's the inner diameter of the bearing cones & the journal machined onto the axle that is larger with the Ford. So the higher rated axle with Ford bearings can still have whatever stud pattern you desire drilled into the hubs or drums.

If you have to go over-ride brakes, then Hydraulic is the better option. The adjustments can be set so that the brakes apply almost as soon as there is movement in the coupling. Mechanical cable brakes require a little slack to stop the brakes from dragging, but then once you start braking with the tow vehicle, the initial movement is taking up that slack and not actually braking the trailer.

Standard "off the shelf" mudguards are usually 9" (235mm) wide. If you mounted these guards directly to the chassis, with a 40mm gap between chassis and inside tyre, the tyres would stick out the guards by around 25-30mm. So you either have to space the guards off the chassis to cover the tyres, or make your own guards, or get them folded, to whatever width you wanted.

Originally Posted by matt9422

Also what type of chassis supporting rails is the strongest? i've only seen cross rails before but am wondering if they are the best option?

Not sure I understand what the question is...??

The mudguards wont be a problem i will make them.

The chassis being rectangle, what railing would you have inside the chassis supporting it? eg. only cross rails or a combination of having RHS lenghtwise where the wheel track will go?

I think I see now.

I will be building myself a car trailer in the future. The plan for the chassis will be 75 x 50 x 3mm for the twin side chassis rails**, and front cross rail, 100 x 50 x 3mm for the rear cross rail, and 40 x 40 x 2.5 for the rest of the cross rails. At the two front corners will be 50mm square uprights at 200mm high. Across the front between these two uprights will be 40mm sq. x 2.5 at 100mm high. Down the length of the trailer will be more 40mm sq. running from the top of the front uprights, tapering up to the top of the front of the mudguard, and from the top of the rear of the mudguard, tapering down to the rear cross rail. These tapered sections will also have uprights spaced at even intervals.

**What I mean by twin side rails is an outside rail the length of the trailer, as well as an additional rail the length of the trailer at around 450mm in. In between these two outside rails, the 40mm sq. cross rails will be about 300mm apart, but between the two inner chassis rails, the cross rails will be around a metre apart.


Clear as mud??

Rather than stopping/starting across the mudguards, could you make the upper side rails continuous (with a peak at the middle) turning it into a truss, thus increasing the strength of the lower side rail? Or do you get this anyway despite the guard being inserted in the middle?

The catch 22 is that you want a car trailer to be as low as possible... easier to load, shorter ramps, etc., but the lower the chassis, the higher the top of the wheels and therefore the guards in relation to the floor. If you then load on a lowered car, or in some cases even a standard height car, you then have trouble opening the doors. This is why I don't even like running clearance lights on the top of the guards.

I have done one before where I cut a square slot in either end of the guard, slid a piece of 25mm sq RHS up the inside edge of the guard and joined this to the taper section at either end. But if you ever damage a guard, it's quite a job to replace it.
I've done another where I met the two tapered sections with a piece level with the top of the guards and then attached the guards to the outside of it to space the guards out from the chassis a little.