Thread: Help with draw Bar opinions

pics of progress

Looks good!

Is that a weld across the front of the original drawbar?

Yeh it is yonnee ( was done by supposed professional).... The jury is still out on whether or not im worried about the drawbar weld.... Ive seen quite a few old very used trailers with welds across the front and been like that for 20years +

i have read on here that some people dont like it..... Ive seen pics on the net of draw bars snapping from underneath but none from the top .... You would need too much weight at the back of the trailer lifting the car up to snap the top of the drawbar wouldnt you? That doesnt really happen with a tandem trailer

loaded car on trailer last weekend

what is acceptable bowing of the drawbar when loaded? (car weighs about 1400kg) it looked like i was getting some bow when i put a flat bar underneath....

with the flat bar placed underneath the draw bar starting about 1meter out from end of deck.....and going back to the leaf mount .... it was sitting about 2-3mm off the drawbar at the leaf mount

as for the deck....i might have to start another thread....HUGE! and i meen HUGE bow in the deck...almost looks like its meant to be a beaver tail lol.....simply not strong enough for my car.....im thinking i may have to sell and look for something with 100x50 side rails or something

I noticed in the pics above in post #32, that the two rails that run from the front of the trailer, up along the guards, and down to the rear in the first set of pictures are now missing. These will have greatly helped with the rigidity of the main deck of the trailer.

they were removed for 2 reasons.....1. the car would not fit between them 2. they were very poorly made and were basically useless because of the poor design

i tried to replace some strength by stitch welding 75x5 flat bar the whole length of the outer chassis rail as you can see in the above picture

im sure this has helped.....but the bow is crazy!....when the car is on the back end sags easily 35mm

obviously cutting out the inner rail and replacing with 75x50 would be awesome and the end of my problems...but thats a HHHUUGGGEEEE job and id sooner sell it to someone with a lighter racecar

i might be able to get away with building a trus through the top of the wheel arch with some 50x50 rhs....

Originally Posted by loveit

loaded car on trailer last weekend

what is acceptable bowing of the drawbar when loaded? (car weighs about 1400kg) it looked like i was getting some bow when i put a flat bar underneath....

with the flat bar placed underneath the draw bar starting about 1meter out from end of deck.....and going back to the leaf mount .... it was sitting about 2-3mm off the drawbar at the leaf mount.

The bow in the drawbar may be partly due to bending of the side rails. However, the drawbar might be stiffer if there were more welding along the join between the 75x50 and the 50x50 sections. From my rough estimates I would have at least a 3 mm fillet weld for about half the length, both sides. That is 100 mm weld and then 100 mm gap, and so on. The critical section is between the leaf mount and the front of the deck.

Vehicles impose loads only at 4 points, and usually higher at the front with a front engine. Side trusses properly designed would greatly strengthen the side rails.

Styx

Hi styx

Yeh adding some more weld easy enough....at the moment it is zig zagged in a way that there is no more then a gap of 20cms between welds on a zig zag

i assumed a bit of a bow would have been acceptable .... Not sure i anyone else has measured thier car trailer for bow when loaded??

Im confident the drawbar is a chunky piece of gear at 125x50 ... As we all were

the deck is extremely pronouced though ..

for me im prepared for 3 options
1. 50x50 truss well designed through wheel arch ( if tyres have room which i dont think they do)
2. Two 75x50 rhs rails welded straight underneath to the cross rails from one end of the deck to the other
3. Sell to someone with a lighter setup .... Im confident it would be an awesome setup for a smaller 4cylinder car..... Not my 1400kg monaro


any advice would be much appreciated..... I have a track day this weekend and i have to rent a dam trailer when i own one at home

I'd go the truss, but then again, I just like their efficiency

As the chord will be in tension, it doesn't need to be a huge section - I'd expect 30x30x2 or even 25x25 would do the job fine. What does need to be solid is the connection each end and the spacers midway, and they have to be sitting above supported points - ie. above a hangar.

I think to work well the truss needs to be designed very well it cant just be slapped on and i have a bulletproof trailer .... Like u say the uprights would need to be in important positions ..and id like to go overkill on the truss in order for this to be the last time i have to touch my welder on this thing ...

I should add that i measured the trailer without the car and it does have a pre existing bow of about 30-35mm which increases to about 60mm when loaded

Originally Posted by loveit

.....
I should add that i measured the trailer without the car and it does have a pre existing bow of about 30-35mm which increases to about 60mm when loaded

Maybe the pre-existing bow in the deck/side rails was due to previous overloading.

You haven't given many dimensions of the trailer, so I have guessed some in the attached drawing.

Truss height should be as high as convenient, the higher the better.

Styx

are you guys confident that this truss system will be the end of my trailer worries....and give me a good 10 years service or something.....or is it really just a band aid that will come back to haunt me in a year?

hi styx....a million thankyous for the pic....i have some questions about it

you can see a pic i came up with last night below...so on this occasion you are recommending to not bow one single piece of rhs over the top like on a draw bar?
but rather use straight then weld 2 diagonals at each end?

as for the size of the truss....im afraid i cant fit in the 50x25 rhs (looks like it will hit tyre) ....would 30x30 be ok...and use this everywhere

i was interested in your diagonals ...why were they shaped like that...and not how i have them below (how i normally see them placed)

PS i was measuring the bow of it this morning....its flat untill the first leaf hanger ....or end of draw bar....then bends perfectly from there to the end....which i thought was interesting....i thought the bend would be after the rear leaf mount....or from axle back

also a recent photo of it


deck1.jpgphoto.JPG

The truss you drew is optimised to support a load on top of it, like a roof.

In the case of your trailer, the truss is kind of "lifting" each end and transferring the load to above the axles, so it's designed a bit differently. Probably the best way to think of it it to imagine Styx's design with the horizontal and angled elements made with string (as they're only ever in tension) and the vertical elements solid as they're in compression.

i did some model testing in my spare time today

styxes design worked really well....but i made some changes while working at the model and noticed some positive effects

one thing i noticed is when i had the outer poles in too far it was less effective then when i had them right out closer to the sides

also i noticed the pull on the tops of the uprights in the outwards directions as shown by arrows

what do you think of this design....where the top of the uprights are trying to pull the diagonals rather then push it