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View Full Version : Building myself a trailer, help with some info first!



JB#3
1st Oct 2008, 12:07 AM
OK guys, Im about to start building myself a trailer for my Kart racing, since my last one is getting pretty old and tired, and its very hard to find something second hand that has what you want it to!

Iv read alot of different threads on here and have found a few various answers to some questions, but am still a bit confused, so though if it was OK, id put all my Qs in this thread and gather as much info as possible.

The frame layout i was thinking would be something similar to this: (sorry for the crappy paintshop drawing)
http://i34.photobucket.com/albums/d113/JB3JB3/framelayout.jpg

Now, what size RHS would you recommend for the various parts above? red being the drawbar and rear chassis rail, ect ect... i really dont no how much the trailer will weigh, as it will depend on what size steel i use, however to give you a general idea, it will be a fully enclosed trailer, with a frame made of something lighter (i was thinking 20x20mm) about 1.7mtrs high with a few shelves ect inside and then fully cladded.
It wont ever have to carry much loaded weight, the Kart (80), tools (50) spares (50) and fuel and misc, should only come to around 200kg, but say 250kg being generous

Next thing, how do i work out where to put the axle / springs? and what rate springs would i look at getting? and while we are on axles, is there anywhere online i can look at purchasing this stuff, or where would you recommend?
Is there any special way of working out what size and length axle to get?

and lastly, how long would you recommend the drawbar extends out the front of the trailer section?


Thanks heaps and sorry for all the questions, I have a fair bit of welding experience and love a mechanical / engineering challenge but just dont have a ton of knowledge when it come to the trailer specific stuff.

Thanks again.

Yonnee
1st Oct 2008, 12:11 PM
OK guys, Im about to start building myself a trailer for my Kart racing, since my last one is getting pretty old and tired, and its very hard to find something second hand that has what you want it to!

Iv read alot of different threads on here and have found a few various answers to some questions, but am still a bit confused, so though if it was OK, id put all my Qs in this thread and gather as much info as possible.

The frame layout i was thinking would be something similar to this: (sorry for the crappy paintshop drawing)
http://i34.photobucket.com/albums/d113/JB3JB3/framelayout.jpg

Now, what size RHS would you recommend for the various parts above?
Red - 75 x 50mm x 3mm...
Green & Blue - 40mm SHS x 2.5mm...
Top framework - 25mm SHS x 2.5mm...
red being the drawbar and rear chassis rail, ect ect... i really dont no how much the trailer will weigh, as it will depend on what size steel i use, however to give you a general idea, it will be a fully enclosed trailer, with a frame made of something lighter (i was thinking 20x20mm) about 1.7mtrs high with a few shelves ect inside and then fully cladded.
It wont ever have to carry much loaded weight, the Kart (80), tools (50) spares (50) and fuel and misc, should only come to around 200kg, but say 250kg being generous

Next thing, how do i work out where to put the axle / springs?
Set up your chassis first, WITHOUT drawbar,
Axle centre should be 1/2" backward of centre for every foot of body.
So, from your drawing and measurement, your axle centre should be 1730mm from the front cross bar.

and what rate springs would i look at getting?
Something around 700kg capacity.
I'll have a look at my books when I get home and tell you how many leaf springs...

and while we are on axles, is there anywhere online i can look at purchasing this stuff, or where would you recommend?
I see you're in Melbourne...
Melbourne Trailer & Caravan Supplies
Ashley Park Drive, Chelsea Heights.
9772 2333.

Is there any special way of working out what size and length axle to get?
Yes. But I need to know what wheels and tyres you're planning on running.

and lastly, how long would you recommend the drawbar extends out the front of the trailer section?
Minimum 4'.
But 4'6" to 5' is better. The longer the point between axle centre and towball, the easier the trailer is to reverse.


Thanks heaps and sorry for all the questions, I have a fair bit of welding experience and love a mechanical / engineering challenge but just dont have a ton of knowledge when it come to the trailer specific stuff.

Thanks again.

That's where I come in:2tsup:

Are you building it for one or two karts?
For the amount of effort to add a second tier for another kart would be well worth the future re-sale value of the trailer.

Are you planning on a tapered section at the front for less wind drag? If so, make this part of the chassis, not just tacked on top of the drawbar.

Calm
1st Oct 2008, 12:42 PM
Being a former Gokart racer (champion*) i am not sure about your sizes. i suggest you lay the karts etc out on the floor as you want them in the trailer and measure around them. Remember that the gokart wheels maybe set wider at times. If it is a shelf trailer (2 karts high) allow extra between them (about 50 to 75mm). Also dont leave the karts sitting on their wheels in the trailer as the small movement (rocking) backwards and forwards wears out the rings and the bore.

Any construction above the floor can be lighter as there is no weight much.

Another thought remember access from the front

i dont think i have any photos of my trailer but it used 2 modified rear subframes from a mini for suspession, It was on 10 inch wheels, tandem, load sharing suspension, very light and great to tow.

Cheers hope that helps.


* legend in my own lunchbox

JB#3
1st Oct 2008, 08:57 PM
Yonnee, you are an absolute superstar, thats pretty much the exact answer i was dreaming off!

Yes it will be built for two karts, one (when required) will be on the ground and one on an upper shelf. The right side kart shelf will continue down the trailer where there will be a work bench and a spot for some stacker draws ect. then around and across the front of the trailer for some general shelving.

The trailer wont have a bullnose section as such, but will be "angled" down the front, similar to this: (just with out the nice fancy curve, just a pointy but joint instead.)
http://i34.photobucket.com/albums/d113/JB3JB3/b4a9_3.jpg



Thanks for your help Calm,

The measurements should be pretty much spot on, max kart width of 1400, plus the 50mm for the two SHS uprights leaves me with 50mm to play with when fitting the struts ect, however I may need to change that measurement once iv worked out how i am going to mount and seal the rear door.

The will be a front access door on the left side, just in front of the kart shelf, which will be 2000mm long, oppersite the door will be the workbench shelf and stacker draws... with some general shelving going across the front.

Thanks heaps for your help guys, any other advice will be greatly appreciated, i will get back to you sometime yonne about axle length when iv worked a few more details out.

Now to chase up some $$$ and start getting some supplies... it will be a longish process, but I havnt got much racing left this year so will make do with my current trailer, my only aim is to have it done for the state titles in early Feb 2009.


Cheers,
Josh

Calm
1st Oct 2008, 10:17 PM
Found a photo (actually the Daughter had one of her kart) - not very good of the kart trailer but you might get the idea.

I built this myself and the straight front is the same height as the car towing it, so i got maximum advantage for storage and the slope was from the car roof line upwards -hpe that helps.

Cheers

Yonnee
1st Oct 2008, 11:26 PM
Something I just thought of while looking at the pictures above...

I was assuming the karts would be placed near the front of the trailer. And therefore, with the weight of the kart/s in front of the normal axle position, this would not be a problem.

But...
loking at Calm's trailer, above, his karts were right at the back. Not so much of an issue with a tandem, but a single axle trailer with 200kg placed behind the axle, that puppy is going to want to swap ends with you on the highway!!! Or at the very least, get the sways up!

JB#3
1st Oct 2008, 11:35 PM
Yehh, that is one issue my current trailer has, axle is to far forward... dusnt tow too badly, but it is bloody annoying when your at the track and sit inside the rear door and the thing tries to tip backwards...

So i guess i have to move the axle further back... anyway i should work out how much? try and find the approx centre of gravity or something?

Cheers,

Yonnee
2nd Oct 2008, 12:00 AM
So i guess i have to move the axle further back... anyway i should work out how much? try and find the approx centre of gravity or something?

Cheers,Yeah, sort of. Have you got a pic of your current setup? How much different will the new trailer be, in size, etc.?
If similar, you could probably move the measurement of the axle placement back about another 12" from your current one.

Where abouts are you? Might be worth a look, and a chat in person. Could even assist with the build.

PM sent.

JB#3
2nd Oct 2008, 12:29 AM
ok cheers mate,

Im living in aspendale gardens, how ever we only just moved here and my current trailer is still at our old place, just moving also means the garage is full of just about everything that shouldnt live in a garage!
So it will still be a little while before i get underway.


Yon ill be in touch at some time regarding your PM

Cheers,

Yonnee
2nd Oct 2008, 12:34 AM
You're kidding... How good's your arm? You could just about land a rock on Melbourne Trailers' roof from your place!!
They're open Sat. mornings from 8:30 till 12noon.

And I know what you mean about moving... nearly 4 years and I can still only get one car in the front garage... AND I HAVE A FOUR CAR SHED AT THE BACK!!!

Calm
3rd Oct 2008, 09:50 PM
Something I just thought of while looking at the pictures above...

I was assuming the karts would be placed near the front of the trailer. And therefore, with the weight of the kart/s in front of the normal axle position, this would not be a problem.

But...
loking at Calm's trailer, above, his karts were right at the back. Not so much of an issue with a tandem, but a single axle trailer with 200kg placed behind the axle, that puppy is going to want to swap ends with you on the highway!!! Or at the very least, get the sways up!

Yonnee the gokart is the light bit. The fuel drums, spare motors & wheels, tool boxes etc at the front are the heavy bit.

I would suggest a drop down leg at the back as a good way to stop it tipping up when you "walk" in. I forget but karts only weigh abour 60 or 70 KG complete without a driver - as a guide the classes are 130kg (light), 150kg (heavy - that was me 84 kg + kart + a couple of Kg lead to come in at 152KG), 170kg (super heavy) combined weight.

Cheers

Yonnee
4th Oct 2008, 11:40 AM
Yonnee the gokart is the light bit. The fuel drums, spare motors & wheels, tool boxes etc at the front are the heavy bit.

I would suggest a drop down leg at the back as a good way to stop it tipping up when you "walk" in. I forget but karts only weigh abour 60 or 70 KG complete without a driver - as a guide the classes are 130kg (light), 150kg (heavy - that was me 84 kg + kart + a couple of Kg lead to come in at 152KG), 170kg (super heavy) combined weight.

Cheers

Point taken... but even 140kg, for two karts, can upset the balance of a single axle trailer. And I'm guessing the heavy part of a kart is at the rear...

If I was building a single axle kart trailer, I'd set the chassis and drawbar up on the floor, and then put a piece of timber/steel across roughly where the axle goes, and then stand on the chassis, adjusting the pivot point so it was balanced with my weight on the back. Then I'd see how that looks, and maybe play with it a little from there.

Just goes to show, there's not always the same rules for building all trailers.

I do agree with a drop down leg, a wind down caravan jack would be ideal, as they have a little wheel in case you bottom out the trailer on steep driveways.

Calm
4th Oct 2008, 09:36 PM
Yonnee your the ideas man:2tsup::2tsup::2tsup::D:D

Yonnee
6th Oct 2008, 05:27 PM
Yonnee your the ideas man:2tsup::2tsup::2tsup::D:D

But I don't have a broom with a hose attachment!!:no:

JB#3
6th Oct 2008, 10:52 PM
OK this question was always going to come...

to brake or not to brake...

Im currently leaning towards brake, but just an over ride mechanical system (I plan on buying a new tow car next year, well nice big diesel van actually, but i also want to be able to tow with my daily driver, so i can take the trailer with me to work or whatever when needed) hence the reason i dont want electric brakes.

Iv worked out the enclosed box section of the trailer will be about 1700 high, and in order to fit it under my garage door, allowing for 17inch rims with 205/45 tyres, and the actual chassis itself, it only left me 100mm to play with for the "bottom of chassis to center line of axle" distance (springs, hangers, suspension travel ect).

So was thinking i should get an axle with 2 1/2inch drop stubs.

Dose this make sense to you 'well learned' people out there? the above statement might be complete and utter BS... in which case just laugh it of and tell me so:p

with average 1000kg 5leaf springs, what would be a normal "bottom of chassis to center line of axle" measurement?


Thanks guys,
Josh

Yonnee
7th Oct 2008, 10:25 PM
OK this question was always going to come...

to brake or not to brake...

Good question, well asked...

If you didn't already know, 750Kg is your limit without brakes. That's unladen trailer, plus load. I'd look at three options;
- One: Build it without brakes. You should be way under the 750Kg. And it's the cheapest.
- Two: Set it up with brakes from the start. (Whatever brakes take your fancy, and even though I hate them with a passion, over-ride brakes are the easiest for several tow vehicles.)
- Three: Set it up to be able to add brakes at a later date. Welding on a four bolt coupling plate, and having brake mount flanges fitted to the axle, will allow you to have it unbraked for now, but adding brakes later is a "bolt-on" exercise.


Im currently leaning towards brake, but just an over ride mechanical system (I plan on buying a new tow car next year, well nice big diesel van actually, but i also want to be able to tow with my daily driver, so i can take the trailer with me to work or whatever when needed) hence the reason i dont want electric brakes.

The Mechanical drum brake is a really good option to set up on a trailer if you have to go over-ride, as the mount for the coupling and the mounts for the brakes on the axle are identical, which means you can upgrade to Electric brakes in the future by swapping the coupling, brake assemblies and drums, without having to remove and replace mounts on the axle.


I've worked out the enclosed box section of the trailer will be about 1700 high, and in order to fit it under my garage door, allowing for 17inch rims with 205/45 tyres, and the actual chassis itself, it only left me 100mm to play with for the "bottom of chassis to center line of axle" distance (springs, hangers, suspension travel ect).

So was thinking i should get an axle with 2 1/2inch drop stubs.

Roughly calculating, from the measurements you've stated, you'll have;
- 615mm overall tyre diameter.
- Approx 240mm centre of axle beam to ground with a 2-1/2" drop axle.
- I'm estimating just over 2100mm from ground to top of trailer, assuming 40mm chassis rails. Using a 4" drop axle will drop you another 40mm, but make sure your 'U'bolt threads aren't lower than your rims, or you'll drag them along the road if you get a flat tyre.



Dose this make sense to you 'well learned' people out there? the above statement might be complete and utter BS... in which case just laugh it of and tell me so:p

with average 1000kg 5leaf springs, what would be a normal "bottom of chassis to center line of axle" measurement?


Thanks guys,
Josh