Calculating trailer floor height

[bishboy]

I'm still in the process of designing my trailer (just checked my posts, been nearly 2 years since I posted my first design :roll:) and just want to work out the proposed floor height.

14" rim with 185 L/T tyre 650mm, therfore centre of axle 325mm


300mm bottom of axle
+
140mm height of springs (from where spring mounts to bottom of axle to centre eyelet)
+
45mm height of spring hanger (centre eyelet to bottom frame rail)
+
75mm frame rail height
560mm


My floor height would be 56cm which seems a bit high. Is this correct or have I forgotten something obvious?

[OldGrain]

Gday Bishboy.Just read through your original posts - phew - some reading. Anyhows you have a choice of sitting the axle on top of or under the springs. Apart from the aesthetics,it would ride/tow better if over given the height.

[Bryan]

I'm going to query your 650 diameter. My hilux wheels have the same size tyres and I just measured one. I make it 635. That's inflated but not fitted to the trailer. It should sag a little with weight on it. Say 10mm? If so that would make your bottom radius 307.

Edit: I guess tyres vary a little between brands. If yours measure 650, disregard the above. I just thought it may have been a theoretical figure.

[soundman]

Um tyres vary very little between brands.... the dimensions are more or less standardised.

yes there is a failure to account for both flattening of the tyre and loading of the springs.

are you over or under sprung ....... sprung over ( axle on top of spring) can add up to 3 inches / 75mm to tray height.

But with all variations in mind 560 is not all that high.

remember lots of commercial trailers do not have main frame rails the springs mount more or less straight to the bottom of the tub.

you can pick up some height here and there

not laying your floor on top of your main rails could potentially save you 75mm.

There is a good reason why 13" rims have been the mainstay of trailers in the past ...... tray height reduction .... though geting adequately rated tyres can be an issue .

One of the reasons slipper springs are used in leiu of shackles at the rear is to reduce tray height.

Ask ya self ...do you need 75 mm frame rails ...... if it is a box trailer remember the sides can be constructed as a truss considerably smaller section would then be well and truly adequate

cheers

[Steamwhisperer]

are you over or under sprung ....... sprung over ( axle on top of spring) can add up to 3 inches / 75mm to tray height.

cheers

If the axle was on top of the spring, wouldn't that make the tray height lower, or am I missing something (as usual :-)

Phil

[soundman]

Exactly .... sprung over ... means spring over axle...... like a hilux .... sprung under ..... most leaf sprung cars........ means spring under axle.

and the difference is the full height of the spring pack and the diameter of the axle pluss packings.

cheers

[Steamwhisperer]

sprung over ( axle on top of spring)

cheers


sprung over ... means spring over axle......

cheers

Hi Soundman
I'll assume you mean the second one. :D

Phil

[bishboy]

Thanks for the reply guys.

I'm trying to get a lower floor height without the expense of overlay/drop axles as the front half will be a camper trailer with a max height of 115cm and I'm trying to maximise the internal height of the trailer. Hopefully I'll get up a chance to put up some of my basic plans later in the week to get some feedback and ideas.

Both a tyre shop and an online search have said that 185/14 light truck tyres are 650mm diameter.

I've got some 50x50x5 so I might use that for the end rails (not long enough for the sides) and then get some 50x50x4 use that for the side rails and the cross rails (I can get 1 side rail and 2 cross rails from one 8m length). That will lower the floor by a huge inch :roll:

If I do do for a drop axle, a 4" drop puts the bottom of the axle about 200mm of the ground, which is pretty low but after measuring my tow vehicle (Territory), the suspension A arms (or whatever they're called) are only 210mm of the ground and the sway bar is attached lower than this.

[soundman]

Remember if you build the sides of your trailer as a truss, you can considerably reduce the weight and the size of the members required.

remember too if you build your flooor flush to the bottom of your side rails rather than on top of them you will gain at least 2 inches.

This is done by installing your cross rails under the side rails.

suspension travel is not compromised.

one thing to be aware of is maintaining hitch height within the specified standard range so the trailer travels at the correct attitude.

if you are not going off road, you may consider going to a lower profile tyre a 185/65R14 passenger tyer will give you a 530Kg load capacity @ 250KPA and 596mm overall diameter dropping you another 2 inches

A 205/65r14 will get you over the 600Kg per tyre load capacity. @ 620mm diameter.

A lot of the typical box trailers rinning 14 inch rims are running lower profile tyres as come fitted to late model commies and falcoons

if you don't need the carcase strength or load rating that will gain you some height.

cheers

[bishboy]

Thanks Soundman

So instead of butting my end rails and floor rails in between the side rails, I attach them to the underside of the side rails, yes?

In regards to building the sides as a truss, do you mean having cross rails, if so what spacing would be required for both the horizontal and vertical rails, and what size rhs would be sufficient would it need to be any heavier if I put a roof top tent on?

I wont be going off road, probably some gravel/dirt roads but given the condition of some of the roads up here and if I have to get off the edge of the bitumen to pass a road train (they're like flies up here) I would probably stick with light truck tyres for that bit of extra sidewall strength, even though it will only be a 2000kg trailer (probably 45mm square axles) it would only rarely if ever be carrying 2 tonnes.

[soundman]

Yes attach the floor rails to the underside of your side rails :2tsup:

If the side of your trailer has one length of material on the bottom and another length of material on the top seperated by some vertical members ..... it already is a truss.

So may trailer designs rely or are thaught to rely on the strength of the bottom rail only ....... say a 50 x 75 mm rhs

If you have a 50 x 50 rhs seperated by verticals of nearly any length ...... it will be way way stronger than a 50 x 100 section.

a little thaught and you should be able to use this to your advantage.

For the most part light trailers are way way heavier than they need to be because of lack of thaught about truss sections and the massivly increased strength they provide.

If you have not experienced this concept ...it might be worth you fabbing up some simple spaced sections in light material ...... just grab a couple of 2 meter lengths of cheap light 25 x25 and seperate them with 100mm lengths of the same material every 300mm and compare the strenght ...... in welded RHS ladders there is little need for diagonal braces.

As for 2 tonnes ...hell man ya not going to carry 2 tonnes on one pair 185/14 light trucks ...they max out at about 850Kg.....a piece and you should derate from that too by about 20%.

It is generally considered Axles running ford hubs max out at 1.5 tonnes ... I would not carry more than 1.2 tonnes on ford hubs further then the local dump or the nearby boat ramp.

I would not try to carry 2 tonnes on anything less than landcruiser hubs.

I don't care what the published towing capacity of the teritory is .....2 tonnes is a lot to have up your @#$!.

I think you need to think about weight reduction.

For the most part people well and truly over build trailers, thinking the answer is bigger and heavier sections ....... and the weight gets out of controll very very fast.

If you want to stay on a single axle with 14 inch rims, think in terms of staying under 1.2 tonnes.

All the steel manufacturers publish mass & bundling data ...... and they are pretty accurate ....... remember going from 2mm wall to 3mm wall in any section increases the weight by 50%.

heavy does not necessarily mean strong

cheers

[OldGrain]

Gday Bishboy. Now vintage caravans mightn`t be your thing but take a look at the vintage caravavan dot com site & in particular the Members Photo section - Page 1 last entry - 1960 Newcastle 10` 8" project - whereby the owner of said van completely stripped & rebuilt it (still currently). 15 pages long so far, he goes into great detail with weights/measures/dimensions both in type & pics. Whilst the bodywork/interior etc probably won`t interest you the chassis steel/spring placement/wheels/guards might. (nope,not mine)

[bishboy]

Oldgrain - thanks for that, very informative and some nice work, I wasted 2 hours last night reading all that and I'm still not finished :U

Soundman - I'm going to run tandem 45mm square axles, 6 leaf springs with HQ hubs (cause that's what I have) and light truck tyres on 14" rims. From what I understand that is sufficient to get a 2 tonne 'rating' although it will rarely have a GVM of 2 tonnes.

It's very difficult to find consistent information on the appropriate steel size to use as there are so many variables between individual trailers. I'll hopefully get my plans up over the weekend and I will welcome any feedback.

[Aufitt]

Im getting 430-450mm deck height from 45mm slipper springs,
10mm flat bar added between axle pads
40mm axle,
front spring hanger mounted horizontal
similar diameter tyres OD- 615mm, Radius- 307.5mm
Without going to a drop axle.

http://www.woodworkforums.com/showthread.php?t=179693&page=5

Sinking the drawbar into the design removes the need to step up the tow itch as 430- 450mm is most towbar tongue heights.

Is vey low, but still have 90mm bump clearance, leaves never move that much.

[soundman]

never seen a "camper trailer" on dual axles before.

If its a 45mm axle it will probably have ford bearing and will rate at 1.5 tonnes.

serioulsy consider you whole weight issue ........ just running dual axles adds considerable weight .... there is probably arround 100KG just in the second axle.

The ATM V payload equasion is an ever present issue in light trailers .....all to often the trailer structure being not particularly clever chews away most of the payload ..... I once owned a 1 tonne ATM trailer that was only capable of carrying about 350Kg .....what a pointless piece of $#@!... it taught me a lesson. ... I still have a trailer that is 750KG ATM and will carry over 500KG legally

As I have said there is very much a problem that heavier is thaught of as being stronger and its not at all hard to build a trailer that consumes all of its payload in excessive structure.

You should be easily able to build a 500 Kg trailer that will carry 1 tonne payload.

As for getting consistent information about appropriate steel size ....yeh well ....... there are a lot of trailers built that where designed on the basis of one size larger than the trailer it was coppied off ....thinking that was a good idea.

Go look at some of the commercially built trailers from the large companies ...companies that are large enough to actually employ someone who has an idea ...... and have accountants that are constantly cracking the whip on material cost ........ you will see how light some of them realy are ...... and they dont seem to break ...... inspite of there being no reinforcement a stress points.

And that is one of the keys ...... you don't need to build a trailer all out of material heavy enough to be strong enough at the stress points.

cheers

[Aufitt]

50mm axle will take over 2000kg,
45mm axle will take 1500kg with parallel brgs.

Easy to go lower with single axle.

[bishboy]

I don't think I've explained what I'm building very well. It's going to be essentially a camper trailer front with an enclosed rear.

I'm looking at doing it this way as the cost of a camping trailer tent to go on top of a bike trailer is horrendous (I'm trying to do it as cheap as possible), but I am still looking into getting a standard camping trailer tent modified to go on top of a bike trailer, but it might also be too expensive/difficult.

As I don't want 2 trailers, I'm playing with the 2 in 1 option and I've attached a rough plan of what it will look like below.

Thoughts/ideas would be appreciated.


347145

[dai sensei]

Reminds me of the 2.5t trailer I was thinking about at one stage to carry my slide on camper, plus lathe on trolley and milling gear in boxs at front, one open with ramped doors and the other shelved and std doors. I was then going to carry timber plus anything else I needed in the ute.

347160

Ended up going with the lazy axle on the ute and kept my old 1.5t trailer. Mainly because I had already laid down money for the ute upgrade, but in hindsight I seriously regret not going for the new trailer idea.

[Michael G]

It's going to be essentially a camper trailer front with an enclosed rear.

Thoughts/ideas would be appreciated.


347145

Just passing through...
First impression when seeing your sketch was ouch!
You are a similar size to a car trailer, so it may be instructive to have a look at a few of those and see how they are made, especially those with truss sides.

However, the ouch was more about weight distribution. If you think about having 2 motor bikes in the back, the centre of gravity for them is likely to be behind the back tyre somewhere. If you assume the the trailer is going to be as light as possible with uniform weight distribution so its C of G sits above the wheels, you will need an equally heavy tent to counter-balance the back end. Without the bikes in the back, the C of G for the heavy tent will be between the drawbar and the wheels, so you will have the opposite problem with drawbar force. (I was once told for the average car/trailer combo the vertical drawbar force should not be more than around 50kg or you risk damage to the towbar when going over bumps/ potholes etc - sounds reasonable) - That is, with bikes but no tent the trailer will want to pull up off the hitch; with tent but no bikes it will be heavily pushing down.
However, tents are (relatively) light, so I would suggest that your design needs to be arranged so that the centre of gravity for the motorbikes is between the axles and then see how you can arrange a tent - on top of the box section? A separate unit? Slide out section between the bikes? Can you load the bikes sideways fore and aft with a box section in the middle (or the other way around).
Just some thoughts
Michael

[soundman]

Yeh I;d be thinking of a shorter trailer with a rooftop tent..... maybe a hard platform folding down onto the drawbar ...... roll out awning out the side with kitchen under.

Y got be able to get this all in under the 1200Kg.

Remember all that extra weight costs you 3 times ...... once when you pay for the steel, once when you pay for the towing capacity and again when you pay for the fuel.

cheers

[jatt]

Perhaps stand your tent trailer on its side and fold down over the guard? At least one bike can go beside it. Would help with weight distribution.

Get the odd cust inquiry with a similar dilemma ie motorbikes/go carts and tent trailer together on one trailer. Go carts of course are lower, so fully enclosed trailer and tent with cover on top, isnt a bad option.

Bikes on the other hand much higher, so if bikes are parked under then your tent has to be a quite high off the ground.

Weight distribution with your design has already been discussed, so wont flog that any further.

Tent trailers we have built here in the past come in at about 100 Kg. Thats your tent work, bars and bed base.

[OldGrain]

Gday Bishboy. Been reading this with interest & also other trailer builds within this section & about eight headers down - Track bike trailer build - comes up as a very interesting & detailed build complete with costings. Every conceivable issue seems to be addressed in this particular build.Taking on board what Soundman says about fitting a hard floor/tent on top could easily be adapted for your use looking at that trailer.

[bishboy]

Thanks for the input. I was concerned by the length of the trailer and I was going to use water tanks etc to even out the weight distribution.

But I might go for something similar to my original enclosed bike trailer design and get a camper trailer tent modified to fit.

Something similar to this, trailer wise. The tent manufacturer wants $5000 for the tent as pictured :o

http://i388.photobucket.com/albums/oo330/bishboy/Trailer/rooftop%20camper3_zpsthlyb3lx.jpg (http://s388.photobucket.com/user/bishboy/media/Trailer/rooftop%20camper3_zpsthlyb3lx.jpg.html)


http://i388.photobucket.com/albums/oo330/bishboy/Trailer/rooftop%20camper2_zpsrvff4hcj.jpg (http://s388.photobucket.com/user/bishboy/media/Trailer/rooftop%20camper2_zpsrvff4hcj.jpg.html)


http://i388.photobucket.com/albums/oo330/bishboy/Trailer/rooftop%20camper1_zpseyxvzegy.jpg (http://s388.photobucket.com/user/bishboy/media/Trailer/rooftop%20camper1_zpseyxvzegy.jpg.html)



With a tent arrangement along these lines, can use as many or few of the sections as you like, even mix and match. Will ask some upholstery places about the cost and effort of adding 75cm arond the top, between the roof and side panels. The poles will be easy enough to sleeve and make longer. The full tent is about $2000 before alterations.

http://i388.photobucket.com/albums/oo330/bishboy/Trailer/camper%20tent%20mytopiastore_2_zpsrd254bkp.jpg (http://s388.photobucket.com/user/bishboy/media/Trailer/camper%20tent%20mytopiastore_2_zpsrd254bkp.jpg.html)


Back to the drawing board I suppose. There is a camping expo up here at the end of June, I'll go to that and have a good look and ask plenty of question.

[jatt]

The tent manufacturer wants $5000 for the tent as pictured
So we are just talking the canvas work, canvas support bows, and bed base as pictured? If so that would'nt be too hard to beat. And yes I do know something about the subject matter. :)


Will ask some upholstery places about the cost and effort of adding 75cm around the top, between the roof and side panels.

When it comes to alterations, extending zip on annex walls can usually be done without too much bother. Other parts are somewhat trickier. It goes without saying time = $