Height to Width Ratio?

[mlhostetter]

Ok here is a question that has probably been answered somewhere along time ago, but I have yet to find it, so here goes.

Being as though I am new to all of this, my concern/question is how high could walls be built on the 4x8 HF. I worry about it being top heavy and high winds. Is there a formula to figure this out?

I know that the aerodynamics are important when building for towing and the last thing I want to do is take a newly built trailer cross country and have to travel through some of those passes where the cross winds eat ya alive and wind up in a ditch on my side. (Getting there is half the fun ) I want to see these places ya know, just not from a flat lyin position.

Would a plan to have the tear drop shape with a wall height of 5'-6" in the center be feasible? I figure this will entail a sandwich wall construction with alot of excess materials, but I think they can be used in other areas. Weight is also a factor. I guess I would have to do without other things in order to compensate for the extra weight of the wall wood to keep it in the limits.

Just a thought.

Marylou

[swissarmygirl]

I don't know if there is a particular formula, but I can tell you that mine is 4' from floor to ceiling which seems to be plenty of room for sitting up and general moving around.
Unless you plan on dancing in there....

[kirtsjc]

Being as though I am new to all of this, my concern/question is how high could walls be built on the 4x8 HF. I worry about it being top heavy and high winds. Is there a formula to figure this out?

Think photographs.... 3x5, 4x6, 5x7, 8x10.... Note the pleasing ratio?

4high by 4 wide is a box on wheels. My weekender is 4x4 from the ends, so I have a box.

If I ever get around to building a second one (and getting fed up building this first one), it will be 4 high, but 6 wide, else 3 high by 5 wide... Length I can add to, to get space for gallery and such...

Sorry, I am in a grouchy mood tonight; guess I should not have even responded...

[Miriam C.]

Marylou,
I have crossed from Colorado to Wyoming in the wind. Smaller is not necessarily a good thing. At the time we were in a pinto. Steering wheel all the way to the left. Forward progress, slightly right.

I think it is the shape and understanding not to cross in high wind.
The design lib. has some taller units. I personall would not for 4 wide and 5'6" high. maybe 5 wide and 5'6" high or some kinda of dropped floor.

(I am giving thought to a dome to accomidate dressing.)
Aunti M

[angib]

Marylou, your post is eerie - I had just posted something similar on another thread (Rimple for 4 design). But I thought I might spell out my logic here.

I have used some assumptions that I think are reasonable:
- What matters is the proportions of the trailer - that is, the ratio of the overall height to the overall width, not the ratio of just the body.
- The limit of the height-to-width ratio should be around the maximum that manufactured trailers reach - in other words, I'm assuming they've pushed the height as far as it's safe to go, and we shouldn't push it any further.
- The centre of gravity of a homebuilt teardrop is not significantly higher than for a manufactured trailer, as a proportion of its height.

Then I looked at manufactured trailers and came up with these limits:
- For travel trailers, the max height is around 12' - on a standard width of 8', this is a height/width ratio of 150%.
- A typical travel trailer height is around 10' 6" - a ratio of 131%.
- Smaller trailers seem to have a lower ratio - a Scamp is down at 110% (88"H x 80"W).

So I reckon a rule of thumb would be:
- a 100% ratio is very safe;
- a 125% ratio is typical;
- a 150% ratio should be the absolute limit.

In your case, Marylou, the numbers look like this:
- A HF 4x8 trailer is about 19" to the top of the frame from the ground so your overall height would be 66"+19" = 85"
- A HF 4x8 trailer is 66" overall width.
- The height/width ration would be 85/66 = 129%.

So I'd say you should be OK, but without a lot of safety margin - there would be days when it would be sensible to not tow this trailer. If you went to one of the new 5x8 HF trailers, your ratio would be 85/76 = 112%, which looks a lot better.

I haven't looked at the weight at all - from what I've seen, all homebuilt trailers are heavier than a manufactured trailer of the same size and, in this one instance, extra weight is not a problem.

I hope this helps more than it confuses!

Andrew

[Lobo]

Andrew,

Very nice analysis!

My current line of thought runs to a five foot wide TD on a four foot wide frame, to include wheel wells. I would think the narrower wheel spacing on the four foot wide frame (compared to a five foot wide frame) would negate (at least to some extent) the actual width of the trailer. That is to say, my H/W ratio would be more indicative if based on the wheel width measurement rather than the actual width of the TD.......ya no what I mean???

Lobo in West Virginia

aka....Teacher of the Arcane (as in mathematics)

[angib]

ya no what I mean???

I knows whatcha mean, but I ain't agreein'.

Most manufactured* trailer wheels are inset inside the overall width quite a bit, so I think using the overall width of a HF trailer is a more-than-fair comparison.

But really we're only talking about an inch or two either way, and that won't make a huge difference to the ratio.

Andrew

* 'Shop-bought' (US: store-bought?) doesn't sound right for a trailer!

[Lobo]

Andrew,

Yeah, store-bought is the phrase we use here in the mountains of West Virginia. Depending on the situation, this might be a derogatory remark!

You're familiar with the old saying, "A little knowledge is a dangerous thing"??
I'm a very dangerous man!

Thanks for the insight into H/W ratios.


Lobo in West Virginia

[angib]

Depending on the situation, this might be a derogatory remark!

I should hope so! You should be practicing the correct delivery to give the guy in the huge RV next door - something like:

"So you weren't able to build your own and had to get a store-bought, eh? Well, I guess that's alright for some folks....."

Andrew

[kirtsjc]

"So you weren't able to build your own and had to get a store-bought, eh? Well, I guess that's alright for some folks....."

I'm feeling better now about "The Ugly" - I shall steal your line, paraphrase it later....

[GregB]

Andrew,

Pardon me for picking nits, but my HF 1740 is only 62" wide and is 20" high at the frame top with the axle under. With the axle over, I get 17" high to the frame top. That changes the H/W ratio to 138% and 134% respectively. The difference isn't great, but strays closer to the limit.

GB

[angib]

Pardon me for picking nits, but my HF 1740 is only 62" wide and is 20" high at the frame top with the axle under. With the axle over, I get 17" high to the frame top. That changes the H/W ratio to 138% and 134% respectively. The difference isn't great, but strays closer to the limit.

Greg,

There do seem to be small variations between the different models of HF trailer - there even seem to be differences between what HF say and how trailers actually measure!

And there are loads of holes that can be picked in this simple check - for example, it would be much better to use wheel track rather than overall width, but this info isn't published for 'store-bought' travel trailers, so we'd be comparing to a guessed standard!

Accuracy to the last few percentage points isn't really needed - we just need to choose between the 'good', 'OK' and 'so-so' categories of stability.

Andrew