Brutalist Bike Trailer

[sgraham]

Hi all

I've caught "the bug" and have been lurking for a while now. I'm especially interested in trying to take foamie down to the very low end for bike weight.

Not having built a trailer of any type before, I largely don't know what I'm doing! So naturally when I started coming up with designs, they had more bells and whistles and curves and hatches than you could imagine.

Eventually I came around to trying to make what could be charitably described as a "very simple" design (or maybe just boring and ugly): it's a 7' long x 3' wide x 4' high, sort of a like a brutalist (as in the architecture style) version of George's "#5" bike build viewtopic.php?f=24&t=73956 . The goal being mostly to learn about how to build with foam and finish something, rather than necessarily the most awe-inspiring trailer.

20" bike wheels at the middle, one door towards the front, and maybe a window in the rear. Similar to George again, 1" XPS on the walls and roof, and either 1" or 2" on the floor (I can't get 2" sheets wider than 24" locally, so the floor would have to be from a pair of 1" 4x8 laminated together).



In any case, I built a quick hack of a wood trailer frame so I'm feeling ready to start gettin' some foam, canvas, and glue. It seems that 10 oz cotton canvas is the standard go-to recommendation? Something like https://hometex.ca/collections/canvas/p ... 7495648371 (I'm in BC, Canada so not all the same suppliers available as down south).

But when I was browsing their site I saw muslin https://hometex.ca/collections/unbleach ... 0468852851 .

This is listed as 4 oz/sq yard vs. the standard canvas, so fairly substantially lighter. The weight savings would be nice given the "bike" target (and I don't mind it being cheaper) but I'm wondering if anyone has tried lighter weights and has a sense of what I'd be giving up in strength? I guess more of the weight will be in the glue/paint though, so maybe it's not worth shaving there?

Thanks for any advice!

[Philip]

The issue I am seeing is the square design. Wind drag is going to be bad even with the lower speeds of a bike. You haven't stated electric or normal bike either That could make a big difference.

You are wanting to build with foam! Myself I would use foam as a base to build a more aerodynamic design. Then lay a couple of layers of fiberglass over that. Remove the foam and have a fiberglass shell to build off of. You could also use the thinnest foam you can find and not remove after glassing.

Two layers of thin glass might be lighter than foam and canvas and paint.

The frame could be made of glass also.

[sgraham]

Thanks for the suggestions!

The issue I am seeing is the square design. Wind drag is going to be bad even with the lower speeds of a bike.

Yeah, I am also worried about that. My thinking is that this is sort of a prototype to learn about building and a box seems like the absolute simplest. Maybe too simple though... The saving grace: I'm slow and out of shape so my speeds will be very much "lower", further reducing wind drag!

You haven't stated electric or normal bike either That could make a big difference.

I only have a manual-powered bike at the moment, so I'm hoping it'll be light enough to reasonable pull with that.

You are wanting to build with foam! Myself I would use foam as a base to build a more aerodynamic design. Then lay a couple of layers of fiberglass over that. Remove the foam and have a fiberglass shell to build off of. You could also use the thinnest foam you can find and not remove after glassing.

Two layers of thin glass might be lighter than foam and canvas and paint.

The frame could be made of glass also.

That sounds pretty snazzy! Apart from not knowing anything about fibreglassing, my thinking behind the foam was that it would naturally provide a nicer (warmer/cooler/condensation) camping experience than a naked shell. I guess it comes down to trying to estimate the weights, strengths, costs, and insulation values of various ideas, and trying to hit the sweet spot. I will have to do some reading on applying fibreglass...

[TimC]

I would put the axle at about 33" to 34" from the rear. You are going to have a teeter totter with the axle in the middle. It may not be as important on a very light weight trailer but most teardrops have the axle at about 40% of the total floor length and weight forward on the tongue.

Another reason for an axle nearer the rear is the doorway can be moved back so you don't have to crawl into it from the front. Sit down and swing your legs through the doorway. Ideally your butt should just pivot to get in or get out.

[Philip]

I mentioned wind drag. You also have to remember side winds. 3'x7' is almost the size of a full sheet of plywood or foam. Wind side loading can be a bigger problem that a frontal wind. Frontal will slow you down. Side winds blow you off the road.

My thoughts. I would build something shaped like a canoe. Narrow front 2' to 3" wide. Thats more than enough width for your feet and a little movement room. Rounded top. take to the 7" you picked for length. I would keep the height to just enough you can roll over in it. Straight cut end. with a door that drops down that you can use for a setting platform.

Fiber glass. Look on YouTube for BoatWorks today. He has some very good vid's on glass working. Also look for strip-built canoe. Those type of vid's will give you a very good idea on how to work glass and how to build a very lite mini camper.

Two layers of 4 ounce glass will not weight much. If I do any epoxy work tomorrow. I'll lay up a couple layers of 4 ounce to get weight and thickness. I'll lay it up as a 1'x1' section.

[sgraham]

I would put the axle at about 33" to 34" from the rear. You are going to have a teeter totter with the axle in the middle. It may not be as important on a very light weight trailer but most teardrops have the axle at about 40% of the total floor length and weight forward on the tongue.

Another reason for an axle nearer the rear is the doorway can be moved back so you don't have to crawl into it from the front. Sit down and swing your legs through the doorway. Ideally your butt should just pivot to get in or get out.

Thanks for both of those, I wasn't clear on the best place to put the axle. I might end up moving the door to one end just due to size, but it would definitely be nice to have it middle-ish to avoid crawling and shimmying.

[sgraham]

I mentioned wind drag. You also have to remember side winds. 3'x7' is almost the size of a full sheet of plywood or foam. Wind side loading can be a bigger problem that a frontal wind. Frontal will slow you down. Side winds blow you off the road.

My thoughts. I would build something shaped like a canoe. Narrow front 2' to 3" wide. Thats more than enough width for your feet and a little movement room. Rounded top. take to the 7" you picked for length. I would keep the height to just enough you can roll over in it. Straight cut end. with a door that drops down that you can use for a setting platform.

Fiber glass. Look on YouTube for BoatWorks today. He has some very good vid's on glass working. Also look for strip-built canoe. Those type of vid's will give you a very good idea on how to work glass and how to build a very lite mini camper.

When you first mentioned laying a couple layers and then removing the foam, you're thinking something like this? https://youtu.be/Qg-Exm8oRP8?t=413 i.e. two layers of 4oz fibreglass could maintain its own structure once the foam's removed??

Two layers of 4 ounce glass will not weight much. If I do any epoxy work tomorrow. I'll lay up a couple layers of 4 ounce to get weight and thickness. I'll lay it up as a 1'x1' section.

Thank you, that would be very interesting!

[sgraham]

Ah, just found this guy doing chopped strand mat for a similar project: https://www.youtube.com/c/DIYKauai/videos . Not sure about the PVC piping as ribs.

[Philip]

Ah, just found this guy doing chopped strand mat for a similar project: https://www.youtube.com/c/DIYKauai/videos . Not sure about the PVC piping as ribs.

Gotta be careful with chopped strand matting. Most has wax on it for use with poly resin. Epoxy doesn't play well with that wax. Epoxy can not dissolve the wax. So bonding is a problem. Most woven glass doe does not have wax. Poly resin for a for a first-time user would not be my first choice. Epoxy takes the guess work out of the mix. Use pumps and it's about fail proof.

That link to the lady building that canoe is funny. If you're going to not use the form. IE foam or whatever. Wrap the form with plastic sheeting. Epoxy doesn't stick to plastic sheeting. Her mold was plastic. In her case she didn't use enough mold release. Her mold was a different plastic than sheeting. Mold relief is a wax. It's applied in multi coats.

The videos to watch are the ones that show details. That video started where they were demolding. It showed nothing in the way of prep work. No details on anything really. I wouldn't be surprised if she didn't do one thing on that build. When I skimmed threw it. She didn't impress me as someone that "works". She appears to be a talking head.

This video kind of drags out. But he is showing steps on building the form. Where he would start to use stripping to make the canoe. Thats where you lay the foam. Then glass over it.

https://www.youtube.com/watch?v=YC628AgGMS8

BTW weather forecast is rain for the next three days. I am glassing outside. So have to wait for the weather.

[sgraham]

This video kind of drags out. But he is showing steps on building the form. Where he would start to use stripping to make the canoe. Thats where you lay the foam. Then glass over it.

https://www.youtube.com/watch?v=YC628AgGMS8

Thanks, good set of videos, seems relatively straightforward. I'll have to add a strip canoe to my list of projects at the very least.

[sgraham]

I went with "when in doubt, copy (steal) the best looking design you can find", by trying to adapt https://web.archive.org/web/20160306093 ... tear55.htm down to bicycle-scale. Not sure how well I did, but I think it covers the wheel, door, wind drag, and overall size feedback, at least somewhat.



I also looked at XPS prices here, and maybe I should just build the whole thing out of solid gold instead! So this design has the additional constraint of only using 24x96x1" sheets, which are more available locally and a bit cheaper. (Or maybe can even get away with some 24x96x0.5", if I do fibreglass+epoxy instead of PMF).

Not sure if it's too narrow to use or not. It's made to fit https://www.exped.com/en/products/sleep ... 0445454353 (72" x 20.5") + a few inches for my toes. I assume if they sell that mat, then at least some humans could cram themselves in that width to sleep, but I'm not sure if I could.

It does feel too tall for its length and width, but I think that's the only way to make the very narrow width sort of work. I'll just have to make sure I'm always riding into the wind.

(I'm also realizing why there's so much variety in what people have come up with for bike campers, so many different tradeoffs to try to optimize!)

[Philip]

(I'm also realizing why there's so much variety in what people have come up with for bike campers, so many different tradeoffs to try to optimize!)

There are still other options that would require some experimenting. You mentioned the price of XPS. Yes, it can kind of put you into sticker shock. To do just a shell XPs is the easiest to use if you're wanting any type of insulation ii the build. If insulation isn't needed all you need is a form of the shape you want it to look like. Your newest picture would be an easier build. No form needed. It's possible that FPR panels might work. I am not to sure Tho. I haven't messed with FRP panels to much.

I don't know if they still make them. There used to be 1/4" thick fan fold type XPS foam. For your small build I don't think much insulation is needed. It's a very small area inside. Ventilation should be a bigger concern.

[Pmullen503]

I recall seeing a bike trailer done with coroplast, a plastic board kind of like corrigated cardboard. I just got a hold of a piece that was about 1/2" thick that might work well for a bike trailer. A local sign maker might be able to order it for you.

As far as height goes, have you thought of doing one with a lifting roof?

[sgraham]

I recall seeing a bike trailer done with coroplast, a plastic board kind of like corrigated cardboard. I just got a hold of a piece that was about 1/2" thick that might work well for a bike trailer. A local sign maker might be able to order it for you.

As far as height goes, have you thought of doing one with a lifting roof?

Yes! This design https://antoniocruz2.wixsite.com/nomadic used both of those tactics, I think to very good effect. I just kind of was going for something a little more "solid" feeling, but that may not be practical while keeping the weight down.

[Philip]

Here is that 12"x12" sample I said I would make. Thickness .040"





This is a waterproof sample. It does flex. It would hold whatever shape you mold it to. It does have moderate impact damage. Weight on my cheap scales came in around 0.50 of an ounce.

Don't pay any attention to the pattern in the epoxy. I did a fast layup on a black trash bag not thinking about the pattern the plastic had in it.