Options for Composite square tubes to build lightweight bike rack

[walter]

Hi Composites Forum, I am new to these materials and would like some assistance.

Planning to build a lightweight, strong hitch mounted bike rack. I plan to use A500 grade B steel for the shank and "hinge" fittings.

The current model I have uses 2"x2"x3/16" square for the mast-a 60" piece and two cross bar pieces at 1.5"x1.0"x1/8" rectangle- each 39".  

I was hoping to use pultruded fiberglass square tubes for this as I was guessing carbon fiber tubes would be expensive and more difficult to work with.

Do you have suggestions as to which composite tubes would be comparable?

I was considering using sleeve bushings and steel plate to join the tubes.

Thanks!

Walter

[John Kimball]

On 9/6/2023 at 12:27 PM, walter said:

Hi Composites Forum, I am new to these materials and would like some assistance.

Planning to build a lightweight, strong hitch mounted bike rack. I plan to use A500 grade B steel for the shank and "hinge" fittings.

The current model I have uses 2"x2"x3/16" square for the mast-a 60" piece and two cross bar pieces at 1.5"x1.0"x1/8" rectangle- each 39".  

I was hoping to use pultruded fiberglass square tubes for this as I was guessing carbon fiber tubes would be expensive and more difficult to work with.

Do you have suggestions as to which composite tubes would be comparable?

I was considering using sleeve bushings and steel plate to join the tubes.

Thanks!

Walter

Hi Walter,

without knowing the function of the fiberglass tubes it would be tough to offer good advice. However, I will say that while pultruded is cheap, a fiberglass pultrusion that is strong enough will be as heavy if not more heavy than an aluminum version that does the same thing. and pultrusions aren’t as stiff as purpose built tubes, not to mention that fiberglass is not stiff in this situation and they tend to break much easier than non-pultruded tubes. i should also note that carbon fiber is just as easy to work with as fiberglass, so keep that in mind.

Hope this helps. Let us know a little more and we can go from there.

[walter]

Hi John, 

Thanks for the info. Let me follow up and offer some example of products I would like to try and build with carbon fiber.  There are several bike racks that I was hoping to try and emulate the best features of with the lightest strongest material.  I have worked with steel but was hoping that a similar design could be done with carbon fiber or fiberglass (which is no off the table). See below for examples.

https://loloracks.com/collections/bike-racks/products/lolo-racks-bike-rack-for-2-hitch

https://northshoreracks.com/products/nsr-4/?v=7516fd43adaa

https://www.velocirax.com/products/velocirax-412

You can see the weight and price of each rack too.

All of these racks have weight rating of 250-275lb (4-6bikes at roughly 45lb/bike). These racks fit a 2" receiver hitch on a car/truck and have a pivot of some variety that allow them to tilt backwards away from the vehicle.  I would guess that carbon fiber may not be the best material for the shank but it might work for many of  the parts.  It would be of benefit to those of use who are getting older but are still active, to have a light weight rack that would work as these products do.  

Do you think this is possible and could it cost effective?

thx!

Walter