Why do all racks use aluminum struts?

[BikeNY]

This has been on my mind forever! Whenever I need a rack, I will pick a steel one if available over an aluminum one, even if it's heavier. I have racks from Nitto, Tubus, IRD, and Dajia, all steel, mostly stainless, but they all use aluminum struts for mounting. Why is that? I think the struts are all solid aluminum, couldn't they be made out of steel tubes and be stronger?

[weisan]

https://onebitewellness.files.wordpress.com/2015/06/weight-scale.gif

[Kontact]

Also to make them bendable to match the frame easily. Steel that is as easy to bend isn't as rigid as aluminum.

[parris]

I could be wrong but i think some of the reasons aer cost, ease of manufacturing, momentum of the industry, and material avability. Decent quality stainless is a fairly recent development so a steel rack in the past may not have been as practical option just from a rust standpoint. Just a few thoughts on it.

[Bradford]

Perhaps because they are strong enough. I've toured with 65 pound loads for weeks at a time and never had a problem with struts. I've broken front low riders, but never even a little bend on struts.

My guess is that the stresses on struts are low enough that aluminum exceeds the requirements.

[alexstar]

It seems to me that the struts don't take much of a load compared to the 'legs' of the rack - they are mostly there to locate and stabilize it. As mentioned, it is also easier to bend the struts for installation when they are aluminum.

I did have a Topeak rack that used flat steel struts - these worked well because they could be bent in one plane but still offered a great deal of rigidity. The greater strength was, I think, an added bonus.

These days I use Tubus racks.

[Ti Designs]

The rack is weight bearing at the bottom, the struts only locate the rack. There are a lot of different designs for rack struts, based on the idea that they have no idea where the pick-up points are going to be on the frame. Blackburn does (or did) use flat steel struts which mount to the top surface of the rack and could be bent to find the braze-ons. Tubus started using their adjustable angel strut mount a few years back, they've shown up on a lot of less expensive racks since. That allows a round strut to adjust to any angle, so there's no bending - that's a key point when talking about aluminum rod.

I guess the answer to your question is that the struts of a rack shouldn't be weight bearing, so they're not worth spending time worrying about. In that respect they're a lot like valve caps.

[BikeNY]

Thanks for all of the replies. I guess it makes sense for rear racks where the struts are not weight bearing, and just used to located and keep the rack level.

I'm in the process of setting up a mini front rack (Nitto M18) to support a small front bag, and the struts are weight bearing. I'll set it up with the included aluminum struts for now, but will investigate some steel replacements. Tubular stainless steel struts with the proper wall thickness should be just as strong, if not stronger, at a similar weight, and would be stiffer and less prone to fatigue failure. Maybe I should investigate titanium!

Yes, I know I'm overthinking this, but it is winter and I need a project...

[Kontact]

I'm not sure why anyone would want stainless where aluminum is already doing the job. It also resists corrosion and is lighter than steel, which is why we use in on bike for cranks, hubs, rims, stems, frames, forks, handlebars, brakes, levers, seatposts, clamps, cages, chainrings, headsets and even spokes. The only things aluminum doesn't work well for are thin pieces or high wear, like bearings and chains.

[palincss]

I'm not sure why anyone would want stainless where aluminum is already doing the job. It also resists corrosion and is lighter than steel, which is why we use in on bike for cranks, hubs, rims, stems, frames, forks, handlebars, brakes, levers, seatposts, clamps, cages, chainrings, headsets and even spokes. The only things aluminum doesn't work well for are thin pieces or high wear, like bearings and chains.

One reason you might want steel rather than aluminum for racks might be fatigue resistance. Remember Bicycling's test of the Bruce Gordon rack compared to a bunch of aluminum rear racks back in the day? They hooked them to a vibration machine. All the aluminum racks broke; Bruce's steel rack broke the vibration macahine. He had info about that test on his web site for years.

[witcombusa]

One reason you might want steel rather than aluminum for racks might be fatigue resistance. Remember Bicycling's test of the Bruce Gordon rack compared to a bunch of aluminum rear racks back in the day? They hooked them to a vibration machine. All the aluminum racks broke; Bruce's steel rack broke the vibration macahine. He had info about that test on his web site for years.

Nice Rack!

[ripvanrando]

Was going to say Bruce Gordan tubular steel.

There is a titanium rack. I forget. Germany? Tubulis? Like 300 bucks. Saves some weight, maybe three snot rockets.

I just used aluminum going up and down the Alps and many other places. Never broke a rack but did sheer off an M5 bolt

[BikeNY]

I'm not sure why anyone would want stainless where aluminum is already doing the job. It also resists corrosion and is lighter than steel, which is why we use in on bike for cranks, hubs, rims, stems, frames, forks, handlebars, brakes, levers, seatposts, clamps, cages, chainrings, headsets and even spokes. The only things aluminum doesn't work well for are thin pieces or high wear, like bearings and chains.

Sure all of those components can be made of aluminum, but they can also be made from other materials(Steel, titanium, magnesium, carbon fiber). Sometimes those other materials are better, sometimes not. But aluminum is almost always the cheapest, which is why it's used most of the time. But that doesn't mean it's the best material for the job.

I'm just thinking out loud if aluminum is the best material for this job. I'd say for a rear rack where the struts are just connecting the top of the rack to the seatstay mounts, aluminum is fine. For a mini front rack where the struts are the main load bearing components, I think steel would be better. I'm sure the aluminum struts would be fine most of the time, but if they failed somewhere in the middle of South America, I'd be pissed off.

And yes, Tubus makes some of their racks in Titanium. While I'm sure they are great, I'm not going to spend that kind of money on a rack! I wonder what the struts are made of on those racks...

[SlowPokePete]

I have a Nitto Marks Rack on my Waterford and bought a second set of struts that mount to one point on the fork leg.

https://farm5.staticflickr.com/4523/26556256449_4a53e4a09a_c.jpg (https://flic.kr/p/GsFKQv)November 10, 2017 (https://flic.kr/p/GsFKQv) by SlowPoke Pete (https://www.flickr.com/photos/156678813@N02/), on Flickr

SPP

[Kontact]

Sure all of those components can be made of aluminum, but they can also be made from other materials(Steel, titanium, magnesium, carbon fiber). Sometimes those other materials are better, sometimes not. But aluminum is almost always the cheapest, which is why it's used most of the time. But that doesn't mean it's the best material for the job.

I'm just thinking out loud if aluminum is the best material for this job. I'd say for a rear rack where the struts are just connecting the top of the rack to the seatstay mounts, aluminum is fine. For a mini front rack where the struts are the main load bearing components, I think steel would be better. I'm sure the aluminum struts would be fine most of the time, but if they failed somewhere in the middle of South America, I'd be pissed off.

And yes, Tubus makes some of their racks in Titanium. While I'm sure they are great, I'm not going to spend that kind of money on a rack! I wonder what the struts are made of on those racks...

Normally, steel is the cheapest material to make things from, not aluminum. Aluminum is cheaper to machine and extrude than steel due to tooling costs, so complex machined shapes end up being cheaper. But a basic welded wire or tube frame is cheap to make out of steel.


Have people had a lot of aluminum rack fatigue failures like in the Bruce Gordon/Bicycling test?


As a general note, aluminum fails due to fatigue if and only if the aluminum is allowed to flex. An old Cannondale will outlast a lightweight steel bike because it is so stiff it doesn't flex enough to work harden, while the steel bike will. If rack fatigue was a concern as well as weight, racks make of oversized aluminum tubing would be a way of dealing with it. How many broken aluminum stems has anyone here seen? Even flexy aluminum forks have great reputations.