SuperPershing

Are Aluminum Crank Spindles Durable as the a Steel Spindle?

Im planning to buy a new Crank which is a Vision Track Crankset. And im going to use it in training and mostly in commute ride. (since covid isnt going away for a long time, here in my country). So are Aluminum Crank Spindles Durable as the a Steel Spindle? like would it grind or degrade like if i used the everyday in my commute or training? And my only bike is my racing bike so probably use that in every case.

Thanks for the Answer in advance!


My Former Crank, Sram Omnium with a CrMo Spindle. Durable af. to races and commute to bombing hills.

Vision Track Crankset with a 7075-T6 Alu Spindle

3alarmer 

...
...the majority of the wear in a crank bottom bracket unit is experienced by the bearings and the surfaces they contact. My guess would be your bearing contact surfaces on the new crank are steel, and probably case hardened steel at that. So not much difference if that's the case. But having said that, there is simply no way to make something like a crank spindle out of aluminum alloy that will be as bomb proof as steel.

As you are aware , it's a high stress area on the bike, with a lot of force applied through the pedals and crank arms to the spindle. Personally, I would not buy any aluminum alloy crank spindle, because the weight saving reward is not worth the accompanying risks of failure.

HillRider

+1. The Vision is a track crank and expected to be used only on Velodromes, not for routine road riding. I would buy a crank with a steel spindle for durability and long fatigue life. This is particularly true if you are going to commute on that bike and it will be subject to bad conditions and wet weather.

Wilfred Laurier

I can’t make any assumptions about strength comparisons, because I am sure the geometry of the spindle is different between the two.

What would concern me is the possibility of using the bike for commuting, ie. inclement weather. An aluminum shaft pressed into a steel bearing and being blasted with road spray might not last long.

Iride01 

I wouldn't worry about it. They have engineers that design them to withstand the expected forces for the duration of their expected lifetime. You fly in an aluminum airplane don't you?

Now if you are going for a no-name crankset maker all bets are off regardless if it's steel or aluminum.

HillRider

What is the "expected lifetime" of a track crank? 500 miles, 1000 miles? I expect a crank to last 50,000+ miles under all conditions and, so far, all of mine have. An aluminum airplane is a poor analogy unless you have a large team of skilled mechanics and inspectors going over your bike every few hundred operating hours.

Iride01 

Wow, I'm impressed. You have no bikes with less than 50,000 miles on them.

I just believe that any name brand manufacturer making a crank will design it to last as long as is normal for that type crank to last whether it is aluminum, steel or cookie dough.

The airplane wasn't intended to be a analogy. Just a response to a perceived fear of the OP that aluminum is weaker than steel. Besides, many airplanes are still flying well beyond their expected life. And despite your belief, they don't get an inspection over every square inch of their structure. Usually just if it looks good it is good. Only the parts that are known or suspected to have issues get detailed attention.

Trakhak

Not sure whether you're arguing for or against the use of aluminum in your example. Perhaps a better analogy would be to aluminum track bike rims, handlebars, and stems. They undergo substantial stress and clearly have low failure rates or else they wouldn't have been the standard choice for decades.

3alarmer 

..are you implying you know this expected lifetime thing for this product ? What is normal for this, exactly ?

3alarmer 

...which is pretty much what has made steel the standard choice for these spindles for decades. Any weight saving on any bicycle component I've encountered in life usually comes with a trade off in durability. If aluminum alloy spindles were such a wonderful materials choice, I have to wonder why they've taken so long to catch on.

As you say, the material itself has been around and in use on bikes for a long time now. It's very mysterious. What could possibly be the reason ?

HillRider

Yeah, I've had and have bikes with less than 50,000 miles on them but I currently have three bikes with more, in one case a lot more, than 50,000 miles each.

Agree 100% but is what the manufacturer considers a normal lifetime the same as the OP does? As 3alarmer noted, steel has been the material of choice for crank spindles for decades with almost no exceptions.

First, aluminum is weaker than steel, it's advantage is light weight, not strength. For many applications that trumps the loss in strength but not everywhere. Also beyond their expected service life, aircraft parts get replaced. The B-52 has been in military service since 1955 but the ones still flying have had nearly every part replace, sometimes several times.

Trakhak

Easy---standardization, or as close as the bike industry every came to it. All BB spindles had been essentially the same diameter since the 1880s. Even when companies such as Campagnolo ventured into using titanium for BB spindles (and pedal axles), they maintained the same diameters that had been used for the steel parts, resulting in many failures in use, given the comparative weakness of titanium in that application.

It's understandable that some people would question the use of aluminum for a BB spindle (although some of them are also likely to refer to titanium as a "lifetime" frame material, despite abundant evidence to the contrary), but, given the large diameter of the spindle in question, I'm not one of them.

3alarmer 

...you understand that both of the aluminum components you gave as examples, bars and wheel rims, are now both widely available with stress points reinforced with steel, right ? Thus we have decades of aluminum alloy bars with a reinforcing collar where the stem clamps them, and wheel rims with the spoke drillings reinforced with steel eyelets.

Why and how do you suppose that those design modifications evolved ?

Reynolds 

"Aluminum airplanes" have a lot of steel parts...

SJX426 

@SuperPershing - To answer your questions, no and don't know. Any good engineer will tell you that steel is the more durable material either with or without the corrosion issue. Which to use in your intended purpose is a different question.

Without a good set of data, including stress analysis report, along with projected life and MTBF, I can not offer a definitive answer. I don't think anyone could. Having been exposed to mechanical design, failure analysis, quality management and practiced risk management, I would recommend steel.
After all "steel is real" in this scenario.
If there is data to show that AL is a durable and reliable alternative in this application, I might be persuaded to consider AL as an alternative. A good demonstration would be touring around the world with one.

Ferrouscious 

I would happily use an aluminum spindle on a two-piece crank. The only accelerant of wear would be not replacing your BB bearings. The bearings are made of case hardened steel and will munch right through the relatively soft aluminum in short order.

Iride01 

I was thinking more of the planes from the 1940's and 1950's that are regularly flown today. Some as simple as a Cessna 140 or Aircoupe that are very likely at airports near you. They only have to get an inspection once a year. And it's only a visual inspection for most of the airframe that can be seen. Much of the internal structure cannot be seen. Although key places have inspection panels that are removed for one to view.

Yes they do. When I was helping the mechanic at the airport back in the 70's, we were tossing out steel parts and replacing them quite often. Steel bearings and races for aluminum wheels, all the steel screws we removed from inspection panels were replaced with new. Steel push rods for control surfaces had to be replaced sometimes. Much more steel was replaced than aluminum from what I remember.


To get back to what the OP is asking. We'd have to know what durable is to them. To me that implies wear. And two piece crank spindles simply do not experience wear. they go through a bearing assembly and part of that rotates with the spindle and it is what gets the wear.

If durability means breakage from sheer and bending forces, then again, don't you think the engineers will have designed it to meet all the forces expected to be put on it?

If durability means longevity, then once again, for the purpose of that part I'm sure it's close enough to steel spindles used in two piece cranks. After all, the Vison Track is a solid forged aluminum spindle. The steel spindles on two piece cranks are typically hollow.

DangerousDanR

Anecdote alert:

I have bent a Hope crank axle by slamming it into a rock with significant forward velocity. If I had a crankset with a steel axle I might have bent the crank arm instead. Lots of Downhill MTB riders have smashed carbon cranks. I have carbon on my road bikes and on the tandem and I don't worry a bit about smashing them.

Do I worry that the aluminum axle on the Hope crank will fail due to fatigue? No. I will bend it again long before that happens. Now, if it was a Shimano Dura Ace or Ultegra crank arm... but I also worry that if I go to Florida the ground will open up and swallow me!

Amt0571

The spindle supports the rider weight and contacts the BB bearings, which are moving parts.

Aluminium is softer, steel is harder. An aluminium spindle is way softer than the bearings it contacts.

I have no experience with aluminium spindles, but my guess is that they're lighter and less durable.

Iride01 

Bearings don't touch the spindle of a two piece crank as the OP is asking about. Only a part of the bearing assembly that holds the race for the bearings. This assembly is turning the same RPM as the spindle. What aspect of durability is being affected by the difference of steel vs aluminum?

3alarmer 

Difference Between Steel and Aluminum | Difference Between

Amt0571

I've seen wear in steel spindles in the area they contact the bearings. Some times because the bearings seized without the rider knowing it. Others because there's an imperceptible amount of play between the bearing and the spindle which wears the spindle over lots and lots of miles.

I've never seen a spindle so worn that it couldn't be used though. To be honest, I assume an aluminium spindle will work perfectly for 99.99% of cyclists, but in extreme, and probably unrealistic conditions, it will probably last less simply because the material is softer.

Then there's fatigue life. But as I said, 99.99% of people will be fine with it.

In any case, If I could choose, I'd prefer a steel spindle.

SuperPershing

Thank you all guys for these wonderful responses! I have been reading all of your comments lately and the answer is simple, Steel is real. Just due to the fact that it is just legit durable, and me, no race season and probably gonna mash this crank in the streets every time like going to deliver this and that.

And with all that, I bought(again due to all of your conclusion) a Sram Omnium (Steel Spindle) with a FSA Chainring!





Again guys! thank you very much for all of your answers!