I was planning on buying a Nimbus 20" Trials unicycle, and the one that I’m looking at says that the cranks are Aluminum ISIS cranks. My friend, who’s very knowledgeable in unicycles, told me that aluminum cranks are pretty weak, and that he bought some that broke within a week. What I want to know if it’s really true that they are weak, and if I should look into some other cranks. Thanks!
It really depends on the cranks. KH Moment cranks are aluminum and they are nearly indestructible. If the Nimbus Trials unicycle you are looking at comes with Nimbus Venture cranks you should not have any issues with them breaking or bending unless you do big drops. If you are worried about breaking the cranks, I would recommend upgrading them to KH Moment cranks.
Ok thanks! I looked on Unicycle.com, and they are Nimbus Venture cranks, so hopefully I won’t have any problems with them!
To summarize:
The strong ones are very strong.
Uh, this works for steel cranks as well. 
In other words, you get much better results if you ask the actual question you want an answer to rather than trying to generalize it.
Haha, ok, thanks. How about this: Should I buy Aluminum ISIS Cranks?
Aluminum cranks one of the generalities that John was referring to. It also depends a lot on the application you’re planning to use them for. There are several brands and designs. Almost any crank is going to be strong enough for an 8 year olds track racing uni, Many cranks are not strong enough for street riding.
That’s actually about a 0% improvement. There are cheap, not-so-strong aluminum ISIS cranks, and there are much beefier ones. But there really aren’t that many on the market for unicycles, so was there a particular model/brand you had in mind?
And for a truly useful answer, we need to know how you will use them.
Ohhhh, sorry. I don’t know much about the different types of cranks. 
I didn’t know that there we any other types of ISIS cranks… I thought it was one pair of cranks you could buy. I’m planning on riding trials, as well as some mUni. The unicycle that I had in mind was the Nimbus 20" Gremlin White Trials Unicycle from unicycle.com. Here’s the link: http://www.unicycle.com/unicycles/trials/nimbus-20-inch-trials-cycle-5.html/
Also, if I need to get different cranks, what size mm do you think would be good for Trials?
Around 135-140 would be a good choice. But those ventures would be just fine if your only starting trials.
Ok, thanks! Yeah, I haven’t done much trials before, I’m just starting, so hopefully they’ll work for me!
Yup, get the Gremlin. Best way to find out if those cranks are sufficient (that’s what I have, but I barely ride mine) is to see if they hold up, and upgrade if they don’t.
Odds are, that’ll be cheaper in the long run than just going for the Moments or similar.