Aluminium vs steel frames

On the 36er (steel) it’s most noticable in a twisting type motion, so it’s like the fork legs are going back and forth round each other. On the steel 29er vs. ali 29er… I’m not so sure. It just sort of feels tighter and more solid, like there’s less overall squish to the frame (So… downwards or for/backward maybe?)

I agree that it’s too hard to make a real apples to apples comparison though. My steelies are both bottom-budget Qu-Axes with stock wheels while my aluminium one is a KH with Nimbus D2 or carbon rim depending what I’m riding, so it’s completely possible that the rims make it feel all stiffened up as well. But to me the flex on the steel frames is between my butt and my feet, rather than between my feet and the ground. It’s subtle but it’s definitely there, whereas on the aluminium one there’s seemingly no give in it whatsoever.

For a typical unicycle frame, the major sresses are when you pedal hard, especially when pulling up on the seat/handle. Your legs put a high amount of twisting torque into the frame. I learned this the hard way when my old carbon fiber frame “failed” out on a trail, miles from the car. This was a 1999 Roger Davies frame, with carbon tubing into aluminum lugs, and there wasn’t quite enough adhesive down around the bearing holders. The torquing force broke the connection, the bearing holder and/or fork tube vs. crown twisted a little, and the wheel stuck against the frame. I could not for the life of me get it to twist the other way, because it was still really tight.

So I had to carry the uni up and back to the car, take it apart and mail the frame back to England. But it was so light, all of that was pretty easy. He fixed it with some aluminum pins, to keep it from turning. and it never had a problem after that.

From that experience I learned from that experience how much twisting force goes through a uni frame. If you ride uphill a lot, race, or do other things involving hard changes in speed, the stiffness of your frame can be a factor in relation to that torquing effect. Stiffer will equal higher performance.

This can be especially troublesome on chrome plated frames, where there’s a lot less friction. Double-bolt seat clamp recommended there. Also you can try “roughing up” your seatpost with a file or similar to create some texture on it.

Steel vs aluminum

I don’t have enough unicycle experience to help. However when after years of riding a steel frame road bicycle, I tried an aluminum frame road bicycle, which happened to have a steel fork. The forks were very similiar, and the primary difference was the frames. I found that I became fatigued quicker on the aluminum frame and had trouble keeping my normal steel frame pace. This was doing weekly group rides with a local club, so I think it was fair of me to judge my ability to keep up with the same riders week after week. What I eventually learned was that aluminum frames are nice and light, but often much stiffer than a steel frame. The aluminum frame doesn’t flex and give as much of a soft ride over small road ripple type bumps. It does however, flex great over the bigger obstacles absorbing those impacts. On my road bike, I tryed a carbon fiber fork in place of the steel fork, which for me only provided a very minor improvement. I then tryed a Rock-Shox suspension road fork, and wow! It was a whole new game. The aluminum bike that was beating me up was now as comfortable as any road bike I’d ever ridden. The suspension fork made up for the stiffness of the aluminum frame and I could keep up with the group again.
So while not dirrectly comparable, I hope the experience helps. On a unicycle it probably depends more on the type of riding surfaces. Lighter is generally always better. But if you ride in an area with a lot of small high frequency ripple type bumps, I would expect aluminum to be a little tougher on you than steel. But aluminum might be better if you take a lot of hops and big drops. And not to sound potentially contradictory, but I have been very comfortable on an aluminum framed road unicycle on smooth roads.

One advantage of aluminium is the resistance to corrosion. Doesn’t matter so much if the paint gets scratched.

I can’t really compare the flex. My 20 and 24 inch unis are steel framed but that is probably too small to notice any flex. Middle sizes are all aluminium and seem quite rigid.

The 36 is a Triton titanium. It is built of quite large section tubing and I have never noticed any flex in it. Corrosion resistance doesn’t come better in any other engineering metal.

The way a unicycle frame is pointed in almost a straight line from contact patch to rider, it can barely act as a suspension, in the way a bike frame/fork can. Where you feel differences in frame stiffness, (as others pointed out) is riding uphill, and other times where you pull on the seat a lot. For riding uphill, as long as the wheel doesn’t touch the frame, and the diskbrake doesn’t rub, I don’t care, it’s just getting used to any particular setup. For hops I prefer a stiffer frame, as I find it confidence inspiring, but it’s honestly not a priority.

If you ride aluminium frames hard, they will fail. My Impact gravity frame developed a crack after 7 years of hops over 75 cm, and a lot of Trials/Street/Flat riding. Outside of those disciplines, frame failures are very rare, as the forces are a lot lower. It’s also probably not a really good evidence either, as virtually all the top riders ride aluminum frames, and they are the ones most likely to break parts.

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Another factor in this discussion apple/pear comparison is shape (construction) of the frame…

Next 1/1/2020 I will be unicycling 25 year exactly. Some of my history of unicycles:
For 15 year I drove steel (Semcycle Pro and XL)
For few weeks I tried alloy (KoxxOne, Kris Holm, Impact)
For 10 year I drove titanium (Triton, 4x Nimbus, and my “Gino” frame).

I would dare the challange to tell blindfolded what kind of frame I ride, but for sure I can tell blindfolded when I ride a Semcycle Pro, which was designed to be flexible.
This kind of flexibility adds to riding-comfort, and makes riding circles more smooth.

A too rigid frame however, isn’t comfortable. Maybe for launching a high-number-of-rev unispin, but not while being seated.

If you’re flexible you bend,
If you’re not flexible you crack.
~karate kid’s master.

That’s one force example, but simply doing corners, with a large wheel; imagine to hold that together with your muscle-power, and probably you suddenly estimate these forces a lot stronger.
Then think of a doing pairs and a spin, or a flague. A 29’er going fast trough a slight bending road.

Early '90-ies track bicyclist Urs Freuler couldn’t sprint anymore when you put him on alu frames. The lack resistance (I don’t call it stiffness) was transported by his muscles and nerves, and some neurologic reflex made it impossible for him to apply force. I think a Austrian university researched it, and in the meanwhile he returned to steel, returning to win 6-days track races again.

Where titanium doesn’t need any anodizing for that.

I don’t know the exact numbers -correct me if I’m wrong- but I think:

  • alloy is more flexible than steel, but less good in returning to it shape.
  • titanium is even more flexible than steel and alloy, but very rapid in going back, where the large wheel is adding up…

So for it’s flexibility and strength I used it for my own frame, which has thin double tubing with the (successful) intention to make it as flexible and responsive like a spring - and strong enough for the extremer forces in pair unicycling.

Beside that I still use the Nimbus Ti. It’s so durable; people still ask wether it’s new (while in reality being about 10 years old). I wont be surprised the moment those will be reproduced. Or maybe they were too good.

Not if you use a stainless steel tubeset.

I think I see stainless steel with maybe a copper layer and likely nickel layer and clearly chrome plating layer.
Not sure if you consider 25CrMo4 a “stainless steel”, but I’ve seen a few ending up having heavy corrosion. With different causes, but probably all initially started at the chrome layer, or directly underneath.
You still better keep it clean and dry.

That’s a polished stainless steel KVA MS3 tubeset, no chrome at all.

Stronger than 6Al/4V Titanium, if you believe the marketing

2 lbs difference(Oracle 26" AL vs. Nimbus 26" Steel)

Hey that’s a big difference. If not for the extra 200-300$. I would definitely get the aluminum. I remember when I first upgraded from my 20" to my 24", I quickly realized that I had to be more “physical” with my upper body movement. That’s the weight and inertia.

So, now two unicycles of equal size but 2 lbs lighter. I just tried it out. Yes, I can feel the difference. I’m not riding fast/cliff dropping, stiffness is a non-factor, but all around riding on smooth, rocks, hopping? So, responsive. No contest. Give me aluminum.

I doubt there is a 2lb difference (I know one says 15 lb and the other 17 in the description), but they have identical parts except for the frames, and the difference in the frames is less than one pound.

For me it wouldn’t be worth it.

My friends all ride carbon bikes and have been wondering when I’ll upgrade my old steel bike. I finally did and basically it was a huge waste of money, I love my steel bike, it’s so smooth and quiet, yeah it’s not as fast as the new carbon bike, but most of my riding is solo so who cares? There are plenty of people who will only ride a carbon bike and love the feel, but it is a personal preference.

I know that comparing bikes isn’t the same as unicycles, but I do feel it applies somewhat. The type of riding will also dictate the stiffness required, just riding along a dirt path it probably doesn’t matter much. Dropping, hopping, more agro riding it will make a bigger difference.

I pretty much only ride roads and gravel tracks, and still love the feel of my ali uni frame with carbon wheel. The stiffness lets me really slam the power up hills and spin up to speed quickly in high gear! I upgraded from an old steel bike to a new aluminium frame/carbon fork bike and really noticed a difference in power transfer as well. I’m willing to bet this has as much to do with modern frame/geometry design as it does material though (That is to say, they can probably create a steel frame with a modern geometry and shape that feels as stiff and responsive as my ali/carbon bike).

If anything I prefer my steel unis for rougher riding as it gives a bit of suspension :smiley:

I actually kept that option open, which is why I started my reply with “I think I see”.
That’s pretty awesome: old technique with new materials.

I noticed some (bicycle) framebuilders using that as sellingpoint, but didn’t expect it to be so widely used already. And used for unicycles!
Any know disadvantages yet?
What is it price-wise like?

A couple years ago I weighed a few of the common Alu and Steel frames available then (see post linked below) - probably not too much has changed weight-wise. I also had a few thoughts on the differences - also still relevant I think.

The stresses that go through a bike frame are very different. As a longer and more elaborate structure, often ridden hard in gears equivalent to a unicycle wheel of 80 inches or more, a bike frame needs to resist twisting.

A bike frame made of aluminium will tend to need larger diameter tubes in order to resist this twisting.

On a unicycle, a good quality aluminium frame such as a KH is more than adequate.

Remember, it is not just the material used, but other things such as the thickness of the walls of the tubes, the profile (cross section) of the tubes, and the quality of the build.

My old Coker was steel framed and flexed horribly because it was thin round-section steel tube. My KH36 is aluminium/alloy and I seldom notice any flex.

KH kit is good. Some people may think that other brands are better, or not, but the point is not whether KH is “best” but that KH is “very good”. If KH uses aluminium, it is because it is better than steel for that purpose.

A bike frame does gain rigidity by virtue of being more “3D” though (3D in scare quotes because it’s primarily in one plane).

This is slightly tangential, but the handlebar setup on my 36er puts a lot of torque on the seatpost and seatpost/handlebar interface. And the handlebar itself is only 22.2mm in diameter and floating out in the breeze, unsupported.

I recently replaced my Shadow base with the new beefed up version after breaking the old one. Now that the base is more heavily reinforced I wonder where the next weak link is. Probably the handlebar itself. There is already some paint mysteriously missing from the bar about 10mm forward of the adjustment clamp, which is where the bending forces would be concentrated. I expect I’ll see a fatigue failure there at some point.

Probably the real answer for handlebar users is a V frame, at the expense of weight and adjustability.

V-frames need to have fewer legs.

If you want rigidity and long reach handlebars (which is thread drift…) then something combining the principles of the Moulton “spaceframe” coupled with some features of the Hatchet (to keep the frame away from the knees) might be a solution.

To me, the solution is riding within the limits of a simple unicycle, sometimes with a short bar, sometimes without. It is the simplicity of the unicycle that appeals to me: a few simple variables (wheel diameter, crank length, tyre section, overall quality of build) and everything else is down to me as the rider.

Here’s a picture of a Moulton spaceframe, for younger readers to admire.

I’ve been riding a Nimbus 29" road with an aluminum Oracle frame. I recently swapped and put the original steel Nimbus frame on it. Its about a pound heavier with the steel frame. Riding it - I can’t tell the difference. The only time I can tell the difference is when I’m lifting it out of the garage.