Titanium vs aluminum?

Well I am starting to think about putting together a freestyle uni and after now having to upgrade every single stock uni I have bought, I want to do this right.

I am a huge fan of Miyata unis, they have history, style, and a great reputation. They also have amazingly light, custom fitted, and strong frames, but they come at quite a price (about 450 Canadian shipped).

The other option I have been looking at is the New Koxx signature frame from municycle.com or maybe someone more local has it. This frame is wayyy cheaper than the Miyata one, (I’m estimating around 280 shipped based on the shipping of the Miyata). But it is also heavier and weaker than the Miyata I believe.

My major question is how much difference is there between Titanium and Aluminum? From what I hear Titanium is both stronger and lighter, but how much so?

Is it worth the extra 170 dollars for something that is custom fitted, and however much stronger and lighter?

Please only give factual answers not just the Koxx frame is sexy and aluminum therefore it is better.

Ask around and see if you can find some reviews on the frames, Just because you know the material, dosn’t mean you know its strength. See if you can find anyone that has broken one of them, and find out how.

Please ask only answerable questions, not just how much difference is there between titanium and aluminum. What “difference” do you mean?

Lighter? You mean denser. Titanium is denser with a specific gravity of 4.5 as opposed to aluminum at 2.7. Both materials are considered lightweight but of course 10 pounds of aluminum is heavier than one pound of titanium, or lead for that matter. Light doesn’t mean anything is this context.

Cost? Although titanium has dropped dramatically in price do to improvements in production and refinement, aluminum is still substantially cheaper. Any alloy of aluminum is cheaper, and there are some strong ones like 7075-T6.

Tensile stength? Ti has a yield strength of 830 MPa making it much stronger than aluminum at 200 MPa.

Machinability? Aluminum, any alloy, hands down. Titanium is a pain to machine.

Weldability? Titanium is a poor heat conductor and, therefore, welds much more easily than aluminum.

Titanium is a cool, high tech material having few, if any, unicycling advantages over aluminum.

I don’t think that’s true. Everyone likes the aluminum KH frames because they’re lighter than steel frames; a titanium frame could be stronger than the KH at the same weight, and wouldn’t fail in the way we’ve seen KH frames fail. With titanium, you could probably have a crown design similar to the KH, but with the seat tube going all the way through the cross-bar, greatly increasing the range of possible seat heights (which on the KH is limited to about 3cm).

But it certainly would be significantly more expensive.

Part of the reason that titanium is popular on bikes is that it can be more flexible than Al - no fatigue problems - so you can get a hardtail that’s got a bit of springyness in the frame so doesn’t have too harsh a ride. That might make a uni frame too flexy, unless it just used thicker tubing, possibly removing any advantages.

Would be damned shiny though.

I was going to say the same thing. Titanium is the holy grail for bike frames because it has the springiness of steel but can be lighter (OK Harper, less massive) for the same strength and doesn’t corrode. The downside is it’s expensive. Aluminium bike frames are far too stiff, feel dead and crack.
But for a unicycle frame, the stiffness of aluminium is probably an advantage because of the pedalling forces trying to move the tyre into the frame. And lightness isn’t really much of an issue anyway because unicycle frames weigh bugger all anyway compared to the wheel, tyre and saddle.


just here to pile on…Ti is to springy for uni frames…Tholub, have you seen any Ti bike forks latly?

The most important component in a good frame, be it bike or unicycle, is good design. The secondmost important component is good build; in other words it was assembled properly with good welds, brazes or joints. It doesn’t matter what it’s made out of if those two requirements aren’t met.

Aluminum is stiff and basically brittle. This means frams generally have to be fatter to retain stiffness. And they have to be stiff, because if they flex, they will fail that much faster. That’s what worries me about aluminum unicycle frames, because all the twisting force that goes into them has to be completely absorbed or the frame is in danger of stress fractures over time. On the other hand, that stiffness is just what you want for most types of unicycling, so it’s fine as long as the legs or crown don’t have to be too fat.

Titanium flexes, which is generally a plus on a bike frame, but is not desirable on a unicycle frame. So you have to design to minimize the flex, which kind of eliminates one of the nice advantages of using Ti. However, if a Ti frame flexes a little bit, it can do that forever without leading to cracks or eventual failure. If the flex is minimal enough it will not be noticeable by the rider while even that amount of flex is probably not acceptable for an aluminum frame.

I love the look of anodized aluminum, but unfinished titanium looks pretty cool too. Nobody wants to paint it, because then you have to tell people what it’s made out of, taking away from that aspect of the coolness factor.

All of that said, the Koxx frames look great. I borrowed one for the coasting and gliding competitions at Unicon and enjoyed riding them. They have very tight clearance on the tire though, so it could limit your tire choices. Also they’re new, so they don’t have an established track record for reliability. I think they’ll hold up fine though, unless you really abuse them. The construction looks very stiff and beefy.

The Miyata frames have been available in Ti for several years, but I don’t know much about them. Most owners of those frames live in Japan, and use them for either track or Freestyle, which generally is a lot less abusive to frames than stuff like Trials or Street. I’ve never heard of a failure (with either frame), and I expect the Miyata ones to hold up as well as, or better than, anything aluminum that’s currently out there.

To me the Koxx frame looks like a better design for stand-up skills, though Japanese riders make it obvious that Miyata frames can work just fine. The Koxx frame may be more of a knee-banger for other skills though, but at least nothing sticks out–it just has the corners at the top.

Looks like you didn’t have a problem answering his unanswerable question…hmm…you must be super man or something.

I know very little about diffrent metal types, strengths and such. But is it true you usualy weld Ti in a bag?

I don’t have much experience with different and exotic frames, so I am curious: Can you actually feel the flex of the frame, i.e. do you speak out of experience? I guess the only problem is the torsion of the frame (of the crown against the axle). But shouldn’t such forces be avoided anyway? I mean, thats what kills rims as well and in such a situation the wheel probably flexes the most anyway.

I also think that it is NOT true that flex is desirable in a bicycle frame in general. The flexing of the frame absorbs a significant amount of the pedal force - which is the last thing you want. So especially for competitive cycling the frame must be as stiff as possible. Only the parts holding the wheels should flex, but that is realised through the shape of the back of the frame.

My father (who is in general pretty cheap) recently got a new road racing bicycle with a Ti-frame. Now he is consistently 3 km/h faster on average (i.e. the average speed on his training round with some hills increased from 30 km/h to 33 km/h. According to him most of that can be attributed to the stiffer frame (previously he had a steel frame).

Superman is one word and is capitalized.

Ti needs to be heavily back purged with an inert gas such as argon or helium or, as you say, bagged. The “bag” is actually an encasement that can withstand the heat and hold the inert gas. Ti oxidizes easily at the melting point and makes brittle welds. So what Evan says about bagging it is true.

Yes. Some frames can be very flexi, like a Semcycle Deluxe frame, which advertises the flex as “more comfortable ride - less saddle soreness.” That is subject to opinion, but it could work in terms of the seat flexing from side to side to do less chafing.

My best example of a non-flexi frame would be my Wilder, with an aluminum box-type frame. I hope it doesn’t flex, because that would lead to cracking.

In between is my carbon fiber MUni by Roger Davies. Carbon tubes with aluminum lugs. The lugs fit inside the tubes, and were fixed in place with strong epoxy. But the fit was so tight on the joints, one of them pushed all the glue out and it came apart after a while. I couldn’t for the life of me get those two pieces back together (Roger fixed it), which told me not only how solidly it was constructed, but also the types of twisting forces that pass through any unicycle frame if you pedal hard.

Even after looking it up, not sure what you mean by torsion. The foce I speak of is basically your hand on the handle or legs pushing the front of the seat to the left, while your pedaling force twists the wheel to the right. Repeat in the opposite direction for each revolution of the wheel. This affects the whole frame from seat clamp to bearing attachments, though how it’s affected depends on the build. On my carbon frame the lug joints were especially vulnerable because they tended to want to “unscrew.” When Roger fixed it he added some aluminum pegs in each joint to keep them from twisting.

Correct. Side-to-side flex=bad; up & down flex, if it works to smooth the ride=good. A well-designed frame will provide the light suspension effect without any side-to-side flex. For racing, depending on the application, you might not want any suspension effect either.

Getting back to the original question, if you ride my Wilder up a steep hill, then you ride an old Schwinn up, you’ll be very aware of the frame flexing and if you’re an experienced hill-climber you’ll be able to feel your energy being sapped by it.

Re: Titanium vs aluminum?

Niko <Niko@NoEmail.Message.Poster.at.Unicyclist.com> writes:

> I don’t have much experience with different and exotic frames, so I am
> curious: Can you actually feel the flex of the frame

I think Shledon Brown has it right:

Any frame will flex around the bottom bracket a bit in response to
pedaling loads. This flex can be felt, and many riders assume that it
is consuming (wasting) pedaling effort. Actually, that’s not the
case, because the metals used in bicycle frames are very efficient
springs, and the energy gets returned at the end of the power stroke,
so little or nothing is actually lost.

That’s an interesting page with a lot of relevant information. But I
also think John Foss hit the nail on the head: A well designed frame
beats a poorly designed one regardless of material.

> I also think that it is NOT true that flex is desirable in a bicycle
> frame in general…

See above. Good (bicycle) riders can make use of the energy stored in
the frame as they mash down on the pedals and whip the bike side to
side during a sprint.

I don’t expect the same is true as a unicycle frame twists, though.

By the way, I don’t believe stifness has anything significant to do
with the perceived harshness of a bicycle’s ride. Tires, even high
pressure road tires, deform farm more than the frame. The
transmission of shocks from the road has more to do with frame
geometry than material.

> My father (who is in general pretty cheap) recently got a new road
> racing bicycle with a Ti-frame. Now he is consistently 3 km/h faster on
> average (i.e. the average speed on his training round with some hills
> increased from 30 km/h to 33 km/h. According to him most of that can be
> attributed to the stiffer frame (previously he had a steel frame).

Don’t believe anecdotal evidence. Even from your dad :slight_smile: If he really
is riding that much faster, it is likely a combination of better fit,
lower friction, and just being psyched to be on a hot new ride.

By the way, I have a minor correction for John: Aluminum is not stiff.
It has a lower modulus of elasticity than titanium (i.e. it the same
shape bends more easily). Aluminum frames use extra material to
achieve the high amount of stiffness needed, as John pointed out, to
protect the brittle material from cracking.


The elastic or Young’s mudulii (?) for the three materials being discussed will vary slightly according to the alloys but they are roughly:

Aluminium 70GPa
Titanium 110GPa
Steel 205GPa

So for a tube of the same size aluminium will deflect or flex 3 times as much as the steel one under the same load.
ali bike frames are stiff because of the tube sizes are so much bigger than steel, double the diameter of a tube and its stiffness will increase by 16 times (I think) easily overcoming the fact that the material is more flexible.

Thank you for those interesting replies. It’s good to hear some well founded arguments instead of just speculating.

Would a heavily ovalized tubing be an option for Ti unicycle frames (increasing stiffness at least in some directions)? The whole tubing diameter can’t be increased by much.

I don’t know if ovalizing helps any against twisting (torsion?). It probably helps some, but perhaps not enough to justify a higher cost in materials or build?

The second axis of force through a unicycle frame is probably stress from pushing-pulling on the seat or handle. This would tend to bend the frame to the front or rear, starting from wherever the bottom of the seat post is inside the frame. That’s another reason why you want a comfortable amount of tube inside the frame…