Velocite Flux Alloy 26, 27.5 and 29er XC frames – why are they the best?


Sloping shape with bowed tubes to enhance vertical flex without affecting torsional stiffness
Sloping shape with bowed tubes to enhance vertical flex without affecting torsional stiffness


Material: shot peened, two-pass welded 7005-T6 aluminium alloy. Cold worked triple-butted tubes
Head tube: tapered 1 1/8″ – 1.5″
Bottom bracket: PF30

EN Tested


Wheel size 26″ 26″ 27.5″ (650B) 29″ 29″
SA 73° 74° 73° 73.5° 73.5°
HA 71° 70.5° 71° 71° 71°
ST 380mm 440mm 460mm 450mm 490mm
BD 28mm 28mm 42mm 63mm 63mm
TT 567mm 573mm 585mm 600mm 620mm
HT 110mm 125mm 105mm 100mm 110mm
RA 386mm 407mm
RC 425mm 425mm 430mm 439mm 439mm
WB 1043mm 1066mm 1068mm 1090mm 1110mm

NOTE: sizes XS and S are 26″, size M is 27.5″, sizes L and XL are 29″


You may have come across some information about our new alloy Fluy XC (cross country) MTB frames (and bikes), but as they are now nearly with us here is more information explaining why, how, what and for whom.

…this article should actually start with “Why did it take you so long?” We made an alloy MTB frame almost 2 years after our class leading carbon fiber Flux model was released. This is because there are many really good alloy frames in the market already, and due to our market positioning and stubbornness we refused to release an alloy frame that was not better than everything else that already exists. We do not believe in offering just another choice, we must make a real contribution.

We thus designed the Flux Alloy frames to deliver 90% of the stiffness of their carbon counterparts at roughly 25% weight penalty. This is actually extraordinary as we are working with 7005 alloy, not carbon fiber thus we are limited in how light we can go before the frame becomes unweldable or too fragile for aggressive off road use…and aggression is what the Flux Alloy is all about.

This is not your average frame….

As mentioned, the Flux Alloy is made from 7005 alloy, specifically T6 tempered 7005 alloy. This makes them one of the few MTB frames that use this high end and expensive alloy. Generally MTB frames are made from 6061 or other closely related 6 series alloys. While 6 series alloys offer great benefits when it comes to their ability to be reliably anodized and factories are very familiar with their welding and handling requirements, after welding and tempering an/or ageing (very important consideration!) 7005 alloy exceeds the 6 series tensile strength at a given weight allowing us to use thinner and larger diameter tubes without a significant weight penalty.

To maximize on the material properties we utilized two pass welding which increases the contact area between the tube and the welding material, spreading the shear stresses and thus increasing the joint stiffness beyond what is possible with a single pass, or especially the smooth type, putty filled welding process. The drawback is that even our factory which has been making alloy frames for 30 years and is considered to be the best alloy frame maker in Taiwan, and thus the world, can only make 10 frames per day using this technique! Their normal throughput for lesser frames is several hundred per day.

The best quality two pass welding on the planet.
The best quality two pass welding on the planet.

After welding, our frames are 100% shot peened to release surface stresses that result from the welding process. This can in theory increase the fatigue life of 7005 alloy 1000 times. Regardless of this theoretical advantage, we end up with a superior engineering solution and  a unique matte finish. The Flux Alloy and the Selene road bike are the only alloy frames on the planet that are shot peened after welding.

Flux Alloy has 90% of the performance of the carbon fiber Flux and by that we of course mean – torsional stiffness. Torsional stiffness (both at the head tube and at the bottom bracket) is the most important performance parameter in any frame, besides its weight. In fact we maintain that high torsional performance is more important than the lowest weight especially if you are a rider that prefers to ride fast or aggressively and wants to feel like the bike is working with them, not against them. If you do most of your competing and riding on the Internet forums then stick with the lowest weight frames…

To reach this high torsional stiffness target (140 N/mm) while keeping the weight reasonable (1680g for size L 29er, with decals and fittings) we had to choose our tubing very carefully. We thus used cold worked and triple butted tubes that were custom prepared for our frame. While hydroforming is a popular way to make modern alloy frames, the current hydroforming methods are focused on making tubes that look “cool” rather than perform well. We like to look cool too, but we’ll take performance any time.

A particular challenge was the rear triangle, chain stays to be more exact. It took us and this super experienced factory (they make most of the high end German brands, and recently that “Made in USA” brand as well) 3 months to figure out how to make just the chain stays… we did not accept any short-cuts or compromises that would affect performance. The Flux Alloy thus ended up with the largest and strongest chainstays of any XC bike in the world. We managed to cold work a single tube into 42mm tall chain stays – that means we did not weld them to a separate yoke – while still achieving a 2.35″ tire clearance (depends on brand and model as this varies a great deal). Single tube, giant size chainstays mean unsurpassed stiffness at the lowest possible weight, and this is not a cliché even though every brand + dog claims the same thing.

The largest single tube chainstays on any alloy XC frame, accompanied by a very large PF30 shell and oversize downtube. This BB is not going anywhere...
The largest single tube chainstays on any alloy XC frame, accompanied by a very large PF30 shell and oversize downtube. This BB is not going anywhere…

The other key elements towards achieving this epic level of stiffness is a PF30 bottom bracket system that uses BB30 cranks and a sealed BB to keep the dirt and at least some of the water away from the bearings, and our trademark 1 1/8″ to 1.5″ tapered head tube allowing us to specify larger diameter down tube and use the stiffest available forks – in our case the Magura TS8.

Oversize tubes for maximum torsional stiffness
Oversize tubes for maximum torsional stiffness

Why is this torsional stiffness thing so important for you? In real world terms – those that you experience as a rider – the Flux Alloy gives you just about immediate response when you press on your pedals. This becomes particularly useful when climbing technical trails with rocks, roots or other obstacles that you need to ride over. In the most extreme case, visualize for a second what happens when your rear wheel gets “stuck” on a rock or a root… you slow down, your balance suffers and your momentum disappears, over and over again… rear suspension will not save you in this circumstance as the compression of the shock will also rob you of momentum as your wheel is still stuck on a rock until your forward force overcomes the damping of the shock and the vertical plane of the rock allowing your rear wheel to finally climb over it.

Now let’s just focus on a hardtail frame, full suspension frames get a bit more complicated due to axle paths, shock tuning, rear triangle flex etc. Your normal hardtail frame that is not torsionally as stiff as the Velocite Flux Alloy (or Flux carbon which is even stiffer) will, in a situation when it hits obstacles and you are applying significant force through the pedals, twist around its bottom bracket instead of transferring your power to the rear wheel to help you get over that obstacle. While you are twisting your normal frame around its BB, you are not moving forward. This twisting is different to what happens when you wind up a watch or a clock as you get none of this energy, or time back. Even when you finally get over that obstacle and the frame springs back to where it should be, that energy goes straight up your leg, not into the rear wheel. It is gone.

With the Flux Alloy, much more of your power goes into forcing the wheel over the obstacle as the power cannot readily flow anywhere else, the frame will twist much, much less. Thus if you have the power to get up that trail, the Flux will allow you to do it. It will not slow you down.

Torsional stiffness in fact helps you any time you are overcoming inertia. If more of your power is directed towards overcoming inertia, rather than being dissipated or delayed due to your frame (or wheels and cranks) twisting and “winding up”, the faster you will overcome inertia and accelerate to the new higher speed. This is simple physics.

It also helps you when it is time to go down again. When descending technical trails your fork takes a lot of abuse and that abuse it transferred directly to your frame through the head tube. It is now important to realize that most of the impacts that your fork (and thus the frame) need to deal with while descending are torsional in nature. Even though the fork moves only in the vertical plane (up and down) your wheel almost invariably contacts the surface at an angle – either due to the rock or root not being entirely flat, or due to the camber of your bike due to pedalling  direction changes or cornering. 

The ability of the frame to resist these strong torsional forces translate to you, the rider, having more confidence because you will feel that you are going exactly where you though you would end up (good or bad), not somewhere “slightly off”. The increased confidence will allow you to go faster, but more importantly it will allow you to have a lot more fun. You will feel in control.

The last, but also a very important element is the geometry of the bike. Due to our positioning of having to make the best bikes on the planet we decided to release our Flux Alloy model in three different wheel sizes depending on the frame size. Thus, sizes XS and S are only available with 26″ wheels, size M with 27.5″ and sizes L and XL with 29″ wheels. There was no other way to preserve the geometry and frame features across all sizes. This means that it is simply not possible to make a size M or smaller of our Flux Alloy 29er and have it retain all of our performance and handling objectives. This also means that the 26″ and 27.5″ frames do in fact reach our objectives, without manufacturing or geometry sacrifices that you’ll find with some other brands.

The Flux Alloy frames will be available for purchase shortly, starting at US$ 589 for a frameset, and US$1789 for a complete bike with SRAM X9 and Magura TS8 fork.

  • I want a new frame… NOW! Great stuff this! Keep up the good work 🙂