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Welcome again to the Bikerumor Ask A Silly Query collection. This week, we’re taking a better have a look at the lesser-spotted utilization of Truss Techniques in bicycle body design. Certainly one of our readers is to know why the usage of trussing, particularly inner trussing, hasn’t been extra broadly taken up by the business. To deal with this query, we’ve approached a number of body designers who’ve, in varied kinds, used a Truss System in manufacturing of their body. Having made use of Truss Techniques themselves, they’re maybe finest positioned to touch upon why this uncommon body design has remained, nicely… uncommon.
Why is there no inner truss system in fashionable bike frames? Sure, we have to hold the floor clean however why isn’t there extra speak about particular person strands of fiber taking a carrying load in a truss system? There might be potential weight financial savings in stiff areas like BBs and head tubes.
IsoTruss: Truss programs do provide benefits in weight and stiffness, however there are some challenges incorporating the truss system with the remainder of the bike body. First, some benefits. In terms of hole composite tubes/sections, essentially the most environment friendly designs have skinny partitions and a big floor space. This makes the partitions vulnerable to puncture and such buildings could be vulnerable to shell buckling. Consider an empty soda can. You possibly can stand on it, however the slightest contact to the wall of the can leads to collapse.
With a truss system, particular person members of the truss are extra sturdy than the skinny partitions of the tube and fewer harm susceptible. The failure modes of a truss are sometimes simpler to foretell, too. Trusses are extra environment friendly, from a strength-to-weight standpoint, than hole tubes leading to stiffer, lighter buildings.
Now a few of the challenges. Essentially the most urgent problem, and the possible cause truss programs haven’t been adopted extra readily, is manufacturing. The truss sections require advanced manufacturing. Every part is made individually after which built-in with different body elements manually. This course of is gradual and costly. For a lot of, the extra price doesn’t justify the enhance in efficiency. Funding into higher manufacturing strategies would possible yield extra constant, cheaper merchandise.
Galaxy Gear Works: Firstly, any inner trussing/bridging/and many others could also be very troublesome or unattainable to perform in a significant or price efficient method on any manufacturing scale. The prevailing manufacturing strategies that produce thin-walled metallic tubing frequent within the bicycle business (aluminum, metal, titanium, or in any other case) preclude the inclusion of inner options. Whereas we are able to manipulate wall thickness with butting processes and shapes with varied forming strategies, we are able to solely produce hole tubes i.e. no trussing. Carbon tubing manufacturing as we all know it on this business would additionally (normally) preclude the creation of inner options whether or not the tubes are shaped on a mandrel or inside a mildew.
Nevertheless… I’ve seen inner bridging within the steerer on a number of carbon forks in the previous couple of years. I don’t imagine it’s common observe. Why not, you would possibly ask? Firstly, I’m sure that it’s an infinite ache within the ass to mildew the steerer with an online dividing the tube. Layup precision and laminate compaction could be difficult to say the least. Bladder equalization and post-cure removing may be vital hurdles. Right here’s one other thought that’s maybe the true cause why it isn’t frequent; a fork steerer has to fulfill sure structural standards that maybe outline the wall thickness to a level that an inner internet/bridge is superfluous. Shear and bending forces on the fork crown apart, the highest of the steerer tube has to withstand the clamping forces of the stem and ham-fisted mechanics.
Although everybody ritually abides by the producer’s torque specs and makes use of a torque wrench to put in the fasteners, it has to resist a good bit of crushing power. Add the real-world stresses with the “fudge issue” that the engineer calculates in there to maintain the legal professionals pleased, and the steerer has to have a fairly hefty wall – actually burly sufficient to deal with regular torsional, shear, and bending masses as nicely.
The steerer additionally has to have that “hefty” wall thickness by way of a lot of its size to accommodate the stem clamp top for an excessive vary of motorcycle sizes, assuming a manufacturing fork. So… does it actually make any sense for inner trussing/webbing/bridging on a manufacturing made fork? In my view, it will require an excessive amount of effort for a lot too little reward. I don’t imagine it might add measurable efficiency advantages or scale back weight at a significant degree.
I’ve additionally seen a number of examples of inner options on metal bikes, and I’m presently driving an MTB with inner bridging within the chainstays. The purpose of the aforementioned options is stiffness. Dario Pegoretti created the Massive Leg Emma with a collection of flat sheet bridges within the downtube. They’re inserted into slots lower into the perimeters of the tube, brazed into place and coated with a tidy, brazed-on gusset. You possibly can see these options clearly on the mannequin web page on the Pegoretti web site.
The tubes on this bike are pretty massive in diameter for metal tubing, and I’m positive that the partitions are fairly skinny. In my view, the bridging plates are lengthy sufficient (in reference to the lengthy axis of the tube) to behave as a truss to extend the tube’s resistance to side-to-side bending forces i.e. all-out sprinting for metropolis restrict indicators on Tuesday nights. How a lot stiffer is it attributable to these inner options? I do not know. It might be measured after all.
My present MTB was constructed as a “shreddy hardtail” so it wanted to be considerably burly. Power and stiffness have been paramount, and people attributes needed to marry with a kinda brief chainstay size and a pair of.8″ tires. With all that in thoughts, the chainstays have been fairly slim the place they have been shaped across the tire. I felt like this slim cross part wasn’t going to supply sufficient lateral stiffness within the stays.
A part of my concern was the true chance of tube deformation and bending beneath pedaling masses. Like the benefits I imagine to be current on the Pegoretti downtube, I believe I added power and stiffness to the tubes by including horizontally oriented plate bridges throughout the inside of the slim, ahead portion of the stays. I executed these additions by slicing the tubes, inserting the sheet-metal plates (about 4 inches lengthy), and welding the plate’s edge alongside the tube intersection.
Now we ask the query, “was it value all the trouble?” I don’t know the reply. I didn’t do any lab sort testing or calculations. I’m no engineer. What I do know is that the bike rides nicely and goes robust after greater than two years of exhausting driving. I additionally know that I rattling positive didn’t save any weight by including these bridges.
Is it attainable that inner bridging/trussing might permit thinner partitions on the tubes? I’d say heck yeah! How would we do it? Maybe 3D printing by some means slightly than laborious hand work or a mixture of each? And would it not come at a value to sturdiness and due to this fact practicality? The reply could be sure. Use the large, however not shocking proliferation of carbon restore providers bobbing up everywhere in the nation now that the quantity of out-of-warranty carbon bikes has reached important mass as proof. The tubes on ultralight carbon street bikes don’t have to get a lot thinner until we see extra quantity of more durable supplies like Dyneema included into the laminates. That stuff is pricey although!
In the true sense, inner trussing doesn’t generally exist on this business. With carbon manufacturing frames routinely coming to market under 900g, is there actually a have to attempt to make them lighter? I’m unsure. And most of the time, these ultralight bikes are loads stiff due to excessive modulus carbon and good laminate engineering.
Frace Bike: A tube in comparison with the truss system is having at all times much less weight for having the identical stiff attribute. So it’s for positive extra weight saving to have a tube – however additionally it is much more boring. Everyone is doing tubes – however we need to have one thing completely different from all of the others. And, for having a totally milled body out of aluminum there is no such thing as a different alternative than selecting such a mode because the truss system. However this truss system is dearer – however it’s wanting nice. Certain it’s a must to pay extra however then you’re getting a novel fashion.
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