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Welcome again to the Bikerumor Ask A Silly Query collection. This week, we’re taking a more in-depth take a look at the lesser-spotted utilization of Truss Techniques in bicycle body design. Certainly one of our readers is to know why using trussing, specifically inner trussing, hasn’t been extra broadly taken up by the trade. To deal with this query, we’ve approached a number of body designers who’ve, in numerous 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 trendy bike frames? Sure, we have to maintain the floor easy however why isn’t there extra speak about particular person strands of fiber taking a carrying load in a truss system? There may very well 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 the case of hole composite tubes/sections, probably the most environment friendly designs have skinny partitions and a big floor space. This makes the partitions susceptible to puncture and such constructions will be susceptible to shell buckling. Consider an empty soda can. You may stand on it, however the slightest contact to the wall of the can ends in collapse.
With a truss system, particular person members of the truss are extra strong than the skinny partitions of the tube and fewer injury 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 constructions.
Now a few of the challenges. Essentially the most urgent problem, and the seemingly 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 increase in efficiency. Funding into higher manufacturing strategies would seemingly yield extra constant, inexpensive merchandise.
Galaxy Gear Works: At the start, any inner trussing/bridging/and many others could also be very tough or unimaginable to perform in a significant or price efficient manner on any manufacturing scale. The prevailing manufacturing strategies that produce thin-walled steel tubing widespread within the bicycle trade (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 numerous forming strategies, we are able to solely produce hole tubes i.e. no trussing. Carbon tubing manufacturing as we all know it on this trade would additionally (normally) preclude the creation of inner options whether or not the tubes are fashioned on a mandrel or inside a mould.
Nevertheless… I’ve seen inner bridging within the steerer on a number of carbon forks in the previous couple of years. I don’t consider it’s common observe. Why not, you would possibly ask? Firstly, I’m sure that it’s an unlimited ache within the ass to mould the steerer with an internet dividing the tube. Layup precision and laminate compaction can be difficult to say the least. Bladder equalization and post-cure elimination is also important hurdles. Right here’s one other thought that’s maybe the actual cause why it isn’t widespread; 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.
Even though 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 attorneys glad, and the steerer has to have a reasonably 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 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 much too little reward. I don’t consider it may add measurable efficiency advantages or cut back weight at a significant degree.
I’ve additionally seen a number of examples of inner options on metal bikes, and I’m at present using an MTB with inner bridging within the chainstays. The purpose of the aforementioned options is stiffness. Dario Pegoretti created the Huge 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 lined with a tidy, brazed-on gusset. You may see these options clearly on the mannequin web page on the Pegoretti web site.
The tubes on this bike are pretty giant 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 as a result of these inner options? I don’t know. It may very well be measured in fact.
My present MTB was constructed as a “shreddy hardtail” so it wanted to be considerably burly. Energy 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 slender the place they have been fashioned across the tire. I felt like this slender cross part wasn’t going to provide sufficient lateral stiffness within the stays.
A part of my concern was the actual risk of tube deformation and bending below pedaling masses. Like the benefits I consider to be current on the Pegoretti downtube, I believe I added energy and stiffness to the tubes by including horizontally oriented plate bridges throughout the inside of the slender, 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 hassle?” I don’t know the reply. I didn’t do any lab kind 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 onerous using. I additionally know that I rattling positive didn’t save any weight by including these bridges.
Is it doable that inner bridging/trussing may enable 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 wouldn’t it come at a price to sturdiness and subsequently practicality? The reply is perhaps sure. Use the large, however not shocking proliferation of carbon restore companies arising everywhere in the nation now that the quantity of out-of-warranty carbon bikes has reached crucial mass as proof. The tubes on ultralight carbon highway bikes don’t must get a lot thinner until we see extra quantity of harder supplies like Dyneema included into the laminates. That stuff is pricey although!
In the actual sense, inner trussing doesn’t generally exist on this trade. With carbon manufacturing frames routinely coming to market beneath 900g, is there actually a must try to make them lighter? I’m unsure. And as a rule, these ultralight bikes are loads stiff due to excessive modulus carbon and sensible 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 it is usually much more boring. All people 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 isn’t any different alternative than selecting such a mode because the truss system. However this truss system is costlier – however it’s trying nice. Certain you must pay extra however then you’re getting a novel fashion.
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