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It's interesting that trackies in the 70s were trying to reduce weight that much. I don't think it's perceived as especially advantageous these days. The high
by loeg 2y ago
It's interesting that trackies in the 70s were trying to reduce weight that much. I don't think it's perceived as especially advantageous these days. The high-ish end track bike I'm assembling now will be a little over 8 kg (almost 18 lb). We also race much bigger gears (typically 95-110 gear inches in mass start racing, bigger for sprinting) than mentioned in the article (72 gear inches). The position that is considered aerodynamic is also much different -- there is much less focus on getting that insanely low, and instead the focus is on being narrow and getting the forearms parallel with the ground.
- Gualdrapo 2y agoNot sure if you know about Merckx's bike for his hour record - they did many interesting modifications to it aiming to reduce its weight
- loeg 2y agoYeah, Sheldon mentions it in this article. I don't think those mods helped. Weight has no impact on sustained speed.
- kevin_thibedeau 2y agoYou slow down incrementally between every power stroke.
- sudosysgen 2y agoA heavier bike would slow down less. At the end of the day the energy is lost to friction.
- kevin_thibedeau 2y agoWind resistance is the primary force slowing you down at speeds where riders care about such things. The tiny micro-accelerations after every dead zone add up in spent calories when you have a more massive bike+rider system.
- sudosysgen 2y agoThat's my point exactly, wind resistance is the principal loss of energy. The microaccelerations in the dead zone will be lesser in magnitude when you have a heavier bike plus system, but it will be more calories per m/s to recoup - while a lighter system will accelerate easier but have more acceleration to do. In the end the dead zone acceleration are calorically going to be exactly the same no matter the weight.
- xpe 2y ago> Weight has no impact on sustained speed. On a nice track, assuming a perfectly smooth surface and zero elevation change, I'm willing to accept the effect may not matter enough to care. But introduce even just a little bumpiness or some elevation change (perhaps in the track curves), and it might matter for someone pursuing the hour record.
- loeg 2y agoYou're not going up and down the track during an hour record. Just doing laps at the bottom (zero elevation change). Track surfaces aim to be very smooth in general.
- xpe 2y ago> You're not going up and down the track during an hour record. Here the English language obscures the physics. Sure, the black line on the track is at a constant elevation. But the tire's point of contact is different from the system's center of mass (CoM). CoM is key here. When a rider tilts in the turns, the CoM lowers. In the straights, it raises. So, you _are_ going up and down during the hour record. The question now becomes: how much effect does this elevation change have? It is one thing to be aware of the effect, run the calculations, and find the result is negligible. Has anyone done this? That would be an interesting analysis, and I'd like to see it. With this in mind, I will make another claim: for a particular rider, there is an ideal line around a velodrome that would minimize center-of-mass elevation change. This line would be faster than the current black line. How much faster? This would be a fun simulation problem. Another interesting connection: center of mass and bicycling explains why pumping works on a BMX track, a pump track, a trail, and so on. (There are other mainstream explanations, but I think the CoM explanation is the most elegant.)
- dahart 2y agoIt’s an interesting question & thought experiment! To the degree that it even matters compared to all the other bigger forces, I would put money on riders naturally adjusting for CoM changes by riding slightly higher during the turns; I’d bet they already take approximately the ideal racing line you suggest. I just watched a couple of velodrome rides on YouTube, and it does seem like riders are often closer to the red line during the turn and the black line during the straightaway, statistically, but it’s noisy and would need to be measured. The CoM’s elevation change on a velodrome track is due to roll rotation around the direction of travel, not to climb & descent. You can’t pedal harder to recover from a lean, so this is a different kind of up and down than straight line elevation changes. It makes sense that work is being done somehow if the CoM moves up and down, but the turns come with necessary changes to the higher moments of inertia anyway that flattening the CoM elevation doesn’t change. I’d speculate that the ideal CoM line might not be flat, in the presence of mandatory high speed banked turns; the fastest line and the line minimizing CoM elevation change might be two different lines. Do also keep in mind that on a velodrome track, a higher elevation line is a slightly larger radius turn & longer travel path. It’s also possible that trying to compensate for CoM elevation change adds as much time as it saves.
- hackingonempty 2y agoRolling resistance increases linearly with weight, so it does have some impact.
- loeg 2y agoOk. Almost no impact. Worth keeping in mind we're talking about a system weight of like 180 lb vs at most 185 lb here (Merckx was ~163 lb), for a relative difference of up to 3%.
- hackingonempty 2y agoIt largely is the streetlight effect: we all have or can easily get tools to measure weight, we all have significant experience with weight, etc... Aerodynamics are much more difficult, especially in the 1970s where you can't just do some CFD simulations on your computer. There also weren't cheap solid state strain gauges to outfit wind tunnels or the bike drivetrain. Since only tiny aero gains are available without banned aerodynamic devices, there isn't much optimization you can do and need sensitive tools.
- cenamus 2y agoMaybe that's just mostly due to the UCI regulations? No point to develop a fully fitted 5kg bike if it has to be 7kg anyways I suppose
- ndsipa_pomu 2y agoUnless you can hide away a 2kg battery/motor combo. (Just joking really as they do scan for hidden motors nowadays)
- bluGill 2y agoIf you have a 5kg bike you can put the extra 2kgwhere you want it. this can make a difference in a race.
- jdietrich 2y agoMost competition bikes weigh significantly more than the 6.8kg limit, because weight just doesn't matter very much. A lot of state-of-the-art road and track bikes weigh around 8kg. On the flat, weight only affects you during accelerations - at a steady speed, it has no significant impact on performance. Aerodynamic drag and rolling resistance are constantly sapping away power, so features that reduce these losses are nearly always worthwhile even if they increase weight. Even on a moderately hilly road stage, aero trumps weight by a considerable margin; on the track, weight is almost entirely irrelevant, particularly in longer events. A lot of riders like the feel of a lightweight bike, a lot of them believe that light bikes are faster, but that's only true on exceptionally steep stages or hill climbs.
- stevage 2y agoYeah I was curious about the weight thing too. The hour record is probably the event in which weight matters the least, since there's no acceleration and no hills.