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So I ditched 85g butyl for 35g TPU inner tubes

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So I ditched 85g butyl for 35g TPU inner tubes

Old 05-20-24, 12:33 PM
  #126  
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I'm well above the scatter graph of pro cyclists, but still liked (past tense, but still a little) to play a weight weenie game within a modest budget. Still like lightweight-ish bikes.

By the way, I just bought a set of latex tubes. Why not TPU? I dunno, it was an impulse buy when a "sale" popped up somewhere. I've always used lightweight and undersized butyl tubes, mainly because the undersized ones are easier to install. Add lightweight, and they're more compact to fit the spare in my saddle bag. As a change from my past attitude, I bought these tubes, not for the weight savings, but I wanted to see if they made any perceptible difference in ride quality with the good quality tires I ride.

Last edited by Camilo; 05-20-24 at 12:48 PM.
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Old 05-21-24, 04:43 AM
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Originally Posted by terrymorse
Yet for those of us "gifted" (cursed?) to live our whole adult lives near the bottom of the BMI graph, it's a thing.

At 185cm & 76kg, I'm definitively too heavy to be a pro cyclist . Lightest I've been is last November at 75kg and I was starting to look like a skeleton. Definitively not my healthy weight.
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Old 05-21-24, 07:39 PM
  #128  
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Originally Posted by Koyote
Extra weight generally equals worse aerodynamics.
way too big of a generalization. If we’re talking about body weight, you have to consider surface to volume ratio. As people get heavier, their surface area doesn’t increase linearly with weight. Thus, comparatively larger riders tend to have better surface to power ratios than little climber guys. ( assuming that the larger rider produces more power from being bigger, and isn’t just fat.)

Thus a bigger racer like Fabio Castelli, can be dominant on a flat tt course with a great power to surface ratio, but not an elite climber because his power to weight ratio s lower than the elite little climbers.

In other words, a heavier rider can be more aero, at least in relation to their power, Than a smaller rider, if the extra weight correlates with more power.
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Old 05-21-24, 08:07 PM
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Originally Posted by merlinextraligh
way too big of a generalization. If we’re talking about body weight, you have to consider surface to volume ratio. As people get heavier, their surface area doesn’t increase linearly with weight. Thus, comparatively larger riders tend to have better surface to power ratios than little climber guys. ( assuming that the larger rider produces more power from being bigger, and isn’t just fat.)

Thus a bigger racer like Fabio Castelli, can be dominant on a flat tt course with a great power to surface ratio, but not an elite climber because his power to weight ratio s lower than the elite little climbers.

In other words, a heavier rider can be more aero, at least in relation to their power, Than a smaller rider, if the extra weight correlates with more power.
Since you quoted my post, you will hopefully note that I was not discussing power, or power to surface ratio, or anything of the sort. You have simply introduced a whole bunch of additional variables that I didn’t even obliquely reference.

The generalization which you quoted is perfectly valid.
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Old 05-22-24, 04:01 AM
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Originally Posted by merlinextraligh
In other words, a heavier rider can be more aero, at least in relation to their power, Than a smaller rider, if the extra weight correlates with more power.
So if the heavier rider is more aero then why do they need more power on a flat TT?
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Old 05-22-24, 06:37 AM
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Originally Posted by PeteHski
So if the heavier rider is more aero then why do they need more power on a flat TT?
Answer: because more weight generally equals worse aerodynamics. 😉
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Old 05-22-24, 06:39 AM
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Originally Posted by PeteHski
So if the heavier rider is more aero then why do they need more power on a flat TT?
they’re relatively more aero in relation to their power output, i.e. watts/surface area tends to be better for a larger rider than a smaller equally fit rider, while the smaller rider is likely to have watts/kg.

As you scale people up, their surface area doesn’t go up linearly with weight. So if the heavier rider is stronger, they’re going to be faster in a flat tt, hence riders like Cancellera, who was a great time trialist, but not an elite climber.
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Old 05-22-24, 06:45 AM
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Originally Posted by Koyote
Answer: because more weight generally equals worse aerodynamics. 😉

Again in absolute terms, the more you weigh, the more aerodynamic drag you have is correct.

However, coasting downhill ( which I believe is where this started), the larger rider’s added mass will more than offset the increased drag because the bigger riders proportionate increase in weight is less than their increase in surface volume.

And if the the large rider has a proportionately higher power output than a smaller rider, the larger rider will be faster on a flat tt, because they have a comparitively smaller surface area in relation their respective weights.

It’s why I can win Tt’s and get dropped on climbs by people I can beat in a tt.
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Old 05-22-24, 07:04 AM
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Originally Posted by merlinextraligh
they’re relatively more aero in relation to their power output, i.e. watts/surface area tends to be better for a larger rider than a smaller equally fit rider, while the smaller rider is likely to have watts/kg.

As you scale people up, their surface area doesn’t go up linearly with weight. So if the heavier rider is stronger, they’re going to be faster in a flat tt, hence riders like Cancellera, who was a great time trialist, but not an elite climber.
Yeah I get that. It’s just a bit odd to state that they are more aero. They are ultimately less aerodynamic, but have enough power to offset the loss.
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Old 05-22-24, 02:48 PM
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Originally Posted by merlinextraligh
in absolute terms, the more you weigh, the more aerodynamic drag you have is correct.
Which is pretty much what I wrote in the first place.

It seems like you dragged this off on a tangent in an attempt to impress us all with your vast knowledge; Next time you feel a need to do that, please leave me out of it.

Last edited by Koyote; 05-22-24 at 03:07 PM.
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