Wider tyres and the rule of 105

The radius of the wheel is included in the inertia calculation - I don’t see any other mechanical principle that would involve “levers” with regards to inertia - except when we are talking about torque transfer and torsional stiffness (which is mostly addressed by choosing the right lacing pattern)

Otherwise, I don’t quite understand where you are getting at here - could you give me a hint?

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[quote=“jctobin1, post:79, topic:2147, full:true”]
Look, I love light stuff and have long been a weight weenie. But when I’m honest with myself I acknowledge that weight savings have had minimal impact on my performance, as opposed to aero stuff which actually does make me faster. [/quote]

That’s what I said. Inertia has no real impact on performance during an acceleration (you can calculate it and you can measure real-life differences, the match is perfect).
Climbing, the sinusoidal nature of our power output leaves the question of a performance impact, yet unanswered (to my knowledge… I think some teams tried to measure it but don’t know the results)

[quote=“jctobin1, post:79, topic:2147, full:true”]
But you’re arguing that you can feel 80g in a total weight difference between wheels, and this is highly improbable if everything else is equal. And all else is rarely exactly equal. [/quote]

As you mention, there are parameters that have a reasonable impact that you can feel and others not… Inertia has this that people can still feel it when it has little real impact.
I can’t remember what is the threshold people “feel”, but doing tests with weights glued on the inside of Tubeless rims, globally (you always have riders that don’t feel anything) Riders were sensitive to those changes, both in terms of acceleration perception or changing direction despite having no real impact on measurable performance.

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True. I missed that.
Now, given

Rotational inertia, or moment of inertia, is the rotational equivalent of mass; this is the quantity that we want to measure to see how much energy it takes to accelerate a wheel.

you have to exert (minimally) that force to the wheel to make it rotate faster.
You exert that force via the chain to the cogs of the cassette mounted on the wheel. So the distance from the cog teeth to the wheel axle is the lever by which you apply the force. The larger the used cog, the larger the lever, and the less force you actually need to apply via the chain to overcome inertia. The smaller the cog, the smaller the lever, and the more force you actually need to apply via the chain to overcome inertia.

Is it then wrong to assume that when sprinting, you are more likely to feel inertia differences, as you have less leverage?

Can you even take it further and say that your are more likely to feel inertia differences, when you are in situations where torque comes into play, rather than pure wattage?

This is entirely false… cyclists have a presumption of sensitivity to weight that makes them exceedingly susceptible to the belief that lighter is better but, back in the real world, that’s not how physics works. In fact, beyond the initial acceleration to set the package of bike and rider into motion, weight at the wheel is virtually irrelevant unless the rider uses the brakes to convert motion into heat and needs to re-accelerate. Even in that case though, you’re not noticing 40g per rim, you just think you are.

I don’t disagree with this at all… but the original point was how much livelier wheels felt because the rims were 40g less, which isn’t something where that 1% human factor is going to matter. You might actually be able to make a case for 40g per rim mattering at the end of a 200km race where you’re exhausted and barely hanging in and need to accelerate but the idea that these wheels were immediately more lively for being 40g lighter at the rim is where I’m saying you were just experiencing a placebo.

I see you are enjoying extended vacations… in the meantime
It’s known from years that rolling test have lead manufacturers to optimize their products to perform well on those test. That’s the reason over time, 23mm tires were closer to 25mm (GP4K on a 17C rim was already 25.2mm and the 25 measured 27+) since tests were done at iso-pressure, the wider the tire, the harder it was, the lower was the rolling resistance. It also lead Continental to make quite stiff tires, the GP4k was quite poor in terms of road-feel but was built to perform well on the rolling tests.

Some of the BRR limitations are also known, they are not using the biggest wheel diameter and have a static undamped weight on the tire then not simulate how the human body damp the vibrations (and consume energy). That’s not really new but it’s not always a problem if we consider few key points:

  • Test is set to simulate same vertical deflection (then similar spring rates)
  • Test is performed at a relatively low pressure (6 bars for a 25mm tire and 5,6 for the 28mm). For “reasonably good roads” You are not at pressures where the energy transmitted to the rider over bumps are yet a problem. Indeed Wheel Energy / Velonews measured that you need to be riding Paris-Roubaix conditions to have those pressures starting to cause damping issues (for the best tires), no doubt that on “normal” roads you are not yet causing harm, then comparison is fairly valid.

What are the alternative data? the zipp white paper? long story short, tire manufacturers I had the opportunity to discuss with, would say “the theory is nothing new, their numbers are exaggerated”.

The irony of saying the BRR protocol’s limitations are known while tossing a fit about someone questioning their protocols is really top material, well done.

So seems you start 2022 with the similar tone you closed the year… first I am not sure who the reminder of how Inertia works was for, thanks, that’s college science program.

Regarding how sensitive some parameters are, I would leave it to: have you done blind tests with Amateurs, Elite, Pro-tour riders ? have you measured performance variation and “blind-feed-back”? I have. I don’t recall confirming that 40g would be noticed, I previously mention I need to look back what the threshold was, I said that Inertia blind-feed-back is way stronger than the impact it has on the road.

Didn’t recall this bit so just re-read the test and confirmed it… this is never claimed by either Wheel Energy nor Velonews. Though they did take a shot at BRR’s protocols that I forgot about, so cheers for sending me back to that for a laugh.

Really do not seem to be able to read more than 2 lines… Limitations doesn’t mean anything is invalid, means you need to understand them. Yet you are unable to provide a single structured argumentation so far… at best I expect another sarcastic pirouette.

Read the complete protocol, twice probably cause it’s in there if you can understand it…

I’m quite capable of reading more than two lines… you just have yet to write two lines worth reading or taking seriously.

Sorry, but when you come running out of the gates contradicting yourself in a desperate attempt to disagree purely for the sake of disagreeing, I’m just not going to take you seriously in any way and I’m certainly not going to put any effort into educating you. Perhaps if you understood the testing protocol, which you clearly don’t after reading your description, or where it falls short in comparison to other tests done, which you clearly don’t given your misrepresentation of the conclusions drawn from other tests, then you would have a better position to debate this but, since you don’t, all I can do is sit back and enjoy the comedy.

That’s the benefit of being genuine… my tone stays the same even as the years change. Better luck next time.

Ho a pirouette

While we can look at you two fighting over internet, you made strong statements against BRR protocol but lacked explaining us, or answering previous @jctobin1 questions.

Is English your second language? Or are you just unfamiliar with what “pirouette” means?

I didn’t make strong statements about anything… I just accurately labeled their protocol as questionable. Had I known the extent of emotive defensiveness that objective recognition would foster, I would have tried harder.

As you are really applying force on the cranks in an up and down motion AND there’s a geared transmission from the chainring to the cog, I don’t think the change of the cog size matters beyond the fact that it’s the variable in the gearing equation.

But I absolutely ageee with what you are actually pointing at here: if inertia is noticeable, it’s only when accelerating, as in a sprint, and I would also think that a high torque, low cadence sprint (usually the start of the sprint) is when acceleration is highest.

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Mmm, need to think about the power conversion thingy. Thanks for the input.

Saying their protocol favors a particular manufacturer is a pretty strong statement. But based on what I’m seeing on this thread I’m not holding my breath for any informed and reasonable explanation.

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Perhaps this will be helpful (posted today):

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Great link…

If you go through some of the source material they link there, these two are great illustrations of how, in the real world, lower pressures are both faster and more comfortable.



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