wphamilton

Unless it's a shark's skin. Then it's faster.

wphamilton

I think maybe the increase in rolling resistance is even less than the minuscule amount calculated above (though I have no quibble with his calculation). I visualize the stiffer section not bending quite as much and the surrounding softer tube bending a little bit more to compensate. That doesn't necessarily mean resistance proportional to the local thickness. Since lower pressure tires have sharper bends, and yet can have lower RR, I reason that the sharper bend at the patch edges has less affect than if it was itself deformed. So ... less than the fractional watt calculated. Maybe,

woodcraft

There, you conceived of it, so we have proved that it's conceivable!

bbbean 

Again, not the relevant characteristic. Per Josh Poertner (google him to check his credibility), the relevant issue is that most glues remain slightly viscous even after curing, and that this viscosity means the tire is constantly deforming the glue slightly, which creates a small but measurable increase in rolling resistance. When he worked with riders attempting the hour record, he used a much harder, less viscous glue to reduce this effect.

Glue isn't necessarily the "justification". The OP (among others, including folks like Poertner and Chung) have simply considered the possibility that anything that changes the shape or function of the tire could impact rolling resistance. That's plenty of justification to consider a problem.


One of the wonderful things about science is that we don't have to rely on "it seems" to determine what works and what doesn't. Once we can determine what the effect is, we can consider whether it "matters". If one is trying to squeeze every single watt out of one's performance, there are a great many things that matter.

bbbean 

Thank God for testing.

njkayaker

I addressed that, You missed my post from 2 hours earlier.

Do racers use track glue on road races?

We don't know the effect of a patch.

One should squeeze larger watts before worrying about tiny watts (doing the opposite doesn't make any sense).

If the OP was trying to "squeeze every single watt", they would be using different tires.

njkayaker

I never claimed it was inconceivable per se. Merely being conceivable doesn't mean anything.

A thing being conceivable doesn't mean it will help the OP at all.

bbbean 

EXACTLY. Hence the OP's question.

njkayaker

Even without knowing, it is very likely not going to matter, at all, to the OP (who is probably not trying to break any records).

It's kind of bizarre to be concerned about the effect of a patch here.

bbbean 

Nothing at all bizarre about being curious and trying to learn. Curiosity is a good thing, as is striving for improved performance.

njkayaker

A real, useful interest in "striving for improved performance" would look at other things that are going to have a large impact first.

If the OP was really interested in "the best performance", he would be using "better" tires (and, likely, other things). Not wasting his time worrying about the effect of a patch.

It's bizarre because discussing this one thing in the absence of other (much more valuable) things doesn't make sense.

bbbean 

Check your assumptions. How do you know what the OP has or hasn't done? For all we know, the OP is getting ready to attempt the hour record and has done all those things. All we know for sure is that he's a racer and he'd like to save a few bucks.

But even if he was a casual rider who posted a question in an idle moment, the question is worth asking. Science and technology progress because people ask questions and test hypotheses. Pure science is where applied science gets its tool kit.

FWIW, I was pondering this very question on my ride this morning and conducted a thought experiment. If we were to assume that we had a perfectly round wheel, tube, and tire on a perfectly smooth surface, we would expect rolling resistance to be very low, right? Now assume we introduce some irregularity to the situation - say a 2mm tall strip laid across the track every 2.1 meters. We would expect a small but measurable increase in rolling resistance, right? Now assume that instead of the irregularity being on the track, it was on the tire. Again, we'd expect a small but measurable increase in rolling resistance over the perfectly smooth tire.
Moving the irregularity to the tube brings in other variables related to the function of the wheel, tube, and tire as a system, but we would still expect some difference between a perfectly smooth system and one with an irregularity.
So I'm hypothesizing that a patched tube would, in fact, have higher rolling resistance than an unpatched tube. What I don't know is the magnitude of that difference. Clearly, you think that difference would be small, and I don't disagree. I would be surprised if the difference were large. Fortunately we have the technology available to measure the difference and to consider the relevance. In a sport where results are measured in tiny fractions of a second, the question is well worth considering, even if the likely answer is "don't worry about it."
Kudos to the OP and to folks like Chung and Poertner who consider topics like this and push the envelope of what is possible.
BB

njkayaker

On GP 5000 tires? Really?

If he was "ready to attempt the hour record", he just would have used a new tube instead of asking about it here.

From the tires, we already know he hasn't "done all those things".

The patch is on the tube. The tube is inside a much thicker casing, which means the patch thickness is pushed towards the center of the wheel. So, compared to your ideal-world example, "we'd expect" the rolling resistance of the patch to be much less. Maybe, on the order of variances of the casing thickness. It's "conceivable" that a patch, in the right place, could reduce rolling resistance.

It's highly unlikely that anybody would go through the expense of the kind of experiments necessary to detect the tiny difference in rolling resistance of a patch.

The mistake you keep making is ignoring that the OP was looking for a practical answer. On GP 5000 tires, he's not "pushing the envelope". You are just wandering off into the weeds taking about what's "theoretical" or "conceivable", avoiding answering the question the OP was really asking.

SethAZ 

I've got no problem with the purely theoretical thought experiment posed here. I think we all agree that, as a practical matter (rather than intellectual self-pleasuring) the patch's effect is, if non-zero, at least utterly insignificant.

There are parallels here with software development, surprising as that may seem, as well as other engineering disciplines. When writing code, how the code is written, compiled, etc. can change the performance of the code. Code writers will often write code, then go back over it and optimize it, trying to squeeze more performance out of it, doing the same computation for less time, energy use, whatever. While any code can, in theory, be optimized, it rarely pays to optimize all code. Rather, profiling tools are used that show where the code is spending most of its time, and then the code that is having the greatest impact on time are optimized first, achieving the best bang for the buck. And, really, the optimization that usually achieves the greatest results occurs during design stages where the basic architecture is conceived; a more efficient architecture programmed without optimization can be way better than a crappy architecture that's then micro-optimized to hell and back.

If the OP were really interested in maximizing his performance, he'd be asking whether he's got the right bike, then the right accessories on the bike, the right tires, the right clothes and helmet, etc. Eventually, way down near the bottom of the list of every conceivable factor that might have a measurable impact on performance, one would find the question of whether a given inner tube was patched or not. This question would probably be just behind whether to shave one's eyebrows, and just ahead of whether or not one should wax the frames of one's sunglasses.

bbbean 

I get it. You're not a curious guy. You are pretty sure you already know what matters and what doesn't, and you're comfortable prescribing those things for other people. Your objections are noted.

bbbean 

How do we know he hasn't already done all those things?

Not to belabor the point, but everyone who rides on tubes will eventually be faced with the choice of whether to replace a tube or patch it. It is just as reasonable to ask whether patched tubes impact rolling resistance as it is to ask whether latex tubes are faster than butyl, or whether one brand of tube is faster than another. If I knew that a patched tube cost me half a watt, it'd be worth an extra few dollars a year to replace tubes in my race wheels. If I knew it dodn't matter, I'd save the few bucks and spend them on something else.

I'm glad the OP asked the question, and I'm glad that folks like Chung and Poertner are discussing the hundreds of small choices we all make that determine whether our equipment is as efficient as it can be.

SethAZ 

I hear ya. If I were competing for world records, the olympics, or the Tour de France I'd probably be looking far and wide for every marginal gain I could find and feasibly get. Since I'm not, I'll prioritize my focus and attentions, and replacing a patched tube over concerns about performance falls well below my personal threshold.

Btw, it's kind of funny to say that the performance drop from a patched tube is in theory measurable but practically insignificant. I say this because while it's true that it's practically insignificant, I'd bet dollars to donuts that it's not even practically measurable. Every machine used to measure the rolling resistance of a tire will have a margin of error, and it wouldn't surprise me in the least if the performance hit due to a patch on an inner tube is smaller than the margin of error of the machines used to try to measure it. So it's probably measurable in some abstract sense, but practically impossible to measure with any confidence.

My equipment is what it is. I'll make changes that seem like they'd actually make a difference worthy of their cost and effort, or that appeal to me in concept enough to motivate me to action (this is, after all, a hobby, so like all hobbies doesn't require justification for every little choice). There's no money riding on any of my personal cycling results, no fame, glory, or the esteem of the world. What I admire the most about conversations like this one are that when one really gets down into the weeds on the physics of something like this, it's not so much an exercise in deriving concrete improvements in one's gear so much as it is an intellectual exercise to understand how things work. That's something I actually admire a lot, and which I feel is undervalued by much of today's society; people in general are way to incurious about how things work, and sometimes (though not in this case) that actually matters.

Sy Reene

Guaranteed: Patched tubes are slower than equivalent non-patched tubes. Discuss. (aka prove otherwise)

RedBullFiXX

Cyclist are still using tubes ?

Joe G

I've never had a problem.

njkayaker

I get it. You want to say things that don't make much sense and be free from anybody commenting about them.

It's fine being curious but the OP was asking a practical question (which you keep ignoring). All I said was that he should be looking at other things first (there is zero evidence that he is doing that).

njkayaker

You keep repeating this like it will magically make it true.

1- We know what tires he's using. If they aren't the "best" in rolling resistance, then it's obvious he isn't doing "all of those things".

2- If he was already doing "all of those things", it wouldn't make sense to worry about an extra few dollars (all that other stuff is much more money).

3- If he was already doing "all of those things", he would have told us he was doing that (like he told us what tires he's using).

Well, you don't know and it's not likely anybody will ever do the test.

There is data on the rolling resistance of tires. It would make more sense to save the few dollars on patching tubes to use on buying tires with lower rolling resistance.

Do you really think that a patch matters more than the tire?

Bizarre.
​​​​​​​

bbbean 

From my first post n the thread: "Yes. Does it make a difference? Depends. If you're a contender for the hour record or time trialling at the Olympics, the fraction of a watt difference could be an issue. For ordinary mortals, however (including most of us who race), the difference isn't enough to measure." I don't think I ignored his question - I think I gave a pretty direct answer.

FWIW, what evidence do you have that he ISN'T looking at other factors?

bbbean 

I keep repeating that because we don't know. I also don't know what his training regimen is, what his diet is, what altitude he trains at, etc. Making assumptions about those things and treating my own personal biases and preferences would be presumptious. Apparently, you don't feel the same way.

Something else I keep repeating is that it is an interesting question. Science shines best when it tests things that seem intuitively true. Consider - not that many years ago, it was universally "known" that a thin, rock hard tire was the fastest possible choice for road cycling. Generations of cyclists trained and raced on sub 21mm tires at 120+ psi. Then a few folks challenged the status quo and now we're all racing on 25-30 mm tires at sub 80 psi. Without asking the questions and testing hypotheses, we don't progress beyond the current technology.

njkayaker

You have EXACTLY NOTHING indicating that he's looked at other factors.

If he's not already using lower rolling resistance tires and worrying about a patch, he's not looking at other factors very carefully.

You keep assuming he's looked at other factors carefully/comprehensively. It's not enough to be merely "looking at" other factors.

I was the only one who asked about tires (a much more important factor than a patch) which provided actual evidence that the other factors may not be being looked at carefully enough.

[QUOTE=bbbean;21384955]I keep repeating that because we don't know.[/QUOTE

We know he's not because of the tires he is using (which, seems are good but not necessarily great).

We know he's not because, given the time and effort such a thing would entail, he would just be using new tubes (not being concerned over "saving a few bucks").

No one is going to take the time and effort of doing this test.