Comfort is also a speed thing.

Back before we were all better informed, I did an Ironman bike leg (St George when it was a full-distance) on like 19mm tires @140PSI. Because that's what everyone in this forum at the time said was fastest. Super obvious. It's just physics. I was vibrated to death on the chip seal after that bike leg. Just ruined me on what should have been a well-paced 112 miles. I'd really like that day back with what I know now.

19mm @110 PSI or something might be good today, for a 40K on a good surface. Personally, I'd think it questionable for anything longer or rougher.

I still love cranking my track tubulars up to 200PSI, though. :)

I don't disagree.

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Perfect, as that's what I have been asking from post 1 - is there data somewhere I can read?

I agree that 19mm @ 140psi is too thin/too high. I assume we can all agree that 40mm @ 50psi is probably not going to be fast enough. So there is a sweet spot somewhere of width and pressure where overall speed of a wheel/tire combo (rolling efficiency and aero drag) are optimized.

Where is it? For, say, smooth asphalt, is it 25mm @ 110psi, 28mm @ 85psi or 30mm @ 75psi (or whatever)?

I realize this will vary by tire/wheel combo. I will settle for 1 data set for one wheel, 1 tire family and 1 type of surface.

(And to be clear - I am not challenging the idea in principle: I am trying to find data on where the sweet spot of tire pressure/width lies. Not anecdotal statements saying "it is faster".)

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Yeah, exactly.

Looking at the data here:
https://www.bicyclerollingresistance.com/...prix-5000-comparison

Wider may be faster. But wider + softer isnt faster. 28mm @ 80psi is marginally slower than 25mm @ 100psi. Getting to 60psi is definitely slower.

The main argument for going with 28mm is that you lose a LOT more in efficiency if your tires are pumped to too high a pressure vs if they are 10psi too low (the Silca blog I had linked to in my initial post indicates that).

But this optimal rolling efficiency pressure is around 110psi for 25mm tires on good asphalt. So if you are 100psi, you are already in "conservative" territory. Now if you got 28mm tires at 80psi, you are giving up a little on Crr AND you are giving up a little on aero. So how is this faster?

Now if you say 28mm tires at, say 90-95psi - maybe that would make sense: as long as you havent crossed the inflection point at which road impedance becomes an issue (and a lower pressure reduces the possibility of doing so), the wider tire will have a lower Crr and this could offset the marginal aero losses.

So wider tires = faster, I get. But not "wider + significantly softer" - that doesn't add up. Not for tires optimized for speed on smooth roads anyway (as opposed to general riding tires or gravel tires).

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This is not true.

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Eric Reid AeroFit | Instagram Portfolio
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i don't mean to pick on you ericMPro ... but can you help me understand why this is the case? is it inherent in the wheel itself? or is it like wheel/fork interactions and varies in situ?

Awe-inspiring as your pithy, concise words of wisdom are, care to actually go past the Wise Sage routine and actually cast a few tangibles pearls of data before us ignorant swine?

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Those who are slower than me suck.
Those who are faster than me dope

Instead of hearing what you're hearing which prevents you from learning, why not try to hear what I'm trying to tell you? If you don't like hearing it from me, I recommend the search function to help frame your understanding, to help you realize that you don't know what you don't know. In the year of our lord 2020 we have discussed this many times before on this forum.

That said, stop trying to find an algorithmic blanket truism shortcut crutch to lean on and saving you from having to think. Instead, think of it operationally and process driven:

1. pick the right tire for the job, and no more.
2. pick the right wheel that matches best with the tire, and no more.

If you frame it that way, and look at what the smart overachieving people are doing, you'll know your answer.

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Eric Reid AeroFit | Instagram Portfolio
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Unfortunately there are more variables, the greater the relative air speed the the more a narrow set up will come out ahead because aero drag goes up by the square of the speed while rolling resistance goes up linearly.
Also weight of the rider and bike I am assuming that a heavier rider will absorb more energy being shook around that a skinny one.
If Zipps marketing is to be believed they now test in the real world where the wind doesn't always flow at a constant rate and interacts with the environment.

To some extent a lot of this deals with heavy riders too. 150 lb riders don’t need 28’s or 30’s to be fast and low crr. 190+ riders do.

The bell curve of size even on the weeknight A ride tends to be a little more “sprinter build plus microbrew belly fat” than “super small Colombian”.

 

there has to be a more constructive way to have this convo.

look. all other things being equal, are you saying that it isn't true that the narrower wheel is more aero? or are you saying that other thing's won't be equal, and that's the reason. if the latter, which things, in particular? flow/geometry interactions? or is it all about the crr?

So instead of you telling me what YOU think i should be doing, let's try something different - how about you actually read the question I asked?

I did not ask for discussions on this subject. I didnt ask for opinions on how to practically test. I definitely did not ask for gratuitous advice on how i should find the optimal tire/pressure combo for myself.

I asked for a link to a scientific comparison of a narrow rim+matching tire combo vs wide rim+matching tire combo as far as differences go

The closest I have seen are the Aerocoach numbers comparing Crr + Cda for different wheels, and Silca's study, which shows the total impedance/efficiency curve for one tire width- it is possible to plot a Crr-vs-pressure curve for a different width, but what it doesnt have is the impedance curve (what Zipp calls vibration curve) looks like for a different tire pressure. If there was some info on this impedance curve, that would allow some comparisons of the tradeoff between tire width and overall efficiency.

There is a specific reason I am looking for this info, which isnt really relevant to the question or the answer.

Your replies - first, 2-3 word non-answers and now you are being a condescending douche by making assumptions about what I want to do with this data ("use it as a crutch for having to think" - oh, the irony). So how about you stop pretending to be a mind-reader and either point me to the link i am asking for or, if you dont care to help (which is entirely your right), at the very least stop being a ass?

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Those who are slower than me suck.
Those who are faster than me dope

I have read and it seems to make sense to me that all else equal a wider wheel can be made to be more stable with a deep rim than a narrow wheel.

I think we can agree that a well-designed deeper rim is aero at zero. So, narrow and deep is best at zero yaw. Problem is we don’t typically ride at zero and narrow wheels can be unstable at yaw. If you are on your brakes trying to stabilize the system then you are not fast.

Once you select your wheel then you need to match up a tire to it. Tire pressure then falls out after that.

Which I think is what EricM is getting at.

This argument works more for the front wheel than the rear wheel.

Fair enough. I've been thinking about this a little as well and you are correct - trying to manage all these variables in a single study would be a little too complicated.

So to elaborate a little more on what I was getting at - one part would be to get a sense of the aero differences between wide and narrow (as asked earlier). Yes, wider is universally accepted as faster at yaw - I am just trying to learn a little more about it: what drives it, what is the magnitude of the improvement, etc.

The other part would be trying to understand the correlation between optimal tire pressure for a given width and overall rolling efficiency. Let me elaborate here.

The Silca blog and Tom A's posts make it very clear there is an optimal tire pressure at which increasing the pressure further results in a significant loss in efficiency, due to what Zipp calls Vibration Losses in their white paper. For a 25mm tire, that optimal point is around 100-110psi on smooth asphalt. So far so good.

So what happens if you go to, say, a 28mm tire? The Crr curve is going to be lower (lower Crr at a given pressure). But what is the shape of the Vibration Curve? Is it the same curve (ie, unaffected by tire width), is it lower or is higher? Because the shape of the curve will have implications on the tradeoff between tire size and pressure.

See below:



Depending on what the Vibration Curve looks like for a 28mm tire, there are insights to be gained about both the optimal tire pressure for a wider tire, as well as how it compares to a narrower tire overall, as far as rolling efficiency goes.

I realize that this is a very academic exercise, but there could be useful insights here. Eg, for me, a big take-away from Tom A's analysis is that it is better to err on the side of too low pressure than too high. Here, understanding the magnitude of the differences will allow some basis for comparison with aero drag numbers.

Does anyone know how the vibration curve/impedance curve changes with tire width?

(And it could be that i am just a knuckle-dragging mouth breather, but i have been trying to google this for a few days now, but havent found an answer).

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Those who are slower than me suck.
Those who are faster than me dope

Yeah, i have read the argument as well. As I said earlier in my posts, I understand that and it makes logical sense to me.

I just want to know what the magnitude of these differences are and was asking if anyone knew of any wind tunnel tests that actually performed this test comparing narrow to wide or some data-based papers on this.

It was a fairly simple (and non-controversial) question, I thought. :)

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Those who are slower than me suck.
Those who are faster than me dope

Obviously a velodrome is very different from any paved road surface. But I don't think it's obvious to the point of facile, since different paved road surfaces also vary dramatically in smoothness from one another.
Like, I think it could be argued that the difference in surface feel between an indoor velodrome and quality smooth asphalt isn't really bigger than the difference in surface feel between quality smooth asphalt and unworn large-aggregate chipseal.

Oh, it absolutely is.

What I'm saying is that I don't think that the wider tire push is happening because people think that 28mm tires are faster on super-smooth roads. It's happening because a lot of people aren't surrounded by super-smooth roads, and the thought is that erring a bit wider than before is a better compromise for catering to the overall market.

Obviously there's value in wheel companies adding more width options to their catalogs. That's part of why road, gravel, and MTB rims etc exist as separate categories in the first place. Narrow-profile deep-section rims hyperoptimized for using skinny tires on smooth roads on calm days is a thing that someone could perhaps make an argument for. But more product permutations means more design cost and inventory overhead, and a more complex situation for marketing.

Fair enough.



Again, fair enough and no arguments there. Also, in my defense, these are points I do understand and am not disputing at all. :)

I am just trying to get a sense of these numbers. Eg, when we talk about the difference between a 50mm and a 60mm wheelset, we generally have a ballpark idea of what kind of watt savings we are looking at. Similarly, for me, it was a bit of an eye-opener to realize how much greater the efficiency loss due to an over-inflated tire is, compared to an under-inflated tire - and also to see how relatively small the difference in RR are, between tires of different widths at different pressures.

What I dont have is an understanding of what the aero differences are between wide vs narrow rims. Or how the optimal point for RR vs impedance plays out for different tire widths (see my drawing above). Or, for that matter, whether it is worth looking into narrower rims for races on smooth roads. I was just looking to see if people had any pointers to published findings i could go read up on , so i could get a ballpark sense of the magnitude of these differences.

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Those who are slower than me suck.
Those who are faster than me dope

You are asking the wrong question, the question should be which tyre transmits less vertical movement.
but there are other questions we dont no the answer to.
How does frequency effect Vibration Losses
how does body composition effect Vibration Losses
Each year bike makers claim more vertical compliance and greater stiffness
Redshift and specialized use suspension to isolate the rider from Vibration does this help
How does air volume effect compliance
Renault used a tuned mass device in Formular one could this be used in cycling

Hello guadizlla and All,

It might be interesting to have an idealized 3D printed wheel/contact patch .... Wheel in this context to mean wheel/tire as one unit.

https://futurism.com/...s-air-or-be-replaced

https://www.youtube.com/watch?v=27iJWJXBmnc



For the present we could make fenders legal and that would help with wheel/tire trailing edge drag .... and riding on rainy days ....

Also if blow out devices were legal it would increase stability and allow a 'near disk' wheel in front and make very narrow wheels practical ... with the blow out devices giving superior cross wind aero drag.

Depending on contact patch needed for manuvering we could develop a very narrow wheel/contact patch that deforms on contact to have the desired size contact patch.

A system to provide variable contact deformity to match road surface would provide a lightweight ... low drag ... non pressurized .... no flat ... inexpensive .... colorful .... wheel/contact patch combo.

What's next!

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Cheers, Neal

+1 mph Faster

This is totally not my field, but I am assuming that a wider rim makes it easier for a rim designer to more gently shape the trailing edge of the rim, and avoid the V-shape that does poorly at higher yaw angles.

Picture two identically proportioned shapes (so same Cd). The smaller one has a smaller area (by definition), so a lower CdA.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Narrow rims and wide rims are by no means proportionally scaled shapes. Because of this, the smaller shape is certainly not guaranteed to have less drag, especially when yaw angles are considered, and they almost always in play

That is my understanding as to why wider shapes are faster as well.

As I said, I am not necessarily disputing the idea. I am just looking for data quantifying these differences. :)

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Those who are slower than me suck.
Those who are faster than me dope

I though the question in bold was pretty much what I was asking, wasnt it? If we try to get a curve showing impedance loss as a function of tire pressure, that is, in effect, factoring in vertical movement (that is one of the aspects of impedance loss or vibration loss).

As for the other points - yup, agreed. There are several more variables that also come into play.

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Those who are slower than me suck.
Those who are faster than me dope

Why are they the same shape?

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Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

“You are experiencing the criminal coverup of a foreign backed fascist hostile takeover of a mafia shakedown of an authoritarian religious slow motion coup. Persuade people to vote for Democracy.”