asgelle

I'm not sure what you're point is. 1.9/(1.9+2.9)=0.40 which is pretty much what I wrote. It's also clear from the original post I responded to that the comparison was total rolling resistance to total aero drag.

Dannihilator

Doesn't need as much air pressure in a tubeless setup because no tube.

garage sale GT

I suspect that your 25s were not at the same pressure as the 23s when you felt less road buzz, although I guess it's possible a wider tire would tend to ride over the aggregate more.

I suspect the various steel drum test graphs showed plots of rolling resistance vs. PSI.

So someone looks at the graph and notes that the plot of the 23mm tires is above the plot for the 25s, and concludes that the wider tires have lower rolling resistance.

However, tires aren't used that way in the real world. If you use a 28 at the same pressure as a 23, it will probably give more road buzz, although if you were riding on a steel drum, maybe in some sort of trainer, the 28 would probably give less rolling resistance than the 23.
Too incoherent to respond to. Who said anything about bunny hopping??You're a little off-topic. I am discussing the difference between a steel drum and smooth asphalt. If my addition of the word "out" to your sentence makes it what you meant to say, then you're completely wrong.Sound and fury signifying nothing.

Burton

Think I`ll pass. What I posted was taught in high school physics 30 years ago. Today its probably taught in grade nine.

Exponential: Relating to an exponent.

Drag (in this case wind resistance) is directly proportional to the square of the velocity.

Power required to overcome drag (in this case wind resistance) is directly proportional to the cube of the velocity.

Please take your arrogant condescending attitude someplace else.

meanwhile

My point was that what drives the decision as to whether you should optimize tyre aero or rolling resistance is tyre aero vs RR, not total aero. In fact, reducing RR at the cost of increased tyre AR can still be beneficial well after total AR is greater than RR.

meanwhile

The problem here is that you are ignorant and arrogant. You assume that

1. Stuff you thought up yourself with no logical reason behind it has to be correct, even though this means that

2. Engineers and tyre companies who have spent years working on this have to be wrong. In fact, they have to be idiots. Because if the steel drum tests and other techniques they have evolved don't work then this would show in real world test rides - especially those using power taps. (Ok: you probably don't know what a power tap is. Trust me, it's useful and relevant.)

3. In fact, you're assuming that because it disagrees with your own personal theory, modern physics' understanding of materials science is wrong!

4. According to your "theory" the wrong guy just won the Paris Roubaix! It was won on a cyclocross bike chosen for its ability to run wider rubber than a normal racing bike at the cost of normally critical qualities like aerodynamics and twitch steering for pack position.

5. According to your theory that high pressure is faster, all professional cyclocross riders - who spend $200 a tyre on tubeless rubber so that they can reduce pressure as much as possible without pinch-flatting are wrong. So are MTBers who use tubeless systems for the same reason. When you're asked about this you're too chicken to answer.

This goes beyond mere lack of knowledge and intelligence into deep "WTF is wrong with this guy???" Seriously, how can you believe that all these people with Phds and decades of experience racing and managing race teams can be wrong and you right? And then how do you explain that what they do works in reality, where as what you think they should do fails?

What impresses me most is that you haven't been able to give a single reason for your beliefs - even a perpetual motion machine addict, flat earther or moonshot denier can manage better than that.

asgelle

Arrogant, condescending; perhaps, but correct. Personally, I'll take being right over being warm, cuddly, and wrong. Try to understand the difference between exponential and power law functions. It's not just semantics.

As to the physics being taught in high school, perhaps at the level of your analysis that's true, but if you did bother to read the article, you'd see the correct treatment is much more complex than that.

asgelle

If that is what you are concerned with, than you have to consider the interaction of the tire with the rim. The effect may be small for traditional or shallow rims, but modern deep section rims are being designed for optimal performance with a particular tire width. The difference in drag for the entire bike+rider can change by much more than the change in drag on the tire alone.

As for me, I worry about speed, and since speed depends on rolling resistance and total drag, those are the things I'll worry about. Aero helmets are a good example. Most aero helmets have higher drag than standard ones, but put a good aero helmet on a rider in a good position and total drag decreases compared to what it was with the standard helmet.

garage sale GT

they never said to judge tires along a given isobar on their graph. To spell it out for you, I am actually saying some of you may not realize what you're looking at.please explain how empirical data and the real world results which you think are relevant have involved material science.if the cobblestones between Paris and Roubaix are the only rational basis of judging bike tires, why not put those tires on velodrome bikes? Why not find out what the winner had and put them on your MTB? I am assured 700Cs will fit in a 26" MTB if the tires are not too tall.no, your bad. I spelled out quite clearly what I was referring to.and yet millions of 700x23 and narrower tires are made and sold every year. Lotta dummies out there.Maybe you should continue to let other people identify and refute preposterous beliefs, especially if you didn't catch my reasons.

garage sale GT

Here's a quote from the second listed source, with my emphasis added:

"Wider tyres roll faster than narrower ones: Many riders have argued for years that narrower tyres – especially on the road – are faster and more efficient than wider ones when in fact, the opposite is true. According to Wheel Energy, the key to reducing rolling resistance is minimising the energy lost to casing deformation, not minimising how much tread is in contact with the ground.
All other factors being equal, wider casings exhibit less casing 'bulge' as a percentage of their cross-section and also have a shorter section of deflected sidewall. How big a difference are we talking about here? For an equivalent make and model of tyre, Wheel Energy claims the 25mm-wide size will measure five percent lower rolling resistance on average – the supposed average limit of human detection – than the more common 23mm-wide one."


The thing is, people who want to minimize rolling resistance would not run the same pressure in narrow and wider tires, so all else is not equal. Who the heck runs 700X28s at 120 psi, like they would with a 700X23?

I think that for lowest rolling resistance, you want the highest pressure that doesn't waste energy causing the bike to vibrate. That pressure will be higher for a narrower tire.

I think I do need to spell out that my theory only holds where both tire sizes are not completely inappropriate when used at proper pressure. Sigh.

meanwhile

Nope. Not for the ballpark accurate analysis I gave here: rim effects are too small. I got a maximum bounding figure by checking the speed-up from a disc wheel.

meanwhile

Once again, you haven't provided ANY evidence for your views.

This is crazy person logic. When steel drums are used to test you complain that they are too smooth and that they are hiding performance advantages that narrower tyres will show on rough roads in the real world. When it is pointed out that pro teams switch from 23s on smooth roads to +28s on rougher ones, you sulk! To the extent that steel drum tests are not accurate they show narrow tyres to be better than are in the real world, because they neglect the ability of wider tyres to absorb vibration and reduce unsprung weight effects.

Oddly, most people are less smart and less knowledgeable about any given branch of engineering than a graduate engineer who has spent decades working in his area. Perhaps only 1% of those people buying tyres have any idea how rolling resistance and aero work or test relative tyre performance using a power tap: the opinions of the rest don't matter. Ignorance doesn't get smarter just because it is repeated.

meanwhile

This is silly. The point is that with a 28 you can replace the 120 PSI you use in your 23 with, say, 80PSI and keep the same RR. Or go to 100PSI and have lower RR. Either way you will have better suspension and grip.

As people keep trying to explain to you, this is stupid. Energy wasting vibration reduces with LOWER tyre pressure, not higher. It's amazing that anyone can be so unobservant that they haven't noticed this, but larger lower pressure tyres have more suspension than smaller higher pressure ones. Which is pro teams are switching to crossers for the Paris Roubaix and running +28mm tyres.

Seriously: what makes you think that high pressure tyres vibrate less? You haven't quoted ANY evidence.

Dude - you're deflating!

garage sale GT

then we hear:
So, do you or don't you use wider tires at lower pressure?

Also, suppose you could explain something to me, Captain Evidence. How is it that you decided you have the same RR with a 28 at 80 PSI as you do with a 23 at 120? You've got a bigger, wider casing, deforming more.

garage sale GT

Sounds like they don't think 28s have less RR than 23s, doesn't it? What does that tell you about the steel drum tests that predicted the opposite?Does that include the aforementioned race teams?

garage sale GT

Gauging from what you said so far, it's not particularly amazing that you never noticed that narrow tires at a given pressure vibrate less also. what does that have to do with the difference between steel drum tests and asphalt? I'd have to cycle about 16 miles to find any cobblestones. I think most road bikers are in a similar situation. More like narrower tires require more pressure before they start to vibrate.One suspects that's the tired old comeback of a dingaling who gets sighed at a lot.

garage sale GT

I do not think that a power meter can tell the difference between rolling resistance and air resistance.

I do not believe that air resistance is the reason 23s seem to run better on a smooth road than 28s. There's only 2.5mm difference on either side. The airflow above the bottom bracket is just going to hit the down tube after passing around the front tire, so unless you also have a 23mm down tube, you're just going to have more drag on the down tube to make up for less drag at the front tire. Most of the rear tire is shadowed by the bike's frame as well. So there's only 5mm X the distance to the bottom of the bottom bracket of additional frontal area.

garage sale GT

You could probably still damage a tubeless tire by snakebiting it. Instead of piercing the inner tube, you might wind up cutting the sidewall cords, which would not have an innertube to cushion the shock of the rim bottoming out on the road. It might just pop instead of slowly losing pressure.

Sixty Fiver

You guys are still here ?

I have been out riding and there isn't a steel drum for at least 60 miles but there are rough roads, frost heaves, and cobblestones to contend with.

Six jours

I just came back from a metric century on a steel roller. I used steel tires and had very low rolling resistance and perfect comfort.

So the wide tire advocates obviously don't know what they're talking about.

dougmc

Is this really true?

It seems to me grip is a function of the amount of rubber on the road (and of course it depends on the road and type of rubber, but you said all things being equal.) Well, the size of the contact patch is a function of the pressure -- not the width of the tire -- and with all things being equal, the pressure is equal, so the size of the contact patch is equal.

It's shape would be different -- wider for a wider tire, longer for a narrower tire -- but the size would be the same.

I think that not all things are equal here -- wider tires usually have lower pressures, which give them a larger contact area.

garage sale GT

The way you drift from steel drum vs asphalt to cobblestones suggests you should consider working out your brain every now and then too!

asgelle

You don't have to take it on faith, there's plenty of data out there. Do a search on "Coggan regression analysis" or "Chung virtual elevation" and you'll see people are doing it all the time. In fact, there was a long discussion of the Wattage group or slowtwitch.com over which of the methods is best suited to simultaneously determine Crr and CdA.

In any event it should be clear that since the equation of motion for a bicycle at steady state on flat ground as the form
P=Av+Bv^3, that a simple plot of P/v vs. v taken on a flat road will give an intercept equal to Crr independent of CdA, and any power meter can easily get this data.

njkayaker

???? What you are "noticing" isn't what everybody else notices.

Wider tires need less pressure to support a given load compared to narrower tires. Lower pressure absorbs the vertical deflections of a rough road surface. Consider how well a solid rubber (essentially, a very high pressure) tire would feel on rough road. Of course, the pressure can be too low as well: if it's too low, too much pedaling power would be directed in making the bike bounce up and down.

You really can't talk about tire widths without talking about tire pressure. Narrower tires (as tires are made) allow the use of higher pressure. That means, we'd have to know what pressure they were using in the different tires to even begin talking about why they use 23s on smooth roads.

garage sale GT

So first it's not what everybody else notices, then it isn't?It seems I read that somewhere else in this thread. Someone pointed out that you can't go by graphs that say a 28 rolls easier on a steel drum than 23s, at the same pressure, because you don't use the same pressure. Now if I could just remember who?

Your post is self-contradictory word salad.