Myths about tires (part 1)

ebike4healthandfitness said:

DOT approved tires (i.e. no bicycle tires) should be mandatory as well for these electric pedicabs.

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Good thing nobody with decision power is listening to you make suggestions about things you don't know anything about.

Chalo said:

ebike4healthandfitness said:

DOT approved tires (i.e. no bicycle tires) should be mandatory as well for these electric pedicabs.

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Good thing nobody with decision power is listening to you make suggestions about things you don't know anything about.

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Once you try a quality tubeless tire on a 17" rim you will never want to go back to that 24" bmx junk (which is high rolling resistance anyway). But just because Chalo will like 3.5" wide tubeless on a 17" rim more than bmx is not the reason to go with dot tubeless. Dot is better for everyone.....especially the passengers

Dot is better for everyone.....especially the passengers

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What passengers? I thought the discussion was about mopeds. Maybe you have _a_ passenger....

And what makes 'dot' so superior? All department of transportation does is set standards for tires. They don't do any approval process or testing or anything like that themselves. I don't think that any of the standards set by DOT are particularly relevant to anything we do.

I mean if you are pushing DOT tires so much lay out what exactly about DOT standards is relevant to us. Like go and find the DOT code and point out what about that makes it so much better. I am not going to buy somebody just making blanket declarations like this while backing it up with nothing.

I mean all of us had have years of experience running around all over the country with things like Schwalb 'e-rated' tires or hookworms or any other decent tire without any serious problems or danger except the normal bicycle flats.

Now you are telling us that we have all been wrong and stupid for decades and that there is something magical about the DOT standards that we all need.

Well what part of the DOT standard is going to make our lives better?



It is not the same thing as trying to buy a UL-listed multimeter versus some random CE-listed tool off of Aliexpress... which actually means something. If I am going to do mains testing it's going to a UL tested tool. This matters.

Were as I can go out and buy the cheapest possible DOT 'rated' tires from Aliexpress that would probably dry-rot within 4 months and be dangerous as hell. I don't see DOT as actually meaning much.

Well I realize now he was talking specifically about pedicabs, but regardless... I trust the industry and people that actually make a living doing this stuff to pick out the right equipment. Not some Federal bureaucrat dreaming up DOT standards in the 1970's that probably never seen a pedicab in his life.

sleepy_tired said:

I trust the industry and people that actually make a living doing this stuff to pick out the right equipment.

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I sure don't.

Money often gets in the way of proper judgement my friend.

There are five hundred licensed pedicabs in Austin-- not drivers, only trikes. There are probably 30 different fleet operators. None of them use motor rims or tires. Not because they can't, not because nobody's tried it-- but because moto tires suck for that job, have terrible high rolling resistance, are a loathsome chore to repair or replace, don't withstand ideal tire pressure when carrying multiple passengers, and weigh an unnecessary ton.

So it's your totally ignorant opinion against the contrary finding of all the owners and riders of 500 money earning trikes locally. Good luck convincing them.

Chalo said:

are a loathsome chore to repair

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You don't know what you are talking about son. You have never used a dot tubeless tire....that much is obvious.

Tubeless dot tires are by far the easiest to repair.

(I am writing because of some recent discussions we had in the forum)

1. Wider tires at lower pressure always have higher rolling Resistance:

Definitely not true!

https://conti-tyres.co.uk/latest-news/165-wider-tyres-go-faster

https://www.cyclist.co.uk/in-depth/8131/can-wider-tyres-and-lower-pressures-make-you-faster

Most people find this hard to believe because if (for example) you compare a narrower tire at 60 psi to a wider tire at 40 psi....the 60 psi tire will always have the smaller contact patch.

So (for example) if the load on a 60 psi tire is 240 pounds the size of the contact patch will be 4 square inches. Likewise if the load on a 40 psi tire is 240 pounds the size of the contact patch will be 6 square inches.

So how could a tire with contact patch of 6 square inches have less rolling resistance than a tire with a contact patch of 4 inches? Assuming the tread pattern is the same, outside diameter is the same, rubber hardness and sidewall suppleness (etc etc etc) is the same it primarily boils down to sidewall deformation. A wider tire even at substantially lower pressure can definitely have much less sidewall deformation than a narrower tire at higher pressure....and even still have lower rolling resistance if the sidewalls are significantly stiffer.

So be very careful when listening to anecdotal tire reporting. If more than one variable is being changed before and after the comparison how can a person know the change in performance is due purely because of the tires? They cannot know.

With ebikes the rolling resistance is less critical

All things equal (pressure, tread thickness and compound, casing material and thickness, wheel diameter, etc.), the wider tire will always have lower rolling resistance. That's because a wider casing doesn't need to flex as much to establish a supportive contact patch. Less flex means less hysteresis in the rubber, thus less energy lost to heat. I've made this case many times for decades, going back to rec.bicycles.tech on Usenet.

Thing is, all else is rarely equal. It's feasible to replace a 700x23 with a 700x25 or 700x28 of identical construction, and you can (if you want) use the same pressure. So in that case, the 28 would have the lowest rolling resistance by a little.

But by the time you're looking at a 700x35 or 38, even if it's the "same" tire model, it's not the same construction. Casings get thicker and coarser, treads get thicker. More rubber being flexed means more hysteresis. But that's not the only factor. If you run a 700x38 at the same pressure you'd use for a 700x23, it will ride horribly. Nobody who knows what they're doing, does that.

So while there's no reason to avoid a wider version of the tire you want for rolling resistance reasons, using a wider tire isn't an effective way to reduce RR. It is an effective way to get better ride quality.

ebike4healthandfitness said:

So (for example) if the load on a 60 psi tire is 240 pounds the size of the contact patch will be 4 square inches. Likewise if the load on a 40 psi tire is 240 pounds the size of the contact patch will be 6 square inches.

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Just to understand the scenario, is the idea that using the same tire, but filled to 40psi vs 60psi, running the lower pressure will have less rolling resistance?

E-HP said:

ebike4healthandfitness said:

So (for example) if the load on a 60 psi tire is 240 pounds the size of the contact patch will be 4 square inches. Likewise if the load on a 40 psi tire is 240 pounds the size of the contact patch will be 6 square inches.

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Just to understand the scenario, is the idea that using the same tire, but filled to 40psi vs 60psi, running the lower pressure will have less rolling resistance?

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I hope that's not what he's saying, but if so, it would be characteristically mistaken.

Working rubber uses energy. Work it more, or have more rubber being worked, and you spend more energy. That's why moto tires are slow and draggy even when they're wide enough and lightly loaded enough to not exhibit much deflection. There's just a lot of rubber undergoing hysteresis.

If your riding surface is so bad that you lose a lot of energy to shocks that are transferred to your body or payload, then the energy saved by shock absorption from soft tires might exceed the energy lost to rolling resistance from soft tires. That's not how most of us ride most of the time. It's more likely to be a factor when folks use tiny thin high pressure tires for speed, and lose more speed to vibrations than they gain from low RR.

Lower pressure can also more efficiently get more power to the road. The higher pressure tire can tend to bounce up in the air more over road irregularities, losing traction. When it is losing traction it is not putting the power to the road.

Some vehicles use nitrogen in their tires, they twist on the green valve cover. I havent looked into nitrogen, must be a scam or what?

I am more into offroading and mud bogging and rock crawling, and lower tire pressure is better for traction on snow, mud, ice but I dont know how low one would go for rock ledges or big boulders. Rock crawling here is creek stones and a boulder in the way.

You ever seen bicyclists dabble in using nitrogen to fill their tires?

Chalo said:

E-HP said:

ebike4healthandfitness said:

So (for example) if the load on a 60 psi tire is 240 pounds the size of the contact patch will be 4 square inches. Likewise if the load on a 40 psi tire is 240 pounds the size of the contact patch will be 6 square inches.

Click to expand...

Just to understand the scenario, is the idea that using the same tire, but filled to 40psi vs 60psi, running the lower pressure will have less rolling resistance?

Click to expand...

I hope that's not what he's saying, but if so, it would be characteristically mistaken.

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Of course, it is not what I am saying.

The comparison is a narrow tire at higher pressure vs a wider tire at lower pressure (re-read OP).

Running the same tire at lower pressure would increase rolling resistance and running the same tire at higher pressure would decrease rolling resistance.( See first chart in first link I provided).

Chalo said:

All things equal (pressure, tread thickness and compound, casing material and thickness, wheel diameter, etc.), the wider tire will always have lower rolling resistance.

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Ya think?

I am going to ask my engineer about this. I think... he would love a question of, or to decipher, the physics, of, and merits of a statement like this. We will see what he says. If he could figure out Three Mile Island, he should be able to figure this out. In the absolutes of math.

BRB.

markz said:

Some vehicles use nitrogen in their tires, they twist on the green valve cover. I havent looked into nitrogen, must be a scam or what?

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Nitrogen's purpose is primarily the longevity of the tires.

......oxygen makes them rot. " Oxidizing" is the terminology. Nitrogen on one side of the rubber negates this.

This is the only purpose of that gas in a tire.

Nitrogen is easy to find.

No one is mentioning tire temperature.

We should address tire temperature if we re modeling the ( Rollin? Rollin. Rolling! Roll On, Brother Mon) friction of the assy, and what different pressures do to the friction, and inherent resistance to traversing, involved.

Tire rot occurs as a result of several different environmental conditions. Exposure to Oxygen – Oxygen reacts with the long-chain polymers in the rubber, causing an oxidation reaction that breaks down these chains.

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I don't know as much as some of you do, but I can tell this when I go out riding without motors on the flat ground near my house.

Mountain bike, 2.4 inch wide tires with knobs, 45 psi which is high for MTB's, it coasts some, but not very far. You just have to keep churning those pedals. I run the high pressure because my MTB tires are always full of thorns, losing some air despite the slime. So I start out pumped up hard.

But my road bike wears really skinny road slicks. Race tires, not trainers. 90 psi or higher. That bike coasts forever compared to the MTB.

Seems to this dumbass, that the skinny tire has lower rolling resistance, which may be mostly because the tire is designed to be hard. NO, its not a real comfy ride. Wouldn't ride it for a daily commute.

So what's my point? Start comparing things with multiple variables, and you are practicing junk science. But you could say something like,,,, tires designed for higher pressure have lower rolling resistance at the designed psi, compared to those that are designed for very low pressure at the designed psi.

Safe enough to say I think, a 5 inch wide tire at 10 psi will drag, compared to a 2 inch tire at 45 psi.

With the same 2 inch wide type tire, same 45 psi, same bike, I could feel the difference between a slick and a knobby tire. One variable, the tread type. But not a ton of drag on the knobby, not enough to give a shit about on an e bike. Couldn't measure the difference on a watt meter riding using the motor. Try that, and too many other variables intrude, like the weather. Tire temp sure, but mostly I mean wind.

Chalo said:

E-HP said:

ebike4healthandfitness said:

So (for example) if the load on a 60 psi tire is 240 pounds the size of the contact patch will be 4 square inches. Likewise if the load on a 40 psi tire is 240 pounds the size of the contact patch will be 6 square inches.

Click to expand...

Just to understand the scenario, is the idea that using the same tire, but filled to 40psi vs 60psi, running the lower pressure will have less rolling resistance?

Click to expand...

I hope that's not what he's saying, but if so, it would be characteristically mistaken.

Working rubber uses energy. Work it more, or have more rubber being worked, and you spend more energy. That's why moto tires are slow and draggy even when they're wide enough and lightly loaded enough to not exhibit much deflection. There's just a lot of rubber undergoing hysteresis.

If your riding surface is so bad that you lose a lot of energy to shocks that are transferred to your body or payload, then the energy saved by shock absorption from soft tires might exceed the energy lost to rolling resistance from soft tires. That's not how most of us ride most of the time. It's more likely to be a factor when folks use tiny thin high pressure tires for speed, and lose more speed to vibrations than they gain from low RR.

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Regarding motor tires - not *just* that, they use extra-sticky compounds for 'confident conrnering', and that means more hysteresis losses (who caresabout a few fractions of mpg if it gets you though the corner w/o crashing?). Butyl tubes roll worse than latex because it has much higher hysteresis.

Regarding 'less pressure roll better on rought surfaces' - this effect seems greater than you think:
https://blog.silca.cc/part-4b-rolling-resistance-and-impedance

Also, (duh!) when you ride soft surfaces, the less pressure the better because you'll lose much more energy plastically deforming ground than semi-elastically deforming rubber.

Back in like 2010 I did a ton of road riding on a 26 inch mountain bike with ritchey speedmax beta semi slicks. Not the kind that are mostly slick with a little bit of channeling for water but the type with knobby outside And a sort of diamond pattern in the middle.
They were 26 x 2.2 so pretty wide. I was doing 50-100 mile rides every couple days over pretty much the same course. Was turning out a pretty respectable 17.8 to 18.1 mph average on those tires and I kept reading articles where people would say that switching to slicks made such improvements. Got a set of the lightest, skinniest 26 inch slicks I can find at the time I think they were Michelin wild run'r 26x1.1"

First few rides I actually lost between .1.- 2 mph As I was spinning out and needed to gear up from a 44 to a 48 tooth chain ring to make up for the smaller diameter. Once I did I made incremental gains of about .3-.5 while getting a lot more flats And having a much less comfortable ride

BalorNG said:

Chalo said:

If your riding surface is so bad that you lose a lot of energy to shocks that are transferred to your body or payload, then the energy saved by shock absorption from soft tires might exceed the energy lost to rolling resistance from soft tires. That's not how most of us ride most of the time. It's more likely to be a factor when folks use tiny thin high pressure tires for speed, and lose more speed to vibrations than they gain from low RR.

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Regarding 'less pressure roll better on rought surfaces' - this effect seems greater than you think:
https://blog.silca.cc/part-4b-rolling-resistance-and-impedance

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The articles covers tests on tires in 23mm and 25mm widths and pressures over 100 psi, which corresponds to what I was saying.

For any tire width, there is an amount of surface roughness and tire pressure that will cause "impedance" to outstrip rolling resistance. But for most of our tires, that's a degree of surface roughness that doesn't occur on intact paved surfaces.

The fashion lately is to use very low tire pressure in relatively large tires, but this does create extra rolling resistance. Thus this fashion trend also includes thin supple tires to reduce RR, plus sealant to make the use of such tires practicable. Overall this system offers pretty good riding efficiency, being inefficient mostly in terms of maintenance.

Fast bikes are making rolling resistance irrelevant. I mean, would you sacrifice safety for a bit of better efficiency?

The more power and speed that you have, the more critical is the choice of tires. When you are riding faster than other vehicles on the street, short braking distance and hard cornering ability are life saving factors. And, it is not easy to do the math. Most of us had to try many tires before finding the proper construction, gum and thread, to best match the weight and speed that we ride. Most of all, the best match is changing with the seasons, in cold winter countries especially.

One of the big problems is that due to natural human perceptions we interpret high vibrations with 'fast' and low vibrations with 'slow'. So stiff road bikes with rock hard tires are going to tend to "feel" faster. Also there is real advantage in having low-mass wheels when it comes to acceleration and this is something that is going to be easily felt by a rider.

So easy acceleration combined increased perception of speed is going to make bikes with narrow hard tires feel like a rocket ship compared to something with equivalent quality tires, but much larger wheel mass and better vibration dampening.

If you are racing or always stopping and starting then skinnier tires are likely to be just better. I could imagine a person in a very high-density urban environment preferring narrower tires for that reason. Even if on rough roads they are bit worse in terms of rolling resistance. But for most of us larger tires are just better overall for most purposes.

It would be interesting to see watt-hour per mile consumption figures for a mountain bike fitted with 2.5 inch 29er tires versus that same mountain bike fitted with skinny 700c. Provided the tires used are of the premium sort in both cases and not super thick for puncture resistance. That way we can be all super scientific with real world measurements and such things.

MadRhino said:

Fast bikes are making rolling resistance irrelevant. I mean, would you sacrifice safety for a bit of better efficiency?

The more power and speed that you have, the more critical is the choice of tires. When you are riding faster than other vehicles on the street, short braking distance and hard cornering ability are life saving factors.

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Generally speaking things like stopping distance and hard corning capabilities is a function of the amount of friction the tires have on the surface. There are complications to simple concepts because of how tires different tires can bend and twist to conform to surfaces... but generally speaking friction is going to be a combination of pressure, surface area, and material qualities.

With narrow tires the pressure in the contact patch between road and tires is higher, but the size of the patch is smaller. With wider tires it's much lower pressure, but you have more surface area. And it ends up becoming the same way either way. If you have 100 pounds on a tire it doesn't matter if it's 1/4 inch wide contact patch versus 1 inch contact patch... the amount of traction you get is the same either way, provided the quality of the rubber is the same in both tires.

When it comes to things like snow... sometimes it's better to punch through the surface and get to the concrete/hard ground below it. In those situations narrow tires are better. Sometimes it's better to have a tire that has tread patterns designed to grab and hold the snow onto the tire (snow on snow traction is better then rubber on snow) and ride on top. It really depends on how much snow it is, how slushy it is, etc. And if you are on ice you are screwed no matter what you have unless you have studs.

The reason race cars use big wide tires is primarily because it allows them to use much softer rubber compound. The wider tires simply has more rubber to use up before it needs to be swapped out. If they had narrow very soft tires they would have to make more pit stops.

So if your wider tire has correspondingly softer/gripper rubber then, yeah, it can be 'safer'.

But normally safety isn't going to be a issue in deciding wide vs skinny.

This is very debatable, of course. Many people claim that wider tires have better chance of taking advantages of cracks in the road surface and other imperfections to improve traction, but I don't think that it is major consideration. Absolutely can be wrong, of course.