e-bikes legal in DC?

[DrP]

@sjclaeys 142065 wrote:

You’re forgetting that there is the factor of e-bikes’ higher speed, which most likely would be higher than that of an over-weight rider on a regular bicycle. I am not 100% sure, but I think that the force of impact is based on the velocity of the object squared, so an increase in a object’s speed has a significantly greater effect on the force of the impact than the mass of the object. But also, many of the e-bikes I see are the larger mountain bike and cargo types that easily are more than 60 lbs. not counting rider and cargo.

The rider with more momentum (mass x velocity, in a straight line situation) will impart a larger impulse on the other rider, which would be the force felt (F = {difference in momentum}/{time length of collision}). The details will depend on the angle of impact and how elastic or inelastic the collision is.

Kinetic energy is proportional to the square of the velocity. This is not conserved in an inelastic collision.

It has been too long since I have thought about such equations.

[lordofthemark]

I’m confused. Is anyone seriously suggesting banning e-bikes from the streets (not trails) of DC? Or is someone objecting to DC’s ban on “dirt bikes”?

[mstone]

@americancyclo 142074 wrote:

But fatter tires have LESS rolling resistance. at the same pressure

http://velonews.competitor.com/2012/03/bikes-and-tech/technical-faq/tech-faq-seriously-wider-tires-have-lower-rolling-resistance-than-their-narrower-brethren_209268

And tires of consistent width have lower rolling resistance with LESS pressure, up to a point. And there’s the caveat that if your tires are too narrow you can’t lower the pressure without bottoming out anyway. Mostly the chasing of high pressure tires is a case of “if a little bit is a good, a lot must be great!” Wider tires will generally have lower rolling resistance than a narrower tire of similar construction. (A studded MTB tire is not going to have lower rolling resistance than a track tubular regardless of the pressure or width of either–the ebike tire rolling resistance thing has more to do with the fact that they’re built like tanks to handle relatively high speeds with high weights and avoid punctures because that’s what their target market wants. Tanks don’t roll well.) Anecdotes involving apples and oranges cloud the question greatly, as do delusions of grandeur. (At a certain point the aerodynamics of the tire dominate, but a whole heck of a lot more people worry about that than are actually governed by it.)

[Steve O]

@mstone 142080 wrote:

And tires of consistent width have lower rolling resistance with LESS pressure, up to a point. And there’s the caveat that if your tires are too narrow you can’t lower the pressure without bottoming out anyway. Mostly the chasing of high pressure tires is a case of “if a little bit is a good, a lot must be great!” Wider tires will generally have lower rolling resistance than a narrower tire of similar construction. (A studded MTB tire is not going to have lower rolling resistance than a track tubular regardless of the pressure or width of either–the ebike tire rolling resistance thing has more to do with the fact that they’re built like tanks to handle relatively high speeds with high weights and avoid punctures because that’s what their target market wants. Tanks don’t roll well.) Anecdotes involving apples and oranges cloud the question greatly, as do delusions of grandeur. (At a certain point the aerodynamics of the tire dominate, but a whole heck of a lot more people worry about that than are actually governed by it.)

I think these discussions need to move over to the tire width thread, tire pressure thread, tire construction thread, tire brand thread and tire tread-type thread.

[dasgeh]

@sjclaeys 142054 wrote:

I would also add that e-bikes also tend to have much more mass than human-powered bicycles, so there is a greater risk from e-bikes due to the combination of higher speed and greater mass.

It’s like 20-30lbs. Are you saying that folks carrying an extra 20 lbs on their hips are creating a greater risk? What about when they’re carrying an especially heavy cargo load? Do folks on CaBi create a greater risk than those on roadies when they’re headed downhill?

[dasgeh]

@americancyclo 142074 wrote:

But fatter tires have LESS rolling resistance. at the same pressure

http://velonews.competitor.com/2012/03/bikes-and-tech/technical-faq/tech-faq-seriously-wider-tires-have-lower-rolling-resistance-than-their-narrower-brethren_209268

Ok, fine, I don’t know the physics behind it. But the tank-like ebikes are slower downhill than road bikes.

[mstone]

@dasgeh 142086 wrote:

Are you saying that folks carrying an extra 20 lbs on their hips are creating a greater risk?

Now that’s a complicated physics question–does the added mass outweigh the improved cushioning? I have no idea!

[hozn]

@mstone 142080 wrote:

And tires of consistent width have lower rolling resistance with LESS pressure, up to a point.

Do you have a source/chart for that?

The one(s) I have seen show rolling resistance inversely proportional to pressure for same width tire.

E.g.
http://velonews.competitor.com/2014/12/bikes-and-tech/resistance-futile-tire-pressure-width-affect-rolling-resistance_355085

https://goo.gl/images/JCSRCi

https://goo.gl/images/f3G4My

[ShawnoftheDread]

@Steve O 142064 wrote:

BTW – This has all been discussed before
]

That’s practically our motto.

[ShawnoftheDread]

@rcannon100 142060 wrote:

Could we then agree to ban e-fat-bikes?? Cause there is one that flies over the 14th St Bridge.

Sounds like it’s the FAA’s problem, not ours.

[mstone]

@hozn 142091 wrote:

Do you have a source/chart for that?

The one(s) I have seen show rolling resistance inversely proportional to pressure for same width tire.

E.g.
http://velonews.competitor.com/2014/12/bikes-and-tech/resistance-futile-tire-pressure-width-affect-rolling-resistance_355085

https://goo.gl/images/JCSRCi

https://goo.gl/images/f3G4My

Those look like old school smooth steel drum tests, which don’t reflect real world performance on actual (not smooth steel) roads. Look for the stuff Jan Heine has published as the most accessible data. You can also do some digging and find that the pro teams are running wider & lower than they used to. Think about it this way–if those charts were real, the pros would have stopped running pneumatic tires and would have switched to steel disks because harder is faster, right? It’s pretty well established at this point that there isn’t an optimal pressure , and that you need to adjust based on the surface texture you’re riding on.

[hozn]

@mstone 142097 wrote:

Those look like old school smooth steel drum tests, which don’t reflect real world performance on actual (not smooth steel) roads.

The Velonews test was done on a textured drum (“[FONT=&amp]To represent a road with cracks or chip seal, we chose a diamond plate on the roller similar to industrial stair treads.”). The other two were just the traditional charts; I imagine done on a steel drums.[/FONT]

@mstone 142097 wrote:

Look for the stuff Jan Heine has published as the most accessible data.

I think I am the only one in the world that thinks Jan Heine’s tests read like 5th grade science projects. They are accessible, I’ll give them that. To be fair, I don’t subscribe to Bicycle Quarterly where I’m assuming there are more details of the science of the tests. I think what his tests do illustrate is that the differences we’re measuring here are small enough to be clouded by many real-world factors.

@mstone 142097 wrote:

You can also do some digging and find that the pro teams are running wider & lower than they used to. Think about it this way–if those charts were real, the pros would have stopped running pneumatic tires and would have switched to steel disks because harder is faster, right? It’s pretty well established at this point that there isn’t an optimal pressure , and that you need to adjust based on the surface texture you’re riding on.

Oh, I completely agree with this. My question was whether there was any scientific evidence that rolling resistance keeps going down as you lower pressures. “Everyone” knows that there’s a sweet spot for rider weight, road surface, tire size/composition. Higher pressures lose energy to bouncing, but going any lower than that is going to increase your contact patch and increase rolling resistance. At least that is what people are saying.

—
Sorry this is thoroughly off-topic.

Closer-to-topic, my coworker is building an e-bike with a 54×13 SS setup to commute in on the W&OD from Leesburg. His plan is to just use the motor for the hills. (I should probably tell him the W&OD is pretty flat.)

[mstone]

@hozn 142101 wrote:

The Velonews test was done on a textured drum[/quote]

Still weak sauce: a slightly less than perfectly smooth steel drum is still a smooth steel drum test. There’s no actual rider, so yeah, there’s going to be minimal suspension loss. The methodology was nuts for saying much in other ways also. (Why were only two pressures chosen? Are those optimal for each tire? Why not 160 psi or 70 psi or 90 psi?) What’s really amusing is that in their conclusions they talk about how lower pressure is better on rough surfaces even though their results don’t show that, as though they’re tacitly admitting that their test setup missed the boat.

Quote:

Oh, I completely agree with this. My question was whether there was any scientific evidence that rolling resistance keeps going down as you lower pressures.

Oh, if that’s what you thought I meant, then of course not! The rolling resistance goes down as pressure increases until you reach a sweet spot then levels off and eventually increases again as the suspension losses increase. That sweet spot, however is almost certainly a heck of a lot lower than the sidewall pressure. What I was responding to was the implication that the only improvement came from increasing the tire width. In reality, nobody runs a 25mm tire at the same pressure as a 21.5mm tire–and that doesn’t mean the lower pressure 25mm is slower than the higher pressure 21.5. (So mostly, the emphasis on “at the same pressure” seems misplaced.) The one thing the velonews piece does illustrate well is that there’s little to no absolute relationship between width and performance, as the results are all over the place.

[dplasters]

TLDR;

So I came up with a conversation flow that got us from e-bikes to rolling resistance/what pressure you running?

• e-bikes are quick and dangerous
• so are crit races
• there is an upcoming crit race in DC
• everyone knows the pros are running motors now
• what is the best tire width/pressure for e-bikes in crits

how did I do?

to answer a question, as unpopular as it may be; Yes, bikes carrying cargo, larger people etc are more dangerous. If only marginally so. What always freaks people (IMO) out about e-bikes is the ability to combine speed and larger mass. We presume the meat powered large things won’t be moving as fast. As I’ve not actually seen an illegal supped up e-bike doing 35mph, I shrug the concept off.

[mstone]

@hozn 142101 wrote:

I think I am the only one in the world that thinks Jan Heine’s tests read like 5th grade science projects. They are accessible, I’ll give them that. To be fair, I don’t subscribe to Bicycle Quarterly where I’m assuming there are more details of the science of the tests. I think what his tests do illustrate is that the differences we’re measuring here are small enough to be clouded by many real-world factors

Well, this is timely: http://trstriathlon.com/talking-tires-with-joshua-poertner/

[Author]

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