randya

https://www.nieuwsuitamsterdam.nl/en/...kamikaze-bike’

DX-MAN

Not a lot of hipsters in Amterdam, I'm guessin'.... Or Switzerland. (So much for neutrality! lol!)

CB HI

Well, Portland can now claim to be even more like Amsterdam.

Digital_Cowboy

Uh, do they really need 65 to a 130 feet to stop in?

robertv

I rode a brakeless fixie with no foot retention there for a while, it's so damn flat that it was never even a problem. Throw in some foot retention and no one should have any problems. And Amsterdam has quite a few hipsters and quite a few people riding fixed. I don't think the Dutch authorities really noticed it until now because so many bikes have coaster brakes to start with.
I love the thought of calling them kamikaze bikes though. I also kind of find the crackdown a bit strange when you consider that 60 years ago many people in holland rode a fixed gear and often without brakes it was called a "doortrapper".

mkael

This has been an issue for so many years already. I think people should have noticed this by now . When the only complaints are about badly adjusted brakes things are like they were before

phoebeisis

I'm pretty sure a forum member who seemed to "know these things" said fixed bikes brake about .3G or slow down at roughly 3 meters/sec per second. At 20 mph-9 meters/sec-they should stop in 3 seconds-the first second they would go about 7.5 meters-the second about 4.5 meters, the last 1.5 meters- 13.5 meters-about 45 feet??
Most folks don't ride at 9m/s-more like 6m/s(13 mph). They can stop in 2 seconds and 6 meters-20 feet.
This all assumes that the .3g fixie "braking" with no brakes is correct.
Charlie

dougmc

It really isn't -- it's not quite that good.

A standard bicycle (not recumbent, cargo, tandem, etc.) with a good front brake (at maximum braking, the back wheel has almost no weight on it, so it doesn't matter) can stop at about 0.66 g before it endos -- and that's with your butt shifted back. You can't beat this (well, not by a significant degree), not with better brakes or tires -- it's a function of the geometry of the bike. (Side note: cars have a lower center of gravity, so they won't endo. So a car with good brakes and tires on dry road can pull around 1 g's of braking force. Race cars with ground effects or effective spoilers can do even better.)

A bike with only a rear brake can do about 0.3 g's -- as you brake, weight is shifted off the rear tire to the front tire which makes the rear brake less effective. Again, this is with you shifting your weight back.

A fixie with no brakes can't even do this 0.3 g's, no matter how strong the rider is. If his legs are strong enough, he can lock the back brake and perhaps skid at 0.2 g's or so -- but even so, that's not as good as a rear brake can do. Grandma in her cruiser with a coaster brake can likely stop more effectively than the best fixie rider once she learns to push her weight back and properly modulate the braking.

If the rider is really skilled, strong and lucky he might be able to not lock up the wheel yet put enough resistance on it to approach that 0.3 g's that a rear-braked bike could attain -- but this is extremely difficult to pull off and sustain for any length of time if not impossible.

larry_llama

I just love this reasoning

phoebeisis

dougmc-so .3g is unlikely-.I really don't have much of an idea what leg braking is worth.I do remember a member suggesting that leg brakes were roughly equivalent to rear wheel braking-.3g.
.2g increases the braking distance quite a bit- 2m/sec/sec means over 4.5 seconds and 8+6+4+2+1/2 or about 20 meters- 60 or so feet at 20 mph.
60 feet and 4.5 seconds is a long way.

I don't really get fixies. I like gears and love good brakes.
When I first started riding brakes-even good brakes like Campy Record 1978 vintage-were just a suggestion to you wheels that you would like to eventually stop. The Matthauser "pads" were a decent improvement, but they were nothing by comparison to current brakes.

Each to his own,I guess.
Charlie

RobertHurst

I have yet to see a formula for max braking on a bike that begins to describe what actually happens within the bike-rider system during a max stop. I haven't seen any formulae that don't ignore rider movement, let alone acceleration of the rider's mass. Anybody with any practical experience with max braking will know that it can't occur without an exagerrated and well-timed body movement. This is much more than just 'your butt shifted back.' Even so, a priori formulae for max braking that account for 'butt shifted back,' but not rider movement, arrive at a number .83 iirc.

This .66 number may be correct if the rider remains seated and static -- I don't recommend that technique. The inadequacy of the .6-.7 figure is easily determined by simple physical experiments. Of course it is difficult to obtain precise numbers but through repetition with multiple riders, carefully calibrated speedometers and a tape measure, anybody will become convinced that .6-.7 is really not that serious of a stop, and that max deceleration for a skilled rider on dry level pavement is actually somewhere around or north of .85, which is better than a lot of cheaper automobiles. Riders can stop even shorter than that, but generally not in a totally controlled fashion. You start to get some tall nose wheelies, jackknifes and crashes.

You mention another popular myth, that one can stop with a front brake alone as fast as with both front and rear. I understand why this myth has flourished, given the feeder myths and assumptions, but it's frustrating because anybody could find out the real truth in about two seconds with the simplest of physical experiments. The truth is that the front brake achieves the vast majority of braking force in a max stop, but one can always make a somewhat shorter controlled stop using two brakes rather than one. Perhaps this is due to the bit of stopping force applied to the rear before it becomes unweighted? I don't know, I'm guessing. But I know it's not really a subtle difference, because I've checked.

Remember, if simple physical experiments disprove one's precious mathematical formulae, it doesn't mean that the forces of darkness and irrationality are vanquishing the forces of light and reason. It just means your formulae are wrong.

phoebeisis

Some years back one of the moto mags did some testing.
60-0 both brakes skilled rider 120 feet
60-0 just front 150 feet
60-0 just rear 200+ feet
This is from memory-and maybe 25-30 years or more ago.
The point was to dispel the old "don't use your front brake, it will crash you myth" that was very prevalent in motorcycle circles in the 60's-70's and even 80's.
Bike would be the same story-lower speeds of course.

Motorcycle riders do slide their weight back when braking hard-easier to do on a motorcycle of course.

dougmc

What movement do you think would help? Shoving your butt back as far as possible (along with everything else connected to it, of course) will help you pull more g's without endoing, but beyond that, what do you think would help? Shoving your butt back off the seat will make it go back and down, doing the same to your center of gravity, but beyond that, what do you think can be done?

Any citations for this figure? The book "Bicycling Science" has a discussion of it, but I can't find my copy of it right now. And I think it gave a figure of 0.5 g's before shoving your butt back and down as far as possible. The math is relatively simple -- you just need to know where the center of gravity is in relation to the front wheel.

It's not a myth, but there's truth to your claim as well.

At maximum braking, right before you endo, all your weight is on your front wheel, and none is on your back wheel. This is obviously true, because if there was some weight on your rear wheel, that would mean you could brake a little harder before you endo'd, so you're not at max braking yet. If there's no weight on your back wheel, that means a brake there would have no effect.

However, this is the absolute maximum. In the real world, if there's no weight on your back wheel, the smallest miscalculation sends you into an endo -- and even if you don't, you still have no control -- so you want to have some weight on your back wheel. And if you do have some weight on your back wheel, then a brake there, properly modulated, will increase the effectiveness of your braking.

Sheldon Brown said this -- "Maximum braking occurs when the front brake is applied so hard that the rear wheel is just about to lift off. At that point, the slightest amount of rear brake will cause the rear wheel to skid."

As for a car, even a cheap car can do about 1 g -- it's not really a function of the car's quality or it's brakes, it's a matter of the tire's grip on the road. If the brakes are strong enough to lock the tires on dry pavement, and all four brakes are properly adjusted to lock at the same time, then a skilled driver can keep the wheels right on the verge of locking up and pull about 1 g of braking power. Of course, large trucks often don't have strong enough brakes to do this, but most passenger cars do, and usually the brakes aren't too far from being ideally matched.

EDIT: I should also mention that it's safer to keep a car "on the edge" of maximum braking than a bicycle. On a car, if the wheels start to skid, you can easily fix that by letting up on the brake, and if you don't, that just means you skid straight ahead (assuming the braking is equal on both sides) and don't stop quite so quickly. Antilock brakes don't make the car stop faster -- a skilled driver can stop faster if the car doesn't have anti-lock brakes -- but they do make sure the tires don't lock up -- it makes a less skilled driver seem like a more skilled driver.

On a bike, if you brake too hard and your front wheel doesn't slip -- you do an endo. If your front wheel does slip (slick spot, on a tandem or recumbent, etc.) then you almost immediately fall over.

Sixty Fiver

braking 101

phoebeisis

Ahh, Sixty Fiver, the member who seemed to "know these things" must have been you? I rounded your .33 to .3 Hope you don't mind.

I have no idea which number is better-in any case the Dutch seem to be waaaay overestimating how long a leg braked bike takes to stop.Their upper estimate of 40 meters-125 feet or so is unlikely except at Tour de France speeds

dougmc

Unfortunately, all it takes is a hill to accelerate a newbie cyclist to "Tour de France" speeds.

I-Like-To-Bike

"Fortunately" those kind of hills will be found nowhere near Amsterdam.

robertv

I'm guessing they arrived at that number by having a cop who has no idea how to ride one get on, ride a bit and slowly try to stop. I can see a first timer taking 20 or so meters to bring a fixie to a stop.
What I think is especially BS about this is how little they explain and what they do isn't true. There's very few fixie riders who take that long to stop. Most can and do stop within in a similar distance to people running brakes. Especially people running coaster brakes like most of the people in holland. Also, they don;t really explain what a fixie is. I read the article in Dutch and they give you nothing to go on. They could have mentioned it's a Doortrapper, which is essentially dutch for fixed gear. Everyone knows their grandmothers all rode doortrappers. Don't let the truth get away from a disinformation campaign.
Although, I know that shop and he laughed at me when I tried to buy a brake.

fosmith

Good!

dougmc

Perhaps, but isn't this crackdown also happening in Switzerland? Doesn't Switzerland have a few places that aren't quite so flat?

And aren't brakeless fixies popular in places other than Amsterdam and Switzerland?

Ultimately, if one assumes that fixie riders don't need effective brakes because they don't go very fast ... well, that's the sort of assumption that is often proven wrong.

I-Like-To-Bike

I suspect that brakeless fixie riders are relatively scarce on the mountains of Switzerland. I also suspect that brakeless fixies are an affect almost exclusively of urban riders, and that those few who ride up and down mountainous terrain do not do it long enough to be a significant presence anywhere.

dougmc

There's certainly a lot of them in Austin, TX. Yes, it's an urban area, but it's full of hills (not mountains, but 3-10% grades are not so rare) -- and reports of fixie riders crashing at TdF speeds and above are not rare. And a lot of them are really strong riders and can hit 20+ mph on their own without too much trouble (though on the bright side, these are also likely the guys who can pull their 0.2 g's of braking/skidding too. Though there are hills in town steep enough that no bike with only a back brake (coaster, fixie with legs of steel, whatever) can stop on -- they'll slide down the hill even from zero mph.)

I don't really know what the urban areas in Switzerland are like -- it's a big place, so I'm guessing there's a lot of variety. I have heard that Amsterdam is almost completely flat -- but then again, I've been told that Austin is too. (Though for Amsterdam, I might believe it.)

Giffen

I can't tell if you are being sarcastic. In Europe, preemptive security measures are much more common than in the United States, i.e., you don't need a cute child to die before a law is passed to regulate something.

I-Like-To-Bike

Apparently these strong riders' ability to pull their 0.2 g's doesn't keep them from "crashing" on their bikes when they stupidly exceed their capability to safely stop and/or stay upright.

BTW the existence of steep hills in an area is not necessarily a magnet for cyclists; many, if not most cyclists (who are not in perpetual training/competitive mode) either avoid steep hills if possible, or choose gears to ease the climbing effort.

dougmc

In case I wasn't clear, that 0.2 g's is about the limit that a skidding rear tire will get you for braking. And even so, it requires a certain amount of strength to do that. And yet that 0.2 g's is a third of what a basic front brake will get you, and having two brakes will get you a bit more than that.

By strong riders, I mean that a lot of the local fixie riders are not slow by any stretch of the imagination. They're often young and ride everywhere -- which is the recipe for building up one's muscles (you can do it if you're older -- it just means you have to work harder.)

Fixies, brakeless or not, are trendy, even if not ideal around hills. And if you're young and ride enough, you can generally power up hills, even without gears -- and they do. And if they can't power up the hill, they'll walk. They're "cool" -- which to many is more important than their limitations.