freckles

OP is a she. And yes, other than being crazy enough to ride a bicycle in LA, my head is OK. No impact to my head.

Maelochs

Well .... no need for me to apologize as your real-world identity is a mystery to me (so is mine more often than I like to admit,) but anyway ... no offense intended and glad you didn't hit your head .... or hit it hard enough you don't remember.

I'd say, "Keep riding" but I am sure you figured out that one for yourself.

I did the urban commuter thing for quite a while .... amazing how many times things are so close to being disastrous but somehow aren't.

billridesbikes

This is why I think disk brakes are overkill for bikes that ride primarily on the road. I think my BF NWT run 37mm tires, but at high pressure so there is only a finite amount of available friction with the road. Disk brakes are so powerful the braking force that is imparted to the wheel will easily exceed the friction of the tire on the road before even maximum force is applied to the brake levers, causing it to lock up the wheel and skid. I've noticed this is very easy to do on disk brake equipped road bikes. Its an inherent danger with disk brakes and skinny tires on pavement that in a panic situation you'll lockup the wheels and skid or go over the handle bars where with rim brakes this might not happen. So until the invention of practical ABS for bicycle disk brakes...

Panic stopping is a 'perishable' skill in that if you. and everyone else for that matter, need to practice regularly. Like some others have mentioned try practicing stopping fast without locking your wheels up so your muscles automatically 'know' how hard to squeeze the brake levers without having to think.

freckles

no apology sought or needed 👍, was just clarifying is all.

still get way more joy riding, I get no joy when driving. And happy that a small road rash was all I got!

livedarklions

Just glad you came out of the incident ok. The more you describe it, the more it sounds like you handled it about as well as anyone could. If someone really is going to race out of a driveway and swerving is blocked, flopping might've been the least bad option. We humans can't anticipate everything.

Korina

Respect for riding the mean streets of L.A. That takes brains as well as guts.

I hope you found some good advice here; I got practice panic stops, including moving your butt back and not locking up the brakes. Muscle memory will save you before your brain realizes what’s happening.

I’m glad you weren’t seriously hurt.

Duragrouch

Sorry to resurrect an old thread, but just saw this, read all responses, and feel I can contribute.

This is wrong, at least possibly in the case of a Bike Friday NWT with disc brakes, I'll get to that. You can apply the REAR brake as hard as you like (though not recommended, but just follow me here), and it can't flip the bike, because the thrust at the rear tire contact point, times the vertical moment arm between the ground and center of gravity (CG), will cause weight to transfer forward, which tries to LIFT (unload) the rear tire, losing traction, and force, thus is inherently limiting. Braking SOME on the rear brake will help, just not so hard that you lock up the rear wheel (static friction, i.e., tire not sliding, is greater than kinetic friction, i.e., the tire sliding, so you want to brake below the theshold of the tire sliding, hence this is known as threshold braking). This is AIDED by *sitting down* on the saddle to put more weight on the rear tire, and lowering your body center of gravity, to reduce the height of the moment arm. Trying to move your butt behind the seat can help, puts CG further aft, this increases weight on the pedals, putting more weight on the rear axle, but it also involves pulling aft on the handlebars, which wants to unload the front tire.

Braking as hard as possible on the front tire, with really powerful brakes, is possible to topple the bike, lifting the rear wheel and the bike and you rotating around the front tire and over the top of it. Not always. A few things need to be satisfied: The braking force aft (aft thrust at ground at front tire), multiplied by the center of gravity height, must create a higher moment (torque), than the center of gravity position aft (horizontal) of that ground contact, multiplied by the downward force of total weight at the CG. The further forward your front tire is with respect to the CG, the more stable the bike is, resistance to flipping. Smaller wheel bikes, generally have a shorter wheelbase in this regard, not as good, but the mass of the bike sits lower, so a shorter vertical moment arm for that, good, but since rider height is dictated by bottom bracket (crank) height, the rider height is the same as other bikes, and the rider is much heavier than the bike, so in general, shorter wheelbase small-wheel bikes, have a greater tendency to flip under very hard front braking, again, depending on if sufficient front brake torque is generated to overpower the bike weight. Heavily loaded rear panniers, low and well aft, might reduce propensity to flip, and also add traction to the rear tire. Not saying you should ride around with loaded panniers all the time, this is just to help understand the forces at play.

That said, most of your braking power is going to be at the front brake. On level ground, sitting on the saddle, hard front braking and a bit of rear brake, you should be able to stop fast without flipping the bike.

As quoted above, lowering the saddle to improve braking? Really silly idea; Saddle height should be optimum for pedaling, too low a saddle and you get knee damage. The professor noted, I'm certain, drew conclusions based on conventionally proportioned bicycles of the day, not short-wheelbase 20" bikes, and perhaps with weaker brakes, versus discs.

On a steep downhill, yes, there is more tendency to flip, as the CG height is higher above the front tire contact then it was before, increasing the flipping moment for the same braking force, and, the front tire will have greater loading and the rear tire will have less loading, due to your downward facing incline.

Disc brakes inherently want to lock more on smaller 20" wheels, because those brakes were usually designed for larger wheels, so the same brake torque will cause greater ground thrust, overpowering the tire traction, and skidding. I experienced that, test riding a 20" with mechanical discs 10 years ago, braking down an incline. Perhaps "road" discs would help, as well as hydraulic for better modulation (and BF now offers cable-actuated hydraulic). But I do not recommend rim brakes on your bike, discs are an upgrade. I have a 20"er, and on long descents, the rims can heat up enough to pop a spoke, due to rim diameter expansion (aluminum has a high coefficient of thermal expansion). Also, living in a city with a lot of hills, I'll wear out a set of wheels by sidewall wear, long before other reasons. My next bike will have discs.

By the way, the reverse is also true; A bike pedaling up a very steep incline, with grippy tires and at the limit of rear traction, has more tendency to pop a wheelie and flip backwards, and this is made worse by a short wheelbase, and if the seat is more over the rear wheel than on a larger wheel bike, and, the rider is usually standing on the pedals, pushing up a steep incline, the CG height is raised a lot. Leaning forward over the handlebars, helps.

I love 20" wheel bikes, I'm a convert. But they take special considerations and understanding the vehicle dynamics, which is my profession. The steering considerations, agile versus stable, is a whole 'nuther conversation.

veganbikes

Just FYI folks this thread is from 2021. Not a particularly old zombie, a young little zombie still getting their zombie legs.

Duragrouch

Yes I realized that before posting. I just felt, this was not just an esoteric discussion, but rather an issue involving safety, and the better the understanding of it, the better. I read all the other posts, hoping someone would make the points I would, but saw none, and in particular, saw some bad advice, touted to be proven by a university professor, but this thread involves a 20" wheel bike, which have unique considerations. I ran across the thread, after the thread starter, appreciated my technical explanation on a different issue. I messaged them a thanks, and happened to see on their profile, what threads they started, ran across this one, read it, and felt I could make an equal contribution.

Leisesturm

Well, thanks to your ... resurecction I read a good many posts in this thread until I realized it was a Zombie. Then I started to scan forward to find out who the _____ was who brought this back. At least you acknowledged the thread was old. It's when someone just brings a thread back from the dead like they are responding to a two day old post. Drives me crazy. But that's not why I'm here. I'm bothering to post because the one thing I haven't seen mentioned is the need to scan ahead while riding!

It is an essential part of Motorcycling Safety to scan ... I don't remember 20 seconds? Seems much, certainly 12 seconds. I think cars can get away with a 6 second scan, but single track vehicles must have the sensory net well out in front making note of anything that comes into the riders path or could. Most bicycles aren't moving even a quarter as fast as a motorcycle can so no need to scan as far ahead but I think 3 to 6 seconds of forward awareness is important even at 12 to 15mph. This is why I can ride in the door zones of many bike lanes in town. I am not riding faster than I can stop/swerve if some mouthbreather throws open a door in front of me. They are the one that's going to be scared. I have already flagged them as potentially dangerous. Driveway puller outer? Noted. Driveway flagged as potenti HA! Thought you got me you cager!

The legal statutes don't leave much wiggle. If you hit it rather than it hitting you, you are at fault. So you can't say "s/he pulled out in fr.... " they won't hear it. No need to practice panic stopping. Practice seeing how far ahead you can catalogue potential ... stuff.

Duragrouch

(above) Re scanning ahead: <insert appropriate Archer quote regarding situational awareness>

tomato coupe

But, your advice is the same advice that would be applied to braking on any bicycle.

79pmooney

I had a thought on what needs to happen before I will ever have a disc brake bike. Anti-lock brakes. I know I will never be able to train out the instinct to squeeze hard in a panic stop. A brake that locks up instantly when you do that? Doesn't belong on my bike. I have the same issue with cars. I learned to drive in an old Willis Jeep. First car was a Volkswagen bus. Subtle pedal pressure didn't do anything. Now I have power brakes so sensitive that a panic stop takes about 10 percent of the pressure of a manual clutch. TG that anti-lock kicks in!

I wonder if there is a way to do anti-lock with only hydraulic/mechanical means, no electricity. And it should be anti-lift as well as anti-lock. (Lifting of the rear tire. In fact, maybe that alone would be sufficient.)

Maelochs

I cannot see a way to do anti-lock without servos and sensors. Actual braking times are so short, a human being cycle the brakes in a real panic stop. All that weight would be carried on the front axle .... Since no one ever came up with a purely mechanical anti-lock system (it's not like engineers were any less intelligent or creative over the last couple hundred years) I have to believe there is no practical way.

As fro anti-lift, most riders can learn to move back a little under braking. Whether the consequent rising up makes it worse .... not according to my experience, but I have never actually attached measurement devices.

Most fairly experienced MTB rider slide off the back of the saddle more easily. I haven't ridden MTB regularly in a a couple decades and have lost the instinct. I still manage t stop pretty well.

As I think I mentioned someone where in the above mess ... I do run my rear brake extra loose because I am right-hand dominant and in actual panic stops, I grab harder on the back brake ... I can see where there might be a similar "white-knuckle" response even with discs on those occasions when a real "panic" (as in "I truly might not survive the next few seconds") situation unexpectedly develops.

LarrySellerz

Undo your rear brake. You fell because you aren’t used to using the front brake in an emergency stop

79pmooney

I love the 1980s full length rear brake housing runs for just that reason. (And no messing of paint when you pick the bike up or set it on pegs under the TT.) On my city bikes, I put Mafac RACERS in front (a big caliber brake with enough flex that is is near impossible to brake suddenly enough for bad results but has lots of power for sustained braking) and the stiffer but less powerful Weinmanns on back. After the softening effect of the full length housing, the Wenmanns fell like the Mafacs; just do less. Those bikes on 28c and bigger Paselas are serious stoppers.

The anti-lock - I cannot see how to do it but there are brighter minds than mine and minds that know hydraulics, etc. like I don't.

PeteHski

One or two finger braking helps. I learnt that from mountain biking and just naturally do the same on my road bike. I would still sign up for ABS if it existed, but I’ve never had a problem with locking hydraulic brakes, except the rear on occasion, but I’m okay with that.

mstateglfr 

There is more than one way to skin a cat, and Larry's way will always be the most pain inflicting way possible.

Maelochs

Based on Sellerz™ physics, it is safer to have no brakes and no shirt .... and based on his reading skills, we can see immediately that his advice is the best.


See, in Actual physics, it impossible to lift the back wheel without strongly applying the front brake. Locking up the rear brake causes fishtails …. Jamming hard on the front brake cause forward weight transfer, which force rotates around the front axle, lifting the rear of the bike in extreme cases.

Mr. Sellerz …. You claim to be a Scientist, working in a laboratory. Surely you have taken at least a high-school physics course?

Please explain how the back wheel lifts under braking if the front brake is not applied and applied very strongly.


Also … you do realize theat the OP is an Actual Human Being who actually crashed, right … not an internet fantasy? Giving totally crap advice to actual people who are actually riding in traffic could actually cause avoidable injury … and actual injury is bad, m,kay?

The OP understands that had she braked less, she likely would have hit the car … Your “advice” is essentially, “Hit the car so the car helps absorb some of your momentum, thus shortening stopping distance.”

Dude, we know you are not stupid, and your persona here is just schtick … but maybe not All of us know that, and maybe be careful when giving people advice which could lead to extremely dangerous situations? What do you think?



Nah, just kidding … I think it was a perfect @LarrySellerzs post. I appreciate the humor, guy …

kcjc

Don't you guys slam on the front brakes to practice keeping your bike vertical when the rear kicks up? That's the funniest part of my club ride when arriving at the end gathering point. It's weird that roadies don't do it often. I don't ride MTB much, but the guys I rode with did it religiously. It's slightly different since the primary purpose is to get sideways and kick up dirt. Occasionally, I'll do it on descents when I'm stuck behind cars and bored. It's nothing major, just enough to lift the rear when I'm slightly upright, squatting, on the bike. You learn a lot about your front end.

Duragrouch

Generally true. But the undesirable conditions I mentioned, get worse, the shorter the wheelbase of the bike gets. Note, not necessarily due to smaller wheel diameter, but if a result of that, is a shorter wheelbase. One of the advantages of my 20" wheel folder, is that there is zero toe overlap with a turned front wheel while pedaling (this could be an issue on my old short wheelbase 700c race bike), because the wheel size has shrunk even more than the wheelbase. And as a result of this, folders in particular, they take advantage of that to try to make the wheelbase as short as possible while still stable, for a more compact fold. Some bikes I have seen online with 16" wheels and even smaller, with even shorter wheelbase, I question the stability of them under hard braking. And remember, the rider is still the same height off the ground, because the crank/bottom bracket needs to be the same height for pedaling clearance.

Duragrouch

(I think) BMW was first to put ABS on production motorcycles, and it was a huge advance.

Technically, ABS is possible with pure hydraulics, even pure mechanical IIRC, but it would involve extremely sophisticated hydraulic logic circuits, or mechanical devices, which would not compensate for different conditions (dry/wet/pavement/dirt), which have been done in the past on very expensive and large applications. But with the extreme miniaturization of electronics, there's no reason to not use that on bicycles. The heavier part is the rotating wheel speed sensor, but that can be incorporated into the brake disc, same as on cars (and by the way, with just a little software, they use that to sense when a tire is going flat, as the rolling circumference changes, that has generally eliminated the internal wheel pressure sensors, except perhaps on very low profile, run-flat tires). The power for caliper pulsing, if just a control valve and not the caliper itself, can be low power consumption and handled by a battery.

A rigid bike, already has "anti-lift", and it's undesirable. Let me explain. If you had a bike with rear suspension, the frame would try to lift when braking. Some rear suspension geometries that have a short rear swing-arm, try to counteract that, and it's bad, because to try to pull the frame back down, is only accomplished by trying to lift the rear tire UP, and this reduces your traction. (And especially ineffective, because the rear wheel on bicycles is so light.) This was a big problem on early GM front drive cars that had a "twist axle" with short arms, tons of anti-lift, and would lock the rear brakes in the wet, all the time. ABS solved that. A rigid bike frame, no suspension, automatically tries to pitch forward, unloading the rear tire, just as bad as with any anti-lift geometry, and it's undesirable. In rear wheel drive cars, they often have "anti-squat" geometry under acceleration, which also usually results in anti-lift under braking, but the latter is undesirable for braking stability. If the car is front wheel drive, no rear drive thrust, it's typically now designed for little or no rear anti-lift under braking.

Bonus info: Before implementing ABS on the Honda Interceptor (VFR800), it had "linked braking system", front and rear calipers each have 6 pistons (3 per side); Squeeze the front lever, 4 pistons squeeze the front caliper, 2 pistons back caliper. Squeeze the rear lever, 4 pistons squeeze the rear caliper, 2 pistons front caliper. Squeeze both levers, all 6 pistons squeeze front and back, with varying pressure according to lever pressure. System debuted to complaints, but by the time of the VFR800, they had it sorted out and was well received. Later models had option for ABS, and I don't know if that had linked brakes or not.

calamarichris

Something similar happened to my idiot ex-gf Terah. We're bombing a downhill (~40mph) on Del Dios Highway in the bike lane. An older Subaru Outback squirts past, merges to the right (into the bike lane) and SLAMS ON THE BRAKES. I immediately look back and look for an escape route. Idiot ex-gf slams on her brakes and goes over the bars, spiral fracture of her humurus.
I'd just replaced her Ultegra rim brakes with Dura Ace 7900 brakes, so she naturally blamed me.
The old idiot woman driving the Subaru saw what happened and drove away. I guess the moral of the story is to either hit the offending vehicle, or at least get their license number, or to practice braking modulation and panic stops.

ScottCommutes

I know this is old thread, and I scanned some parts of it, but....

More important than learning to emergency brake is learning how to not use the brakes. Look first at the moving cars, then the stopped cars that might move, then the places the cars might appear from. If you've got all that, memorize the scene around you.

Bikes also avoid accidents differently than cars. My preferred path seems to often be straight ahead and to the left. Think about what might happen to you after the initial problem - don't get stuck in the middle of an intersection with an opposite light turning green and nobody expecting you there - especially if you are on the ground.

Sometimes speed helps, to match traffic. Other times speed kills.

You only need a couple feet of escape path.

Frequently update your mental "threat level". Green - no danger. Yellow - hands on brakes. Red - High danger identified.

Also treat every car like a giant metal safety barrier from other cars.

Bleeding away any energy via your brakes before a crash is always better. A slow crash beats a fast crash.

Pratt

A very similar thing happened to me a few years ago. In thinking back and analyzing the situation, I have concluded that the best thing I could have done differently is to have been driving a loaded log truck.