elcruxio

You keep throwing out numbers and jobst brandt quotes but you don't really specify your arguments other than something is safe and something else is unsafe.

Could you explain the whole cornering maths like you were explaining it to say, a complete layman? How exactly does it work out? I'm all ears.

sheddle

I usually just straighten out my line (if practical) and brake gently

terrymorse 

Okay, I'll try to explain it using only high school level math.

When braking, there is a force generated on the tire-road interface that is in the direction of travel.

When turning, there is a force generated on the tire-road interface that is perpendicular to the direction of travel.

We call these two forces vectors, as they have each a value and a direction.

When both braking and turning, the resulting force at the tire-road interface is the sum of these two force vectors. But since the turning and braking vectors are perpendicular to each other, they can be combined using the Pythagorean Theorem (which should familiar to any high school student):

Where:
a = turning force
b = braking force
c = combined force

As I wrote in my example earlier, pick a turning force of a very substantial 0.9g, and the braking force a substantial 0.2g.

The combined force at the tire-road interface in this case is:

square root of [ cornering force squared + braking force squared ], or

SQRT[ 0.9^2 + 0.2^2 ] =

SQRT[ 0.81 + 0.04 ] =

SQRT[ 0.85 ] = 0.92

This example demonstrates that even when turning at 0.9 g, and braking with 0.2 g, the force at the tire-road interface only increases by 0.02g.

As shown, substantial braking can be done in a turn with very little increase in tire-road force, and thus the warning that braking in a turn substantially increases the risk of slipping out has no merit.

Metieval

If I said "riding without hands is a good way to crash"
Is that saying "you will crash", if you ride without hands?

NO SIR it is not ! So Quit twisting words.

the same applies to handlebars, one way leaves your self open to a crash, it doesn't mean that you will crash.

2 groups of people, those who elect to ride drops on a dropbar, and those who claim "that is not my Drop bar!!!!"

elcruxio

I'll have to get back to this after I discuss it with a friend who's a math wiz but at first glance the formula seems too simplistic to factor in all relevant forces. Just the formulae for cornering forces without braking are much more advanced as are pure braking force calculations.

I suspect that there are a few more vectors involved as well.

Also the numbers are off which makes me heavily suspect the whole validity of Brandts expertise on the matter. Cornering at 0.9g's with a bicycle is unlikely if not impossible altogether. Racing motorcycles with specially formulated sticky hot tires on hot tarmac can reach 1g or even go just above it. However for a bicycle I'd say the theoretical maximum cornering force is below 0.8g's as that's within the typical coefficient of friction achieved with bicycle tyres on tarmac.

It's wholly beside the point but considering that brandts example rider would have wiped out before he ever touched the brakes just takes a good chunk of validity out of his argument.

Happy Feet

Never said never brake in a turn. Did say that it was sub optimal. Your argument was for always using drops as being optimal so suggesting sub optimal braking techniques is contradictory to the theme.

And, going slow isn't because one is unsure of skill - it is a skill. It's called critical thinking.

Your explanation (while entertaining in a theoretical semantic school physics exercise sense), lacks any application in the real world. As admitted, if you don't have an instrument to measure fractional G forces, talking about combining .9 and .2 (as your example) is just bafflegab. Not able to apply IRL. In real life, measuring actual grip vs potential remaining grip becomes more difficult the closer to the edge of performance one goes which is why... tires suddenly lose complete traction and slide out when cornering and trying to apply brakes. It's a failure of traction that is in a practical sense unpredictable at the small numbers you are making up out of your head.

The skill therefore, if one has a near miss while braking and cornering at the same time, would be to slow the rate of speed before the curve next time. Otherwise one would need to brake from the aerobars so you could work the calculator.

radroad

The allez has a 155 mm headtube on a 54 cm. That's not at all aggressive. That's well within range of endurance geometry.

The main problem as several have alluded to, is obesity.

The average adult male in the U.S. has a waistline of over 40 inches, and weighs 200 lbs. Adult females in the US have almost caught up, nearly 39"!

The bottom line is that most Americans are way too fat to be riding in the drops.

Miele Man

What I don't understand about braking in corners is the effect that wants to make the bicycle go upright and which then causes the bicyclist to veer off the line they intend to go in. hat seems to be what causes crashes whilst braking and cornering at the same time. That's why braking in a corner is considered to be a high-skill and is not recommended for most bicyclists.

Cheers

wphamilton

Centripetal force, ie momentum, is what causes the bike to go upright and pushes you wider. Your lean counters this force (as far as pushing you upright goes.)

The big issue in braking in a corner is misjudging and losing traction. There's only a certain total amount of traction available to our tires, and both cornering and braking need some of it.

I haven't followed this discussion so I don't really know how it came up, but having drop bars vs straight bars has no impact on how well the bike can take a corner, braking or otherwise.

Miele Man

I've read of cases where a bicyclist brake hard in a corner and the bike straightened up vertically to such a point that the bicyclist lost the ability to turn and the bike and bicyclist went off the side of the road - sometimes with dire results. I still think that for most bicyclists any braking in a corner should be very gentle or even not at all depending on their level of skill.

Thanks for your reply.

Cheers

wphamilton

I would tend to agree with you in that there's not a whole lot of point to it on the road unless you're racing in a pack, and a big reason there is simply that most of them will be doing it and accelerating on the far side so it's better to not be yoyo'ing from the pack. We're not going to lose much if any speed on our road riding by slowing down first and coasting around.

But it's good to know how and have a bit of confidence in it, when you happen to find yourself at the bottom of a hill going way too fast and have to make that turn. I've been there.

terrymorse 

And you are incorrect. There are many very good reasons to brake in a turn, with essentially no downside.

terrymorse 

That is not what happens when you brake in the middle of a turn.

What does happen: the turn radius gets smaller. This in itself is a useful technique, especially when you come around a blind right curve to find a car over the center line and encroaching into your lane. Grab some brake, tighten your turn radius, slip past the car on the right. I have use this method more times than I can remember.

You can demonstrate this radius shrinking effect to yourself: Go out in a parking lot, pedal around in a fairly tight circle, until you are leaning the bike over (but not enough to ground a pedal!) and traveling at a moderate speed. Now, grab some brake and watch what where your bike goes.

Miele Man

Sorry, but that's not what I've read about happening on winding descents where someone without the NEEDED SKILL braked fairly hard on a curve. In one particular case the bicycle of the woman who braked hard straightened up, took a new line towards the edge of the road and went over the edge. I can't remember if her fall down the side of the hill/mountain killed her of just seriously injured her.

Seems that others disagree with braking a turn.

GCN video, Mistake #2.


https://www.bicycling.com/training/a...cending-hills/

Quote. "The biggest mistake people make descending: They wait until they're in the middle of a turn to brake. Instead, scrub speed before the turn. If you have to brake in the turn, you didn't slow enough to begin with. Then, push your outside pedal down (right turn, left foot down) with pressure on that foot. To initiate the turn, lean the bike--not your body--into the turn (right turn, lean bike right). The faster and sharper the turn, the more you'll lean the bike. This action is similar to downhill skiing: The lower body angulates into the turn while the upper body remains upright. To exit the turn, gently straighten the bike."

Like I said before many people brake too hard in a turn and thereby lose control of their bike often to the point of not being able to regain steerage/control before crashing.

Cheers

terrymorse 

If your rear wheel starts to skid out during a turn, your natural reaction is to turn towards the skid and straighten up, and your bike's path will straighten out. I've seen riders do this a couple of times. One rode straight across the road into a pasture. The other ended up on the guard rail with some scrapes and bruises.

More common mishap is braking hard before a turn and losing traction, before you can start into the turn. If you can't start your turn in time, you're going straight. You can see this often in pro races.

That happened to me once descending Ebbets Pass. I was going fast down a long straight section that ended in a left hairpin. As I was braking hard, I hit a bump that caused the rear wheel to jump, then skid, and I wasn't able to initiate the turn in time. I straightened the bike, kept on the front brake, rode straight as an arrow, and slowly exited the roadway. No harm done.

I think we can all agree that braking too hard, no matter where it is done, is by definition not a good idea (see "tautology"). Yet some people say that any amount of braking in a turn is "too hard", and that is bad advice.

Braking during a turn is a useful skill that improves with practice, and it's a skill that can avoid unpleasant outcomes. Of course, suddenly grabbing two big handfuls of brake--at any time--is a bad idea.

EDIT: Here's an example of what happens when your rear wheel loses traction as you start a turn. Your track straightens out.

wphamilton

More likely she veered outside the turn because she was going too fast and was afraid to lean over and turn sharply enough. That happens, and it's scary, but it's when you lose your nerve or don't have the skill to take the turn at that speed. I don't think the braking per se, will push you out.

When you slow down (braking) centripetal force is less, which would naturally tend to lean you more into the curve, not less.

L134 

Entertainment only! I don’t even know what the original post really means. My drops are in fact there.....I think.

Happy Feet

You live in an alternate reality my friend. Probably taking competitive racing concepts and assuming they apply in other settings.

Your "no downsides" flies in the face of every safe driving course out there. I wont argue it any more. Anyone who's ridden a bike for a while understands the problems of braking while in a curve. Your saying there isn't doesn't make it so.

Metieval

on the hoods, squeeze squeeze harder, whoops too much brake.

Is it coincidental , that hood riding and fear of braking in corners goes hand in hand?

Miele Man

When I searched You Tube for that video I posted above there were a LOT of other videos in the Search return that showed motorcycles sliding out in turns. They were talking about low-side crashes as well as high-side crashes. Thus improper braking in a curve is not limited to bicyclists and seems to be a rather advanced skill t hat a LOT of people don't have. hence the advice given by many to non-racing bicyclists to not brake in a curve. Do what works for you.

Cheers

terrymorse 

Every safe driving course? Even the written course material from, say, driversed.com?

Curves

Reduce speed before entering the curve, and slowly lighten the pressure on the brake until reaching the apex point (where the car is closest to the inside of the curve line). At the apex or exit point, apply light acceleration to pull the car out of the curve.

I wonder why driversed.com would every advise braking in a curve when such action is, as you claim, is "suboptimal".

Happy Feet

Like I said, an alternate reality. It has to be to misinterpret that statement so completely. Let's brake it down (pun intended)...

Reduce speed before entering the curve, - That's brake before the curve

and slowly lighten the pressure on the brake until reaching the apex point - That's ease off the brakes in the curve.. not apply them.

Thanks for the example btw.

Happy Feet

The reason you go upright and flip over the outer side of the bike when applying the brakes too hard in a curve is the forward momentum of your body over taking the arc of the bike. The bike slows but the mass of your weight continues forward towards the outside edge of the bike and over it if the braking force is too hard.

If you could remain low on the inside edge (think cafe racers cornering) you could control that force but your mass might then kick out the tires and you would lose traction. Road bikes typically do not have the sidewall tread design to make that work.

Many people don't anticipate the reduced inner turn radius of the bike when that happens and so they are too high. As they begin to lose balance outward the reflex is to brake even more, which exaggerates the effect.

If you ever downhill mtb and take sharp switchback turns you learn that real quick when applying the more responsive front brake. As you begin to pitch forward you instinctively hit the brake more and over the bars you go! Then you realize you should brake more from the rear in that situation and skid the back tire around.

Kapusta

20 pages of replies and maybe 10 posts that actually address the OPs point.

That’s actually pretty good by BF standards.

Happy Feet

In this video it is pretty easy to see the riders foot comes off the pedal. They appear to become preoccupied for a second and lose concentration to correct the trajectory path to complete the turn at that speed and veer wide to the point of neither being able to slow down or turn enough. Nothing about lost traction.

In racing there are lines you follow through turns. At Daytona this is a case of going to high and hitting the wall.