Braking while turning

Quoted message said:

Is there a physics explanation for this? Even the seasoned riders at the bike shop give me a wierd
look when I tell them I hardly ever use the rear brake.

FWIW, if you lose traction on the front in a turn, it is very likely you will crash. If you lose
traction on the rear in a turn, it is usually recoverable unless your lean angle is extreme.

Braking the rear in a turn may cause the rear to skip causing the effects you mentioned. But when
you brake with the front, weight is pushed forward onto the front wheel and giving it heavier
steering, etc.

--
Phil, Squid-in-Training

Squid-in-Training said:

Quoted message said:

Is there a physics explanation for this? Even the seasoned riders at the bike shop give me a
wierd look when I tell them I hardly ever use the rear brake.

You are doing it right, by the way.

Quoted message said:

FWIW, if you lose traction on the front in a turn, it is very likely you will crash. If you lose
traction on the rear in a turn, it is usually recoverable unless your lean angle is extreme.

Yes, if you lose traction on the front in a turn, you will go down. But you will usually go down if
you skid the rear as well, and it is much, much easier to skid the rear in any circumstances. In
good weather on a good road, it is impossible to skid the front.

Quoted message said:

Braking the rear in a turn may cause the rear to skip causing the effects you mentioned. But when
you brake with the front, weight is pushed forward onto the front wheel and giving it heavier
steering, etc.

Any braking of either wheel will shift the weight distribution forward. That is why the rear wheel
skids so easily when you apply the rear brake, since the amount of your weight on the rear can go
to near 0.

--

David L. Johnson

__o | The trouble with the rat race is that even if you win you're _`\(,_ | still a rat. --Lilly
Tomlin (_)/ (_) |

David L. Johnson said:

Squid-in-Training said:

Quoted message said:

Is there a physics explanation for this? Even the seasoned riders at the bike shop give me a
wierd look when I tell them I hardly ever use the rear brake.

You are doing it right, by the way.

Caution. Don't take such recommendations too literally and think you can do without ever braking
with the rear. It mainly depends on the amount of sustained braking you must do.

It happened recently to me to have to go down a steep, long hill with only my front brake in good
order. I was scared to death. Besides the concern about possiblly overheating the rim and having the
tube explode, the hand operating the front brake got so tired that it could no longer grab
efficiently. Also, if you must come to a halt where the gradient is substantial, it is a lot easier
if you can brake also with the rear, if not only with that.

So often discussions and warnings against 'going over the bars if braking too much' scare people
about braking at all.

That is how recently an American lady picked up much too much speed down the reknown Fedaja road to
Malga Ciapela and crashed into the woods. A helicopter had to come in rescue ... .

Sergio Pisa

WE ARE LOOKING FOR THE LAB'S COMPUTER PRINTOUTS GENERATED BY THE LAB VEHICLE!! this inorder! to! pin
down the language into numbers. then we can conceptualize from the other side. anybody who goes
reaaaaalllly deeeeeep into the corners care to cawment???

"g.daniels" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

WE ARE LOOKING FOR THE LAB'S COMPUTER PRINTOUTS GENERATED BY THE LAB VEHICLE!! this inorder! to!
pin down the language into numbers. then we can conceptualize from the other side. anybody who
goes reaaaaalllly deeeeeep into the corners care to cawment???

LOL - reading this was just too much. Not to be condescending, but is English your first language?

--
Phil, Squid-in-Training

David L. Johnson said:

Quoted message said:

Quoted message said:

Is there a physics explanation for this? Even the seasoned riders at the bike shop give me a
wierd look when I tell them I hardly ever use the rear brake.

You are doing it right, by the way.

Yes, if you lose traction on the front in a turn, you will go down. But you will usually go down if
you skid the rear as well, and it

It's an important discussion, I don't mean to be flippant. But I find there is more to worry about
than skidding with the front. If, for example, a stone large enough to lift the wheel off the ground
is hit, the front wheel will stop. When it hits the ground again, an end over is a given. So on
turns on steep grades coming out of hills like in Malibu where rocks are prevalent, I am very
reluctant to use the front brake.

Quoted message said:

is much, much easier to skid the rear in any circumstances. In good weather on a good road, it is
impossible to skid the front.

Good road, good weather. But even then, that lone stone. I just see too many. I practice rear wheel
skids actually to reduce trouble, but yes, they can be nasty too, although never has one brought me
down (all handful of them).

Doug

Phil said:

FWIW, if you lose traction on the front in a turn, it is very likely you will crash.

Yes, but it will always be a lowside. Because of the forward weight shift, front wheel traction
increases as the brake is applied. This effect permits more braking while steering than most folks
think possible-- provided the tires are adequate to the task.

Quoted message said:

If you lose traction on the rear in a turn, it is usually recoverable unless your lean angle is
extreme.

In my experience, if you go into a turn hot enough, or downhill enough, to have to brake while
turning, a slip at either end will put you on the ground. In those circumstances, it is much easier
to lose the rear. Furthermore, slipping the rear can cause a highside, flinging you into the land of
broken clavicles.

Chalo Colina

<[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

One thing I have noticed is how differently bicycles handle when the rear brake is applied
compared to the front brake.

While braking with the front wheel and turning, the rear wheel naturally swings around follows
through the turn. The steering feels the same as if the brake wasn't applied.

When the rear brake is applied while turning it feels like a force is pulling rear tire in a
straight line backwards causing it to not want to swing around and follow the path of the front
tire. The bike plows though the turn. Even when the bike is traveling in a straight line the bike
doesn't feel nearly as controllable as it would with the front brake is applied.

Is there a physics explanation for this? Even the seasoned riders at the bike shop give me a wierd
look when I tell them I hardly ever use the rear brake.

We've discussed that here before and you're right. Note Sheldon's comments on applying the rear
brake of a tandem with nobody in back.

For a more dramatic example, just increase the speed and vehicle weight. Try tapping the brakes
during an aggressive corner in a rear engine car. You'll only try that once!

--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

Quoted message said:

the rear. Furthermore, slipping the rear can cause a highside, flinging you into the land of
broken clavicles.

Really now? In my experience, highsides have been limited to the domain of motorcycles, where the
speeds of the bikes and massive grips of the tires have the potential to cause a highside.

Uh... wait. I recall highsiding on my MTB commuter once. I landed on my forearms, so nothing broken.
I now have a dolphin-shaped scar on my arm. Nevermind what I said.

--
Phil, Squid-in-Training

Quoted message said:

It's an important discussion, I don't mean to be flippant. But I find there is more to worry about
than skidding with the front. If, for example, a stone large enough to lift the wheel off the
ground is hit, the front wheel will stop. When it hits the ground again, an end over is a given.
So on turns on steep grades coming out of hills like in Malibu where rocks are prevalent, I am
very reluctant to use the front brake.

Why does the front wheel stopping cause an endo? I would think that once it hits the ground
again, it will either skid or start to rotate again, depending on the amount of traction
available. Is it because the coefficient of friction between the brake and the wheel is higher
once the wheel stops rotating?

--
Ray Heindl (remove the X to reply)

Just how hard are you applying the rear brake? If it feels like your rear wheel is going straight
while the rest of the bike is going through a turn, you're skidding the rear wheel. And yes, there
is a "physics" reason for this. It's called inertia. An object in motion tends to move in a straight
line unless acted upon by another force. (sic.)

If your front wheel slides out, it too will go in a straight line. With disastrous results.
Actually, the best thing is not to brake at all in a turn, Do all your braking before.

The tires have a limited amount of "grip" on the pavement, any that's diverted towards slowing the
bike down is being taken away from the amount holding it in a curved path.

If you must apply brakes in a turn, do so very gently, and it's best, in this case, to favor the
rear. If that gives away, you have a much better chance of riding it out.

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": geocities.comczcornerOpen ↗

(Chris Zacho 'The Wheelman') said:

If your front wheel slides out, it too will go in a straight line. With disastrous results.
Actually, the best thing is not to brake at all in a turn, Do all your braking before.

It may be the safest thing to do, but if you want to descend fast, it's poor technique.

Quoted message said:

The tires have a limited amount of "grip" on the pavement, any that's diverted towards slowing the
bike down is being taken away from the amount holding it in a curved path.

Not really. First off, it is unlikely that you will be riding right at the limits of adhesion. For a
simple test, with your bicycle beside you, lean the bike over, with one hand on the stem and the
other on the seat. Push into the bike. See how how far over you can lean the bike until the tires
slip. You should be able to get the bike to around 45 degrees. Do you corner anywhere near that lean
angle? Few do.

Second, because the total force on the contact patch is the vector sum of the cornering force and
the braking force, which are applied perpendicular to each other, it is possible to apply
considerable braking force while barely changing the total force. For example, let the braking force
(fb) be 20% of the cornering force (fc). The total force is then

ftot = sqrt(fc^2 + fb^2)
= fc*sqrt(1+(fb/fc)^2)
~ fc*(1+(fb/fc^2)/2) for fb << fc
= fc*(1+(2/10)^2/2) = 1.01*fc

With a mere 1% increase in contact patch force, you can be slowing considerably.

Quoted message said:

If you must apply brakes in a turn, do so very gently, and it's best, in this case, to favor the
rear. If that gives away, you have a much better chance of riding it out.

This is poor advice. Better to learn and practice skills so that you can corner at a comfortable
speed with safety. If you only learn to brake with the rear, you won't be able to stop or slow down
when you really need to.

Joe Riel

"> It may be the safest thing to do, but if you want to descend fast,

Quoted message said:

it's poor technique.

Actually, its better to brake and accelerate in straight lines. Don't ask me to explain, its
physics...

I have a nice scar on my left bicep from braking in a corner and running wide into a barbed wire
fence. Grab brakes in the middle of a turn and the bicycle will have a tendency to stand up and
widen the arc of the corner you're taking. If you don't know its going to happen, you too can end up
with a nifty scar like mine. I learned the hard way that if you go into a corner too hot and have to
brake, to make for damn sure that you're planning on cornering even harder to counteract the bike
standing up.

If you have to brake, do it just like in cars and motorcycles: brake before the corner, corner, then
accelerate as you're exiting.

If you can help it, don't brake. That's the fastest way down the mountain...

Mike

"Mike S." <mikeshaw2@coxDOTnet> wrote in message news:ZKKSa.13074$Bp2.9976@fed1read07...

Quoted message said:

"> It may be the safest thing to do, but if you want to descend fast,

Quoted message said:

it's poor technique.

Actually, its better to brake and accelerate in straight lines. Don't ask me to explain, its
physics...

The physics have been explained. It doesn't support your claim.

Quoted message said:

If you have to brake, do it just like in cars and motorcycles: brake before the corner, corner,
then accelerate as you're exiting.

This isn't true, for the reasons given.

Quoted message said:

If you can help it, don't brake. That's the fastest way down the mountain...

No a particularly helpful suggestion.

Joe Riel said:

... Do you corner anywhere near that lean angle? Few do.

Ok, so you first establish that on flat pavement with no surface gunk friction is very high. And
you argue that few folks ride anywhere near this limit on corners. So for most people fc is not
that high.

Quoted message said:

Second, because the total force on the contact patch is the vector sum of the cornering force and
the braking force, which are applied perpendicular to each other, it is possible to apply
considerable braking force while barely changing the total force. For example, let the braking
force (fb) be 20% of the cornering force (fc). The total force is then

You then argue that 20% of fc (which we established is not that high) is a "significant braking
force". For some reason, I disagree. :-)

Quoted message said:

ftot = sqrt(fc^2 + fb^2)
= fc*sqrt(1+(fb/fc)^2)
~ fc*(1+(fb/fc^2)/2) for fb << fc
= fc*(1+(2/10)^2/2) = 1.01*fc

Here is a much easier way of solving (and understanding) this, with the bonus of getting a more
accurate answer:

ftot = sqrt(fc^2 + fb^2)

Assume that fc = 1unit. Assume that fb = .2*fc = .2units

ftot = sqrt(1^2 + .2^2) = 1.02

Now, if you assume that the rider is cornering somewhat conservatively, because they fear that there
might be a patch of sand or tar on the corner somewhere, then you can assume that fc is not too
high. What happens if they are also going down a steep hill, and want to brake to maintain their
speed? If fc=fb, then this changes to:

ftot = sqrt(1^2 + 1^2) = 1.41

You have just lost 40% of the margin of safety you planned to have in the corner.

I do agree that the best way to learn this is not through math, but through practice. I found that a
great way to learn how to deal with low traction conditions in corners is to go out and ride just
after a fresh snowfall (before the plows come by). Very low traction, loads of fun, and if you
happen to fall then the snow offers some padding...

Chris
--
Chris Colohan Email: [email hidden] PGP: finger [email hidden] Web: www.colohan.com Phone:
(412)268-4751

Mike S.' mikeshaw2@coxDOTnet said:

"> It may be the safest thing to do, but if you want to descend fast,

Quoted message said:

it's poor technique.

Actually, its better to brake and accelerate in straight lines. Don't ask me to explain, its
physics...

I have a nice scar on my left bicep from braking in a corner and running wide into a barbed wire
fence. Grab brakes in the middle of a turn and the bicycle will have a tendency to stand up and
widen the arc of the corner you're taking. If you don't know its going to happen, you too can end
up with a nifty scar like mine.

I doubt that you would have been better off without braking. The point being, unless you are willing
to go slow all the time, you are better off learning how to brake in turns. The time to learn is not
when you need it...rather practice under known conditions.

Quoted message said:

If you have to brake, do it just like in cars and motorcycles: brake before the corner, corner,
then accelerate as you're exiting.

You think cars and motorcycles don't brake in turns? That's nonsensical. Furthermore, the amount of
acceleration available to a cyclist is trivial compared to the deceleration. Learn to use.

Quoted message said:

If you can help it, don't brake. That's the fastest way down the mountain...

Not one with real turns.

Joe Riel

"Phil, Squid-in-Training" <[email hidden]> wrote:

Chalo said:

Quoted message said:

Furthermore, slipping the rear can cause a highside, flinging you into the land of broken
clavicles.

Really now? In my experience, highsides have been limited to the domain of motorcycles, where the
speeds of the bikes and massive grips of the tires have the potential to cause a highside.

Uh... wait. I recall highsiding on my MTB commuter once. I landed on my forearms, so nothing
broken. I now have a dolphin-shaped scar on my arm. Nevermind what I said.

Though I've not actually seen video of it, the crash that took Beloki out of the Tour this year
(which commands its own thread right now) has been described as a highside.

I've highsided both pushbikes and motorbikes, and motorbikes are worse. ;^)

Chalo Colina

Christopher Brian Colohan said:

Joe Riel said:

... Do you corner anywhere near that lean angle? Few do.

Ok, so you first establish that on flat pavement with no surface gunk friction is very high. And
you argue that few folks ride anywhere near this limit on corners. So for most people fc is not
that high.

Quoted message said:

Second, because the total force on the contact patch is the vector sum of the cornering force
and the braking force, which are applied perpendicular to each other, it is possible to apply
considerable braking force while barely changing the total force. For example, let the braking
force (fb) be 20% of the cornering force (fc). The total force is then

You then argue that 20% of fc (which we established is not that high) is a "significant braking
force". For some reason, I disagree. :-)

Quoted message said:

Quoted message said:

ftot = sqrt(fc^2 + fb^2)
= fc*sqrt(1+(fb/fc)^2)
~ fc*(1+(fb/fc^2)/2) for fb << fc
= fc*(1+(2/10)^2/2) = 1.01*fc

Quoted message said:

Here is a much easier way of solving (and understanding) this, with the bonus of getting a more
accurate answer:

The reason I expanded the term was so that the math would be easier
(i.e. I wouldn't have to do the square root in my head). Alas, I apparently can't do squares in my
head. My formula gives 1.02 when done properly.

Quoted message said:

ftot = sqrt(1^2 + .2^2) = 1.02

Now, if you assume that the rider is cornering somewhat conservatively, because they fear that
there might be a patch of sand or tar on the corner somewhere, then you can assume that fc is not
too high. What happens if they are also going down a steep hill, and want to brake to maintain
their speed? If fc=fb, then this changes to:

ftot = sqrt(1^2 + 1^2) = 1.41

You have just lost 40% of the margin of safety you planned to have in the corner.

That's why it's called margin 8-).

Consider this. The maximum braking force on dry asphalt is limited to approximately 0.7g, to prevent
flipping over. Assume that the maximum contact force (where sliding initiates) is about 1g. It is
then possible to be simulateously braking at the maximum (0.7g), while cornering at 0.7g! Cornering
at 0.7g corresponds to a lean angle, from upright, of approximately 35 degrees. I have crudely
measured my lean angles and know that 35 degrees feels quite aggressive; I consider myself a
reasonably fast descender---certainly one of the faster in my club. The point being, the typical
margins riders deal with are wide indeed. Naturally, stuff in road can reduce the margins in a
hurry, but one of the points of practicing is to learn to maneuver at speed.

Quoted message said:

I do agree that the best way to learn this is not through math, but through practice.

Agreed, but I like doing the math anyway...

Quoted message said:

I found that a great way to learn how to deal with low traction conditions in corners is to go out
and ride just after a fresh snowfall (before the plows come by). Very low traction, loads of fun,
and if you happen to fall then the snow offers some padding...

I guess that's one of the downsides to living in San Diego; we don't get much snowfall here 8-). To
improve my cornering I have used stiff wire attached to the rear dropout and set to touch the ground
at a preset lean angle. Start with a lean angle of about 30 degrees, ride and corner progressively
harder until you just hear the wire scraping on the ground. Then gradually increase the lean angle.

Joe Riel

Joe Riel said:

Christopher Brian Colohan <[email hidden]> writes:

[...]

Quoted message said:

Quoted message said:

I found that a great way to learn how to deal with low traction conditions in corners is to go
out and ride just after a fresh snowfall (before the plows come by). Very low traction, loads of
fun, and if you happen to fall then the snow offers some padding...

I guess that's one of the downsides to living in San Diego; we don't get much snowfall here 8-). To
improve my cornering I have used stiff wire attached to the rear dropout and set to touch the
ground at a preset lean angle. Start with a lean angle of about 30 degrees, ride and corner
progressively harder until you just hear the wire scraping on the ground. Then gradually increase
the lean angle.

Joe Riel

I have to try this...

--

Chris Bird