Is using front brake alone really the most effective way to stop?

fergalr

So, someone made this claim in another thread:
http://www.boards.ie/vbulletin/showpost.php?p=60300195&postcount=57

Tau wrote:

If you're braking as much as you can with the front brake, then there will be absolutely no weight at all on the rear wheel (ie. you're just on the point of flipping the bike over). Then if you even touch the rear brake, the rear wheel will skid.

The fastest way to stop is with the front brake only.

Can someone explain this to me?
First off, my intuition about wheels and how they work isn't keenly developed - I'm not a mechanical engineer.

However, from cycling, when I try model how it'd feel in the head, I reckon using the back brake would also help.
Now, I know the front brake is much more powerful, and is the main stopping force.

But as I think about it, when I pull the front brake, and my weight shifts forward, applying the rear brake a little causes a little more force between the rear and the ground, and I feel my weight start to shift back; thus increasing the amount of front brake I can apply before endo'ing (ie, before starting to go forward, as if over the bars).

This would seem to be more effective, to me, than just using the front brake.

Also, it means the rear brake is acting on the rear wheel, trying to force it to slow down - this would seem to be making use of the rear wheels contact patch with the ground, which doesn't happen when you just use the front brake. (Although, I'm on shaky ground here, I don't totally understand the mechanics of the interaction?)

Does anyone agree with this position? Or can you provide a mechanical argument to prove that the front brake alone is the fastest way to stop?

Thanks, be curious to hear responses - should I be learning to brake with front brake alone? Or is the original quote incorrect?

abcdggs

the most effective way to stop is at the point where al your weight is on the front wheel ie you are just about to "endo" at which point theres is no weight on the rear wheel so it has no contact point with the ground. but up until this point the rear wheel will help slow you down.

fergalr

abcdggs wrote: »

the most effective way to stop is at the point where al your weight is on the front wheel ie you are just about to "endo" at which point theres is no weight on the rear wheel so it has no contact point with the ground. but up until this point the rear wheel will help slow you down.

Is the argument then that you are supposed to apply your front brake to the precise point where the rear wheel is about to lift, and as using the rear brake in this case would create a skid (because it's right about to lift, so has practically zero traction), therefore you shouldn't apply the rear brake at all?

This would seem to be a highly idealised argument, but I guess it makes sense, in the situation where forward pitch is the limiting factor (as opposed to surface traction or brake quality/force_of_brakes_on_wheels).

It's very ideal though, you'd have to be able to pull your front brakes instantly to that precise point; in practice maybe you'd be better applying both for the time it takes you to find that point with your front, and then backing off the rear? Or always applying the rear slightly? I'm also thinking that if you just grab the front you probably don't have the very brief time needed to put your weight back behind the saddle; maybe use both brakes till you get into that position, then switch solely to front?
Is this what people do?
How would you instinctively react if someone steps out in front of you? Or would you just grab both brakes and skid?

(I locked the rear wheel recently, ever so briefly, when a car made a sharp left turn into their driveway over my cycle lane. (they came up from behind me too))

abcdggs

only ride a single speed, which only has a brake on the front. i think the convention is to use both because presumably in a practical setting it is not ideal to have all your weight on the front wheel.

Thomas_S_Hunterson

fergalr wrote: »

But as I think about it, when I pull the front brake, and my weight shifts forward, applying the rear brake a little causes a little more force between the rear and the ground, and I feel my weight start to shift back; thus increasing the amount of front brake I can apply before endo'ing (ie, before starting to go forward, as if over the bars).

Your weight doesn't actually shift back, this is entirely in your head. The fact that you're slowing down (doesn't matter where the brake is) pushes the weight toward the front. You can verify this yourself. Apply the back brakes hard enough and the back wheel will skid. Try the same on front and you'll end up on your head. The front wheel will not skid.

DirkVoodoo

From Wikipedia:

Front wheel braking

The limiting factors on the maximum deceleration in front wheel braking are:

* the maximum, limiting value of static friction between the tire and the ground,
* the kinetic friction between the brake pads and the rim or disk,
* pitching (of bike and rider) over the front wheel.

For an upright bicycle on dry asphalt with excellent brakes, pitching will probably be the limiting factor. The combined center of mass of a typical upright bicycle and rider will be about 60 cm (23.6 in) back from the front wheel contact patch and 120 cm (47.2 in) above, allowing a maximum deceleration of 0.5 g (4.9 m/s² or 16 ft/s²).[8] If the rider modulates the brakes properly, however, pitching can be avoided. If the rider moves his weight back and down, even larger decelerations are possible.

Front brakes on many inexpensive bikes are not strong enough so, on the road, they are the limiting factor. Cheap cantilever brakes, especially with "power modulators", and Raleigh-style side-pull brakes severely restrict the stopping force. In wet conditions they are even less effective.

Front wheel slides are more common off-road. Mud, water, and loose stones reduce the friction between the tire and trail, although knobby tires can mitigate this effect by grabbing the surface irregularities. Front wheel slides are also common on corners, whether on road or off. Centripetal acceleration adds to the forces on the tire-ground contact, and when the friction force is exceeded the wheel slides.

Of course, the angle of the terrain can influence all of the calculations above. All else remaining equal, the risk of pitching over the front end is reduced when riding up hill and increased when riding down hill.

Rear wheel braking

The rear brake of an upright bicycle can only produce about 0.1 g deceleration at best,[8] because of the decrease in normal force at the rear wheel as described above. All bikes with only rear braking are subject to this limitation: for example, bikes with only a coaster brake, and fixed-gear bikes with no other braking mechanism.

John_C

What's written in this thread is correct. The harder you brake the less weight is on your back wheel. If you're braking at your hardest, there's no weight on the back wheel and the back brake is useless. If you're braking less than that, there is some weight on the back wheel and the brake is of some use.

TinyExplosions

From the god himself...

niceonetom

You can increase the ferocity that you can mash the front brake with before tipping forward by pushing your weight back on the bike. The force will all be transmitted to the front wheel (good), but if your arse is as far back on the saddle as possible and your arms nearly straight you create a longer lever acting against the apparent upward force imparted to the back of the bike.

A rear brake is useful though, for scrubbing speed off on a descent for example or in very low grip conditions where using the front brake can make the front wheel disappear from beneath you.

crazydingo

There's no point in not using a back brake if it is there. Even if the front brake was to take all the force it can't hurt to use the back brake just in case you don't have perfect brakes

John_C

crazydingo wrote: »

There's no point in not using a back brake if it is there. Even if the front brake was to take all the force it can't hurt to use the back brake just in case you don't have perfect brakes

The back break will cause the back wheel to skid if you're breaking quickly.

Lumen

John_C wrote: »

The back brake will cause the back wheel to skid if you're braking quickly.

Rear wheel skids are not a problem. Better to just jam on the back one and worry about modulating the front - you can't focus on both at once.

John_C

Lumen wrote: »

Rear wheel skids are not a problem. Better to just jam on the back one and worry about modulating the front - you can't focus on both at once.

Rear wheel skids aren't a problem but they're not a solution either. If the wheel has lost traction it's doing little or nothing to slow the bike.

Reading through the original question again, the misunderstanding is here: "applying the rear brake a little causes a little more force between the rear and the ground, and I feel my weight start to shift back". Your weight doesn't shift back when you apply the rear brake, it shifts forward when you apply either brake.

Lumen

John_C wrote: »

Rear wheel skids aren't a problem but they're not a solution either. If the wheel has lost traction it's doing little or nothing to slow the bike.

Unless you are able to decelerate using a perfect stoppie (and I'd like to see that) the rear wheel will always have some grip, so what I've suggested still applies.

In general a locked tyre provides plenty of braking (ISTR that ABS is only used to allow steering whilst braking and prevent water buildup that would cause aquaplaning). Hence the motorsport saying "when you spin, both feet in".

mickbyrne

The advice from my instructor for advanced motorcycling lessons I took was:

- On a dry surface, apply front brakes slightly before applying the back brakes. The force created by this 'pushes' the front wheel into the ground increasing the pressure and surface contact area. The later application application of the rear break 'pulls' the back tyre into the ground which also increases the friction
- On a wet surface, front and back brakes should be applied at the same time, and depending on conditions the back brakes should be applied with greater pressure. This forces downward pressure on both wheels reducing the possibility of the front wheel from sliding out. (From experience, this is not a nice thing!)

On a bicycle, I always use both, the front gives more stopping power, but the back helps keep control of the bike, especially the direction.

Civilian_Target

Yes, for sure the front brake stops you the fastest.

But if you don't want to fly, you need to put your weight over the back wheel and put the back brake down to the verge of skidding. I've found that this technique can take me from full throttle to stopped in less than the length of a car, and has saved my ass twice.

steinone

abcdggs wrote: »

only ride a single speed, which only has a brake on the front. i think the convention is to use both because presumably in a practical setting it is not ideal to have all your weight on the front wheel.

You mean a fixed gear right? If your actually using just a front brake on a singlespeed please get a rear brake too!
For your own sake do!

concussion

If you want to stop the bike immediately, grab the front brake as hard as you can.

If you want to stop the bike immediately but remain on it, push your weight as far back as you can, brake hard and smoothly with the front and modulate the back to keep it from skidding. With practice you can safely go from warp speed to zero in a few feet.

snollup

steinone wrote: »

You mean a fixed gear right? If your actually using just a front brake on a singlespeed please get a rear brake too!
For your own sake do!

i have to admit to riding with only front break. since i flipped the rear wheel to the fixed hub i've always had just the one. am not the quickest going about on the bike but feel fairly safe with this setup. between fronty and the pedals can stop fairly quickly.

fergalr

Sean_K wrote: »

Your weight doesn't actually shift back, this is entirely in your head. The fact that you're slowing down (doesn't matter where the brake is) pushes the weight toward the front. You can verify this yourself. Apply the back brakes hard enough and the back wheel will skid. Try the same on front and you'll end up on your head. The front wheel will not skid.

So, I accept the fact that I'd be slowing down means that the bike is basically exerting a force on my body, stopping my body moving forward, which means I feel my weight go forward.
In other words, braking on a bike causes the bike to apply a force 'backwards' on your body, so it feels like your body is going forward.

The question is, does using the rear brake - before the point where maximum front brake is applied - slow the rate at which you are pitching forward?
I'd actually say that perhaps it does.

I consider the case where I just use a front brake - say, to 3/4 of the force at which the rear wheel will lift (Its an emergency, I'm braking fast, I don't want to endo, so I'm erring on the side of caution.)

So, all the force slowing me down is reaching the ground through the front wheel, around which there's a turning effect, not yet strong enough to counteract my weight and pitch me forward.

If I was to decrease the front braking force slightly, and apply (a fair bit of) rear brake instead to make up, wouldn't there be less turning force around the front wheel? Some of my braking is now transferring to the ground via the rear wheel, so there's less of a pitching effect around the front wheel, but I'm still slowing the same amount.

In practical terms, this gives me less risk of pitching over the handlebars, but still slowing quickly, while I find the sweet spot in terms of front brake application.

Thinking about it, I think this is a better way to stop then using just the front brake - and it's what I think I do on the bike instinctively anyway - is there something wrong with the line of thought?

pburns

concussion wrote: »

If you want to stop the bike immediately, grab the front brake as hard as you can.

If you want to stop the bike immediately but remain on it, push your weight as far back as you can, brake hard and smoothly with the front and modulate the back to keep it from skidding. With practice you can safely go from warp speed to zero in a few feet.

Yeah, but in the heat of a 'O SHI...!!!!' moment there is a big danger of going over the handlebars. Well for me anyway:o...

I always adjust the front brake to be weaker than the back and use it after pulling the back brakes, or very carefully using it to adjust speed on gravel etc.

Maybe not the copybook fastest way of stopping but more idiot-proof. It doesn't help that different bikes I rode for a while had brakes set up on opposite sides...

fergalr

Investment in Science is an essential part of the plan for economic recovery.

So:

We will need two riders, of equal weight and height, Rider A committed to the idea that front brake only is the fastest way to stop, and Rider B committed to the idea of both brakes being best.

The riders will take turns on the test bike.
They will start a predefined point on a hill, and coast, downhill, to a second point. Independent witnesses will observe that they are not braking prematurely; they will be required to fist the handlebars until they reach the second point.

At this second point they will have to stop as quickly as possible.
Whoever logs the shortest stopping distance, over multiple iterations (to correct for rider skill), proves their point.

Rider A's rear brake will be disconnected during testing.

Djouce is a suitable hill.
Volunteers?

concussion

Your front brake is your biggest asset, embrace it!! Tighten it up again and practice emergency stops, when/where safe to do so. Gain some confidence using it and you can avoid describing a ballistic path when you need to stop in a hurry

fergalr wrote:

they will be required to fist the handlebars until they reach the second point.

Err, they have to do what?? :eek::D

steinone

snollup wrote: »

i have to admit to riding with only front break. since i flipped the rear wheel to the fixed hub i've always had just the one. am not the quickest going about on the bike but feel fairly safe with this setup. between fronty and the pedals can stop fairly quickly.

Oh no you have misunderstood, or I said it wrong, I was waning him on the dangers of riding singlespeed with one brake, riding fixed gear with one brake is perfectly safe.
Sure I ride brakeless.

fergalr

concussion wrote: »

Err, they have to do what?? :eek::D

Grab the bars with their fist, as opposed to having free fingers to pull the brakes.

The word is used in that context in the book 'Mastering Mountain Bike Skills' (See: http://tinyurl.com/pwpjxj)

I don't know what you are thinking of; but I would remind you that Scottish law can act as precedent here.

fergalr

steinone wrote: »

Oh no you have misunderstood, or I said it wrong, I was waning him on the dangers of riding singlespeed with one brake, riding fixed gear with one brake is perfectly safe.
Sure I ride brakeless.

Without wanting to deraille my own thread (we haven't even got to the bit about the ticker tape timers yet) but are you sure that's wise?
I mean, I've had chains break on me a few times; I'd hate to have it happen coming down a hill on a brakeless fixie - or maybe you just don't go near hills?

Lumen

fergalr wrote: »

Without wanting to deraille my own thread (we haven't even got to the bit about the ticker tape timers yet) but are you sure that's wise?
I mean, I've had chains break on me a few times; I'd hate to have it happen coming down a hill on a brakeless fixie - or maybe you just don't go near hills?

You'll be needing this thread then.

fergalr

Lumen wrote: »

You'll be needing this thread then.

It's ending up in the same territory; although the other poster was originally really writing about an incident that happened them, not how brakes work in general, which is why I started this one.
I also didn't see anyone mentioning there the possibility of a chain breaking on a fixie. I'm not going to judge anyone for deciding their own acceptable levels of risk (although if you milled into someone crossing the road at the bottom of a hill, might feel different), just perhaps they haven't considered chain breakage as a possibility - I guess the chain on a fixie is stronger than on a typical 9/10speed drivertrain too.

steinone

Not getting into the debate either way, so dont bother asking.
I said I run brakeless, I didnt say on the streets, I didnt say on the track nor did I say I just ride my bike around my living room.
I know the risks, I know both sides of the debate I was just saying it to get the point across that it is fine to just run a front brake on a fixed gear OK?

B00MSTICK

A very large proportion of BMX riders run brakeless

steinone

Yes he does mean freewheeling bmxs.

crazydingo

Isn't that illegal?? :eek:


Just kidding, I am so sick of that debate now :pac:

fergalr

steinone wrote: »

Not getting into the debate either way, so dont bother asking.
I said I run brakeless, I didnt say on the streets, I didnt say on the track nor did I say I just ride my bike around my living room.

You also didn't say whether you were referring to bicycles or your single speed brakeless motorboat... In the context, I thought you meant on the street - I think that was a fair interpretation, actually; apologies if not.

steinone wrote: »

I know the risks, I know both sides of the debate I was just saying it to get the point across that it is fine to just run a front brake on a fixed gear OK?

Sure, do whatever you like. I only mentioned it in case people hadn't considered the possibility of the chain breaking.


It comes across as a little strange you taking the whole "I know the risks, you don't know me, don't lecture me" line after what you just said to another poster:

steinone wrote: »

You mean a fixed gear right? If your actually using just a front brake on a singlespeed please get a rear brake too!
For your own sake do!

But hey, each to their own.

Personally, my city bike is a single speed, non-fixed. I use two brakes - in case one fails, or in case the conditions are wet.
Even if I ran fixed, I'd still have at least one brake - if I had less than the legal minimum of brakes and this caused me to hit someone, I think it'd be pretty bad; each to their own, though.

rottenhat

fergalr wrote: »

I guess the chain on a fixie is stronger than on a typical 9/10speed drivertrain too.

I have heard it said that the quality of the average 1/8" width chain isn't all that and that they are if anything more likely to break than a standard road chain, even though they look pretty burly.

Thomas_S_Hunterson

rottenhat wrote: »

I have heard it said that the quality of the average 1/8" width chain isn't all that and that they are if anything more likely to break than a standard road chain, even though they look pretty burly.

I think the mantra of "getting what you pay for" holds.

abcdggs

rottenhat wrote: »

I have heard it said that the quality of the average 1/8" width chain isn't all that and that they are if anything more likely to break than a standard road chain, even though they look pretty burly.

not trying to be pedantic but would that have anything to do with your average track chain being used differently to your average 9/10 speed chain.

rottenhat

I was thinking that one over while I was posting and I'm not sure - are the forces exerted by skid-stopping on a fixie any greater than the forces exerted by pedalling forwards?

abcdggs

surely the rate at which they are exerted is much greater, then if they are used to speed up as well as slow down then they surely have to deal with twice as much force as a 10 spd chain

rottenhat

I would have thought that would make it wear more quickly (though the wider chain and cog combo counteracts that) rather than make it more likely to break, but I'm no engineer.

niceonetom

I have a super chunky KMC 1/8" BMX chain on my fixie that has to be much stronger than a 10 speed. The thickness of the the plates and the extra contact this creates between the plates and the pins has to give it more strength. 10 speed chains might be stronger per unit weight but surely not absolute strength. There are some very cheep singlespeed chains out there though - I'm sure they don't compare to a quality chain of any dimension.

I'm sure that skidding and skip stopping exert a much greater peak force on the chain, and shock loading is a real test of material strength.

as for wear? well, with a good chain line and reasonable maintenence a single speed chain can last a very long time. Chain stretch is only a real problem when the chain has to deal with different cogs, as with a cassette. As a single speed chain stretches it wears the cog and chainring to fit it and works really well. If you get a new cog or chain it suddenly becomes noisy again so my tactic is to just leave it alone (but keep it clean and lubed) and then change it all every few years - a very different tactic to the way I change chains on my roadie fairly regularly.

@stein - aren't you planning on doing the w200 fixed? Dear god tell me you plan to put a brake on before that. You may not want to have the debate, but that isn't exactly how internet discussion works...

rottenhat

niceonetom wrote: »

I'm sure that skidding and skip stopping exert a much greater peak force on the chain, and shock loading is a real test of material strength.

Yeah, I was thinking that the back wheel skidding acts as a limiting factor on the peak force but even so, you're probably right.

niceonetom

rottenhat wrote: »

Yeah, I was thinking that the back wheel skidding acts as a limiting factor on the peak force but even so, you're probably right.

It's the skip I think would really do it. If you're clipping along at 40kph and lift the back tyre and stop it through the chain, when tyre comes back to earth the moment imparted to the stationary wheel by the ground for the fraction of a seconds before the tyre starts to skid must be huge. All that energy has to be withstood (if only very briefly) by the chain. If I was Lumen I could do the maths... but I'm not. I'd say plain skidding where the rear wheel never really leaves the ground wouldn't be as severe.

Front callipers make me faster.

rottenhat

niceonetom wrote: »

Front callipers make me faster.

Moi aussi...I rode fixed with no brake for a year when I was working as a courier and it does teach you a lot about reading what other people are doing but by the end of it my knees were not feeling good.

fergalr

rottenhat wrote: »

Moi aussi...I rode fixed with no brake for a year when I was working as a courier and it does teach you a lot about reading what other people are doing but by the end of it my knees were not feeling good.

I've read plenty of people on interweb forums complaining about sore knees after riding fixed for a while.

Do you reckon that's because of the act of trying to brake with the drivetrain, or because of having to mash the (single) higher gear when going up hills, or both?
I'm riding singlespeed in the city for about a month now, and I find it's generally fine; sometimes my knees are tired, but not sore as such.