Physics of brake tricks

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10/19/2018 11:54 PM

I just got new involved in a conversation on a mid school group on Facebook about chainstay brakes vs seatstay brakes. Loads of people were saying how with seatstay brakes, the brake flexes away from the frame, therefore isn't as good. I bought up a point about how when you do any brake related trick, the bike will be trying to travel backwards, therefore seatstay brakes won't flex (think about a little alley oop into a tyre tap).
I can't think of a single brake trick where you'd be travelling forward. My logic being, if you travel forwards and pull your brake, the front will drop.
Thoughts?

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10/20/2018 1:57 AM

I mean, I guess the front always wants to drop when the brakes are on, but wouldn’t the wheel’s rotation mean that, no matter where the point of contact of the brake pad on the rim, the brake will still want to flex the same direction?

Like, I see how on seatstay-mounted setups the brake arms wanna flex downwards but on chainstay setups it’s not like the brakes don’t wanna flex downwards as well. But I totally agree that it seems logical to say chainstay brakes work well for the backwards-into-tricks stuff like the 270 tap.

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Scooter kid trying to ride BMX.
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10/20/2018 3:11 AM

readybmxer wrote:

I mean, I guess the front always wants to drop when the brakes are on, but wouldn’t the wheel’s rotation mean that, no matter where the point of contact of the brake pad on the rim, the brake will still want to flex the same direction?

Like, I see how on seatstay-mounted setups the brake arms wanna flex downwards but on chainstay setups it’s not like the brakes don’t wanna flex downwards as well. But I totally agree that it seems logical to say chainstay brakes work well for the backwards-into-tricks stuff like the 270 tap.

That's a very valid point. The brake will pivot vertically whether your bike is going forward or backwards, no matter where the brake is positioned.
The whole conversation started with some guy quite aggressively stating that brakes should be on the chainstays, and loads of other mid schoolers agreed saying seat stay brakes don't work as well, which I think is bollocks. If you imagine rolling backwards, seat stay brakes would do the same as chainstay brakes when moving forward. And for most brake tricks, you alley oop a smidgen into them, therefore the brake flexes toward the frame? That's my thinking anyway.
A few of them started going on about travelling forward to do brake tricks, but that would just make the front drop. They denied the alley oop thing entirely saying you don't alley oop a bit for stuff like tyre taps.

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10/20/2018 3:52 AM

grumpySteve wrote:

I just got new involved in a conversation on a mid school group on Facebook about chainstay brakes vs seatstay brakes. Loads of people were saying how with seatstay brakes, the brake flexes away from the frame, therefore isn't as good. I bought up a point about how when you do any brake related trick, the bike will be trying to travel backwards, therefore seatstay brakes won't flex (think about a little alley oop into a tyre tap).
I can't think of a single brake trick where you'd be travelling forward. My logic being, if you travel forwards and pull your brake, the front will drop.
Thoughts?

You are both right. The less flex the better but if you don’t have a tiny bit you will not stop as good as you can. But if you really think about it then you know that no matter where you’re brakes are. The post is going to flex some (unless welded on) so seat or chain stays is pretty much the same. Now at a point in the change to mostly seat stay brakes something happened. They got stiffer too, meaning again it’s about equal. The original idea was to move the arms away from the sprocket so you didn’t hit anything with a leg or shoe. Now I have seen some going back to chain stays because of the frame designs now.

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10/20/2018 4:40 AM

Seatstay mounts were because 25t sprockets became the norm, and the chain would rub the mount bolt. And removable posts sit a little higher. Even now frames with removable chainstay mounts will usually recommend using 28t or higher. With welded cs mounts you can just about get away with a 25t

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10/20/2018 6:27 AM

I think, basically, it is a strawman argument. From a physics standpoint the only thing really flexing is the brake arms which are flexing against the brake mount. With that being said; would not, the direction not matter? The only advantage of flex toward the frame would be if the brake arm flexes enough to actually touch the frame; then the frame would stop it (which I don't think I ever seen). Does that make sense?

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10/20/2018 6:31 AM

Lol shit's to complicated with physics and shit for me to chime in looool

I just like sest stay brake more becuase they're eay easier to work oncool

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I don't crash, I do random gravity checks...

10/20/2018 6:36 AM

HondaCRFRacer wrote:

Lol shit's to complicated with physics and shit for me to chime in looool

I just like sest stay brake more becuase they're eay easier to work oncool

That's why you need to listen in schoolwink

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10/20/2018 6:40 AM

HondaCRFRacer wrote:

Lol shit's to complicated with physics and shit for me to chime in looool

I just like sest stay brake more becuase they're eay easier to work oncool

Rabbe wrote:

That's why you need to listen in schoolwink

But I'm not in physics class yettongue

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I don't crash, I do random gravity checks...

10/20/2018 6:56 AM

People worry about the most meaningless stuff. The amount of deflection is minuscule compared to whatever eleastic motion the tires/tubes are going through.

I have taken a physics class.

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10/20/2018 7:08 AM

SupaShawn wrote:

I think, basically, it is a strawman argument. From a physics standpoint the only thing really flexing is the brake arms which are flexing against the brake mount. With that being said; would not, the direction not matter? The only advantage of flex toward the frame would be if the brake arm flexes enough to actually touch the frame; then the frame would stop it (which I don't think I ever seen). Does that make sense?

Yeah completely. My argument was more about cs mounts not actually being better enough to make a difference. They were all convinced I was wrong

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10/20/2018 7:09 AM

JPC wrote:

People worry about the most meaningless stuff. The amount of deflection is minuscule compared to whatever eleastic motion the tires/tubes are going through.

I have taken a physics class.

I literally just wanted to hear opinions, not have people back me up. And this opinion is spot on smile

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10/20/2018 7:18 AM

JPC wrote:

People worry about the most meaningless stuff. The amount of deflection is minuscule compared to whatever eleastic motion the tires/tubes are going through.

I have taken a physics class.

grumpySteve wrote:

I literally just wanted to hear opinions, not have people back me up. And this opinion is spot on smile

I wasn’t talking about you. Sorry if it came off that way.

It’s clear you know what’s up.

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10/20/2018 8:18 AM

You're on a midschool group, of course they're gonna cream their pants over CS setups. They make no sense for modern bikes since chain shit gets all over the arms and the physics differences between the two dont matter. A good brake setup matters much more.

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10/20/2018 11:01 AM
Edited Date/Time: 10/20/2018 11:03 AM

grumpySteve wrote:

I just got new involved in a conversation on a mid school group on Facebook about chainstay brakes vs seatstay brakes. Loads of people were saying how with seatstay brakes, the brake flexes away from the frame, therefore isn't as good. I bought up a point about how when you do any brake related trick, the bike will be trying to travel backwards, therefore seatstay brakes won't flex (think about a little alley oop into a tyre tap).
I can't think of a single brake trick where you'd be travelling forward. My logic being, if you travel forwards and pull your brake, the front will drop.
Thoughts?

The force applied to the brake is always trying to make the distance between the rim and stay bigger.

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10/20/2018 11:27 AM

was it the bmx museum facebook group haha

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Lessons not learned in blood are soon forgotten

10/20/2018 11:49 AM

Can we all just agree, brakes are for losers?

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10/20/2018 12:07 PM

Bulletpup wrote:

Can we all just agree, brakes are for losers?

Yeah dude brakes are gay

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I don't crash, I do random gravity checks...

10/20/2018 12:19 PM

RonnieRawdawg wrote:

was it the bmx museum facebook group haha

That group is full of right wing weirdos.

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10/20/2018 12:21 PM

What the hell is a 'brake mount' ???

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10/20/2018 12:27 PM

Real men do fufanus on coaster brakes.

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10/20/2018 12:30 PM

JPC wrote:

People worry about the most meaningless stuff. The amount of deflection is minuscule compared to whatever eleastic motion the tires/tubes are going through.

I have taken a physics class.

Exactly so it doesn’t matter what spot you have brakes. The brakes are all that is going to flex under load.

I have seen people say that they are sure that the brakes flex towards the ground on CS mounts. They do the SAME with SS mounts so they are doing the same thing

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10/20/2018 5:34 PM

CHILDISHGAMBINO wrote:

That group is full of right wing weirdos.

buncha old guys jerkin their dicks to corny mongooses and kuawaharas

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Lessons not learned in blood are soon forgotten

10/20/2018 5:44 PM

Super-Pawl wrote:

You're on a midschool group, of course they're gonna cream their pants over CS setups. They make no sense for modern bikes since chain shit gets all over the arms and the physics differences between the two dont matter. A good brake setup matters much more.

Mid school era was the best era of bmx period

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It’s all bmx

10/20/2018 5:44 PM

RonnieRawdawg wrote:

was it the bmx museum facebook group haha

CHILDISHGAMBINO wrote:

That group is full of right wing weirdos.

RonnieRawdawg wrote:

buncha old guys jerkin their dicks to corny mongooses and kuawaharas

Don't forget overpriced made in china nostalgia Haros.

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10/20/2018 5:51 PM

Francky wrote:

Real men do fufanus on coaster brakes.

On a kick turn ramp

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It’s all bmx

10/20/2018 7:39 PM

My point was, with most brake tricks, the wheel is actually trying to turn backwards. If you don't pull your brake, you'd end up rolling backwards.
Alex Leech posted a video just to call me out and prove me wrong. But that started a whole other debate about how to do proper fuf's (he called his trick a fuf, but it was a tyre tap). And proved my point that during a fuf, your wheel is trying to move backwards.

Not the first time I've argued with Alex Leech either XD

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10/20/2018 8:35 PM

JPC wrote:

Don't forget overpriced made in china nostalgia Haros.

saw a guy selling like a 2000 haro backtrail x2 i had one of those he wanted like 600 bucks like wutttt

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Lessons not learned in blood are soon forgotten

10/21/2018 1:38 PM

RonnieRawdawg wrote:

saw a guy selling like a 2000 haro backtrail x2 i had one of those he wanted like 600 bucks like wutttt

That homie is on crack

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10/21/2018 1:39 PM

Super-Pawl wrote:

You're on a midschool group, of course they're gonna cream their pants over CS setups. They make no sense for modern bikes since chain shit gets all over the arms and the physics differences between the two dont matter. A good brake setup matters much more.

adamnmexican wrote:

Mid school era was the best era of bmx period

Idk dude early NS like 2007-2010 was straight up magical

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