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  1. #1
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    Braking 101 - a public service message from your Uncle Sixty.

    Here's the simple math... and you can look this stuff up too.

    When you ride any kind of bike that only has a rear brake (and can skid) you can pull off a .33 g stop.

    With a front brake you can pull off a .6 g stop.

    Actually...you can pull off .66 g's but this is the point where you usually get ejected from the bike.

    Nothing can stop you faster than a well applied front brake... unless you slam into something... like a car.

    Any questions ?

    So... I don't care if you ride with or without brakes as that brake-less fixed gear can stop as fast as my old coaster bike (and I ride that everywhere).

    I understand and accept the risks of riding a bike that has an antiquated braking system and ride accordingly... which is usually much slower than usual.

    So...

    Do not presume to think or tell people that you can stop faster without a front brake... because you can't.

    Don't tell people that the words "fixed gear" and "brakes" are mutually exclusive.

    Don't tell other people they shouldn't run a brake (for whatever reasons)... because that is irresponsible.

    I'm done.

  2. #2
    Senior Member miamijim's Avatar
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    If I can apply my front brake so hard that the rear wheel lifts off the ground but the front isnt skidding wouldnt that be 1g?

    Back in my more reckless days I'd get myself over the back wheel and slam on the front brake to point where I could hear the tire beginning to lose grip. You'd be amazed at how much steel top tubes fork blades flex.
    WWW.CYCLESPEUGEOT.COM 2005 Pinarello Dogma; 1991 Paramount PDG 70 Mtb; 1976? AD Vent Noir; 1989 LeMond Maillot Juane F&F; 1993? Basso GAP F&F; 1989 Terry Symmetry; 2003 Trek 4700 Mtb; 1983 Vitus 979

  3. #3
    Newb spitfighter's Avatar
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    Quote Originally Posted by miamijim View Post
    If I can apply my front brake so hard that the rear wheel lifts off the ground but the front isnt skidding wouldnt that be 1g?
    Nope.

  4. #4
    Senior Member the_don's Avatar
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    Get the g-force measurement software for the iphone(it was made for cars to measure the g-forces experienced for turning and braking). Stick it in your pocket and give it a go!

    Although I don't know how accurate it would be.

  5. #5
    Senior Member miamijim's Avatar
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    Quote Originally Posted by the_don View Post
    Get the g-force measurement software for the iphone(it was made for cars to measure the g-forces experienced for turning and braking). Stick it in your pocket and give it a go!

    Although I don't know how accurate it would be.
    Whats an iphone?
    WWW.CYCLESPEUGEOT.COM 2005 Pinarello Dogma; 1991 Paramount PDG 70 Mtb; 1976? AD Vent Noir; 1989 LeMond Maillot Juane F&F; 1993? Basso GAP F&F; 1989 Terry Symmetry; 2003 Trek 4700 Mtb; 1983 Vitus 979

  6. #6
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    Quote Originally Posted by miamijim View Post
    If I can apply my front brake so hard that the rear wheel lifts off the ground but the front isnt skidding wouldnt that be 1g?

    Back in my more reckless days I'd get myself over the back wheel and slam on the front brake to point where I could hear the tire beginning to lose grip. You'd be amazed at how much steel top tubes fork blades flex.
    Jim - When that back wheel starts to lose traction that is when you have maxxed out your stopping ability... but you still won't be pulling 1 g.

  7. #7
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    OP, i always thought u were a girl. maybe im thinking of someoone else in the norcal forum

  8. #8
    Senior Member prawza's Avatar
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    Gw 65'er
    Cycle instead

  9. #9
    Senior Member the_don's Avatar
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    the brake debate is on overdrive today! everyone is all riled up!

  10. #10
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    don - This is just a simple lesson in physics.

  11. #11
    Senior Member the_don's Avatar
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    Yeah I know. I personally ride with a front brake and a helmet, I guess I am kinda a proponent of that position too. Whilst i also think that brake-less also looks pretty smooth.

    I recently had a friend who started riding (race bike) that he should use the front brake more, especially in an emergency because that is where the braking power is, the rear is no where near as good. I ride DH MTB's too. It is quite obvious when you ride down a mountain where the power is to be found!

    Oh, and thanks for the lesson, how did you calculate the numbers though?
    Last edited by the_don; 10-04-08 at 10:35 PM.

  12. #12
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    Riding a bike period is a risk. I think riding with out a front brake is just a rebellious thing. Something to raise the stakes. I think it's more like riding a motor cycle 100MPH down the freeway with tennis shoes and shorts on.

    I think it's more for the thrill and "style" than anything else.

    There is definitely a generation gap in this new "fixie craze". It is noble of you to bring up the issue but I think the argument is going to continue.

    It's not much different than the stop sign argument. We all know what the facts are and we all know what the laws are. But I'm not going to stop at a sign at 5:30 in the morning when I can see a half mile in every direction and there is no one in sight.

    If someone is told that the front brake is most of your braking force and they still want to ride with out it than so be it.

    The next craze will probably be "stoppies" and everyone will want front brakes.

  13. #13
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    +1 on the OP's do's and don'ts!

    The maximum braking force can be adhesion limited (think of riding on mud or snow) or center-of-gravity limited (more typical on dry roads or steep downhills). I think the OP's numbers assume CG limited braking on a flat road for a "typical" road bike - the actual max g's depend on the exact location of the bicycle/rider center of gravity with respect to the contact point of the front wheel. Skipping the derivation: gmax = distance of CG behind contact patch divided by height of CG above contact patch. (Note that dropping your backside off the seat and getting low under heavy braking helps increase the numerator and decrease the denominator in this equation, thereby increasing your stopping power.)

  14. #14
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    sticky this biatch.

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    To start off, Im a clyde 240lbs(more like a walrus!!!). A few months ago I borrowed my roomates portable accelerometer and strapped it to my handlebars to see what kind of G's i could pull. my acceleration was just a laughing matter, but when stopping i was hittin over .6 G's no problem. then on the last run while trying to impress myself i pulled the rear tire off the ground and squeezed a little harder, the front locked up and I went down!! the last number i saw was .72, but when i checked the memory of the unit it said somethin like 1.4(from the bike hittin the ground). I'd like to see a person half my size try this, minus the wreck of course, to find out what they can do!!!

  16. #16
    Senior Member the_don's Avatar
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    Quote Originally Posted by Omnicycler View Post
    +1 on the OP's do's and don'ts!

    The maximum braking force can be adhesion limited (think of riding on mud or snow) or center-of-gravity limited (more typical on dry roads or steep downhills). I think the OP's numbers assume CG limited braking on a flat road for a "typical" road bike - the actual max g's depend on the exact location of the bicycle/rider center of gravity with respect to the contact point of the front wheel. Skipping the derivation: gmax = distance of CG behind contact patch divided by height of CG above contact patch. (Note that dropping your backside off the seat and getting low under heavy braking helps increase the numerator and decrease the denominator in this equation, thereby increasing your stopping power.)
    Yes, but you are limited by the coefficient of friction of your tire's contact surface area and the road surface you are in attempting to stop on. As soon as you exceed that, then your front wheel will skid and no more stoppy stoppy, and more like crashy crashy!

  17. #17
    Senior Member the_don's Avatar
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    Quote Originally Posted by evilmcbane View Post
    To start off, Im a clyde 240lbs(more like a walrus!!!). A few months ago I borrowed my roomates portable accelerometer and strapped it to my handlebars to see what kind of G's i could pull. my acceleration was just a laughing matter, but when stopping i was hittin over .6 G's no problem. then on the last run while trying to impress myself i pulled the rear tire off the ground and squeezed a little harder, the front locked up and I went down!! the last number i saw was .72, but when i checked the memory of the unit it said somethin like 1.4(from the bike hittin the ground). I'd like to see a person half my size try this, minus the wreck of course, to find out what they can do!!!
    Ah, wow, there is a perfect example of the coefficient of friction for the front tire being exceeded and the resulting consequences one can expect!

  18. #18
    Perineal Pressurized dobber's Avatar
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    Quote Originally Posted by miamijim View Post
    Whats an iphone?
    The cell phone of choice for brakeless fakengers.
    This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.

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    Senior Member NewYorkMantle's Avatar
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    (excluding the g-force estimates, which i do find interesting)

  20. #20
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    Quote Originally Posted by evilmcbane View Post
    To start off, Im a clyde 240lbs(more like a walrus!!!). A few months ago I borrowed my roomates portable accelerometer and strapped it to my handlebars to see what kind of G's i could pull. my acceleration was just a laughing matter, but when stopping i was hittin over .6 G's no problem. then on the last run while trying to impress myself i pulled the rear tire off the ground and squeezed a little harder, the front locked up and I went down!! the last number i saw was .72, but when i checked the memory of the unit it said somethin like 1.4(from the bike hittin the ground). I'd like to see a person half my size try this, minus the wreck of course, to find out what they can do!!!
    It's always good to see people who are willing to take one for the team and especially, in the name of increasing scientific knowledge.

    I hope you weren't seriously injured.

  21. #21
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    Honestly, I am so bored of this.

  22. #22
    uke
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    it's easy if you let it. uke's Avatar
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    Quote Originally Posted by NewYorkMantle View Post


    (excluding the g-force estimates, which i do find interesting)
    I lolled.

    JesseDuncan:I just love how "cars will be forced to cross the double yellow lines on dangerous limited visibility roads".

    I don't want to have a head on but oh god, I HAVE to fling myself into oncoming traffic to pass, theres no alternative!!!

  23. #23
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    I figure I'll just stick this up for a bit.

  24. #24
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    I picked up some new numbers from The Art of Cycling that state that a very skilled rider can pull off a .8 G stop without having the rear tyre lose contact (this is the point where the bike tends to flip).

    This is the kind of stopping power you get from 4 wheel disc brakes in a car.

    I found this because there was a debate on whether a bike can stop faster than a car and in some cases... they can.

    If they have brakes.

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