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Thread: Skid

  1. #1
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    Skid

    On our ride last Sunday we managed to skid the rear tire when braking. This has never happened to us before. I wasn't sure it was possible.

    I try really hard not to use the brakes. Why waste energy? However, we were trying to make a green light which turned yellow just as we approached and I had to get on the brakes pretty hard. The asphalt was clean & dry but the rear tire locked up very briefly and I could feel it just begin to swerve left. Nothing too dramatic, just surprising.

    I seem to recall Bill McCready describing how to skid both tires on a tandem. I've never tried this and I don't want to be in a position where it is necessary.

    Anyone else have experience with skidding tires on clean, dry pavement?

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    Senior Member Stray8's Avatar
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    Only once on a motorcycle when I hit the rear brake without using the front brake and the rear started fishtailing. I recovered but that effectively taught me not to use the back brake only...

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by oldacura View Post
    Anyone else have experience with skidding tires on clean, dry pavement?
    Yup... but only with the rear disc in one of two circumstances and noting as always that we're a fairly lightweight team @ 285 lbs using fairly narrow tires at very high psi:

    1. Using nearly full front braking power for a stop such as the one you described with a moderate amount of rear disc brake applied, the rear wheel will always lock and skid as the tandem's momentum moves a disproportionate amount of our weight to the front tire. If the stop is also on a slight down grade it will happen even more readily.

    2. Almost at will, I can skid the rear tire using only the rear disc at speeds under 10 mph using full lever force. However, the skid doesn't occur instantaneously: it takes a second or two for the rotor and brake pads to fully bed-in in combination with the aforementioned shift in weight as the initial braking action shifts the weight towards the front of the tnadem before the rear tire will skid.

    Note: I try NOT to do this as a rear tire skid flat-spots our skinny 23c & 25c tires which isn't a good thing.

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    pan y agua merlinextraligh's Avatar
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    You want the brakes to be capable of locking both wheels. In actually using them in a panic stop you want to modulate them so that they are just short of locking up, which gives you maximum braking, as well as retaining control.

    Locking the rear brake is no big deal. Locking the front brake is a bad idea, its much harder to recover from a skidding front wheel.
    You could fall off a cliff and die.
    You could get lost and die.
    You could hit a tree and die.
    OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.

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    Senior Member zonatandem's Avatar
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    Only while riding solo on tandem on a test ride.

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    sch
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    Check that tire tread real close, bet you scrubbed off 500-1000mi of tread wear with that skid.
    If the carcass shows, change the tire. If not, get in the habit of checking the tire every few
    hundred miles til the carcass does show up.

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    I did a quick check of the tire & couldn't find the spot. I'll check again more carefully.

    I think Merlin's advice agrees w/McCready - that you should be able to lock both wheels if needed.

    It's hard to imagine with that much weight transferrence that one could lock the front wheel. Also, I don't think I have the guts to try it and I'd likely have to replace the front tire afterwards.

    Anyone ever locked the front wheel on purpose or otherwise?

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    Senior Member Stray8's Avatar
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    Quote Originally Posted by oldacura View Post
    Anyone ever locked the front wheel on purpose or otherwise?
    I know that dependent on your speed and the road conditions, if you lock the front wheel one of two catastrophic things could possibly happen: 1. You fly over the handlebars ("high-side" exit) or 2. the front end tucks and you drop the bike onto one of your legs ("low-side" side exit). Don't ask me how I know this.


    .
    Last edited by Stray8; 06-18-09 at 02:32 PM.

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    I seem to recall that Bill McCready gives a lengthy description on how to deliberately skid the front wheel on a tandem (and not get hurt).

  10. #10
    hors category TandemGeek's Avatar
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    Quote Originally Posted by oldacura View Post
    I seem to recall that Bill McCready gives a lengthy description on how to deliberately skid the front wheel on a tandem (and not get hurt).
    From the Tandem@Hobbes Archives circa 1997 (that would be over 12 years ago), when V-brakes had just started to replace cantilevers, carbon forks for tandems were not yet available and disc brakes were few and far between and not all that great aside from light drag brake duty on a few Erickson tandems and the like:

    Quote Originally Posted by Tandem@Hobbes Archives
    Archive-URL: http://search.bikelist.org/getmsg.as....9704.0639.eml
    From: SANTANAINC(AT)aol.com
    Date: Wed, 16 Apr 1997 18:57:24 -0400 (EDT)
    Subject: How2: Emergency Stops

    How2: Emergency Stops

    A follow-up posting from Bill at Santana---

    Tandem emergency stops: three common limitations.

    Limitation one: The brakes themselves. You should be able to instantly lock
    either or both wheels of your speeding loaded tandem, even when your hands
    are cold and tired. If you can't readily skid both wheels, it's time to take
    a good hard look at your brakes, pads, levers, cables and housings, and even
    rims. We know from our testing that when a tandem is fitted with "tandem
    specific" brakes and levers it is possible for the average male (strong
    hands) with a same-weight stoker to lock both brakes using one hand (and
    dual-cable lever). John Schubert will remember this experiment.

    Limitation two: Your ability to continue to apply the brakes even while your
    brain is screaming NO, NO, NO. Every cyclist will have a tough time
    overcoming premature modulation. Your single bike experience has taught you
    to let up on your rear and then your front brake as certain rates of
    deceleration are perceived. Applying a tandem's front brake hard enough to
    attain a front skid will, at first, seem suicidal. Actually, the real danger
    is riding a tandem without knowing how to do this.

    Limitation three: In an emergency stop, your tandem's front brake provides
    80% of your stopping power---probably 3-5 times more power than can be
    applied by the front brake of a single. Assuming your tandem has adequate
    brakes and you have the skill to use them---limitation number three is
    control. Because I know Mark Bulgier, I can tell you he's a
    bigger-than-average guy. And any bigger-than-average guy who has ridden one
    will confirm Mark's report: a Vitus (single bike) with its stock fork can be
    really scary for fast stops. It shudders! A Vitus rider who weighs less than
    150# will deny the problem. A brake application severe enough to induce fork
    shudder will send a lightweight rider over the handlebars.

    Because most tandem riders (including tandem builders) have never tested the
    limits of their tandem's stopping ability, they can safely continue to insist
    that their brakes are "really powerful" and their fork is "plenty beefy."

    And my point here is NOT to make fun of tandem riders or their bikes. It IS
    to say that fast deceleration is a primary safety issue---just like wearing a
    helmet. Actually, now that I think about it, braking ability is arguably MORE
    important than wearing a helmet. Personally speaking, in thirty years of
    enthusiastic cycling I've only hit my head once (a solo mountain biking endo
    that shattered my Giro)---in the same span of years I've successfully used
    maximum braking to avoid a number of serious accidents (mostly cars turning
    across my path). And while not wearing a helmet may increase your odds of
    visiting the hospital, if you can't decelerate quickly enough to avoid an
    accident while riding a tandem you'll put yourself AND YOUR STOKER in the
    emergency room.

    So how do you learn effective tandem emergency braking? As others have
    already surmised (from learning to effectively stop a motorcycle or even a
    car with ABS braking), if you want to stop short of having an accident,
    you'll need adequate "tandem specific" practice.

    Materials: Your tandem, a pair of tires you want to replace anyhow, a good
    floor pump, tire irons, a big empty parking lot (one with a 2-3% incline is
    best), a stoker that is as heavy, energetic and fearless as you are [insert
    Tim Allen grunting sounds here], and two hours when your regular stoker would
    prefer to be elsewhere. Actually, your best training partner will be another
    tandem captain willing to share the cost of a new pair of tires. Why the
    floor pump and tire irons? Because of rim irregularities, most skids will
    occur along one section of the tire. During your practice session you'll need
    to occasionally mark and rotate the tire (on the same rim) to keep from
    wearing a hole through it.

    First lesson---mastering the rear wheel skid. Use the downslope to reach 25
    mph before using the rear brake only to lay down a long skid mark. Note that
    when the rear tire skids, the tandem's wheelbase (and lack of front braking)
    keeps the bike from sluing sideways.

    The rear wheel should skid readily---it doesn't count if the tandem is
    already halfway stopped before the rear brake develops enough grip to slide
    the tire.
    Further, because it's easier to skid the rear tire when you apply both brakes
    together, using the rear brake by itself is the only way to properly judge
    its effectivenees.

    Next is to learn to modulate your braking at the limit of rear tire adhesion.
    Keep practicing until you can leave three successive yard-long skid marks.

    Lesson two---mastering the front wheel skid. Psyche yourself up a bit: this
    next part is scary. Remember, a tandem with an adult stoker will skid instead
    of flip. In years of playing this game I've never seen a captain skid their
    front tire on a first attempt. Actually, this is just as well. At a degree of
    front brake application below the amount that will cause a skid, the front
    fork becomes very active. As you learn to apply the front brake harder,
    tandems with inadequate forks can buck like a bronco. How far can a fork
    flex? On cheap tandems (and tandems with suspension forks) this type of
    testing can produce skid marks on a tandem's down tube.

    Through successive laps, build your skill (and courage) to where you can
    either skid the front wheel OR to where you have explored the limitation
    imposed by your tandem's fork (the heavier the team, the greater the
    fork-imposed limitation). A good fork can easily withstand the front wheel
    skids of a 400 pound team. A tandem with an insufficient fork will shudder
    and buck enough to make a tandem uncontrollable.

    Assuming your brakes and forks are up to muster, you will get to where you
    can readily skid the front tire. Because you can't really steer a skidding
    tire, a sustained front tire skid should be avoided. As with the rear wheel,
    keep practicing until you can modulate your front brake well enough to
    produce three successive yard-long skid marks.

    Lesson three---using both brakes. Because you want to learn braking one wheel
    at a time, don't use both brakes together until you've mastered lessons one
    and two. By now, you may think you're a real hot-shot [more grunting noises].
    Ready for a test? From 30mph try producing four successive skid marks by
    alternating between your front and rear brakes. When you can modulate your
    tandem's brakes with this degree of skill, you truly deserve your stoker's
    confidence.

    Lesson four---if you haven't fully exhausted your time, energy or
    treadlife---have a contest to see who can stop shortest. Because this type of
    practice session expends essential carbohydrates, the loser can buy the beer.

    In an earlier rejoinder someone remarked because he wouldn't be so careless
    as to ride a tandem faster than he would ride his single, he really didn't
    need better brakes. I not only don't want to be this guy's stoker, he's
    wrong. (Even if he does ride his tandem at single-bike speeds, it won't
    prevent cars from turning in front of him). Because of its weight, wheelbase
    and (potential) braking ability, tandeming can be superbly safe and stable,
    especially at high speeds and/or in an emergency situation. If you've got
    good skills, adequate equipment and a clear road, why would any tandem
    enthusiast want to limit their downhill speed to that of a single bike? Jan
    and I have used the left lane on downhill freeways to pass plenty of cars
    traveling at the old 55mph speed limit---it's a blast.

    Bill McCready
    (out of town this week)

    P.S. I screwed up and "washed" the disk with your contest answers. Because I
    Steve's on vacation this week (and I still don't have a modem) I can't
    retrieve your entries again. So instead of making you wait until I return
    from the Tapei trade show, even if you weren't the first post the correct
    answer, if you did post "forks" phone Steve at 909/ 596-7570 to receive a
    free pair of tandem brake cables by mail.

    PPS: I enjoyed the dislodged stoker postings and can assure you this can be a
    real problem. Because accidents were avoided in both cases, my stokers were
    very understanding.
    Last edited by TandemGeek; 06-18-09 at 04:47 PM. Reason: Footnoting the date and age of this posting to put it in context, e.g., pre-Avid BB7, etc...

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    So - how many have tried skidding the front tire (not me)?

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    I don't care what he says, I ain't doin' that unless I have to.

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    Senior Member Stray8's Avatar
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    Quote Originally Posted by oldacura View Post
    So - how many have tried skidding the front tire (not me)?
    Not on a tandem. Just on a single.


    .

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    Quote Originally Posted by oldacura View Post
    So - how many have tried skidding the front tire (not me)?
    It's not that big of a deal if you're comfortable doing so. If you're going straight then the bike tends to go straight. Any kind of a corner and you're going down, which I have avoided. It's actually easier on the tandem because it responds much slower than a single, HOWEVER, the stoker does not appreciate these maneuvers. My tandems do not have enough power to lock the front wheel on dry pavement, but good motorcycle brakes have the power to either skid the wheel or lift the back end up,depending on speed and traction. In my younger days in northern Wisconsin a motorcycle was my only transportation. I have actually been stuck in deep snow several times.
    It's good to know your vehicles limits and to be comfortable up to those limits.

  15. #15
    PMK
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    Tandem road bike, never skidded either end but am confident with the 203mm disc it can be done. Can't say as I've ever skidded a front tire on the road. Possibly the front disc could accomplish it but stress on the fork would be pretty significant. Also anything less than vertical may not be good.

    On the tandem mountain bike, don't like to but have skidded the rear many times. Usually under hard braking just prior to the moment of letting the brakes free and accelerating. No big deal, even the few times the rear stepped out. Never skidded the front on this bike.

    On the single MTB, and off road motorcycles, when needed I will grab a handful of front brake while leaned into a turn. I do this to change lines without steering input, as in crossing behind another riders rear tire, especially if they aren't moving quick enough to be gone as I come through. As for skidding the front under normal braking in off road riding, I'm certain it happens, but I just don't notice it. Not something I really think about doing or worry about, except when racing on wet grass.

    PK
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    And most important, someone special that enjoys them with me (except the KTM's)

  16. #16
    pan y agua merlinextraligh's Avatar
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    Quote Originally Posted by jgg3 View Post
    I don't care what he says, I ain't doin' that unless I have to.
    I get McCready's point. You get maximum braking force by modulating the brakes, just short of the point the wheels skid. An obvious way to find that point is going just past it, locking both wheels, to learn how much force it takes to lock them, and then in actual use, apply just short of that force.

    However, I think you can get a pretty good idea of the threshold of the front wheel locking without setting out to purposely skid your front wheel.
    You could fall off a cliff and die.
    You could get lost and die.
    You could hit a tree and die.
    OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.

  17. #17
    Senior Member zonatandem's Avatar
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    Have locked up front/back wheels without ever touching either brake . . .
    Descent on steep hill at 30+ mph, chain inexplicably dropped/bounced from small cog to between dropout and freewheel. Instant stop.
    Yes, front wheel buckled, pilot did his paratrooper roll over the bars and stoker went down with the bike.
    No broken bones, lotsa road rash.
    Stuff happens . . .

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    Don't know if anyone uses a front disk but if they do and attempt to use the front brake at a rate near lockup, wouldn't this create a large "torque steer" trying to force the left fork blade ahead and make the bike want to turn right?

  19. #19
    hors category TandemGeek's Avatar
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    Quote Originally Posted by oldacura View Post
    wouldn't this create a large "torque steer" trying to force the left fork blade ahead and make the bike want to turn right?
    You might get a little torque steer, but not a lot and even then I'm not sure you could even perceive it... despite what some marketeers have written.

    Bear in mind, motorcycles nearly all of the early street bikes and just about every off-road bike have used a single front disc and the rotor off-set from the steering axis isn't all that great and neither is the torque steer effect. The off-set on a bicycle's front wheel is far less than that of a motorcycle's.

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    I have been able to get the front brake to essentailly "ABS" by applying enough force to quickly slow the bike but not enough to lock the wheel. I can feel the front brake lever pulsing in my hand. I have not been able to accomplish the same thing with the rear brake. I am thinking in part because I am 175-ish and my stoker is under 105.

    It is a weird feeling but I know it is better than locking the front brake. I have both front and rear disc.

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