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Oh S*** moments.....

Old 08-20-08, 02:31 PM
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Sam Farrow
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Oh S*** moments.....

Alright guys,

Not sure if this is the right place to post this message, but one of the above mentioned moments got me thinking yesterday.

Picture the scene: it's absolutely shredding it with rain and you're on your road bike with lovely skinny tires on a pretty horrifically greasy road and a van/bus/whatever pulls out in front of you. What's the quickest way to stop? I crank my front brake as hard as I can and that wheel keeps on rolling - no issues with that - but what's quicker? A locked back wheel (from practically yanking the handle off the bars) or putting just enough brakes on so that the wheel doesn't lock?

Any ideas on the subject?

Sam
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Old 08-20-08, 02:48 PM
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You'll stop faster if you don't skid. This is because the coefficient of friction becomes less when you skid.

You need a front brake that is capable of stopping the front wheel and you want to almost, but not quite, make the front wheel skid.

In a panic stop the rear brake is pretty useless because of weight transfer. Weight transfers to the front, the rear wheel becomes unweighted and has little to no stopping power. If all you have is a rear brake, lots of luck. In the situation you describe, it will be very difficult to avoid skidding the rear wheel.

Last edited by JRA; 08-20-08 at 02:54 PM.
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Old 08-20-08, 03:01 PM
  #3  
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Originally Posted by Sam Farrow View Post
Picture the scene: it's absolutely shredding it with rain and you're on your road bike with lovely skinny tires on a pretty horrifically greasy road
...

Any ideas on the subject?
Don't primarily plan for what to in response to the worst happening. Expect it to and instead ride within the limits of the existing conditions/equipment so the worst event won't turn to the worst result.

Also applying the brakes gently on occasion helps keep the rim/pad interface friction better (but nothing can be done about tire/road which then becomes the limiter) and allows you to test what those limits are.

Al
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Old 08-20-08, 03:24 PM
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Locking the back wheel is not a problem when travelling in a straight line, it just drags. Locking the front is going to take you down. So, lock the rear and feather the front. I'd rather hit the side of the bus than go under it.
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Old 08-20-08, 03:28 PM
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Ounce of prevention >> pound of cure. And braking/releasing is better than skidding. That's why anti-lock brakes were invented.
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Old 08-20-08, 11:49 PM
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Originally Posted by Sam Farrow View Post

Picture the scene: it's absolutely shredding it with rain and you're on your road bike with lovely skinny tires on a pretty horrifically greasy road and a van/bus/whatever pulls out in front of you. What's the quickest way to stop? I crank my front brake as hard as I can and that wheel keeps on rolling - no issues with that - but what's quicker? A locked back wheel (from practically yanking the handle off the bars) or putting just enough brakes on so that the wheel doesn't lock?

Any ideas on the subject?

Sam
Sam,

I'm picturing the scene. I'm in London, right? Where it rains quite a bit and it has a lot of buses- pretty big buses and I'm riding my road bike with skinny tires?- out for a training ride? I'm not actually commuting on that bike am I? I mean my commuter is set up exactly for these conditions. Wider tires, upright flat bars, I ride a bit slower, especially in the rain.

Now my road bike- getting out of the city for a good training ride- I might be inclined to skip it were it shredding it with rain. But maybe I've just got to get some miles in- I'm hellbent on getting some miles.

Well, I'd probably be going pretty easy 'til I was out of the bad stuff- like oil slicked, busy roads but maybe I got a little feisty. In that case, brakes may or may not work my inclination is collision avoidance via an evasive maneuver, if possible, hop a curb, roll across grass, a hard turn. If all else fails and it looks like crash time I'd do my best to lay that bike down on it's side and slide...
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Old 08-21-08, 07:42 AM
  #7  
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Reminds me of a joke:

Jimbo and Bubba are in truck driving class.

The instructor asks Jimbo "You are driving a Semi down a 14 percent grade and your brakes go out. No runaway truck lanes to be found. At the bottom of the hill traffic is stopped due to a rock slide. What are you going to do?"

Jimbo replies: "I,m gonna wake up Bubba."

Instructor: "What good is that going to do?"

Jimbo: "He ain't nevah seen a wreck like the one we fixin to have!"

==============================

So that's my answer to the OP. I'm gonna wake up Bubba.
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Old 08-21-08, 07:59 AM
  #8  
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vehicle pulls out in front of you on a wet greasy road and you can't stop? if you can't avoid the vehicle, aim for the front tire and hood. windshields actually give when you hit them hard enough!

Slowing down in the wet would definetly be recommended, i laid a skinny tired road bike down in a corner of a slick, greasy road this winter while moving downhill at a high rate of speed and the results were not positive.

like buzzman says, a rain bike with wider tires is a solid choice; 700x32c tires have a much bigger traction patch.

(your front brakes should be powerful enough for you to lift the back wheel off the ground while braking, the OP's front brake is not adjusted correctly.)

some rain riders swear by disc brakes, some riders swear at them.

Last edited by Bekologist; 08-21-08 at 08:03 AM.
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Old 08-21-08, 08:54 AM
  #9  
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Originally Posted by JRA View Post
You'll stop faster if you don't skid. This is because the coefficient of friction becomes less when you skid.

You need a front brake that is capable of stopping the front wheel and you want to almost, but not quite, make the front wheel skid.

In a panic stop the rear brake is pretty useless because of weight transfer. Weight transfers to the front, the rear wheel becomes unweighted and has little to no stopping power. If all you have is a rear brake, lots of luck. In the situation you describe, it will be very difficult to avoid skidding the rear wheel.
How can the coefficient of friction change? i thought that was dependent on the two materials and that skidding was the direct result of surpassing the coefficient of friction.
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Old 08-21-08, 09:37 AM
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Feather the front and rear brakes, and stear towards a point which will cause you the least injury.

Though just pulling around the defective driver would probably be safer.
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Old 08-21-08, 09:52 AM
  #11  
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Their are two different coefficients of friction static and sliding, static friction is the energy required if you were to stand up and try to slide your foot along the ground without removing weight(beginning a skid), and sliding is the energy required if you were to slid your foot on the ground with your weight on it continuously(skidding). the coefficient of static friction is much greater than that of sliding friction, so in result skidding will not slow you as fast as a borderline skid. Q.E.D.
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Old 08-21-08, 10:17 AM
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Originally Posted by littlewaywelt View Post
How can the coefficient of friction change? i thought that was dependent on the two materials and that skidding was the direct result of surpassing the coefficient of friction.
Google "coefficient of sliding friction vs coefficient of static friction"
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Old 08-21-08, 02:28 PM
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Alright guys,

Thanks for all the input.

I wasn't really looking for advice as I've been riding around London traffic for longer than I care to remember, but it's all good stuff and it's been taken on board - especially the bit about aiming for the windscreen for a bit of cushioning "if you hit it hard enough"... That's desperation. On the occasion I mentioned in my post which happened ages ago now, nailing my front brake did the trick and it always does, I very rarely use my rear brake in traffic unless I'm really crapping myself (which has only happened a couple times in the years i've been riding) and it pretty much just locks up the rear wheel when I go into reflex mode. I've never locked my front brake and really don't intend to!

Are there many other Londoners on these boards?

Sam
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Old 08-21-08, 02:57 PM
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Many years ago, when I took the Bondurant driving school, they suggested steering around a potential collision was often better than trying to stop in front of it.
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Old 08-21-08, 03:11 PM
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Originally Posted by Sam Farrow View Post
What's the quickest way to stop?

Any ideas on the subject?

Sam

impact
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Old 08-21-08, 10:57 PM
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Um.. Turning the wheel so that you go around the bus, maybe?
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Old 08-22-08, 09:21 AM
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Originally Posted by natebike View Post
impact
lol That is what I thought. Hitting the vehicle is going to stop you plenty fast.

I am no expert but my thought is to do whatever I need to do to slow down as much as possible without going down. Assuming you can't turn to avoid it, in that scenario, you are possibly going to hit whoever pulled out in front of you in any case. But I don't want to get under their tires if I go down and start sliding.

Also, try to relax as you are flying through the air after the impact. That seems to help drunks.
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Old 08-22-08, 05:06 PM
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Originally Posted by littlewaywelt View Post
How can the coefficient of friction change? i thought that was dependent on the two materials and that skidding was the direct result of surpassing the coefficient of friction.
Take it from an AP Physics wiz. The coefficient of friction is greater when the tire is not sliding.

Have you ever pushed a heavy box along the floor? If not, take all the books you own and stack them into a box and then push to box across the floor. You will find that it takes more force to start the box than to keep the box sliding at a constant velocity. And believe it or not, the patch of rubber on the tire that is in contact with the road is at 0 mph/kph, whatever you go by. So, that patch of rubber is like the box that is still. It has a higher coefficient of friction than if the patch of rubber was sliding.
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Old 08-22-08, 05:16 PM
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I had one last night. I broke a spoke. I'm going along and hear this "ting-ting-ting" noise. Then I notice my front wheel is badly out of true. Huh? A quick examination, and I found the broken spoke.

It's ok. I've got 35 more.
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Old 08-24-08, 01:02 PM
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I had one the other day. I'm living in Detroit this summer, which is definitely an anti-cycling city. The drivers and pedestrians attitudes are negative. They try to run you off the road. I was going along the MUP on Belle Isle. The road is 2 lanes, one way, but the MUP is 2 way. A truck turns towards me and drives IN THE MUP straight at me. I was going to bail and jump in the grass but she turned about 25 feet from me.
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