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Drafting Like A Boss
May 2, 2012 6:59 PM   Subscribe

How to do 55 mph on a bicycle
posted by klausman (80 comments total) 8 users marked this as a favorite

 
I didn't think drafting would allow you to keep up with a vehicle with so much more power than you ... At best, by cutting the wind, I thought it could help you go faster than if you were cutting the wind yourself. But being right up on the tail? How is that possible? Holding on?
posted by jayder at 7:02 PM on May 2, 2012


I have gotten up to 48 mph, riding down a long and rather steep hill. That's when I was 20.

I don't understand how I lived to age 30, considering how stupid I was back then.
posted by Chocolate Pickle at 7:09 PM on May 2, 2012 [4 favorites]


Was that MPH or KPH? That doesn't seem to be the original uploader.

Anyway, with the widespread adoption of dash cams in Russia, we get more and more road craziness recorded everyday.
posted by Burhanistan at 7:11 PM on May 2, 2012


It's totally possible and I've done it myself, almost all the resistance you get when cycling is from the wind hitting you.

Last summer I was going down this small hill near my house and a giant dump truck passed me just barely so I merged into its slipstream since it was barely going faster than me and then I realized I could just coast with so much wind blocking me (I was staring at the brake lights with my hands poised to slam on the brakes if they so much as tapped theirs). I followed this truck, barely pedaling at all for five minutes and covered a distance of three miles. Every time I glanced down at my bike computer I couldn't believe I was going 35-40mph with almost no effort.
posted by mathowie at 7:11 PM on May 2, 2012 [10 favorites]


I thought that drafting worked by a vortex effect, such that being in that drafting position actually caused you to receive a certain amount of wind energy pushing you forward. If I'm right, then it doesn't seem totally crazy that something as light as a cyclist might find it easy to keep up with a giant truck.
posted by fatbird at 7:12 PM on May 2, 2012 [1 favorite]


Chocolate Pickle, I've hit 48 on a hill during an MS150 in Texas and had to slow down to avoid overtaking cars. That's plenty fast on a bicycle, never felt the need to go faster, just the thought of my skin scraping across asphalt at 50mph is enough to slow me down. It's hell getting old, I used to never have those thoughts.
posted by Grumpy old geek at 7:12 PM on May 2, 2012 [2 favorites]


The rolling resistance of a road bike tire on pavement is extremely small, though given that the guy wasn't really pedaling much I suspect the road was also slightly downhill. The world record for this sort of thing is 167 mph, which required two chainring/cog combinations (in series) to get an appropriate gear ratio.
posted by 0xFCAF at 7:14 PM on May 2, 2012 [2 favorites]


that sh!t cray
posted by nikoniko at 7:20 PM on May 2, 2012 [2 favorites]


Just like in the movies.
posted by Winnemac at 7:21 PM on May 2, 2012 [1 favorite]


A friend of mine was riding a a pack ride in Melbourne a couple of years ago. A rider behind him clipped his back wheel, resulting in my friend losing his line, hitting someone else, and going over the handlebars. In skidding across the asphalt, his shorts and jersey were actually torn off him, the bike got trashed (frame snapped - stupid brittle carbon), and he lot a lot of skin off his right arm. Plus a bunch of severe bruising.

All that, at 35km/h.

The prospect of 55mp/h is utterly terrifying to me.
posted by His thoughts were red thoughts at 7:23 PM on May 2, 2012 [1 favorite]


I thought it could help you go faster than if you were cutting the wind yourself. But being right up on the tail? How is that possible? Holding on?

If you have no resistance to overcome, then even the slightest force accelerates you, so you can accelerate indefinitely to whatever speed you like.
Bikes have seriously seriously low resistance. The only things that limit your speed is either wind resistance, or the work involved in lifting mass up a hill. Remove those too factors and...

(This is also why it takes 200 horsepower to get a car to 100mph, and then another eight hundred horsepower to get past the next 100mph. Air resistance absolutely eats power.)
posted by -harlequin- at 7:26 PM on May 2, 2012


My reaction to this video is more or less, "look ma, no helmet!" Dumbass.

I've done almost 60 down a mountain... that was scary.
posted by killdevil at 7:27 PM on May 2, 2012


(This is also why it takes 200 horsepower to get a car to 100mph, and then another eight hundred horsepower to get past the next 100mph. Air resistance absolutely eats power.)

Err, I screwed up those figures. Go watch Top Gear for the correct values :)
posted by -harlequin- at 7:29 PM on May 2, 2012


I've done over 60 MPH downhill off road. Well, on single-lane fire road that went down the wall of a canyon at an angle, but straight as an arrow for about a mile.

I don't know how fast I actually ended up going because I was getting rattled to pieces by the washboarding of the road (on a no-suspension early mountain bike) and I literally couldn't read my bike computer anymore because my eyeballs were rattling and vibrating right out of my skull, but the last numbers I could read were 63 MPH.

Shortly after that my hands vibrated right off the handlebars and I fell off my seat, crushing my crotch on the crossbar and then sliding with my feet on the sandy loose ground of the fire road. I managed to get my hands back on the bars and start braking, and all I could really do was lock up the back wheel and slide-ski on my feet until I stopped. I probably slid for a few hundred yards.

I was so freaked out and high on adrenaline I just pulled over to the side of the road and fell over on the grassy canyon wall with my bike still between my legs just so I could hold still and enjoy breathing for a bit.

I've approached 50 downhill and on a paved road within the last year (Seattle has some major hills) but it's super sketchy. It's probably less scary to do 100 on a motorcycle.
posted by loquacious at 7:41 PM on May 2, 2012 [4 favorites]


I know people who drive at 80 mph is automobiles while drinking coffee and messing with the radio. They think they are safe in their SUVs. This guy knows he's moving and my bet is that he's paying a lot of attention to what's going on around him.

While i wouldn't draft like that (I like to see where I'm going, and prefer not to breath exhaust) I've been at 50 often (downhill). It's not that big a deal on a good road without technical corners. Pros hit 70 sometimes.
posted by cccorlew at 7:42 PM on May 2, 2012 [1 favorite]


Looks like he could have used an extra-large chainring. Overdrive.
posted by Flashman at 7:45 PM on May 2, 2012


Every time I glanced down at my bike computer I couldn't believe I was going 35-40mph with almost no effort.
posted by mathowie

Stop that!
posted by msali at 7:51 PM on May 2, 2012 [1 favorite]


Look up road rash if you want to lose a meal or two. This is never a good idea. Most road rash is from riding a motorcycle. I guess you get street cred if you get it from going over the handlebars of a bike.
posted by Splunge at 7:53 PM on May 2, 2012


Have we already linked to this: Šílenec na kole na dálnici D1? 100 kmh + police chase + awesome slavic keystone cops swearing? (I'm hoping for someone to do subtitles.)
posted by RandlePatrickMcMurphy at 7:54 PM on May 2, 2012 [1 favorite]


I've done 55 MPH (just) unassisted on the Kancamagus Pass in Vermont and at least 50 MPH on US 12 in Idaho (on a 12-speed Trek).

Between Helena and Missoula, US 12 joins up with I-90 and you have to ride on the berms of the freeway. Even from 20 feet away, each time one of those 90-ft-long triple-tandem 'road trains' passes you, you can temporarily gain 5 MPH or so as you're dragged along in its wake.

I followed this truck, barely pedaling at all for five minutes. . . I couldn't believe I was going 35-40mph with almost no effort.

Not as dramatic, but in the peleton coming out Portsmouth on TOSRV Sunday, I've routinely averaged over 25 MPH for the first 30 mile leg, barely breaking a sweat or breathing hard (until it's my turn at point, that is).

167 mph

Ja, Fred Rompelberg. Here's how he did it. Can you imagine what would happen if the draft vehicle pulled ahead or veered off at that speed?
 
posted by Herodios at 7:56 PM on May 2, 2012


Oh wait. Apparently a fake.
posted by RandlePatrickMcMurphy at 8:02 PM on May 2, 2012 [1 favorite]


Look up road rash if you want to lose a meal or two. This is never a good idea. Most road rash is from riding a motorcycle. I guess you get street cred if you get it from going over the handlebars of a bike.

Yeah, me and all the other bike racers I know have the same scars: hip, elbow, outside of the knee, ankle.

Also, at the risk of inflaming the cautious amongst us... I've been in similar situations. Not quite that close or at that speed, but still. For a bike racer - on a much more maneuverable (and fast-braking) vehicle, and for a person who's used to riding within sweating distance of a hundred other people - it's really not terribly difficult. Nor is it more dangerous than just riding along a street with cars driving on it.

And elsewise about speed, here's a video of some skinny guys going around 65mph (since they started bumpdrafting after the moto took a look at its speedo).

Going that speed on a bicycle is an absolutely transcendent experience.
posted by entropone at 8:07 PM on May 2, 2012


Doing this in a controlled environment (or at least in coordination with the driver) is called motor-pacing. John Howard got up to 152.2 miles per hour at Bonneville back in 1985 (warning: terrible music).
Which surely ought to bring an end to the 'well I've gone this fast' comments.






About 65 mph, if you must know.
posted by $0up at 8:09 PM on May 2, 2012


cccorlew: "This guy knows he's moving and my bet is that he's paying a lot of attention to what's going on around him."

That guy's not paying attention to what's around him because he can't see what's around him.

I draft off buses frequently. You'd be very surprised at how quickly a loaded bus can slow down. It would be impossible for this guy to slow down fast enough if that truck were to decelerate even modestly. At this speed, a tap on the brakes by the driver could easily mean death for the cyclist.
posted by klanawa at 8:12 PM on May 2, 2012 [5 favorites]


Look up road rash if you want to lose a meal or two. This is never a good idea. Most road rash is from riding a motorcycle. I guess you get street cred if you get it from going over the handlebars of a bike.

Yeah, I've had some major road rash injuries, but I was raised on a steady diet of various kinds of dermal abrasions from skateboarding and skimboarding and biking.

I actually still have a major but mostly invisible scar on my left arm that runs from wrist to elbow where I laid down my bicycle doing about 20-25 on flat ground. I had almost maxed out the gears on my 18 speed bike and made the mistake of hopping off a curb and trying to shift for that last gear while the chain was still slapping around.

Chain came off and (again) I wracked my crotch on the cross bar and slid on my feet for a ways, but fell over in the middle of the 5 lane suburban road that I was crossing.

I slid across the remaining two lanes and up a concrete driveway and bounced off a wall. My arm basically looked like a bag of raw ground beef, except, you know, pouring out blood everywhere.

The part that messed with my head wasn't the injury or the blood but the fact I literally left a stain and streak on the ground. It started out small and grew wider and wider like a great big crimson paintbrush stroke and was especially noticeable on the concrete of the driveway/sidewalk where I finally stopped moving. I almost threw up when I saw that.

In retrospect I probably should have had a skin graft on that abrasion because it was obviously (again, in retrospection) down into the subcutaneous layer. It took months and months to heal completely, and I was a really fast healer especially when it came to road rash and scabs and stuff.

Granted it probably didn't help that I went out to a really sweaty ska show like 3 days later after the crash as it just started to scab over. After a few hours moshing/dancing the huge scab actually glued to the inside sleeve of my jean jacket I was wearing, and I couldn't bend my arm because of it. I was at the Whisky A-gogo in Hollywood for some all ages ska show. When I went to the totally filthy bathroom and peeled off my jacket the whole scab came with it, and there was a much older crusty punk guy at the urinal next to the sink where I was standing.

He looked over and watched me peel the sleeve and huge scab with it and he immediately puked in the urinal.

So, yeah, I guess you're right about the street cred. I managed to totally gross out a crusty Hollywood punk.
posted by loquacious at 8:13 PM on May 2, 2012 [20 favorites]


I won't ride 55
posted by Flashman at 8:15 PM on May 2, 2012


Sometimes, if the wind is going just the right way, and you get into the pocket of air behind a screaming eighteen-wheeler, you don’t even have to poon it. The vacuum, like a mighty hoover, just sucks you in. You can stay there all day. But if you screw up, you suddenly find yourself alone and powerless in the left lane of a highway with a convoy of semis right behind you. Just as bad, if you give in to its power, it will suck you right into its mudflaps, you will become axle dressing, and no one will ever know. This is called the Magic Hoover Poon. It reminds Y.T. of the way her life has been since that fateful night of the Hiro Protagonist pizza adventure.
posted by the painkiller at 8:20 PM on May 2, 2012 [4 favorites]


MetaFilter: Magic Hoover Poon.
posted by loquacious at 8:26 PM on May 2, 2012 [4 favorites]


What's the rush? Was he late for the Darwin Awards ceremony?
posted by Blazecock Pileon at 8:30 PM on May 2, 2012 [12 favorites]


I remember when Alan Abbott was the record holder. I had a 1977 edition of the Guinness Book and I was astounded by the size of the sprocket in this picture of him and his record-setting bike.
posted by mr_crash_davis at 8:36 PM on May 2, 2012 [2 favorites]


You can ride quite a bit faster than that on a bike if you're willing to ride vertically.
posted by twoleftfeet at 8:36 PM on May 2, 2012


klanawa: "I draft off buses frequently. You'd be very surprised at how quickly a loaded bus can slow down. It would be impossible for this guy to slow down fast enough if that truck were to decelerate even modestly."

As long as you have the room to get onto your (front) brake before rear-ending the bus, you'll have no problem stopping faster than that bus. Or a semi, or a dump truck, or any other large vehicle. They take for freakin' ever to stop.

The problem is that first bit, having enough time to react.
posted by wierdo at 8:56 PM on May 2, 2012


I wonder how a tandem would fare with a draft like that. I've watched a pair of strong cyclists effortlessly reach 60mph on a mild downhill with no draft on a tandem.
posted by braksandwich at 9:03 PM on May 2, 2012


It's probably less scary to do 100 on a motorcycle.

I've gone over 40mph on a bicycle, probably around 45 or maybe a bit higher. And I've gone well past 100mph on a motorcycle many times. Going fast on a bicycle is far, far scarier. The brakes are crap, the tires are tiny, things routinely fall off or stop working (I couldn't begin to count how many times I've had a chain malfunction on a bicycle, for example, or the time my forks simply failed and folded in half while I was riding along), and usually all you are wearing is a tshirt and shorts.

On a motorcycle I have much better brakes and tires (plus lights and horn), and I'm wearing head to toe protective gear. Given an equal choice, and assuming that you aren't going to smack into a wall or a guardrail, I think I'd rather go for a slide at twice the speed in full leathers, rather than at 45mph in what is effectively my underwear.
posted by Forktine at 9:14 PM on May 2, 2012 [3 favorites]


> What's the rush? Was he late for the Darwin Awards ceremony?

I'm not going to argue that it's not risky, nor deny you your excellent one liner - but you could say the same thing about everyone who gets on a busy freeway at 80+ MPH in one of those flimsy foil cages that people call cars. Or who walk too fast near the pool. Or takes some stairs two at a time. Or you could say the same thing about Chuck Yeager or Gus Grissom.

Because, holy shit. That guy is going crazy fast on a bicycle without pedaling very much. That's pretty cool.
posted by loquacious at 9:25 PM on May 2, 2012


It's probably less scary to do 100 on a motorcycle.

100 mph on a motorcycle is plenty fun but not actually that scary - normal freeway speed is 75 mph, after all, so we're only talking 1/3 more. Assuming you're hitting 100 because you're out on some wide-open road, and not because you're playing the idiot squid in traffic, you still have plenty of maneuverability and braking power at your command if anything should come up.

I would guess that people who don't ride motorcycles would imagine 100 mph on a powered bike to be about as terrifying as the idea of 50 mph on a bicycle sounds to me.
posted by Mars Saxman at 9:27 PM on May 2, 2012 [1 favorite]


And elsewise about speed, here's a video of some skinny guys going around 65mph (since they started bumpdrafting after the moto took a look at its speedo).

Holy crap that's intense. I only missed catastrophe on that offroad at 60+ because I was on huge 2.25 inch fat tires on a dead straightaway. I would lose my freakin' mind trying to ride like that on those racing tires and bikes.


I would guess that people who don't ride motorcycles would imagine 100 mph on a powered bike to be about as terrifying as the idea of 50 mph on a bicycle sounds to me.

Grass is greener scenario, I suppose. I'm very comfortable on bicycles, and motorcycles scare the shit out of me, yet I paradoxically I don't seem to have a problem with going near motorcycle speeds on a contact patch the size of a quarter or two, sometimes on wet roads in traffic. That 50ish MPH downhill was down Pine in Seattle from the top to the bottom in downtown, but it was 4 AM, no one was out at all and I had greens the whole way, and I know the road pretty well. Still was much more, uh, stimulating than a roller coaster.

I think part of it is that I know I can slip through really small gaps if I have to and a bicycle will literally turn on a dime and jump curbs if you know what you're doing.
posted by loquacious at 9:41 PM on May 2, 2012


I've gotten up to 62mph on a bicycle, according to my cyclo-puter, on Massachusetts Avenue in DC headed back into downtown from upper NW. It was after 4am, foggy and drizzly, and the road was all mine and I decided to push it; not drafting, just riding all-out on the open road. Every second I knew I was taking my life in my hands (no helmet because I was a supreme idiot a decade ago), but it was a sublime experience and I'm sure I never want to do that again.
posted by peeedro at 9:42 PM on May 2, 2012


Forget watching the brake lights, what exactly is the game plan for pot holes, shedded truck tires and other road debris?

This is cute and thankfully on the highway he's only risking his own life, but people who overestimate their own reaction times and think they have superhuman control over their vehicle are bad news, such as the total a-hole in the deadly bicycle-on-pedestrian SF Castro district bicycling accident. (http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2012/04/24/MNDS1O8C59.DTL)

Bikes are super safe, but people in general take transportation safety for granted.
posted by Skwirl at 9:49 PM on May 2, 2012


For anybody still wondering, bicycles can't brake as hard as cars, not close. As a cyclist in city traffic it often feels like you can accelerate faster and brake harder, but that feeling comes from the fact that cars aren't trying most of the time.

I'll draft at 15-20 feet behind vehicles with windows a can look through to see what's going on ahead. Believe it or not you still get a big benefit even at those distances. No chance I'd ever try to draft a truck though, that's nuts.

foggy and drizzly,

Dude....
posted by Chuckles at 9:53 PM on May 2, 2012


Dude....

Yeah, bad judgement, but I lived to tell the tale.

But the most dangerous thing I ever did on a bicycle was to let my ego get goaded into a race through Rock Creek Park with a DC bicycle cop who happened to be my bosses' boyfriend. The deal was either we switch bikes, my road bike for his clunker Smith & Wesson police bike, or I carry 40lbs of gear to simulate the weight of his vest and cuffs and gun and radio.

So I rode my own bike, laden with 40lbs of bottled water in a backpack and destroyed this DC Police chump. But guess what, for a solid two years after this I was pulled over weekly while riding my bicycle in the city; just checking for registration or making sure my lights were in compliance with the law. I was never cited for anything but hassled on a regular basis.
posted by peeedro at 10:11 PM on May 2, 2012


You know what else is drafting in the low pressure zone behind that truck? A shitload of sand and dust and fumes and crap. Good luck with your lungs.
posted by weapons-grade pandemonium at 10:25 PM on May 2, 2012


bicycles can't brake as hard as cars, not close.

well, if both are using disc brakes capable of locking the wheels and both have rubber tires the stopping distance should be exactly the same. i remember a high school physics class where the stopping distance in a skid depends only on the static coefficient of friction of the material (both rubber in this case) not on the masses involved.

drafting cars safely should just come to reaction time and following distance. .1 to .2 second reaction time means 3-6 meters following distance at 60mph.
posted by dongolier at 10:26 PM on May 2, 2012


i remember a high school physics class where the stopping distance in a skid depends only on the static coefficient of friction of the material (both rubber in this case) not on the masses involved.

More contact patch=more friction. Way more rubber meeting the road for 4 or 6 truck tires than two bike tires.
posted by RikiTikiTavi at 10:34 PM on May 2, 2012


heres one derivation using kinetic energy: http://www.csgnetwork.com/stopdistcalc.html
posted by dongolier at 10:43 PM on May 2, 2012


there is a problem in that static coefficients of friction are lower than dynamic (hence anti-lock brakes superiority on dry surfaces) so if the driver brakes hard but doesnt quite skid, the cyclist does the same but brakes slightly harder and skids the cyclist will catch up with the car and collide from behind.
posted by dongolier at 10:48 PM on May 2, 2012


This is why the Flying Spaghetti Monster invented mountain-bikes.
posted by PareidoliaticBoy at 11:22 PM on May 2, 2012


My reaction to this video is more or less, "look ma, no helmet!" Dumbass.

You think a bicycle helmet will have any effect in a crash at these sorts of speeds? They're generally designed to specifications that say they should withstand a crash at up to 12mph. At 50 mph the energy of a crash is orders of magnitude greater. A bike helmet is irrelevant at such speeds.
posted by normy at 11:47 PM on May 2, 2012


RikiTikiTavi: "More contact patch=more friction. Way more rubber meeting the road for 4 or 6 truck tires than two bike tires."

You're forgetting the gigantic difference in mass. Dump trucks take for freakin' ever to stop, as do loaded semi trucks.

Also, threshold braking is something any competent driver or cyclist should be capable of doing. Even though cars have ABS, the car's tires (usually) still lock up intermittently due to the way the system is designed. Sadly, most drivers are incompetent.

Another factor I hadn't thought of, at least with regard to rim brakes, is that you can pop a tube if the rim gets too hot. I don't know how fast you'd have to be going to do that in a panic stop, though.
posted by wierdo at 2:58 AM on May 3, 2012


This is how we used to get the ancient VW bug up to 60 mph. You know you have to get really, really close to the ass of the truck for this to work. Better hope nobody pulls out in front of him......
posted by caddis at 3:07 AM on May 3, 2012


I don't know about the actual *paper* physics involved but in the real world where the rubber meets the road - I have never, ever been caught up short by any motorized vehicle when it comes to braking. A good bicycle can stop in *feet* from a high speed with good brakes and brake modulation, which is effectively the same thing as anti-lock brakes but powered by an entire human brain with direct sensory feedback to both road and wheel.

Seriously, the idea of even an unloaded truck or bus being able to stop in less distance than a bicycle going the same speed is pretty goddamn ludicrous.
posted by loquacious at 3:48 AM on May 3, 2012 [2 favorites]


I've done 55 MPH (just) unassisted on the Kancamagus Pass in Vermont...

No, you haven't. It's in NH.
posted by Kirth Gerson at 4:17 AM on May 3, 2012 [1 favorite]


The received wisdom from the moto training classes I've taken is that motos stop essentially instantly compared to four wheelers (assuming no drop/flip), so when in shit traffic it is wiser to ensure more space behind you rather than in front of you, giving the ignoramus behind you time to stop without turning you into a trophy. Mass makes a tremendous difference; a moto weighs 1/5 of what a car would, and a velo (with rider) is 1/10 of a car. Kinetic energy (which is what must be scrubbed off for braking) is linear with mass, but uses the square of velocity. So a velo braking from the same speed has 1/10 the energy of a car to soak into the brake pads.

Anyway, I think I hit 50 coming down a long, winding pass in Durango, CO a few years ago, and was catching up to cars. That was really dumb. But at least I have the memory of it now and am not tempted to do anything like it again. All it takes is one thing to break, and SPLAT.
posted by seanmpuckett at 4:42 AM on May 3, 2012


Why some people think they're doing a very smart thing, yet they're doing an incredibily stupid one?
posted by elpapacito at 4:49 AM on May 3, 2012


You only have a short time period to hit the breaks before you hit the truck. Here is a story problem to consider. Bicycle (B) and truck (T) are traveling at 100 kilometers per hour. B is 1 meter behind T. T weighs 5000kg and B weighs 100 kg. T brakes and decelerates to 0 kph in 100 meters in 10 seconds. Assuming no change in velocity by B, how long before B hits T. What is the force of the impact on B? If B decelerates at 4(T) what is the reaction time required by B to avoid any collision?

The answer is that the second train arrives at midnight...
posted by humanfont at 4:50 AM on May 3, 2012


there is a problem in that static coefficients of friction are lower than dynamic

Other way around.
posted by indubitable at 5:03 AM on May 3, 2012


I thought that drafting worked by a vortex effect, such that being in that drafting position actually caused you to receive a certain amount of wind energy pushing you forward.

If you wear a scarf while riding a motorcycle with a tall windshield, the scarf flies out in front of you.
posted by jon1270 at 5:06 AM on May 3, 2012 [1 favorite]


No way. No thanks. I chilled out last weekend when I hit over 40 kph on a downhill. I just have no wish to revisit what it's like to pick grit out of my skin. Did that plenty as a kid. I just wanna have fun and burn calories, so I can eat more fun things.
posted by Goofyy at 5:14 AM on May 3, 2012


Can the mod add some more tags to this post like "stupid" "darwin awards nominee" "kids don't do this ever" "deathfilter" "how to commit suicide and shut down down a highway"?
posted by JJ86 at 5:32 AM on May 3, 2012


That's a big truck with a long wake, I wonder why he's drafting so close.

I've done 80kph (50mph) drafting trucks like this, but at least 2 car spaces back (at least 10m). Anything closer is a deathwish, there's no way you can react fast enough to braking or avoiding uneven road surfaces.
posted by sukiyakidjango at 5:38 AM on May 3, 2012


Seriously, the idea of even an unloaded truck or bus being able to stop in less distance than a bicycle going the same speed is pretty goddamn ludicrous.

I agree, however the danger is limited reaction time; that rider has no idea what's ahead of him or pavement conditions (potholes, etc). This takes balls!
posted by sukiyakidjango at 5:42 AM on May 3, 2012


A bike helmet is irrelevant at such speeds.

Not entirely true, but I think more to the point is that if one is so inclined to entertain oneself by drafting about a foot behind a semi on a push bike at speeds that are effectively unpedalable, safety gear of any kind probably isn't really high on the agenda.
posted by the painkiller at 5:44 AM on May 3, 2012


Here is a story problem to consider. Bicycle (B) and truck (T) are traveling at 100 kilometers per hour. B is 1 meter behind T. T weighs 5000kg and B weighs 100 kg. T brakes and decelerates to 0 kph in 100 meters in 10 seconds. Assuming no change in velocity by B, how long before B hits T. What is the force of the impact on B? If B decelerates at 4(T) what is the reaction time required by B to avoid any collision?

The answer is that the second train arrives at midnight...

The train is a red herring. The key question is 'when does the ECNALUBMA arrive'?
 
posted by Herodios at 5:47 AM on May 3, 2012


On long motorcycle trips sometimes you get bored. Really, really bored, like singing nonsense songs in your helmet bored, or at night alarming the car behind you by making sparks by dragging the metal caps on the toes of your boots on the road bored. So I've played around with drafting semi trucks at highway speeds (70-80mph) quite a few times, just out of curiosity and boredom. The cool thing is how quiet it gets, because you are sitting in this pocket of still air. You can hear all the sounds of your valves tappeting away, tires humming, and so on, rather than the normal sounds of the air rushing past your helmet.

The other obvious thing is that there is no way in hell you have enough time to react to a bad situation, like the truck driver slamming on the brakes or road debris appearing from under the truck. Even with better brakes, there's just not enough reaction time with things so close. It takes time for your eyes to see something, send the message to your brain, process that, decide to brake, send the message to your fingers...

It also tends to make the truck drivers cranky, because they have no interest in having you spatter yourself on their back bumper. They'll radio each other about it and other truck drivers will try and signal you to back off.
posted by Forktine at 5:49 AM on May 3, 2012 [1 favorite]


That's a big truck with a long wake, I wonder why he's drafting so close

I drafted a hay truck once, at a similar kind of distance, and I can tell you the reason from first-hand experience: because if you get further off the truck's rear bumper than about one metre, you find yourself in turbulent air that throws you around a lot and does nowhere near as good a job of sucking you along the road as that tiny little pocket right behind the truck.

It's eerie back there. There is no wind rush noise at all, and all it takes to keep up is the occasional burst of frantic 180rpm pedaling like you see the cyclist doing in the linked video.

But CHRIST it's scary. I have never focused on anything as hard as I focused on keeping the distance between my front wheel and that rear bumper absolutely constant.

I followed that truck for about 5km. It was as effortless as riding down a good steep hill, and I would have gone for longer except that I got sneezy from breathing little bits of hay.
posted by flabdablet at 5:54 AM on May 3, 2012 [1 favorite]


From $0up's link about motor pacing:
This type of record was invented by Charles "Mile-a-Minute Murphy" who drafted a train to set a 60 MPH record at the turn of the century. A mile of plywood sheets was attached to the railroad ties, so Charles would have a smooth surface. He had to be lifted onto the train just before they ran out of the plywood surface!

Like the youtube comment says
see hes not really drafting the gravitational pull from his massive balls is pulling him towards the truck.
posted by Killick at 6:51 AM on May 3, 2012


Seriously, the idea of even an unloaded truck or bus being able to stop in less distance than a bicycle going the same speed is pretty goddamn ludicrous.

Any data on this? I have grown more skeptical about the claim that a bicycle can stop any better than a motorized vehicle at the speeds being discussed here, regardless of reaction times.
posted by 2N2222 at 8:12 AM on May 3, 2012


My top speed, downhill, was 39 MPH. Coincidentally, that's when I stopped glancing down at the bike computer and realized just how bad the winding road was that I was plummeting down. Pumped the brakes carefully and slowed up.

I was only about a third of the way down that hill. I shudder to think what would have taken me out first: a rock, a hole, or my front tire suddenly doing the shimmy.

Absent all of the above, how fast would I have gone by the bottom?*

* Rhetorically speaking. I might have gone to plaid.
posted by Celsius1414 at 8:18 AM on May 3, 2012


Bicycle (B) and truck (T) are traveling at 100 kilometers per hour. B is 1 meter behind T. T weighs 5000kg and B weighs 100 kg. T brakes and decelerates to 0 kph in 100 meters in 10 seconds. Assuming no change in velocity by B, how long before B hits T.

Assuming constant deceleration of the truck, 100km/h to zero in 10 seconds is an acceleration of -100km/h × 1000m/km ÷ 3600s/h ÷ 10s = -2.8m/s2. So if the bike stays at a constant speed, its acceleration wrt the truck will be the negative of that i.e. 2.8m/s2.

For constant acceleration, distance traveled* = acceleration × time2 ÷ 2. So for the bicycle to cover the 1m to the back of the truck would require √(1m × 2 ÷ 2.8m/s2) = √(0.72s2) = 0.85 seconds.

Interestingly, this result doesn't depend at all on the starting speeds of truck and bike, only on their initial separation distance and the braking deceleration of the truck. So let's stop making up stories and look at some actual numbers:

Here's a paper on truck braking tests. It's old, but it will do. The table on page 15 shows maximum deceleration for an unloaded light truck with some wheels locked as 28ft/s2 and that seems like a reasonable worst case.

Converting that to SI units: 28ft/s2 × 12in/ft × 25.4mm/in ÷ 1000mm/m = 8.5m/s2. Plugging that in where we used 2.7m/s2 before shows that a bike that maintains a constant speed starting 1m off the back of a truck under heavy braking would catch up with it in √(1m × 2 ÷ 8.5m/s2) = √(0.23s2) = 0.48 seconds.

That's not much margin, even allowing for total adrenalin overload and assuming that the cyclist could indeed switch near-instantly from intense concentration on a rear bumper with occasional furious pedaling to near-1G braking without coming to grief. So there you have it: drafting trucks feels all kinds of scary for good and sufficient reasons.

*The stopping distance for the original fictitious truck would be 2.8m/s2 × (10s)2 ÷ 2 = 139m, not 100m.
posted by flabdablet at 8:22 AM on May 3, 2012 [1 favorite]


This is cute and thankfully on the highway he's only risking his own life...

Seriously, the idea of even an unloaded truck or bus being able to stop in less distance than a bicycle going the same speed is pretty goddamn ludicrous.

If that truck even taps his brakes to slow down a few miles per hour, that biker is dead before he even has time to react. After he hit the truck and started cartwheeling or sliding down the highway, the following cars are going to try to not hit him by swerving into the next lane or perhaps the shoulder where they most likely will crash. If they are lucky there won't be other fatalities but there will be plenty of other damage and injuries.

First off this is a horrible idea to do and secondly is a bad post to glorify on MeFi. It is much better suited for 4chan.org
posted by JJ86 at 8:31 AM on May 3, 2012


my front tire suddenly doing the shimmy

That happened to me once. It was night, I was euphorically* going balls-out down a steep road in top gear, and all of a sudden the whole front end developed a life of its own and started wobbling like a really wobbly thing. I had never heard of the phenomenon before, so I just hung on like grim death and braked (fairly gently) and it didn't stop - it kept on wobbling until I'd pretty much halved my speed, and then it just steadied up as quick as it had started.

So glad I didn't come off at that speed.

*Why is cannabis not classed as a performance-enhancing substance?
posted by flabdablet at 8:34 AM on May 3, 2012 [1 favorite]


Hanging on like grim death, by the way, is the Wrong Thing.
posted by flabdablet at 9:09 AM on May 3, 2012


my front tire suddenly doing the shimmy

On a motorcycle we call that a "tank slapper" (at about 0:12 in).

It will make a grown man wish for dry diapers.
posted by 1f2frfbf at 9:41 AM on May 3, 2012


well, if both are using disc brakes capable of locking the wheels and both have rubber tires the stopping distance should be exactly the same.

The limiting factor for bicycle braking is tipping over the front wheel. This happens long before the front wheel locks up. Better brake mechanisms can get you to the tipping over point more easily, but (slippery conditions aside) contact patch has no bearing on the problem at all.

People talk about adjusting riding position to make tipping over less likely. I'm not sure I buy it exactly.. Certainly lowering your centre of gravity, and pushing your centre of gravity back toward the rear wheel will both have a positive effect on the amount of braking force you can apply. In my riding position, I don't feel like I have any options like that though. With a lower seat you can put your crotch behind the saddle, and your centre of gravity is lower to start, but for power and healthful biomechanics you really want the seat at the optimal height for going, not the optimal height for stopping.

Trucks don't stop nearly as well as cars, and bikes may in fact stop as well as trucks sometimes...
posted by Chuckles at 9:44 AM on May 3, 2012


*Why is cannabis not classed as a performance-enhancing substance?

It is. Although apparently the breadth of the classification is being reconsidered.
posted by Flashman at 12:27 PM on May 3, 2012


Dang Cutters!
posted by thanotopsis at 12:53 PM on May 3, 2012 [1 favorite]


wierdo: "As long as you have the room to get onto your (front) brake before rear-ending the bus, you'll have no problem stopping faster than that bus."

If the driver of a bus hits the brakes and decelerates at 3m/s/s (supposedly the max safe rate of deceleration for trucks) the bus would appear to a cyclist to lurch backwards by something like 3m in one second. Bikes can decelerate quickly, but if you factor in reaction time, it would be completely impossible for a cyclist following within a couple of meters compensate. Also factor in the fact the road bikes have virtually zero traction and applying the brakes full-force at speed is a good way to wash out and crash.
posted by klanawa at 5:11 PM on May 3, 2012


indubitable: Other way around

"kinetic" coefficient of friction, μk, is for a skid; "static" , μs, applies when youre braking but not yet skidding (i had them switched).

the problem still remains that a braking bicycle can skid into the back of a braking-but-not-yet-skidding truck even if they we're travelling at the same speed because kinetic (skidding) friction is lower than static friction. if you estimate μs for rubber-asphalt of .7 to .9 g and μk of .5 to .8 g, you can imagine as much as one third of one g difference in deceleration between the front guy and the bike---enough to close a following distance of 3m in about a second even if the cyclist immediately started the skid after seeing the brake lights.

you really need to see ahead of the guy youre drafting (like Chuckles upthread) or invent some anti-lock brakes for bikes...

or take the human element out all together and create a hydraulic surge brake on a big long post that applies your bicycle's hydraulic brakes with the lightest touch from the truck---the safest following distance would be zero!
posted by dongolier at 2:00 AM on May 4, 2012


Bicycles cannot brake at 1G accelerations. If a cyclist tries to brake that hard, they will go straight over the handlebars.

Taking figures for braking distances from http://www.rospa.com/roadsafety/adviceandinformation/driving/hgv-truck-braking-systems.aspx

A motorbike can brake at about 1.5g, a car which doesn't skid can manage about 1.1g. Loaded trucks can manage around 0.6g.

Taking figures from http://www.beckforensics.com/CMRSC14BeckBicycle.pdf the theoretical peak braking performance for a bike on tarmac is around 0.67g, but in real world tests, cyclists manage somewhere around 0.5g.

In other words, a cyclist cannot out brake a fully laden HGV.
posted by pharm at 3:30 AM on May 4, 2012 [1 favorite]


I'm sure whoever gets his kidneys will be happy.
posted by cacofonie at 8:11 AM on May 4, 2012


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