MythBusters Episode 80: "Big Rig Myths"
Air Date: June 6, 2007
A tire on a big rig can explode with lethal force.
confirmed
The MythBusters first tested whether a big rig tire could actually explode. They managed to obtain several truck tires and subjected them to actual road conditions, to try to replicate certain circumstances that could cause a tire to explode. Although they could not make a tire fail catastrophically, they managed to cause it to disintegrate violently by running the tire flat at highway speed, though the flying debris failed to hit the dummy set up next to the tire. However, the MythBusters were able to measure the velocity the debris. Taking an actual piece of the exploded tire, the MythBusters launched it at its measured initial velocity into a pig spine-equipped ballistics gel dummy behind a car window. The piece of debris smashed through the window and literally decapitated the dummy, proving the myth was in fact possible.
Drafting behind a big rig will improve your car’s fuel efficiency.
confirmed
To test this myth, the build team procured a car, a big rig, and a device that could measure a car’s fuel efficiency. They then drove the car behind a moving big rig at various distances ranging from 100 to 2 feet and measured the amount of fuel the car consumed. The Build Team discovered that the closer the car was to the big rig, the less drag is produced, thus the more fuel saved. At just ten feet, the car managed to increase its fuel efficiency by 40%. Drafting at two feet was slightly lower than the ten foot distance, mainly because Grant had to keep working the car pedal to maintain distance from the truck. However, that did not dispute the fact that drafting actually can increase your car’s fuel efficiency. However, the Build Team has warned that drafting is incredibly dangerous because the truck driver may not able to see you and you may not be able to react in time if the truck were to make a sudden stop.
As seen in the TV series Knight Rider, a moving car can safely transition from a road into a moving big rig via ramp.
confirmed
To test this myth, the MythBusters first started with a small scale test using a toy car. Simulating the Knight Rider stunt, the MythBusters found that the toy car could enter the big rig safely without a sudden and dangerous acceleration that many people had feared. They then tested the stunt at full scale using a Chevy Camaro, the rebadged version of the Pontiac Trans Am used in Knight Rider. They tested at both 30 miles per hour and 55 miles per hour with no difficulty. The MythBusters explained that, even when hitting the car’s ramp, the car’s inertia keeps it going at the exact same speed relative to the ground — which lets it safely drive into the big rig, with no surprising accelerations. Jamie then reinforced the myth by safely exiting the moving semi truck in reverse. Also all of their experiments took place during a rain storm.
Cyclists can draft behind a big rig and achieve "crazy speeds".
plausible
the Build Team decided to test whether a cyclist would have an easier time riding if he were to draft a big rig. Tory was chosen as the cyclist and performed a control test by cycling up to 20 miles per hour unaided. To ensure accuracy, Grant kept track of Tory’s heart rate and Kari measured his speed via radar. By the end of the control run, Tory was exhausted by the effort. During the actual test, however, Tory literally coasted along behind the big rig and rarely had to pedal at all. Due to the obvious difference in performance and the fact that professional cyclists draft during competitions, the myth was plausible.
Newer: Episode 81: "Grenades and Guts"
Older: Episode 79: "Western Myths"
20 years ago when I was 15 I drafted an RV in Florida at least 10 miles averaging around 35-40mph. I actually passed a group of cyclists in a paceline like they were standing still.
You have to test this again with a cyclist and find this confirmed.
June 23, 2007 at 4:36 PMYears ago in the mid or late 80s i remember hearing of a bicycle drafting a streamliner and getting to some retarded speeds, heres a link to it
http://www.canosoarus.com/08LSRbicycle/LSR%20Bike01.htm
June 23, 2007 at 9:04 PMMore than plausible! Looks like you barely tried to test this. The principles of drafting and motor pacing have been known and used by cyclists for more than 100 years. Do a search for “mile a minute Murphy” http://www.bikereader.com/contributors/woodland/murphy.html
June 24, 2007 at 10:20 AMI went on a cross country bike ride with my friend Jim a few years ago.
June 24, 2007 at 11:04 PMOn our trip he learned that a loose jacket wuld slow him down.
He and I were busting our asses to do 100 miles a day.
Jim was faster and caught the draft of some peice of farm equipment which moved so much air it draged him along, he had to use his brakes to keep from hitting it.
The farmer was really surprised to see Jim in his mirrors.
They traveled for miles.
The farmer gave Jim a signal when he was going to turn.
He said the ride was amazing!
When I was in my 20’s (and, like every other 20-year-old, still immortal) several of us cyclists used to do this every chance we got. I don’t know how many times we had to put a hand on the back of the trailer during extreme braking, but it was quite exciting to say the least. The fastest I personally ever got up to was barely over 50mph, because of the gearing. John Howard set a speed record of 152mph in 1985 on a specially-modified bicycle while drafting behind a Bonneville salt flats car.
June 25, 2007 at 11:05 AMdidnt torey test that…drafting on a bike
June 25, 2007 at 1:55 PMI have a releated question: When a bike drafts off another bike, does it require extra effort on the part of the “puller”, or is the drafter simply capitalizing on an existing vortex?
June 26, 2007 at 8:12 AMRegarding bike’s drafting behind each other:
Extra effort is applied to the puller.
Typically (although perhaps not in competition) the puller will pull for a while then drop to the back of a pack so the person who was second now becomes the puller and the original puller gets a break.
Competitive teams will often allow their stronger rider to draft behind the group to save his energy for perhaps a straight-away, climb, or final big push.
June 26, 2007 at 11:00 AMNo, no, no. In cycling (and in most race car drafting) the “puller” benefits from having someone drafting behind him. Obviously, not to the extent of the following cycle, but there is a benefit.
June 26, 2007 at 7:29 PMIn auto racing, there are some other factors at play, most of all, downforce. A drafting car might benefit the lead car by reducing his drag, but he also might reduce his downforce, making his car less controllable. The benefit to a lead cyclist is small compared to the comparative advantage gained by the drafting cyclist. So, unless you are going to take turns leading, the lead cyclist might not make it easy to draft. In my younger years, I used to go a UPS site to draft their tractor trailers. Their trailers wre unique in that they were very closet to the ground and and the air was very clean behind them. I reached what I thought were amazing speeds.
So, while a lead car might be getting a slight benefit from someone drafting behind, in practice it is often not a benefit because he is not getting a comparative or reciprical advantage. The lead car might be able to go slightly faster and burn slightly less full with a car in tow, but the drafting car is reaping big benefits - easy speed - speed without fuel consumption.
June 26, 2007 at 7:32 PMA few years back before i had to do major repair to my mountain bike i was out one night and decided to hit one of the longest steepest hills in town and the speedometer i had on the bike maxed out at 56 MPH and ill tell you what doing over 50 on a bike is scary as hell the whole time i was thinking (God i hope i dont hit something or have a tire fall off) i knew that if i did fall off i would have prolly tasted about 100 feet or concrete
but this was under the power of the hill and me no drafting invalved the wind may have been going my way that night cant really remember just know i was haulin hoping i got pulled over for speeding… would have framed that ticket
June 28, 2007 at 6:02 AMTodd, When you draft behind a UPS or moving van, both with low profiles, the air is very calm and you don’t get the same sense of speed that you would have screaming down a hill. Of course, the consequences of a crash would be the same.
June 28, 2007 at 2:38 PMShouldn’t “the inertia of the car is the exact same..” be “the momentum of the car”, since inertia is the resistance to motion?
June 28, 2007 at 4:06 PMCurrent record appears to be 167 MPH
http://www.fredrompelberg.com/en/html/algemeen/fredrompelberg/record.asp
June 28, 2007 at 6:53 PMGordon McCall is hoping to push the record to 180 mph in Oct. 2007.
http://www.teammccallusa.com/vision.html
June 28, 2007 at 6:58 PMSide-drafting the big rigs works pretty good too.
June 28, 2007 at 10:14 PMOK, I very seldom post to anything, but having been a service manager at a truck stop in the late 70’s, I think I may have something to contribute.
June 28, 2007 at 10:34 PMTruck tires (and especially the rims) are massive. The key thing you need to know is that for the for dual-wheel 16 inch rims on one-ton trucks up to the 20 inch rims that grace most 18 wheelers, the outside ridge of the rim is detachable. So, they are called split rims.
I repaired and/or changed several hundred split rim wheels at Rinehart’s Truck Stop, at the South end of Petaluma, CA. The first truck stop Northbound on 101 after the Golden Gate.
They always go in a cage made of 2 inch steel pipe to be inflated after repair or replacement. Always. I have, thankfully, never seen a hoop of steel (weighing perhaps 7 pounds) come flying off a rim.
On the other hand, there are bold mechanics, and there are old mechanics, but there are few old, bold mechanics.
Mythbusters is fine as far as it goes, but sometimes it may not go far enough into the story to make sure they have the details…
Jeff, I’m not exactly sure what you are saying. Don’t go down the inertia road - inertia is a slang word in physics - used when nobody wants to be precise or do any math. In this case, narrow the focus to drag. One thing that is tough to imagine is that the space behind a moving car is a factor in a car’s drag.
June 28, 2007 at 10:35 PMI used to draft big rigs in my little Ford Ranger and you could tell when you got in the zone as you could let off the gas pedal and still do the same speed. My question is how does this affect the mileage of the big rig?
June 30, 2007 at 12:01 AMGreg, in most cases, a drafting vehicle will provide a very small, trivial reduction in drag for the lead vehicle. You start to see observable effects when you crank up the speed and decrease the following distance - think NASCAR. But even in NASCAR, the lead car is giving more than he is receiving and on the big tracks, a drafting car reduces the lead car’s drag only enough to reduce or disturb his downforce, causing him to be “loose” or less controllable.
June 30, 2007 at 6:17 AMI got a new Schwinn bicycle in about 1960. As part of the modest factory advertising brochure, they posted a drawing of a fellow riding behind a shield fastened to the back of a train….a wooden board pathway had been build between the rails for this stunt…..and he was able to make 60 mph–of course, the drawing had a front sprocket as big as the pedal travel circumference
July 10, 2007 at 10:56 AMIn the mid 60’s I had a 63 VW that I would drive back and forth from college to home. It would take approximately a 1/2 of tank of gas each way. Being the typical college student I didnt have a lot of extra money to spend on gas. I traveled on the interstate most of the way and met some truckers at a truckstop when I would stop for coffee.. One suggested that I follow close to his rear. It was late and very little traffic so I said yes. He knew I was there so he would give me ample warning if he had to slow down. I was shocked that when I got to my destination that I had used less than a 1/8 of tank of gas. Drafting is dangerous! but it does work.
July 11, 2007 at 10:50 AMI always wondered about the Knight Rider scenario. But I would have hoped that having confirmed the myth, you would have tried with a front drive car to see if that made a difference.
July 11, 2007 at 2:09 PMOh yeah. I’ve found truckers generally HATE drafters. Once they know you’re there and what you’re up to, they’ll typically slow to a crawl until you finally give up and pass them.
July 11, 2007 at 2:14 PMThe tire exploding myth is based not on the tire exploding and shredding but on the split-ring wheel coming apart and failing catastrophically. The rims would throw the spilt-ring outward at very high speed and several people have been killed, although usually during the inflation of a newly mounted tire (which is why this procedure is done with the wheel assembly inside a cage). Still, the idea of being next to a truck at speed when the 120psi tire throws one of these rings is not something I’d want to experience.
I suggest a new test to see if the crew can get a split-ring to fail and kill the motorcyclist.
July 11, 2007 at 11:03 PMThe big rig tire myth is not based on split rims. Three-piece rims have not been widely used in over 15 years. I started driving trucks in 1993 and we had one-piece rims, simply because the three-piece rims are so dangerous.
The tire blowout killing someone is based on re-treads and not new tires. If a driver does not make sure he has the right tire pressure on a recapped tire, over time the tread will indeed separate from the tire. Surely you have seen the pieces of tire on the side of the road? I have personally had a recap completely remove the mudflap and bracket from the truck, severely dent the fuel tank, and depart the truck at 65 mph. If that piece of tire comes through your windshield, it will hurt you and likely kill you.
I was surprised that the Mythbusters did not actually consult any truck drivers when they did this myth.
July 12, 2007 at 9:40 PMin one show you tried blow a car over with a jet engine and failed. On a u.k programe topgear they tried and blew it over.
July 15, 2007 at 12:31 PMIs it true that when traveling at night with ones highbeams on attracts more bugs?
July 24, 2007 at 3:14 PMDamrod:
You should visit college…”inertia” is not slang…I think you should have knowledge of the words before you present yourself as an expert so many times.
Down draft is control related and does not address the issue of proving that a car “pulls” more if there is a drafter…
August 9, 2007 at 12:00 AMMy mate has had a truck tyre explode while he was passing. He wasn’t hurt, but it made a heck of a loud bang and scared the crap out of him. This could cause an accident. So if the flying debris fron an exploding truck tyre don’t get you the fright might.
And I agree with Physics, the word inertia is not slang.
August 14, 2007 at 8:57 AMBeing a trucker I can say Totally True. But a bicycle couldnt get enough speed to even start to keep up with me! :-) On a blown tire I have actually seen steel from the blown tire stuck in the tire next to it. We dont want people scared of us just respectful.
August 30, 2007 at 8:10 PMOne other thing, inertia is not resistence to movement, it the tendency of an object to remain at rest, or in motion. According to Newtons laws inertia is constant unless acted upon by another force.
August 31, 2007 at 11:58 PMAnd I thought the reason lead cyclists, and even lead birds in v formation, moved to the back because the lead position was the most strenuous to maintain.
August 31, 2007 at 11:59 PMDrafting a big rig does work.13-14yrs ago when I was single and owned a Suzuki Sierra soft top 4WD ,I used to travel out west of Sydney , Australia hunting and would often pull in behind the big rigs and ask over the CB radio if they minded if I just sat there for a while instead of having to overtake them all night.Sitting 40-50ft behind them at 100km/h I was able to take my foot off the accelerator and be dragged along at the same speed until the truck rounded a corner and when you’d have to check and adjust your speed ,but on the long straight highways a 20-40ton big rig could pull you along saving fuel.
September 15, 2007 at 12:03 AMAbout 2 years ago a rig was passing me on the highway when his tire exploded. He was right next to me and I had my window down. It sounded like a gun shot! Bits of tread flew backward, up and out ahead of the rig raining down in the road, but no tread came directly at me.
October 1, 2007 at 3:52 PMthe way to reduce your risk in doing this is to keep your left foot over the brake pedal. i know momma said never to do this, but the fact is you reduce your reaction time, and that is the issue. any decent car will be able to stop faster then a truck, its the reaction time that will get you
October 28, 2007 at 3:52 PMon debris from a tire going through the window of a vehicle… when have you ever seen a tire fly from under a tire and go through a side window ? i believe the front windsheild and hood would deflect the force enough to just cause damage to the windsheild if this were to occour in a real life situation on a highway if the piece would get high enough from the road surface to get over the bumper.
November 1, 2007 at 9:31 PMHmm, I don’t believe the confirmed myth for the exploding tires. Last time I’ve crossed canada I was actually hit with a blown tire. They didn’t take the fact that the tire is actually turning and when the tire explode it doesn’t go in a straight line. I Think its not dangerous at all. it didn’t stratch my car for f@kes sakes. The wind is another fact not in there equation. There research was pointless!! Sorry guys from muythbuster.
December 9, 2007 at 11:11 PMI ride a lot in and drafted more than my fare share of cars trucks (it scares the hell out of people). It didn’t increase my speed at all it just helped my keep my pace a lot longer normally i can keep a pace of about 30 - 40 MPH on my own
December 18, 2007 at 2:32 PMlove the results on blownout tires…they can truly mess you up if hit i’ve blown tires on my tractor trailer and the first thought is oh my god sure hope no one gets hit with the flying tread…also remember folks,the idea of drafting a big truck at 10 ft worked great for the experiment,but if the steer tire[front tire]goes or any other reason for the truck to stop quick,fuel mileage will be the least of your concerns.be safe out there.
December 21, 2007 at 11:26 AMmy friend found a damaged tire on his car and replaced it with the spare tire
December 22, 2007 at 4:42 PMhe put the damaged tire in the trunk of his car and went to work
when he returned home, he found the tire exploded in the trunk of his car
it busted the latch and blew out his tail lights and speakers
My friend worked at a gas station late night in the 80’s. Once this Jamacian guy was using the air hose to pump up his car tire and it blew up. He bleed from the ears, nose and eyes and died as a result of the explosion. I guess it was a just a bit overinflated. Ya Think?
December 29, 2007 at 2:12 AMI use to work for a tire shop, we dealt with Commercial vehicles only, we had a cage in which we had to inflate the tires in case of a “zipper break” in my first week, we had 2 tires zipper break, one was from a big rig, and it just went BOOM. The second was from a Very LARGE fork lift, and it bent the cage and threw it across the room. The cage alone weighed a couple hundred pounds.
December 30, 2007 at 1:27 AMregarding tyres on big rigs, i was in a tyre place having several replaced on my semi , and they had a safety leaflet there showing that a tyre had exploded outside a cage , killed the fitter and went out throught the roof,the pics dont lie ,i expect its the backyarders and amateurs who still do this type of thing, peter
January 7, 2008 at 7:39 AMMythBusters episode #79 “Big Rig Myths”
Hey, that myth that when a tyre on a big rig blows it is lethal I think is true and that the MythBusters got a good result.
January 12, 2008 at 7:47 AMBUT their methods of going about it I think are ridiculous.
First of all why try to explode a tyre from the side when most tyre failures are from flexing (as mentioned) and wear. In my experience and relative to newtons laws, the tyre would wear so thin as to break but instead of flying sideways as the MythBusters implied. It would continue around the wheel rim until it was flung out from underneath the wheel.
And that was only what was wrong with the first experiment.
With the workshop experiment they faced the truth that the tyre flies out from underneath the tyre in a backwards direction but when testing it with the head, how on earth would a persons head be in line with the exploding tyre and why would they be side on. Wouldn’t the obvious situation be that they were following the big rig!
With regard to the drafting myth, They should have tested to see what happens to the fuel economy of the vehicle being drafted. It has been my experience from following trucks this way that the drivers record the fact that though can’t see a car in the blind spot behind them that they can feel their presence because their rigs feel like they have taken on some extra load. I’m guessing that your presence in their wake zone disrupts the airflow over their vehicles and reducing their vehicles effeciency.
January 18, 2008 at 9:16 PMI really liked the drafting behind a truck myth. I remember some years ago I tried this, driving very close to the back of a large semitrailer truck. I was driving an old VW bettle. By drafting, I did get better fuel economy, but also was able to go faster than normal. We were in a 110kmh zone but I couldn’t get the VW to go that fast, until I drafted behind the truck. I was so close that I wished I could press a button on the dashboard and a couple of arms would come out of the curved front of the VW and latch onto the bar at the back of the truck, turn off the engine and coast along (in neutral of course).
January 19, 2008 at 5:16 AMIt would have been good to see a test of trucks drafting other trucks. Groups of trucks are often seen travelling on highways drafting each other. Perhaps on a round 2 of group of these tests in future…
I don’t think that the mileage of the big rig that is being drafted is affedted very much because of it’s weight. I pull a 30 foot fifth-wheel trailer with a pickup and I can tell when someone is getting to close to the back of the trailer. I have to push down with the right foot a little. When this happens I just slow down and make them pass me. Years ago I had a motorhome and I installed a wind shield to diredt the air coming off the roof to go down the back of the motorhome to keep the rear window clear during rain. The mileage increased a little. I think that the drafting would be less if something was used to break the suction behind the big rigs. Maybe they will try this when the revisit the drafting again later on.
January 28, 2008 at 4:22 PMThe tire tread chucking dyno speeds were incorrect. The truck they used to spin the truck tire and then the trailer tire in the shop has an open rear. I know this because in one scene the left tire was spinning and the right tire was stopped. That means the left tire was spinning 2 times as fast as the speedometer was reading. That is what an open rear does. It allows the tires to spin at different speeds. If you stop one tire, the other will spin twice as fast. The test they did at 40 miles per hour was actually 80 miles per hour. If you shoot anything heavy at 80 mph it will cause serious damage to whatever it hits. That being said i don’t want to get hit at 40 mph either.
Jim
February 3, 2008 at 10:18 AMI use all these in my drivers education class.
Thank you
August 10, 2008 at 5:43 PMregarding the tire. I’m a truck driver and they totalled screwed up this myth. they were using a “virgin” tire, its never been recaped. they should of used a recap because those are the tires that blow up and have chunks of tire fly at you. because no matter what you do to a regular tire, you went get it to explode like a recap. and another part of the myth about exploding sideways. it doesnt blow you sideways, you gotta remember the tire is turning really fast, when it blows up it will come out the back or underneith. they need to retest this myth. all the other myths theyve tested they asked professionals or doctors or whatever the case may be about the myths, why not ask truck drivers or tire professionals about this myth? I also think they should do more semi myths, theres alot.
November 24, 2008 at 5:40 PMIn the 1950s I had a 52 Chevrolet that came with stock Firestone Super Champ tires. Over time all four of the original tires separated at the weld or seam. They were replaced under warranty. In all, seven of the eight tires failed at the factory seam. So it is NOT just retreads that blow apart.
November 28, 2008 at 1:36 AM