Power Pulling - Farm Dragsters
August 19, 2006 9:20 AM   Subscribe

Serious Horsepower. Some beautiful machines pulling more than just dead weight .
posted by rmmcclay (33 comments total)
I can't get any of these links to load. :(
posted by mr_crash_davis at 9:28 AM on August 19, 2006

correction: except for the last one
posted by mr_crash_davis at 9:30 AM on August 19, 2006

Yeah, it seems to be MetFilterDotted. Or something. On a Saturday morning? Odd.
posted by intermod at 9:33 AM on August 19, 2006

So, what's the idea, here? These machines compete to see how far they can pull a weighted sled, is that it?
posted by normy at 9:36 AM on August 19, 2006

Never mind, a quick search turned up this explanation. The exploding part sounds entertaining.
posted by normy at 9:41 AM on August 19, 2006

I've got the "hohahohoho RACEWAY PARK!" voice in my head now. Nitro-burning funny car action, wheee dogies.

I always wondered with tractor pulls how they worked. Like, what made the resistance happen and why that load slid along the trailer while it was being pulled. It was hard being a nerdy kid in the midwest before wikipedia.
posted by Eideteker at 9:46 AM on August 19, 2006

On second read, I still don't entirely understand how the resistance is increased. If anyone who knows can explain it better (I like diagrams), I'd appreciate it.
posted by Eideteker at 9:50 AM on August 19, 2006

Yeah, farmer engineering at its best. Those ole boys are running top fuel NHRA motors without all that dagnab safety equipment. Good way to get a faceful o' 6-71 blower.
posted by klarck at 9:56 AM on August 19, 2006

Here's a good video of some pulls via Google...
posted by rmmcclay at 10:02 AM on August 19, 2006

Jaysuz look at the exhaust those things pump out in that Google link.

Is there any skill involved, here, or do you just gun it?
posted by It ain't over yet at 10:17 AM on August 19, 2006

Umm, what exactly do you consider "beautiful" about these macho trucks? Interesting, yes. Beautiful? Not in my world.
posted by citizenkane at 10:18 AM on August 19, 2006


Well, yeah...human technology is beautiful to me. Machines, buildings, robots, computers, spacecraft, and medical devices for starters.

So are sunsets, the full moon, and curvaceous bikini-clad girls.

And what be beautiful in your world?

posted by rmmcclay at 10:26 AM on August 19, 2006

I'm still not entirely clear on exactly how winning is measured. Speed? Distance? Style points?
posted by normy at 10:47 AM on August 19, 2006

Anyone have any links to a video of one of the multi-turbine tractors?
posted by [expletive deleted] at 11:11 AM on August 19, 2006

The sled gets "heavier" because it has wheels in back, and a "skid plate" in front. As the sled is pulled, a large weight is moved from the back to the front by the turning of the wheels.

So at the beginning, the weight is mostly carried by the wheels, and thus is comparatively easy to move. At the end when the weight is on top of the skid plate, they're basically just dragging it along the ground without the benefit of any wheels.

It's hard to describe how loud these things are if you've never been to a pull. Think about having several top fuel dragsters going all-out at the same time, except that they mostly sit in once place rather than rocketing away at 300mph...
posted by reborndata at 11:52 AM on August 19, 2006

@normy - Distance.

It's just: How far can you drag that thang?

Here's some further musing on tractor pulls and mechanics:

Re: Why do tractors in a tractor-pull puposely spin their tires? Date: Wed Aug 29 16:38:23 2001 Posted By: Steven Miller, Mechanical Engineer, NCR Corporation Area of science: Physics ID: 998018238.Ph Message:


Sliding friction coefficients are generally lower than the static coefficients for the same object/surface as illustrated in introductory physics classes.

Regarding tractor pulls in general: The competition occurs generally on dirt. The load on the sled is dynamic - it provides increasing resistance as time elapses. According to the American Tractor Pullers Association at http://www.atpapullersonline.com , it involves:

"Weight Transfer -otherwise known as the sled, it is hooked to the pulling vehicle by a chain. As the competitor takes off down the track the load will get heavier to pull. The two major components of the sled are the box and pan. The pan is sliding on the ground without much resistance at the start of the pull. The pan will increase friction with the track as the box, which is chain driven comes towards the front of the sled. Inside of the box are lead blocks... Once the box stops the friction of the pan is greatest and the pulling vehicle slows to a stop."

Basically, the concept of spinning the tires for traction is kinda complex but analagous to the type of thing you see NHRA dragsters doing on dragstrips.

Because the sled is lightest in the beginning of the pull this is where the tractor puller wants to both gain distance and momentum; as the load increases the puller will lose momentum and eventually stop. The quicker they leave the line the farther they will pull. What makes pulling a challenging sport is there is no set formula to apply all the horsepower these tractors can develop to the ground. I said above it is complex and this is because there is a balance that must be achieved for the given conditions - too much power and the tractor will sit in one place and the tires will spin very fast with little effect ("buzzing the tires" see http://www.outlawpulling.com , go to glossary and see 'miss the balance') - too little power and the tires may just begin to dig a hole in the track or even kill the engine (though not likely!). A correct power balance allows the tractor to kinda float on the hard packed dirt without "damaging" that surface that the tires are using for traction - this is referred to as "hooking up". "Shaved" tires are generally used which present a less aggressive tread pattern (more akin to a racing slick but not quite) to aid in hooking up. While the static coefficent of friction between the tire and hard packed dirt may initially be high, this is what actually leads to the destruction of the dirt surface and starts the tires spinning in the first place.

Long and very complex story made short - the sliding friction coefficient between the hard packed dirt and the shaved rear tires of the tractor turning at (very) high rpms provide more tractive force for pulling than in trying to control wheelspin - the dirt surface simply wont withstand the forces exerted by the tires. That being said there may be tracks and conditions where pullers will try to start with minimal wheelspin (difficult with in excess of 2000 hp). It just depends on the conditions and how the tractor is set up.

Compared to the weight of the sled and tractor, it is unlikely that much benefit is gained by imparting momentum to the dirt being kicked out by the rear wheels. Most likely this actually would lead to a negative effect because the dirt moved would either accumulate on or in front of the sled being pulled creating even more resistance.

And of course none of the above applies to the mud bog folks who use the viscous forces created by their spinning tires for forward momentum.

Hope this helps.

Sincerely, Steven Miller smiller@kahuna.sdsu.edu Bachelor of Science, Mechanical Engineering
San Diego State University (Alumnus)
posted by rmmcclay at 11:52 AM on August 19, 2006

@ [expletive deleted] Here's a vid with a mix of turbine-driven tractors as well as one with an aircraft piston-driven engines and others...
posted by rmmcclay at 12:19 PM on August 19, 2006

These machines make Max mad.
posted by 517 at 12:24 PM on August 19, 2006

I really hope some of the folks from this thread, the ones who were so panicked over Mcdonalds giving away plastic toy Hummers, have a look in here and learn to know true outrage. See Paris and die, folks.
posted by jfuller at 12:54 PM on August 19, 2006

Oh, we see it. We're just too disgusted to speak.
Christ, this is like watching the monkey, only with rednecks instead of more highly-evolved primates.
CHrist, I'm so glad I didn't end up going to Cal Poly.
posted by lekvar at 1:25 PM on August 19, 2006

Pud Pull! Great stuff. Too bad people get their panties in a bunch about this. It's got a long county fair history, from way back when farmer A would put his stock John Deere up against farmer B's stock Ford tractor. Now it's entertainment.
posted by fixedgear at 2:13 PM on August 19, 2006

rmmcclay please stop with the @username thing, the username is all that is required.
posted by Mitheral at 2:32 PM on August 19, 2006

You're not telling me about anything new, I went to these as a kid. However, it's not just "how far can you pull it." Technically, after 300 feet it's a "Full Pull" and that driver advances to the next round, etc. etc. I think that time in getting the "full pull" is the tie-breaker.
posted by Cyclopsis Raptor at 2:45 PM on August 19, 2006

I also enjoy beautiful machinery pulling weight.
posted by Wolfdog at 3:22 PM on August 19, 2006

that'll be bio-diesel?
posted by marvin at 6:29 PM on August 19, 2006

I would like to point out that you are at this very moment missing the National Tractor Pulling Championships in scenic Bowling Green, Ohio.

I went a few years ago. I found it challenging to watch, yet beautifully loud.
posted by benimoto at 6:55 PM on August 19, 2006

Ooookay, I live near farms and I can assure you: these are not tractors.
posted by five fresh fish at 8:11 PM on August 19, 2006

They're at least tractoresque, though.
posted by flaterik at 9:58 PM on August 19, 2006

That, I grant you. Though they're also rather drag-raceresque, too. I should go look for myself, but ask it here: are these engines that accept diesel, kerosene, and other fuel oils? 'cause if they're using av-gas, I'm thinking that's contra-tractor.
posted by five fresh fish at 10:56 PM on August 19, 2006

That black, black smoke spewing from those exhausts says diesel in at least some of 'em.
posted by jfuller at 5:03 AM on August 20, 2006

Low-RPM, high-torque = tractor, in my mind.
posted by five fresh fish at 7:34 AM on August 20, 2006

I think that time in getting the "full pull" is the tie-breaker.

Also, sometimes they do a re-pull all the full-pullers but advance the weight on the sled faster, don't they?
posted by techgnollogic at 1:00 PM on August 20, 2006

I'm not much for motor sports in general, but somehow the sheer unlikeliness of of the contraptions fielded in unlimited-class tractor pulls always holds my interest.
posted by subtle_squid at 7:57 AM on August 21, 2006

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