Drawbar pull capability

[sportscarclinic]

Weight was mentioned in post 12, 30, 31, 34 and 39. So seems to me a lot of people already recognized it.

Merely 'mentioning' weight as one of the factors in a broad discussion that also mentions every other variable is hardly the same as recognizing that it is *the* determinant, at least when comparing equal rear wheel HP under standardized soil conditions. The post I referenced was the first to do precisely that.

 

[LouNY]

Merely 'mentioning' weight as one of the factors in a broad discussion that also mentions every other variable is hardly the same as recognizing that it is *the* determinant, at least when comparing equal rear wheel HP under standardized soil conditions. The post I referenced was the first to do precisely that.

Because it is not the determinate factor, there are multiple factors that will apply.

 

[WinterDeere]

Merely 'mentioning' weight as one of the factors in a broad discussion that also mentions every other variable is hardly the same as recognizing that it is *the* determinant, at least when comparing equal rear wheel HP under standardized soil conditions. The post I referenced was the first to do precisely that.

It is not. Again, drawbar is typically given in horsepower (power), not pounds (force). This has already been discussed in several prior posts in this thread.

Measuring the pulling power rather than simple force, allows the collection of data in higher gears, where available torque cannot simply overcome friction/weight, while also providing a more useful measure of the true work a machine can do. After all, gear a lawn tractor low enough and put enough weight on the thing, and it will pull the world... in pounds force.

People have been doing this for years, and these problems have been worked out many times before. Do you honestly believe your first glance at the subject is somehow more informed than practices that have developed over decades?

 

[sportscarclinic]

Because it is not the determinate factor, there are multiple factors that will apply.

I disagree. Once you recognize that "horsepower" *is* the measure potential pulling power, the only remaining variable is the ability to put that power to the ground, i.e., traction. And traction is simply the co-efficient of friction (soil condition and tire construction) x mass (weight delivered to the soil).

 

[WinterDeere]

I disagree. Once you recognize that "horsepower" *is* the measure potential pulling power, the only remaining variable is the ability to put that power to the ground, i.e., traction. And traction is simply the co-efficient of friction (soil condition) x mass (weight delivered to the soil).

Yes... power. But again, pull in a higher gear. You will measure higher pulling power, both due to elimination of tire slippage and due to reduced gearing losses through the drivetrain.

Think of the tractor pull sled, not a tractor tied to an immovable tree stump.

 

[LouNY]

I disagree. Once you recognize that "horsepower" *is* the measure potential pulling power, the only remaining variable is the ability to put that power to the ground, i.e., traction. And traction is simply the co-efficient of friction (soil condition) x mass (weight delivered to the soil).

co-efficient of friction (soil condition) x mass (weight delivered to the soil).

that simple little co-efficient of friction has a 1000 variables, and the mass is not a simple number either a lot of varibles in there depending upon how the weight is biased front to rear and high or low, for just a couple and there are hundreds more.

 

[sportscarclinic]

Yes... power. But again, pull in a higher gear. You will measure higher pulling power, both due to elimination of tire slippage and due to reduced gearing losses through the drivetrain.

Think of the tractor pull sled, not a tractor tied to an immovable tree stump.

Think about neither for a moment. Rather, consider pulling on a scale attached to the draw bar which records peak pulling power. Yes, gearing and wheel diameter can be used to multiply the engine torque delivered to the rear wheels, but at a lower speed. Nonetheless, the measure of rear wheel horsepower remains the same (force x distance/time). Against the infinite scale, at some point the tractor's rear tires will break lose, or the engine will stall. That is the point of peak pulling power of that tractor. Adding rear wheel weight may increase the motive force up to the point of stall, decreasing weight may increase motive force by preventing stall. In either case, weight is the determinant.

Another commentator earlier posted a very informative, and scholarly exposition on the topic. Unfortunately, it appears that he decided to delete it.

 

[sportscarclinic]

that simple little co-efficient of friction has a 1000 variables, and the mass is not a simple number either a lot of varibles in there depending upon how the weight is biased front to rear and high or low, for just a couple and there are hundreds more.

Ultimately all those factors boil down to co-efficient of friction between the tire and the earth (here soil conditions, tire construction, etc.), and the weight presented to the ground by the tire's surface, however it gets there (ladder bars on a drag car, or wheel weights on a tractor). Of course, if you want any sort of meaningful comparison between tractors, the soil part of the equation must be held constant.

 

[rScotty]

Speculation is a great way to learn basics. It's fun, too.

I used to wonder if our old 90 hp farm truck would outpull the old JD tractor getting a trailer out of the mud..

For a deeper understanding, the Nebraska Tractor test procedures are worth reading. They've been beating on the subject for a long time.

Among other variables, their pull testing procedures measure: peak and constant HP, pulling speed, tire slippage, and fuel temperature.

 

[sd455dan]

You mean turbocharger?

Maybe if it was a transplanted Detroit 2 stroke