[AT] Horsepower Question

[Will Powell]

Yes, weight is the classification, not HP, at least from what I have seen in the antique tractor pulls. 

Back to my college physics.... (Long ago). It's all about friction... a force that is created whenever two surfaces move or try to move across each other. In tractor pulling, the friction of the tractor is trying to overcome the friction of the sled. 

Surfaces being equal, friction is proportional to the weight. 

F = u R F = Frictional Force retarding motion, or (whats required move it...) 
R = is the force keeping things together (Weight on a tractor) 
u = (pronounced mew), coefficient of friction (an index less than 1.0) Think of it as Basically a measure of how rough or smooth a surface is. 

So, lets say the u is a .8 constant (just a guess) and the weight of the tractor is 3000 lbs. 

Then F = .8 x 3000 

F = 2400 Or, a 3000lb tractor can pull 2400 

Now, double the weight 

F = .8 x 6000 
F = 4800 Or, a 6000lb tractor can pull 4800 

Again, just throwing basic examples out there to prove the weight pulling stuff... 

There are other factors in a tractor pull, like more HP. If you have a lot of HP you can get the sled moving faster at the start before sleds full force is applied, and then you get into momentum variables/formulas.... But, if you have a high HP tractor with no weight, it's not going to help you... 


I think I'm right about this, or at least close... 

I did a calculation in College that measured how fast a dragster could theoretically go in a 1/4 mile based on the coefficient of friction. I think it was about 265 mph. How can today's dragsters push over that threshold? It's the tires, they are so tacky they are actually gripping the asphalt kind of like a train on a cog railroad... 

Regards, 

Will 

----- Original Message ----- 
From: "Ben Wagner" <supera1948 at gmail.com> 
To: "Antique tractor email discussion group" <at at lists.antique-tractor.com> 
Sent: Wednesday, October 6, 2010 8:23:08 PM 
Subject: Re: [AT] Horsepower Question 

On 10/6/2010 11:47 AM, Will Powell wrote: 
> Ben, 
> 
> You said: 
> 
> "So in reality, horsepower is not really the important number; torque and 
> RPM is what matters?" 
> 
> The Torque and the RPM are variables in the HP calculation... Tourque and RPM matter based on their application. 
> 
> High HP low torque = Light engine, good for lawn mowers, automobiles, race cars, airplanes, usually high ware, shorter service life. Cheaper to build? 
> 
> High Tourqe, Low RPM = Heavy engine, good for Trains, Tractors, Trucks, excavating equipment. Applications that welcome weight for pulling or pushing. Low wear, long service life. More expensive to build. (more metal) 
> 
> 
> The other factor that makes things different between a lawn tractor and a farm tractor is weight... 
> The main measure of a tractors pulling strength is related to its weight... Try pulling a 1 row plow with your 20hp lawn tractor...... 
> 
> Regards, 
> 
> Will 
> 
> 
> ----- Original Message ----- 
> From: "Ben Wagner"<supera1948 at gmail.com> 
> To: "Antique tractor email discussion group"<at at lists.antique-tractor.com> 
> Sent: Wednesday, October 6, 2010 10:17:32 AM 
> Subject: Re: [AT] Horsepower Question 
> 
> On 10/6/2010 10:00 AM, charlie hill wrote: 
>> Ben, the lawn mower engine is rated in gross hp with no drive train load. 
>> The tractor engine is rated at net hp, either at the wheels or the PTO. 
>> There may well be some fudging on the lawn mower engine as well. Also, HP 
>> is torque in ft/lbs. times RPM. You can make hp with high rpms and low 
>> torque or high torque and low rpm. Your tractor is high torque and low 
>> rpm. that is what allows it to move a load easily. 
>> 
>> Charlie 
>> 
>> -------------------------------------------------- 
>> From: "Ben Wagner"<supera1948 at gmail.com> 
>> Sent: Wednesday, October 06, 2010 9:00 AM 
>> To: "At"<at at lists.antique-tractor.com> 
>> Subject: [AT] Horsepower Question 
>> 
>>> Here is a puzzler that maybe someone with a better knowledge of 
>>> engines can answer. I was asked this question, and had to announce 
>>> that I needed to look it up. What better place than the AT Mailing? 
>>> 
>>> I have a Super A with four cylinders, producing c. 20 HP. 
>>> 
>>> I have a lawnmower, with an engine that says it is also 20 HP, with only 
>>> two cylinders. 
>>> 
>>> What is going on? Is this two different measures of HP? Or has 
>>> technology improved that much? What makes a little two cylinder "small 
>>> engine" have the same HP as four cylinder "tractor" engine. 
>>> 
>>> Thanks, 
>>> Ben Wagner 
>>> 
>>> 
>>> _______________________________________________ 
>>> AT mailing list 
>>> http://www.antique-tractor.com/mailman/listinfo/at 
>>> 
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> So in reality, horsepower is not really the important number; torque and 
> RPM is what matters? 
> 
> Ben Wagner 
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Thank you, everyone, for your replies. I will have a better 
understanding know of the horsepower issue now, so I think my friend 
will have his answer. 

As for the weight in pulling power, is that why in tractor pulls the 
classes are defined by weight? 

Thanks, 
Ben Wagner 
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