Explain Lawn tractor HP Ratings to me?

3997 Views 19 Replies 13 Participants Last post by Stewart, Apr 15, 2011

Fatbob

Discussion Starter · Apr 12, 2011

I have drag raced for years, until my reaction times, and eyes went to heck. I understand torque, gearing, weight, and so on. How can these companies rate a brand X box store tractor with a POS hydro at 25 HP when it will not pull a greasy string out of a cat's ass. I have a POS X320 JD. The old trashed out 448 will work circles around it, and cuts better even with worn out blades. 18 HP Never bogs, pulls down, just mows, and plows, or spins. I really don't understand a $4,000 buck mower that pales in comparison to a old 448 I bought for $450.00. I gave the JD to my Son with 9 hours on it. I may as well burned that 4 grand. The dealership has kept it more than me. Anybody got any cheese for this whine. :thumbdown:

1 - 20 of 20 Posts

99flhr

· #2 · Apr 12, 2011

Well, no cheese, but IIRC those old Farmall Cubs are rated @ 9hp.
Still capable of a fair amount of real work.
I agree with you but don`t have the science to explain it.
Just ask my wife, I`m a dumba$$

Fatbob

Discussion Starter · #3 · Apr 12, 2011

I got it. It's a BS rating instead of HP rating. :facepalm:

Phaon

· #4 · Apr 12, 2011

Well, I’m not an engineer or mechanical expert, but I have about 25 years of anecdotal experience with these tractors. I would say that it’s about two primary things.
First off, the hydraulic drive system is extremely efficient. It frees up the engine to devote an amazingly consistent and high percentage of its available horsepower to the PTO. Mowing thick grass uphill seems to affect the engine power output only marginally more than downhill, for example. So you’ll need a higher horsepower engine in a less efficient brand to get the same power to accessories, and it will never be as consistent.
Second, they’re just better constructed. Little things like bushing and bearing quality, weight distribution, PTO construction, all are minor on their own. But put all of these together, and you just have a better machine. They last longer and are just better at what they do. It’s why we love ‘em :+1:

Chris

99flhr

· #5 · Apr 12, 2011

Fatbob said:
I got it. It's a BS rating instead of HP rating. :facepalm:

Well, having tall tires and a 200lb flywheel never hurt anybody. LOL

Hydriv

· #6 · Apr 12, 2011

Try going to Wikipedia and asking for the definition of horsepower. The document is several pages long with about 5 or more explanations. In recent years, the box store air compressor manufacturers faced a class-action lawsuit over HP ratings that were bogus. The OPE engine manufacturers faced a similar class action suit that got settled out of court.

Those of us who really know these tractors also know that the torque of the Kohler K and M series engines as well as all the Onan CCKA, B and P series engines is legendary, especially when you compare them to the claimed HP ratings. These modern twins have had all kinds of HP ratings applied to them for the prime purpose of marketing the tractor it is placed in.

There is no real solution to the issue. Some of the engine manufacturers don't want to post HP ratings anymore. Instead, they want to post internal displacement and/or torque ratings. The problem is.....John Q Public only understands HP. The other two measurements don't really compute for them. That's the dilemma but the irony here is this. John Q created this problematic pissing match because he bought into it every time he bought a new mower. The amount of HP under the hood influenced his buying decision. The marketers gave him what he wanted.

See less See more

xfolkboat

· #7 · Apr 13, 2011

It's the torque/power curve that has changed-what's available at 3600 rpm isn't going to help at 2800 when the going gets tough.

I imagine some engines are missing the midrange power the older engines had, they are certainly smaller these days.

Hydriv

· #8 · Apr 13, 2011

It's tough for a lightweight modern engine to compete with a long-stroke cast iron engine with a massive flywheel.

Nutcase446

· #9 · Apr 13, 2011

Larger tractors give 2 HP ratings, engine HP and PTO HP. For running most implements PTO HP is the most important one. It's whats left when you factor in all the other things that the engine is spinning. Things like hydrostatic transmissions, charging systems and power steering or hydraulic pumps. Another # that you don't hear much would also be more important than engine HP is rear wheel HP. How much of that HP is actually getting to the ground to pull. I think that Tom and 99 hit the nail on the head though. These new engines are so light and have so little rotating mass that they fall on their face fast. Todays average consumer when shopping for a tractor to mow the lawn is only concerned with 3 numbers: horse power, width of cut and price. They are uneducated buyers and the salesman at Home Depot likes it that way. Gregg

ByCo

· #10 · Apr 13, 2011

In the early 1900's all kinds of wild power and performance claims were being made for ag tractors. Some time around 1918 the state of Nebraska directed the University of Nebraska to establish a tractor testing laboratory to test the actual performance of the tractors and a law was passed that only tractors that had been tested by the Nebraska Tractor Test Laboratory could be offered for sale in the state of Nebraska. It wasn't long and all the wild claims disappeared. The law was latter changed to apply only to tractors of 40 advertised HP or more. All major ag tractor manufacturers thoughout the world now send their offerings to the Nebraska Tractor Test Laboratory , or one of it's overseas satelites, to establish their performance ratings.

It's to bad that nothing like this exists for lawn and garden equipment. Can you imagine having something like this, http://www.tractordata.com/farm-tractor ... tests.html , for garden tractors?

ByCo

Toadroad

· #11 · Apr 13, 2011

https://lawnmowerclass.com/ the cash award claim has exspired, but those who are entitled can still get a certificate for a 1 year warranty on certain makes and models of push and riding mowers bought in time brackets. im a member of this class action over hp ratings and will get check for 35 bucks plus 1 year warranty on my 6.5 hp lawnboy made buy toro and now got lawnboy out and found its got bad coil pack. this link will tell you all who is able to get warranty. deadline for warranty is feb. 2012

Rockdog

· #12 · Apr 13, 2011

'Nebraska' tests drawbar HP so it pretty much difficult to bs your way around an engine hp value. I'm not sure on lawn and garden type equipment the marketed hp is for the machine. Correct me if I'm wrong but I believe its the hp of the engine based on engine testing.

Not too sure the weight of an engine is going to hinder its performance. Rotating mass will under certain conditions. I'll take aluminum for heat dissapation for sure. Heavier flywheel is good to keep from lugging down too quickly.

One thing that is quickly picked up on when it comes to 25 hp box store 'tractors' is that they are no more than 25 hp riding lawn mowers. Just like the Cub Cadet I own. Its from the 90s though and has been a very very good machine and mows quick nicely. And it HAULS ARSE compared to my old 444. They make and sell those things to make money. They make that money by selling lots of tractors. They sell lots of tractors by designing what the 'masses' want. The 'massses' want a good looking, low priced, low maintenance, easy to handle, machine that does it QUICKLY. You want a TRACTOR you're gonna pay a hell of a lot more than a few grand.

Hydraulic drive being 'efficient'? Not sure I'd say efficient but its pretty much infinitely variable so you can use your rated HP over wider range of work. Would be really awesome of there was a controller working the valves.

See less See more

Bob MacGregor

· #13 · Apr 13, 2011

On lawn and garden tractors the horsepower rating is strictly for the engine that is installed. The tractors ability to apply the engine horsepower to the rear wheels depends solely on the drive system design. Most of the time the drive system is belt driven and this is where a large amount of power loss happens. The rest of the drive system could be geared or hydrostatic with hydrostatic being another source of power loss to add into the mix.
The horsepower numbers on the tractor have become an effective marketing tool in the sale of low end lawn and so called garden tractors.
My neighbor has an 18 HP Kubota, a 26 HP Craftsman, and a 16 HP Gravely. So based strictly on HP, the Craftsman should be the winner when in fact it will not pull his DR self powered leaf vac, but the other two machines pull it with no problem. The Craftsman has trouble just getting up the hills on his property with the mower deck not running.
I have a Scag ZTR mower that has belt drive to the hydro pumps, but this belt system is extremely well designed and effective. And of course I have an Ingersoll 4018, my pet!!
Bob MacGregor in CT :mowlawn:

See less See more

Kenc

· #14 · Apr 13, 2011

I think the biggest issue with the newer ratings is the RPM rated versus RPM in real use.

The OHV twins are comparable to late automotive engines, capable of excellent air/fuel mix flow through the heads/valves. But that airflow can only fill the cylinder to whatever the max volume is, less some losses. The amount of mix is what determines the power created by the burning, so smaller engine = less power per ignition event.

So the 'solution', spin it faster, get more power strokes per minute. I would expect these little guys, like my Vanguard to make a lot of power above 4000rpm, maybe as high as 5k. But, rate it at 4-5k and mow at 3600, see the problem?/

xfolkboat

· #15 · Apr 14, 2011

The old flatheads were generally larger for a given [email protected] rating, and would have their best cylinder-filling capabilities (and best BMEP) at a lower RPM, so their torque would be higher at a lower RPM than at the max power rating.

I noticed my friend's riding mower had "25HP" emblazoned on the side. Why 25 HP was needed I cannot fathom.

Bob MacGregor

· #16 · Apr 14, 2011

If the power doesn't get to the rear wheels then it is wasted. Putting big HP engines in the low end tractors is just a marketing tool to sell low end tractors to those that don't know better and or don't care and are impressed by bigger numbers on the hoods.
Over the years I have had folks look down at my 18 HP Ingersolls and I tell them all that I'll be at their place at a time set by them and we can have a pulling contest, never have had anyone set a time and place. I have owned an Economy tractor and that is one machine that I know would be tough to beat if at all. :446:
Mad Mackie in CT

Rockdog

· #17 · Apr 14, 2011

Take a new camaro or corvette with over 500 hp and see if it can pull a 40ft plow.

Hydriv

· #18 · Apr 14, 2011

Rockdog said:
Take a new camaro or corvette with over 500 hp and see if it can pull a 40ft plow.

I just checked with my local Vette dealer and he tells me that GM is no longer offering the CAT 3 hitch as an option.

Reactions: 1

CASE 220/4

· #19 · Apr 14, 2011

Rockdog said:
Take a new camaro or corvette with over 500 hp and see if it can pull a 40ft plow.

my camaro can. :trink:

Stewart

· #20 · Apr 15, 2011

CASE 220/4 said:
Rockdog said:

Take a new camaro or corvette with over 500 hp and see if it can pull a 40ft plow.

Click to expand...

my camaro can. :trink:

I'd like to see a picture of that. :thumbsup:

1 - 20 of 20 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.