Does engine HP affect driving power

[CobyRupert]

If you want another simple test get a 10 speed bike and see how it handles the grades...when I use to ride one soon learned how to down shift or strain very hard on slopes.

Yes! Nothing like 1st hand (or leg) experience!
There’s three concepts to be aware of: Energy, (horse)power, and torque. 4, if you include time.
It takes the same amount of ENERGY to climb a hill no matter how much horsepower, how fast / how much time it takes, or how much torque (the 10 speed’s chain and your legs (the motor) experience).

(Horse)power is just a measure of how fast you burnt that energy. Hp=Energy/time. If you climbed hill in 1/2 time as another person, your horsepower output was 2x the other persons.

As every 10 speed bike rider knows, Torque is the tension the chain, and your (motor) legs, are experiencing. ICE motors and your legs have a maximum output. This we have to pick a gear and rpm that doesn’t exceed this. This determines maximum climbing speed.

So, if you want to climb the hill (Energy) in the same amount of time (same horsepower), in 10th gear as in 1st gear, your torque has to be off the charts, while your rpms are minimal. You won’t have the strength and will stall. Conversely, in 1st gear, your rpms are off the chart, and the chain is experiencing very little tension. You will blow the motor or your heart.

Basically, or theoretically, any horsepower motor can pull any load up any hill if you have enough mechanical advantage (“low gears”) and an infinite amount of time to go that slow.

 

[Blue Mule]

Thanks for all the input. For those that asked have been trying to decide on which Orange tractor to get the L series has the 25hp 33 and 39. All the same frame. Just wantframe make sure I wasn't paying extra for the extra hp if it didn't help

Years ago tractors used to list drawbar power which essentially gave a rating at how well the tractor could maintain momentum under load. Hydro tractors are incredibly easy to use and for loader or work that has constant F/R or finesse work they win hands down. Plus the ease of use is well liked.

The one spot where they fall flat is drawbar power. A gear shift or a power reverser tractor will run circles around a hydro in pulling of similar hp. The kubota L2500 DT (25hp) I had will out pull my JD 4400 hydro (34hp) at a higher speeds. With a hydro you loose all the centrifugal force from the engine/flywill to help drive the tires because there's no solid connection. You are moving by fluid flow. If the fluid isn't flowing as fast as it should then the system goes into relief to save the pump.

If your heart is not committed on hydro I would recommend trying a couple sizes with a direct drive transmission. If heart is set on hydro then hp is your best option for better performance.

I agree with this 100%. I went from a 29 HP gear drive to a 40 HP hydro and both feel like they've got essentially the same pulling power up hills and on gravel roads, but I'd take the 40 HP hydro over the gear drive six days a week and twice on Sunday. I say buy the most HP you can afford.

Sure, you can gear down to low range on a 25 HP tractor and do anything you want to do. But what if you don't WANT to go walking speed all the time? I paid for 3 gear ranges and I wanted to be able to use any of the 3.

 

[hube2]

...Sure, you can gear down to low range on a 25 HP tractor and do anything you want to do. But what if you don't WANT to go walking speed all the time? ...

To be completely honest, I'd love to go faster in some cases. Tried to mow my lawn in high and it seems to pulls the hill fine, but my lawn is bumpy and I thought it would going shake my kidneys out. This is the main reason I go slow, that and mowing the lawn is one of the ways I get "quiet time". As long as I'm out mowing no one bothers me

 

[Farmer495]

I road my tractor and several other frequently.
From my place to the farm is three miles with several hills,
with just the bare tractor and front end loader (80 engine Hp) I can pull all the hills in high gear.
Drop my bucket off and install the grapple and carry the bucket at least one hill will require a down shift.
Hook up the brush hog, a trailer, or snow blower and three hills will require down shifting.
One of the places that we chopped corn on has a couple of hill that will make a 7130 IH Magnum drop a couple of gears empty by it's self,
when I have the pull type forage harvester and self unloading wagon with a load behind me two of the hill will make me downshfit from 18th gear down to 10th.

Depending on the bucket size many tractors couldn't pull steep hills with a full bucket of gravel in high gear.

That's right.

I drove two tractors the same model years ago that wouldn't pull a slight upgrade EMPTY in high gear, too heavy for the power they had.

Other thing is hill size comes into play as well along with bucket size. What some call a hill others may call a speed bump or a mountain.

I do a lot of roading as well, pulling loaded wagons 13-14k lb at times. My largest hill makes me drop two gears on an 8 speed and it's not lugging in the gear I pull the grade in, likely about the same as your Magnum going from 18th-10th speed wise

 

[Gord Baker]

My father in law let's me use his 25hp HST tractor quite often. Some of it's use is maintaining the road we live on. It really struggles going up any kind of hill especially with a load of gravel. I know the engine hp doesn't affect lift capacity because it's really based on what the hydraulic pump can do. But what about a HST transmission. Really not that familiar with how those work. Are they hydraulically driven. Basically I'm asking about it I buy a tractor and get a 40hp or so engine will that alleviate the issue of not being able to pull hills very well

These drivetrains are NOT made for pulling or overloading if it is the Hydrostatic type. Do NOT use it for scraping roads. It is meant for mowing lawn. Is it up to you to scrape and maintain the road?

 

[Red Eye]

I had a 34 hp Kubota, now have the 60 hp. The 34 hp would struggle going up a hill with a bucket of gravel, always operated in range 2 or even 1. Now with the 60 hp, almost never use range 1, always in 2 or 3. So yes, long winded answer to your question. 25hp is quite inadequate to be doing hills or hauling gravel. I learned the hard way.

 

[CH4Ohio]

My father in law let's me use his 25hp HST tractor quite often. Some of it's use is maintaining the road we live on. It really struggles going up any kind of hill especially with a load of gravel. I know the engine hp doesn't affect lift capacity because it's really based on what the hydraulic pump can do. But what about a HST transmission. Really not that familiar with how those work. Are they hydraulically driven. Basically I'm asking about it I buy a tractor and get a 40hp or so engine will that alleviate the issue of not being able to pull hills very well

You must be in high range which isn't for work. My 30 HP HST Kubota would crawl up a vertical wall in medium or low range. It will whine and slow down in High range on any slope with a load or when pulling, but the engine won't really bog down -- just doesn't have the power so you lose speed.

 

[1953NAA]

An HST transmission is not super efficient. At best about 80-85%, so that means out of the 25hp, you only have 20 or so HP available to the wheels. I have a 35hp Kioti with HST and a ‘53 NAA (30 or so at the PTO). I can easily pull a two bottom plow with my NAA in second gear. The Kioti bogs down pulling it in mid range and struggles/crawls in low range with the same plow.

I love the HST for bucket work, mowing and clearing snow but I should have accounted for transmission losses and gotten a 40hp to be on paar with my NAA but that would have put me into a bigger tractor. Something you should keep in mind.

 

[Garson]

My father in law let's me use his 25hp HST tractor quite often. Some of it's use is maintaining the road we live on. It really struggles going up any kind of hill especially with a load of gravel. I know the engine hp doesn't affect lift capacity because it's really based on what the hydraulic pump can do. But what about a HST transmission. Really not that familiar with how those work. Are they hydraulically driven. Basically I'm asking about it I buy a tractor and get a 40hp or so engine will that alleviate the issue of not being able to pull hills very well

HST tractors are designed for convenience and are the only way to go if you are just pushing snow or mowing grass. If you want to work the tractor your best choice is a manual transmission with shuttle shift. Many of these models have syncro-meshed gears with the range you have selected- low, medium or high. You have to stop to change ranges. So pushing forward and back is simple - engage the clutch and shift up or down on the run.

Your power loss on an HST tractor is severe. You pay for the convenience. Typically, they will lose 33% of their horsepower in the hydro system. Perhaps more. They all say in their specs they loose 5% but don't believe it. Ask anyone who has compared a 25 HP manual tractor vs HST. I had a little 20 HP shuttle shift 254 International with a larger frame and would pile half a cord on the back box, half a cord on the front loader and a cord or two twitch behind it. It easily hauled this up over a steep mountain and back down again from a mile back. The tires were loaded and it would spin tires before it would lug down.

My neighbour had a 25 HP HST tractor and it wouldn't haul a trailer with a cord of wood up the mountain. In low range it would drive up the hill a few feet and bog right out. Understand that a manual transmission tractor is only limited by its traction, so long as you select a lower gear, it will not bog down, but it will go slow. My 72 HP tractor with shuttle shift pulls the same load mentioned above, but it drives home in 10th out of 12 gears at the speed of a jog. The 20 HP manual transmission tractor pulled at a slow walk in 2/12 gear but did it well.

Go to a dealer and ask to try two tractors, manual and HST, of the same HP. Push them into something immovable and you'll see the difference instantly. Good luck.

 

[sportscarclinic]

Thanks for the thread and discussion. I'm now, more than ever, very grateful to own a geared tractor. Apart from mowing lawns, I cannot imagine why anyone would want an HST. The power transfer inefficiency (work done to heat liquid) is massive, and there's a constant threat of one day being surprised by a tractor that won't move, requiring the payment of a huge repair bill to fix it. It's no surprise that the majority of parts tractors that you see partially disassembled in yards are HST models. I think the best advice you could give the OP is sell the tractor while it still moves, and buy another one with gears.