Help...shoudnt the tires spin ???

[SPYDERLK]

But I want to point out that this is not an INHERENT limitation of HST. Beef up all your hoses and fittings and stuff, set the relief higher, and you could snap an axle off the same as you could by abusing a geared tractor. If you engineer the drive train of a geared tractor just barely strong enough that it won't be broken by sudden, full-stop traction against its engine running at full tilt...and you design the HST system of its otherwise twin brother to relieve just before breaking the other drive train components also, then they could put exactly the same maximum torque to the ground.

As you imply, we implement the relief because we don't want users approaching and exceeding the limit without feedback. So instead of suggesting that HST systems are deficient, what you're really saying is that both can put the maximum safe reliable torque to the ground, but that a geared tractor will let you go beyond that and break it if you want. To CobyRupert I'd say I'll take the infinitely variable ratio and the built-in protection, thanks.

"Stuff" includes pump and hyd motor that, due to the automatic protection relief, have been designed close to the original specific torque point.

A gear typically has a large performance margin to start with. Try nearly tripling the weight of an HST tractor and see if it will spin the wheels with AGs on good ground. A gear will.

 

[Jhiphop72]

"Stuff" includes pump and hyd motor that, due to the automatic protection relief, have been designed close to the original specific torque point.

A gear typically has a large performance margin to start with. Try nearly tripling the weight of an HST tractor and see if it will spin the wheels with AGs on good ground. A gear will.

Exactly... When was the last time you saw a HST win a tractor pulling contest???

 

[peter3759]

I'm not interested in winning a tractor pull but I know I can move faster with a lot less effort when moving dirt and other various tasks with my hydro! If I needed every ounce of power to the ground with everything I did then I MIGHT consider a gear tractor but I don't! I moved a lot of dirt today and just thinking about all the clutching I would of done on a gear makes my knee hurt! For all of you who are masters at a gear tractor that's awesome because it's becoming a dying art but for me and MY applications hydro I went and I'll never look back!

 

[Woodshaver]

Everyone, let go of the past, gears are good but things change . Embrace new technology when it makes things more productive and easier.

 

[dfkrug]

But I want to point out that this is not an INHERENT limitation of HST. Beef up all your hoses and fittings and stuff, set the relief higher, and you could snap an axle off the same as you could by abusing a geared tractor. If you engineer the drive train of a geared tractor just barely strong enough that it won't be broken by sudden, full-stop traction against its engine running at full tilt...and you design the HST system of its otherwise twin brother to relieve just before breaking the other drive train components also, then they could put exactly the same maximum torque to the ground.

True, it is not an inherent limitation of HST; you can make an HST tractor of the same size/weight/hp deliver the same torque to the rear wheels as an equivalent gear tractor. Won't go as fast up a hill, but that's a power and efficiency issue.

A tractor's designer can play with not only the RV pressure and final drive gear ratios (incl tire diameters), but also the volumes of the HST pumps and motors.

This issue has been dealt with in several other threads, but I have had the 3 distinct design variations of an HST tractor:
> goes to relief
> spins tires
> bogs engine

while my gear CUTs all either:
> spins tires
> bogs engine
no gear tractor should ever slip the clutch

All situations are in excellent traction (hi weight, AG tires, great surface) in lowest range at full engine speed.

IMO, the designer should shoot for the "spins tires" condition for all CUTs up to a weight of at least 2x naked weight in high traction conditions. Maybe even higher.

The fact that some of my gear tractors have failed to do that (bogging engine) implies that even the designers of gear tractors sometime fail to make the "correct" tradeoffs.

My own tractor is a little deficient (RV opens), but I can live with the rare conditions that cause that.
I am almost up to 2x naked weight as well (6000#).

I have never had any Deere HST ever fail to spin tires, BTW.

 

[SPYDERLK]

I'm not interested in winning a tractor pull but I know I can move faster with a lot less effort when moving dirt and other various tasks with my hydro! If I needed every ounce of power to the ground with everything I did then I MIGHT consider a gear tractor but I don't! I moved a lot of dirt today and just thinking about all the clutching I would of done on a gear makes my knee hurt! For all of you who are masters at a gear tractor that's awesome because it's becoming a dying art but for me and MY applications hydro I went and I'll never look back!

Yes! Id sure love to have a 14K# HST tractor platform for loader work. The advantage in control is huge. The only time Id miss the gear is if there ever came a time the wheels wouldnt spin.

 

[SPYDERLK]

All situations are in excellent traction (hi weight, AG tires, great surface) in lowest range at full engine speed.

IMO, the designer should shoot for the "spins tires" condition for all CUTs up to a weight of at least 2x naked weight in high traction conditions. Maybe even higher.

The fact that some of my gear tractors have failed to do that (bogging engine) implies that even the designers of gear tractors sometime fail to make the "correct" tradeoffs.

My own tractor is a little deficient (RV opens), but I can live with the rare conditions that cause that.
I am almost up to 2x naked weight as well (6000#).

I have never had any Deere HST ever fail to spin tires, BTW.

Did that gear tractor have a rather high 1st gear, or the conventional 1 to 1.5 mph? All the ones Iv ever encountered with the 1.5 low will hold a spin at about 1K engine speed. That would be about 0.6 mph wheel rate.

 

[4570Man]

I am running over double naked weight on the L3240 HST. I can still spin the wheels even on asphalt. A gear tractor could spin the wheels faster, but please explain how a gear could pull any harder. The old F2550 gear could spin the wheels idling in first or second gear. Running 2500 rpm it would spin in 5th gear. I don't care how much faster a gear tractor can spin the wheels I'll take a HST every time.

 

[SPYDERLK]

I am running over double naked weight on the L3240 HST. I can still spin the wheels even on asphalt. A gear tractor could spin the wheels faster, but please explain how a gear could pull any harder. The old F2550 gear could spin the wheels idling in first or second gear. Running 2500 rpm it would spin in 5th gear. I don't care how much faster a gear tractor can spin the wheels I'll take a HST every time.

No advantage to a fast spin as far as force delivery. In a gear to gear comparison it would give an idea of the surplus power available. ... But comparing between types it would be very hard to judge due unknown hyd losses.

I am impressed at your 2x spin on asphalt - particularly if 4wd and you have R4s that are not overinflated, and asphalt that has good exposure of grit. Still, from test measurements I have done with R1s on good ground I find they have a traction coefficient of 1 or a little more in that application. I dont think tractor rubber on pavement can meet that number. But R4s would be a little better there than R1s.

 

[4570Man]

I was pushing a wood pile that was right on the edge of the driveway. The tractor was in 4wd, but the front wheels were off the driveway on dirt. I have R4 tires on the tractor.