Drawbar Pull - tracks vs. tires?

[davidwyby]

I got curious about skidder pull vs. dozer pull. Didn't find much about skidder pull online with a quick search, so I thought I'd try to generate some discussion. Appears dozers can pull at least 1.5 times their weight. For grins, here is my "Skidder".

 

[northmanlogging]

traction traction traction...

dozers can push more then they can pull, skidders can pull more then they can push

on a skidder you can get the wieght up on the rear tires and pull a crazy amount on dry hard ground, bit pushing the blade only werks good if you can get under a log.

dozers the blade "pushes" on the tracks, getting more traction, but pulling lifts the front reducing traction some

 

[JRM]

https://www.northernstrands.com/sling-tension-calculator.aspx

 

[JRM]

To add to the above. Since your scale is not pulling straight on some of that 6000 lbs the scale is reading is showing line tension and needs to be considered. It looks like you've got a pretty decent angle on the bridle so it's not going to be a big difference but a difference nonetheless. . At 60° on the bridle the tension factor for each leg is 1.16 x what a a straight pull would be. So if your scale is showing 6k lbs, 6000 ÷ 1.16 = 5172lbs x 2 (2 leg bridle @ 60°) = 10,344lbs is what you'd actually see if that scale was hooked to the main line behind your rig.
The wider the bridle gets the more tension you will see on each leg.
At 45° on the bridle the tension factor becomes 1.4x a straight pull. 6000 ÷ 1.4 = 4285 x 2 (2 leg bridle @45°) = 8571 lbs pull if the scale was on the main line behind your rig.
Now widen the bridle out a good bit, 30° tension factor is 2x straight line pull. So that same 6000lbs on your scale ÷ 2 = 3000 x 2 (2 leg bridle @30°) = 6000 lbs pull if the scale was on the main line behind your rig. As you can see the wider the angle of the bridle the higher the line tension of each leg.

 

[davidwyby]

@JRM thanks! That calc will come in handy.

I took a basic rigging class a long time ago and was aware of that, but have only used it so far as to avoid much angle when lifting/pulling to avoid overloading, but also have used it to my advantage with stuck vehicles. Pull tight between two objects, and then sideways in the middle to increase force.

 

[Billhook]

My only experience was when I had a contractor here on the farm with a New Holland TF46 combine that had driven over a Spring hole in an otherwise very dry field and was stuck with one drive wheel spinning. The contractor had joined together two 150 hp four wheel drive tractors with a chain and another chain to the combine. All eight wheels of the tractors were spinning plus the combine wheels.
The contractor asked me if I thought that "Daisy Etta" my 1956 Caterpillar D7 could pull it out. I told him I did not know as I had only recently bought it. It had a big blade on the front. We chained it up.
Pete, one of the old school tractor drivers with a pipe, said "Well if two " expletive" tractors could not pull it how to you think that "expletive" is going to do it?
Anyway sat on the old girl and gently pulled the clutch lever to introduce 14 litres of Cat's finest. Only 120 hp but massive torque at very low revs and all that traction with maybe nearly 20 tons of weight.
The engine only grunted, no track slip and the combine popped out like a champagne cork!
Pete's pipe dropped out of his mouth followed by another expletive!
America's finest leads the World!

 

[davidwyby]

My only experience was when I had a contractor here on the farm with a New Holland TF46 combine that had driven over a Spring hole in an otherwise very dry field and was stuck with one drive wheel spinning. The contractor had joined together two 150 hp four wheel drive tractors with a chain and another chain to the combine. All eight wheels of the tractors were spinning plus the combine wheels.
The contractor asked me if I thought that "Daisy Etta" my 1956 Caterpillar D7 could pull it out. I told him I did not know as I had only recently bought it. It had a big blade on the front. We chained it up.
Pete, one of the old school tractor drivers with a pipe, said "Well if two " expletive" tractors could not pull it how to you think that "expletive" is going to do it?
Anyway sat on the old girl and gently pulled the clutch lever to introduce 14 litres of Cat's finest. Only 120 hp but massive torque at very low revs and all that traction with maybe nearly 20 tons of weight.
The engine only grunted, no track slip and the combine popped out like a champagne cork!
Pete's pipe dropped out of his mouth followed by another expletive!
America's finest leads the World!

Great story, thanks.

 

[Billhook]

BTW it is Daisy Etta in my Avatar, levelling the chalk roads on the farm with the blade angled, helped by my two Airedales, Gillie and Lena ( name came from a story by Theodore Sturgeon called Killdozer where the Mexican driver referred to the D7 as De Siete. but everybody thought he was naming it Daisy Etta)

 

[catbuster]

What we now commonly refer to as a bulldozer was for the longest time known as a track type tractor, and Caterpillar will still refer to them as such in many occurrences.

In the vast majority of applications a bulldozer/crawler tractor will put more tractive effort to the ground than anything on tires, pound for pound, and especially if we’re looking at equal horsepower. Pulling or pushing non withstanding. It’s all at the expense of speed, though. I doubt you’ll find a dozer doing more than 4 miles per hour whereas skidders top out at probably five times that and tractors in the 30s.

 

[Bubster]

I know a 977L Cat trackloader with street pads can snap a 1/2 inch chain in 2nd gear at idle. I can't count the chains I snapped with that ol brute. If they didn't snap, they could stand up by themselves after a good load. But a logging arch as on a skidder or dozer does do wonders if you can keep the front end down.