Track Ground Pressure "kPa"

[Allan M]

I'm curious to what degree track ground pressure is a factor in the purchase and use of excavators. I think a 20k lb machine might have the same track PSI as my 12.5k lb machine. Is it normal for excavators to have less that 10 PSI ground force exerted by the track? I would think that in some situations more track PSI would mean greater traction and an advantage; in other situations less track PSI would be desirable or you wind up using bog mats or destroying delicate surfaces.

Also, do steel tracks generally offer a lower track PSI ground force than rubber on the same machine? I'm thinking that steel tracks actually have better ground contact than rubber tracks of a similar size.

 

[ronbourd]

When we talk about track ground pressure, we need to take in account that on small excavator with rubber tracks , when there is only 3 smalls carrier rollers , plus the big front idler and the sprocket ,that supports the total weight of the machine. the load is not equally spread on all the surface of the track that contacts the ground. This is the reason that an excavator with rubber tracks leave a very heavy footprint on soft ground.(grass). On a snowmobile ,the track rides on slides, so all the surface contact is equal, and it "floats" much better! Did some of you ever try to add more rollers so the the track would be better supported at more places than only at 3 places... Thanks for yours reply...Ronald Tb016..

 

[mudnducs]

I'm positive the manufacturers simply divide the running weight by the area of the track on the ground. An engineering analysis of the track load would be difficult with many simplifying assumptions....and pointless...and nobody cares anyway. I think its more of a marketing ploy than anything else.
2 cents

 

[ronbourd]

If the rubber track would be support by more rollers on the ground, the track could have better chance to last longer...

 

[KSSS]

It likely would last longer, since the track wouldn't flex as much but it would be brutal to drive. The position of rollers allow some flexibility of tracks to help stop some of the "teter toter' effect of moving over uneven ground. It also allows more of the track to stay in contact with the ground and give more traction. The ASV/MTL track is very effective as it has a ton of rollers, but they are suspended and there is no steel in the track only Kevlar (more flexibility) That allows the track to flex over the terrain, keeping more track on the ground and with the rubber covered rollers it is quiet and comfortable to run. Downside of course is the maintenance can be brutally expensive depending on where and how you run it.

As it is, selecting a tread design for tracks on a mini excavator is pretty important as it is for a CTL. The overall pressure that an excavator puts on the ground I think can be pretty important. I agree that the number is pretty generalized. It likely varies over different parts of the track. My 6 ton machine puts 6 pounds per square inch. One of the reasons they imprint on grass is due in part to tread design and depth. The 6 psi is over the whole track. The track with say a 50 percent void layout puts a lot more weight on top of the tread, it tends to sink until it gets past the tread to the belt itself. Anyone that has a set of about wore out tracks and crosses grass knows that to be true. The damage is a lot less because the weight is carried by the belt instead of the tread.

 

[Allan M]

Input from John C., Senior Member, that he gave me directly. I thought that sharing his insights might be useful to others. Thx. Allan

“Ground pressure is a big deal if you are working in any kind of soft ground. It is the amount of surface area of pads on the ground divided by the weight of the machine. Wider pads means more surface area and less pressure on the ground while narrow pads means the opposite. It makes a big difference on large machines like say a 100 ton excavator having 36" and long track frames with three top rollers. Wide pads do cause more wear on the track chains so on dozers you want to run with pads as narrow as you can to extend life as long as you don't have to work in some soft material. So to your question about a larger machine, yes they can have the same amount of ground pressure.


The other part of that conversation was about rollers point loading against the ground with rubber tracks. On standard tracks the rollers ride against the track chains which equalize out the point on the roller. On rubber tracks there is a little bit of point load but the bands seem to do pretty good at spreading it out so that it isn’t a total point on the ground. The other part of band tracks is that they usually go on smaller machines. What has changed on that are the agriculture machines.”

 

[Willie B]

When we talk about track ground pressure, we need to take in account that on small excavator with rubber tracks , when there is only 3 smalls carrier rollers , plus the big front idler and the sprocket ,that supports the total weight of the machine. the load is not equally spread on all the surface of the track that contacts the ground. This is the reason that an excavator with rubber tracks leave a very heavy footprint on soft ground.(grass). On a snowmobile ,the track rides on slides, so all the surface contact is equal, and it "floats" much better! Did some of you ever try to add more rollers so the the track would be better supported at more places than only at 3 places... Thanks for yours reply...Ronald Tb016..

I don't often use an excavator. I have always had a backhoe. When I dig for a customer, I "run what I brung". Early week I had a small change order job for a customer I had advised to buy a backhoe, not an excavator. His property is steep! He has two parcels 2 miles apart by road. I felt the better ability to move at a moments notice made the backhoe a better choice.

He went ahead & bought a Kubota 8 ton on rubber.

I was disappointed, it tears up lawn something awful! The house is on the peak of a steep hill. Lawn surrounding it is steep. I could approach with a backhoe, set, and do the small excavation needed. When complete, I'd use a couple hand tools to level out the lawn where the stabilizers & bucket had been. With the excavator, it was 1/4 acre! I couldn't move straight on the tilted lawn without tearing up sod!

 

[Don.S]

That is user error. A good operator can run a mini like that and leave very little marks.

 

[Willie B]

That is user error. A good operator can run a mini like that and leave very little marks.

This is 8 tons, I don't think of it as a mini.

I couldn't go straight! It wanted to slide down hill, not dangerous slide, just enough to bugger the sod. Only way to turn, was swing the boom uphill, then it'd slip sod loose, but turn. I'll prefer steel tracks. My preconceived notion was that rubber tracks would be easier on sod.