question of tyres

[jac]

Simon and myself are trying to put together a wheeled sledge for timber extration.. Picture a bunk about 16″ off the ground on 12″ x mabey 8″wide tyres… question is this… a 1 ton log of 12′ with 3’over the front of the bunk.. what is the actual load on the tyres bearing in mind we have foot wide skids around the wheels with only 3″ below skid level ?? doesn this make ANY sense :o… thanks in advance Andy haha

[Tim Harrigan]

John, you could probably make it complicated but with a 12 ft log at 2000 lbs you are basically 167 lbs per foot or about 500 lbs over the bunk plus 1/2 of the rest of the log so 500 + 750 = 1250 lbs. If the sled and rider, if it is built for one, add another 500 lbs you would have 1750 lbs / 2 tires = 875 lbs/tyre. Not an excessive load for most vehicle or utility tires. That is, if I picture your sled correctly.

[jac]

Thanks Tim.. we will be able to get foot high tyers to suit that ok.. Thanks again.. this forum rocks !!!! …. John

[Tim Harrigan]

John, I replied too quick when I was heading outside they I realized I overlooked an important part. Re-read it, I corrected it. It is actually a little more complicated than that because of the tilt of the log and the overhanging log but that is pretty reasonable for the purpose of this type of equipment.

[Andy Carson]

Hey john,
I am glad you are doing this. I have had ideas about partially wheeled sleds that have been rolling around in my head for a while and I am excited to see what you come up with. The idea seems great, but braking could be a limiting factor depending on how you rig it up. Are you going to have a pole to hold the load back? If you have 2500 lb load, and are only dragging 750 lbs, you only have maybe 375 lbs of drag. The whole thing could take off on you on a downhill of 15% or more. Something to think about… if you put the wheels behind the bunk and elevate them compared to the runner height, the wheels will only engage when there is a pull in the front of the sled, which elevates the front sled runner. In a braking situation, where there is no pull in the front, the runners would be engaged ( not the wheels). If designed carefully, you could have the draft advantages of wheels, and the brake and loading advantages of a sled, best of all, the braking would be automatic and exactly proportional to the load. If you put a pole on this, you could have even better braking than with a sled b/c braking would essentially jackknife the front of the sled into the ground. Something like this is what I kept toying with in my mind. Feel free to take it if you want. I am curious to see what you come up with. 😮

[simon lenihan]

Andy,
scandinavian sledges were in the most part designed for the single horse, however it is no big deal to convert to a pole for a team. i agree that a pole will assist braking but it is not really necessary as there is a sledge designed to cover most terrain and slopes. Picture 1 is of a sledge i owned many years ago, this was a super piece of kit and believe me i had it on slopes greater than 15 degrees, on steep slopes i would load with the light end on the bunk with the butt end acting as a brake. The wheels had several adjustments to raise or lower the sledge, where the wheels lost contact with the ground the skids took over. The whole unit was hinged at the bunk so we had complete articulation.
Pic 2. This is the bergan wheel sledge, this is a sledge for serious slopes and this sledge has a trailer attachment for total suspension. The braking system on this sledge is simple and has been around for yonks. When the sledge starts to run, the runners push down on the crossbeam pushing the end of the shafts into the ground. It is my opinion that all sledges should have wheels of some size to assist the horse, better again if the wheels can be removed when working on snow or mud. Its like scoots on bare round every time i see one i think how much better and efficent these would be with wheels on. If you can increase your load size by even 5% every trip out of the woods with wheeled equipment it sure adds up at the end of the year. Happy saint patricks day to all on the forum. simon

[Andy Carson]

Very nice. Thanks for sharing Simon. Both of these designs have the bunk placed ahead of the wheels (just a few inches in the first picture, a few more inches in the second) and they would have the automatic braking effect I was referring to. All these neat little ideas that seem to roll around in my head seem to be already invented by Scandanavians. Funny… I really like these designs, particularly the red one.

[jac]

We plan to base it on the 1st foto but had hoped to use a wider wheel an skid… is there an optimum width of skid to use before the friction of the skid overtakes the carrying benefit ?? the 1st machine can be doubled up to make a 4 wheeled forwarder which looks pretty cool too…

[Andy Carson]

Are you making this for one horse or two? How much articulation will there be between the from of the the runners and the shafts or pole? This might seem to not matter much, but if the runners are able to lift up a little in the front, it would put almost all the weight on the wheels. If this happens, the skids would primarily be for braking and would change how they might be designed.

[jac]

It is mainly ment to be a single horse machine Andy… the shafts on Simons foto were fixed and there is only forward and back articulation at the end of the bunk.. you can just see the pin in the foto..I have dabated with Simon over whether the shafts should be able to move up and down freely but as im a beginer at logging on a big scale Im not sure..was just looking at it from an engineering point of view an thought it would give another bit of articulation and act like an automatic brake when the horse sits back in the breeching ?? havent welded anything up yet and Im hoping Simon can nip over one nite this week to have a look .. getting plastic for the skids is proving hard..and freakin expensive too !!! like £97 a skid..any ideas on that front….

[PhilG]

Jac
we get some plastic barrels over here from blown in insulation, cooking oil and other stuff that is pretty tuff, a couple layers might last a season, about $20 for used barrels, some free.

[jac]

thats a great idea Phil.. wouldnt mind changing it even twice a year if its cheap … John

[Andy Carson]

@jac 33487 wrote:

I have dabated with Simon over whether the shafts should be able to move up and down freely but as im a beginer at logging on a big scale Im not sure..was just looking at it from an engineering point of view an thought it would give another bit of articulation and act like an automatic brake when the horse sits back in the breeching ??

From where I’m sitting, I think your are both right. Verticle articulation would not only act as an automatic brake when the horse sits into the breeching, but would also maximally load the wheels when it pulls and take most of the load off the skids. A good thing in my mind. If you had unlimited articulation, however, you would just pull the wheels out from beneath the thing and it would flip backwards. You could have the best of both worlds if you found a way to limit the articulation such that the skids could be lifted up off the ground, but the wheels couldn’t be pulled out from underneath. Lots of ways to do this on paper, and I think you know what I mean. That one of the things I really like about the red design in the photo. It looks to have limited articulation from those chains, although I can’t exactly figure out how that central connector works… Perhaps this is a tilt limiter or sorts?

[near horse]

I thought John Plowden used this plan (seen in Simon’s post) as a prototype and built something similar (he had it at NEAPFD 2010). There should be some pics somewhere (maybe on here).

[carl ny]

I know this is kind of an old thread but I just found this site a few weeks ago. Just an observation,tall tires will roll a lot easier,also narrow tires will roll easier and go through the mud easier also. JMHO

carl ny

[Author]

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