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post #1 of (permalink) Old 11-25-1999, 02:24 PM
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Axles\' weight

Does anyone happen know know the typical weight of different axles? Is there a web page out there somewhere with this information?
I wam wondering about the weight differences between Model 30s, Dana 44s, Dana 35s, Ford 9"s, etc. I don't necessarily want to haul around more unsprung weight than I have to but if a Dana 44 doesn't weigh that much more than a 30 (for example) that I'll go with more beef.

Thanks.

Harry

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post #2 of (permalink) Old 11-25-1999, 03:40 PM
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Re: Axles\' weight

dana 44's not much heavier than a 30, maybe 50-100 lbs tops. a 9 inch or dana60 is heavier by a fair bit.

post #3 of (permalink) Old 11-26-1999, 09:09 AM
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Re: Axles\' weight

Don't know the weight differences per axle, but do know that my CJ-2 gained 1200 lbs. with an axle swap (swapped in a dana 44 and dana 60) and a V8 conversion. Question: Is un-sprung weight a bad thing in a 4x4, seems like it would help the tires bite a bit more, and help with articulation
Rob

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post #4 of (permalink) Old 11-26-1999, 09:25 AM
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Re: Axles\' weight

[img]/wwwthreads_images/icons/tongue.gif[/img] Unsprung weight is rarely a good thing. You have zero control over how much sits on each tire, and the axles or suspension doesn't respond as good to the changing conditions of the road. I was in oval track asphalt racing for several years, and we did everything possible to reduce unsprung weight. Traction is usually a function of how well the suspension works at getting the vehicle weight where it needs to be.[img]/wwwthreads_images/icons/tongue.gif[/img]

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post #5 of (permalink) Old 11-26-1999, 05:28 PM
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Re: Axles\' weight

Wouldn't your unsprung weight be more effected by the weight ouside the springs (hence the term unsprung weight?). I autocross some and to lower the unsprung weight of the car you run the lightest wheels that you can find. Of course the RX-7 I race has coil springs and independent front and rear suspension and I am not sure how you would compare the geometry to that of a Jeep. I guess the question you would have to ask yourself, would be, if it was worth giving up some road worthiness for stouter axles. And if you want to run large tires which weight alot more than small tires, a heavier duty axle would be better (remember none of the weight of the tire and rim is supported by the spring but by the end of the axle).


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post #6 of (permalink) Old 11-26-1999, 05:58 PM
 
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Re: Axles\' weight

My yard is like sanford and son. I got 27, 30 and 44 laying around. Everytime I need a certain part i must move axles. They really is not much different in weight between all three. I think most of the weight going to be in the big tires you run. i think the different between a 44 and 27 might be no more than 20 lbs. If you want to get rid of weight, Run small 28 tire , no more than 5 gallon in the tank, no hard top or doors, ditch the rear seat, no winch, cable, passagers or hi lifts. ditch a/c compressor, roll bar, windshield, toolboxes and even that 16 oz coke.

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post #7 of (permalink) Old 11-27-1999, 08:47 AM
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Re: Axles\' weight

I would agree with you in the case of Circle Track racing, or Drag Racing. But I've never seen a Jeep doing either. At the low speeds required in trail driving or rock crawling, a higher unsprung weight acting on the springs should allow that axle to follow the trail better.
I never ramped my CJ with the stock axles, but there were a few times that my riders would have to bounce on the bumper to get traction to a wheel. With the axle conversions, it ramped a 980, and there's no more bumper bouncing required. I did add a few inches in width to the axles when I converted them, and that also helps with the articulation.
Just my thoughts, as I don't know the math. It just seems that if you have 50 lbs. acting o
post #8 of (permalink) Old 11-27-1999, 09:15 AM
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Re: Axles\' weight

[img]/wwwthreads_images/icons/tongue.gif[/img] I know this unsprung weight thing is difficult to really get your mind around sometimes, but it IS true, and it DOES actually make it tougher for a vehicle to handle right, and especially to stop. When the Army had the Humvee built, they went to independent suspension to get good ground clearance of course, but the other reason was "unsprung weight". If all the stuff wasn't so weak and chintzy, some IFS and IRS systems would have merit off road, but they rarely are well built enough to take much abuse. The modern SUVs with the independent front suspension are strictly a pavement and concrete driveway machine in my opinion. Just try to visualize a pair of huge off-road axles with a rail frame, a seat, and a Volkswagen engine; that would put the unsprung weight at a max, and handling would be; at the very least; tricky, since there would be no real suspension load to get downpressure and bite. No doubt there is a ratio that automakes work with between GVW and unsprung weight. Did you ever drive a truck-tractor with dual rear axles and NO semitrailer? Sheesh! Talk about unsprung weight. It's like you are MARGINALLY in control, but not much more. If anything happens and you have to maneuver, forget it![img]/wwwthreads_images/icons/crazy.gif[/img]

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post #9 of (permalink) Old 11-27-1999, 11:37 AM
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Re: Axles\' weight

CJDave I know that you know what you are talking about, no doubt in my mind that you are right, BUT it doesn't make sense to me. If you are moving fast and worried about precise control at high speeds, low unsprung weight. But I would seem to think that in a Jeep(or other suitably equipped 4x4) that on a trail you would want the heavier axles to keep the wheels on the ground?? Now I am probably wrong but I just can't understand why??

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post #10 of (permalink) Old 11-27-1999, 04:39 PM
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Re: Axles\' weight

There is an important relationship between 3 things here.
1) Weight of axle, tires, wheels etc. - UNsprung weight
2) Weight of the rest of the vehicle - Sprung weight
3) Strength of the springs.

You have to consider the springs THREE different ways.
1) Support of the vehicle ABOVE the springs
2) Restraining factor on remaining portion of the veh BELOW the springs.
3) Downward force exerted by the spring.

It is actually the percentage of unsprung weight to total vehicle weight that is important as long as the springs are properly rated for the load. Vehicle control is at its ultimate when each wheel exerts the same amount force (weight) on the ground.

Go to each extreme. 100% sprung vs 100% unsprung. 4,000 pound vehicle equally divided on each tire (1,000 pounds per tire).
100% SPRUNG. A vehicle whose wheels, tires and axle weigh nothing. The strength of the springs is adjusted so that each spring has good flexability when 1,000 pounds is sitting on it. One wheel drops into a hole. Our goal is to keep 1,000 pounds on each wheel at its contact with the ground. On this 100% sprung vehicle what causes the wheel to go downward into the hole. Can't be the weight of the axle, because it weighs nothing. The tension on the spring which is created by the weight it is holding up forces the wheel downward. So the wheel does not DROP into the hole, it is PUSHED into the hole by the tension on the spring.
100% UNSPRUNG. In this case the springs will do nothing because there is no weight on top of them to compress them. Each wheel still has 1,000 pounds on it. Each wheel will follow the contours of the ground just like the 100% Sprung vehicle, but what happens to the portion of the vehicle above the springs? Our magic vehicle still has a body, seats, engine and all. It just weighs nothing. Since there is no weight above the springs, there is no spring action. When a wheel drops into a hole, all that force is transmitted to the portion of the vehicle above the springs. It is just as if the axles were solidly mounted with no spring action at all, so if the body of the vehicle does not twist, the wheel will not drop. Either that or the wheel on the opposite corner will raise up off the ground. Again, even in this case when ALL the weight is below the springs, it isn't the axle weight that causes the wheel to drop into the hole. It is the spring action pushing it down, and in this case since there is no spring tension and no spring action, the wheel does not follow the contours of the ground.
As our mythical vehicle proceeds from 100% UNsprung toward 100% Sprung, the closer it gets to 100% sprung, the more evenly the downward force is exerted at each wheel WHEN UNEVEN TERRAIN IS EXPERIENCED and the less effect the uneven terrain has on the sprung portion of the vehicle.
A guess on my part, but a graph of the effect of going from unsprung to sprung would probably start off at a small incline then increase until it got into the 75% or so sprung range where the incline would start to flatten until it reached 100% sprung. If this is the case, changing the axle weight of a fairly well balanced vehicle would have some effect, but not a great deal of effect unless the weight change was substantial, because the sprung weight, body etc., is in the upper portion percentage wise of the total weight - the area where the curve is in its flattening stage at the top of the graph.

In the expample that CJDave gives - the tractor/trailer - removing the trailer puts the sprung weight way down the graph where not only does each pound have more of an effect individually, it is also way down in an area where the strength of the springs needed to support the vehicle when fully loaded causes the axles to act as if they are solidly mounted to the frame with no spring action at all. This is a good example of not only too much unsprung weight, but also springs that are not properly rated for the work load. If you took that same tractor, reduced the strength of the springs to work properly WITHOUT the load of the trailer, the handling would be much improved. Newer tractors have accomplished this by using air bag suspension instead of springs. The bags are aired up to a certain HEIGHT. More weight equals more air pressure to attain the proper height - less weight, less air pressure which results in a much better ride both loaded and empty and better handling characteristics. The practicle effect is "adjustable spring strength".
Final thought: As speed increases, balance becomes more critical. Balance is less noticable in an engine running at 1,000 rpms than at 10,000 rpms. An out of balance engine might run for years at 1,000 rpms and seconds at 10,000 rpms before it shakes itself to pieces. Using the same logic, a vehicle traveling at high speed is much more vunerable to the "out of balance" condition created with high percentages of unsprung wight than it is at low speed. REASONABLE changes in unsprung weight will probably have very little noticable effect on slow moving off road vehicles. Large changes in unsprung weight would have a noticable effect on body lean since the weight of the axles would tend to pull the vehicle toward the distended wheel more so than a lighter axle and tire wrould, but this gets into the area where the springs are no longer acting as support for the weight above them and instead are acting as a restraining device to prevent the wheel from destending any further - again having the characteristics of a solidly mounted axle. When the springs begin to restrain the axle instead of pushing it down, the traction and handling characteristics begin to sharply decline.


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