Choosing your axle capacity?

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Choosing your axle capacity?

Postby Section 8 » Mon Sep 10, 2007 8:14 am

How are you guys choosing your axle capacity based on your intended travel weight for the offroad trailers? Aside form uprating the actual axle and downrating the suspension to get som extra toughness and keep your ride acceptable, is there a rule of thumb for Choosing the right axle capacity? I have read in other forums on the board that people usually get their axles for 50% over their typical traveling weight, is this what the rough road trailer builders are doing as well?

Thanks.
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Postby jagular7 » Mon Sep 10, 2007 8:29 am

Look at it in a way of size and weight. Take a 1000# axle rating vs 3500# axle rating. The size difference is tremendous, but the weight is considered minimal. Size plays a big part in capacity. Weight plays a big part in towing capacity of the tow vehicle.

I've gone with a 3500# axle using 14" tires. From a 2300# axle, there is a size difference just due to the capacity rating. But the weight difference was only 18# for the axle. I also added electric brakes and a parking brake for a minimal charge when I ordered the Dexter axle. For offroad, I'd be more concerned with the structurability of the trailer frame and suspension to absorb the impacts of the variations of the road at speed.
When driving, put your hand over your vehicle's door gap. You can feel the door gap get larger and smaller. Imagine that amount of twist on the frame of the trailer.
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Postby Gerdo » Mon Sep 10, 2007 10:55 am

I went with a 3500# axle also. I did pull out the smallest leaf from the spring pack (1 of 4) I first towed it with all 4 leafs and it was hard. Much better with 3 leafs. I also added shocks. They made a huge difference.
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Postby Section 8 » Mon Sep 10, 2007 11:18 am

Thank you mike. I guess that I am not wording my question properly.

I was initially planning a 1500 pound capacity Torflex, but I think that my finished weight is going to be no more than 600-800 pounds, since it seems that my camping gear doesn't weight nearly as much as I thought.

The lady at Dexter was not helpful at all, in deference to what everyone else has said. I must have got her after something unpleasent or something. Anyway, she was generally evasive about making any recomendations, and basically replied to any wauestion about what to order with "That is for the designer of the axle to determine" or "we build axles to specifications specified by the designer". Absolutly no help in helpig me decide "how much" axle I need for a particular trailer weight.

How do I determine the capacity of the axle that I want? If the trailer estimate ends up being 600# without the axle, should I order a 900# capacity axle, and simularly if the trailer estimate without axle is 800# go with a 1200 pound axle?

I am building something like this:

http://expeditionportal.com/forum/showthread.php?t=5864
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Postby madjack » Mon Sep 10, 2007 12:54 pm

8, I always recommend a 50% over capacity...we build our trailers with a 1500# capacity axle even though the trailer weight is around 800#s, this gives extra capacity for ANY gear we might want to bring along...also, if you want 900# axle, it wil be the lighter weight axle(#7 Torq) the next step up is rated to 2200#s and can be derated to 1100#s(I think), so you get the capacity you want in a unit with heavier running gear........
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Postby Section 8 » Tue Sep 11, 2007 10:13 am

Gerdo wrote:I went with a 3500# axle also. I did pull out the smallest leaf from the spring pack (1 of 4) I first towed it with all 4 leafs and it was hard. Much better with 3 leafs. I also added shocks. They made a huge difference.


I didn't see your post the last time I posted. Thats weird, thanks for your reply as well!
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Postby Section 8 » Tue Sep 11, 2007 10:25 am

madjack wrote:8, I always recommend a 50% over capacity...we build our trailers with a 1500# capacity axle even though the trailer weight is around 800#s, this gives extra capacity for ANY gear we might want to bring along...also, if you want 900# axle, it wil be the lighter weight axle(#7 Torq) the next step up is rated to 2200#s and can be derated to 1100#s(I think), so you get the capacity you want in a unit with heavier running gear........
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I don't want to be a pain in the rear, but being a numbers guy as well as a first time builder (aka AAANAAAL)... Do you mean 100% over capacity? Your example is about 87% over capacity which leads me to believe this is what you mean. Or in other words, the trailer is only 50% of the axle's rated capacity? Or am I just reading to far into it, and you just spec your axles on the heavy side?

I will be using (approximate, actual size is metric) 31x8 inch E load rating tires, would this make any difference in how much "extra" you would rate the axle for to keep it rolling smooth? The backspace of the wheels is going to make installing a shock very diffacult as the torsion arm is going to be inside of the wheel, and I don't feel like designing a crazy 4 bar system for it. :lol:

Thank you.
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Postby madjack » Tue Sep 11, 2007 10:37 am

...we spec a 1500# axle to allow for a 1000# trailer...or 50% over capacity...I wouldn't add shocks to a torsion axle...they aren't needed since that is one of the features of a torsion axle(built in dampening).......
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Postby Section 8 » Tue Sep 11, 2007 12:38 pm

Thank you very much.
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Postby brian_bp » Wed Sep 12, 2007 7:17 pm

Selecting reduced-length rubber rods to "derate" and soften a rubber torsion axle is like using fewer leaves in a leaf-spring system: the rest of the components keep the full rated capacity, but the springs are better matched to the load (and still need to be kept highly rated enough for the maximum load).

madjack wrote:...I wouldn't add shocks to a torsion axle...they aren't needed since that is one of the features of a torsion axle(built in dampening)....

Any leaf-spring axle has built in damping as well (by interleaf friction or a sliding "slipper" end). Although the rubber-sprung axles are apparently better - and good enough for most people - they are equipped with shock absorbers as an option in Europe, and as standard equipment on Airstreams.

I'm not saying you need shocks, only that they are beneficial, even with a rubber-sprung axle. How much? Who knows.. it depends on the trailer and towing conditions.
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Postby angib » Thu Sep 13, 2007 6:21 am

brian_bp wrote:Although the rubber-sprung axles are apparently better - and good enough for most people - they are equipped with shock absorbers as an option in Europe

In Germany, possibly the strictest country in the world for automotive things, having dampers even on a torsion axle is one of the requirements to get your trailer into the higher of the two speed limits they have for towing.

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Postby jimqpublic » Tue Sep 25, 2007 10:43 am

Another consideration is brakes- If you're going to use 13" or bigger wheels then you can go with the 10"x2" drums which have more than double the braking area of the smaller 7"x1-1/4" brakes. This would be important if you're in steep mountains with big tires.

The lightest duty axles are only compatible with the smaller brakes.

On the rating- I don't know. We have leaf springs rated for 2900# (3 leaves). With approximately 2200 pounds of load we broke both sides on one trip with very rough extreme washboard and potholes. After getting back home we added the Dexter shock kit and haven't had a problem in the 5 years since- plus the trailer rides noticably smoother on bumpy roads. I considered going up to 4 leaves to match the 3500 pound rating of the frame and axle but feared that would make the ride too rough on the contents.
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