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[Andrew Gibbens]

With leading arms the brakes will not work as well.

I can't see why this is true. If fitting a new axle (that had been designed and built to work with trailing arms), I can see there would be some sense in swapping the brakes over so what the manufacturer thought was the LH brake was still mounted on the left when the axle has been switched to a leading arm orientation.

But I can see no reason why the brakes would not work as well - indeed, if anything, I'd expect an improvement. As leading-arm axle will rise (ie, anti-dive) on braking, it will be slightly more resistant to snatch-locking when first applying the brakes.

Andrew

[Benny K]

I think that the problem with a leading arm suspension brake is that if the brakes are applied, then the trailer would want to lift itself up using the brake arms as a pivot point....in a trailing arm situation it would simple drag.....just like when it absorbs shocks as it pushes up, squishing the rubber, then it would want to lift the trailer and try squishing the rubber in the opposite direction and this could possibly really make the trailer bounce on the road like a ball .....does this make sense? If not, then push a pencil forward on desk with a slight down ward angle and put your finger in front of it to resist forward motion and as you keep pushing, it will try to lift the back end of the pencil over the front and if the front of the pencil had some traction it would start to hop.......can`t think of a better way to explain myself without a drawing, LOL....Benny

[Roy in TO]

I think that the problem with a leading arm suspension brake is that if the brakes are applied, then the trailer would want to lift itself up using the brake arms as a pivot point....in a trailing arm situation it would simple drag.....just like when it absorbs shocks as it pushes up, squishing the rubber, then it would want to lift the trailer and try squishing the rubber in the opposite direction and this could possibly really make the trailer bounce on the road like a ball .....does this make sense? If not, then push a pencil forward on desk with a slight down ward angle and put your finger in front of it to resist forward motion and as you keep pushing, it will try to lift the back end of the pencil over the front and if the front of the pencil had some traction it would start to hop.......can`t think of a better way to explain myself without a drawing, LOL....Benny

Better get that pad and pencil out Benny, draw that picture, scan it and upload it.
I was thinking along the same lines. Tried comparing it to a bicycle with caliper brakes, hit the front ones too hard and you can fly over the handle bars.

Leading edge would want to make the trailer rear lift on braking, but if you think about it, that will cause a weight shift (more correctly a vector force) to front of the hitch. While at the same time the rear of the TV rises as it's nose drops. The two should somewhat counter act each other and tend to keep both more level something like a counter balance.

OTOH with a trailing edge the load comes off the axle when braking and making the tires more prone to skidding. (using the bike analogy).

Now I'm more confused

[Benny K]

Don`t feel bad Roy, Sometimes think, along with every body else on this site, that I`m always confused,LOL....but like I said on an earlier post, I have another axle and may make up a jig to fit over the axle shaft, and weld brake backing flanges onto it just for the fun of it when I get a chance.....and on the tires skidding or hopping, I think that would depend whether the leading type axle was down or up in relation to centre....up and it would possibly skid and I think if was 25 degrees down it would try to lift... ....One time I had a car trailer with brakes on both axles and when it was empty and at about 45 mph I dynamited the brakes with the controller to see what would happen and this made the trailer jump about a foot off the highway, (made sure there was no one around me), and assume that spring windup made it act like that because there way no extra load on the trailer....with a car on it the wheels probably wouldn`t have locked up and the result would have been different...if they had locked up the trailer may have skidded....?....If I had brakes on my 13' I`d try panic locking the trailer brakes on the highway just to try it.....Benny

[Don Meyer]

The brakes on a leading arm axle will not stay in contact w/the road as well as a trailing axle..........Don Meyer

[Roy in TO]

The brakes on a leading arm axle will not stay in contact w/the road as well as a trailing axle..........Don Meyer

My inquisitive mind would like to better understand how this is the case.

It's one of those concepts that needs a little explanation to get the neural pathways to connect with it. Even with a bit of a mechanical background and university level physics it took a bit of mental gymnastics to understand how anti sway bars on a car or weight distributing hitches worked.

Sounds to me like you might just be the guy that can explain it. Would you mind helping me understand the concept Don?

Roy

[Byron Kinnaman]

My inquisitive mind would like to better understand how this is the case.

It's one of those concepts that needs a little explanation to get the neural pathways to connect with it. Even with a bit of a mechanical background and university level physics it took a bit of mental gymnastics to understand how anti sway bars on a car or weight distributing hitches worked.

Sounds to me like you might just be the guy that can explain it. Would you mind helping me understand the concept Don?

Roy

I was wondering the same thing. Don, could you shed some light on how that would work?

Thanks

[pjanits]

My two cents.

Whatever you choose to do just remember to leave enough slack in the brake magnet wires to go along with the swing of the axle.

The guy that had my trailer didn't and the wires sheared right off.
Brakes were never used at all. Good for me tho, I just fixed the wires and I had brakes.

[Don Meyer]

My inquisitive mind would like to better understand how this is the case.

It's one of those concepts that needs a little explanation to get the neural pathways to connect with it. Even with a bit of a mechanical background and university level physics it took a bit of mental gymnastics to understand how anti sway bars on a car or weight distributing hitches worked.

Sounds to me like you might just be the guy that can explain it. Would you mind helping me understand the concept Don?

Roy

The leading arm axle wheels bonce when the trailer rises & they loose contact w/the road. The trailing axle does not loose contact since when the brakes are applied the trailer squats placing more of a load on the tires, thus keeping them in contact w/the road.

Don

[Andrew Gibbens]

The leading arm axle wheels bonce when the trailer rises & they loose contact w/the road. The trailing axle does not loose contact since when the brakes are applied the trailer squats placing more of a load on the tires, thus keeping them in contact w/the road.

Don,

I'd say the exact reverse of what you've said:

While the leading arm axle is trying to make the trailer rise, it will have more contact with the road - the wheel is pressing harder into the road to make the trailer rise.

And while the trailing arm axle is trying to make the trailer squat, it is pressing less onto the road, and so will be more liable to lock up.

Once the trailer has finished rising or squatting, the load on the wheels is the same, whatever suspension it has - all of them have to obey Netwton's 2nd law!

Andrew

[Roy in TO]

Don,

I'd say the exact reverse of what you've said:

While the leading arm axle is trying to make the trailer rise, it will have more contact with the road - the wheel is pressing harder into the road to make the trailer rise.

And while the trailing arm axle is trying to make the trailer squat, it is pressing less onto the road, and so will be more liable to lock up.

Once the trailer has finished rising or squatting, the load on the wheels is the same, whatever suspension it has - all of them have to obey Netwton's 2nd law!

Andrew

I've been thinking about this, but don't have an answer yet, maybe if we put our collective minds together we can come up with the answer. All I get is more questions. I suggest we start off using the same example and discussing it from there.

Imagine we are standing curbside watching a trailer go by from the left hand side of the screen to the right. The trailer wheel will be turning clockwise. If the trailer brakes are applied the resultant force on the arm will be clockwise.

For the leading arm, that means the brake force will tend to lift the trailer up at the axle.
For the trailing arm, the resulting force will tend to pull the trailer down at the axle.

In both cases, there will be an increase in force on the torsion suspension, not a shift in the direction of the force.

Is everybody OK with that so far? From here on, I think we need to set some standards for discussion. If not, then things start getting a little too complicated. I wouldn't mind disscussing the effects of some of these things afterwards though.

Lets assume the trailer is connected by a regular hitch, not a weight distributing hitch.

Assume the leading arm has a -ve start angle and the trailing arm a positive start angle as my understanding is these are the typical design. Next we have to determine whether the trailer braking is greater than, equal to or less than that of the tow vehicle. Who wants to pick one and carry on from there?

[Don Meyer]

I've been thinking about this, but don't have an answer yet, maybe if we put our collective minds together we can come up with the answer. All I get is more questions. I suggest we start off using the same example and discussing it from there.

Imagine we are standing curbside watching a trailer go by from the left hand side of the screen to the right. The trailer wheel will be turning clockwise. If the trailer brakes are applied the resultant force on the arm will be clockwise.

For the leading arm, that means the brake force will tend to lift the trailer up at the axle.
For the trailing arm, the resulting force will tend to pull the trailer down at the axle.

In both cases, there will be an increase in force on the torsion suspension, not a shift in the direction of the force.

Is everybody OK with that so far? From here on, I think we need to set some standards for discussion. If not, then things start getting a little too complicated. I wouldn't mind disscussing the effects of some of these things afterwards though.

Lets assume the trailer is connected by a regular hitch, not a weight distributing hitch.

Assume the leading arm has a -ve start angle and the trailing arm a positive start angle as my understanding is these are the typical design. Next we have to determine whether the trailer braking is greater than, equal to or less than that of the tow vehicle. Who wants to pick one and carry on from there?

Your point of view seems resonable, but ALL trailer mfgs. have gone to trailing arms. Just call one & ask the engr, dept why they have done this. The principle also applies to cars - when you apply the brakes the nose goes down & helps w/tire contact.

If you get more info please report back to us........Don Meyer, mech engr.

[Brian B-P]

The Trillium Outback which I have looked at on a local dealer's lot still has leading arms. It is also the only fiberglass travel trailer in current production in Canada (to my knowledge) which is only 13' overall (the rest are 17' plus). This appears to me to be a choice driven by packaging considerations, as the axle tube can be under the stepped-up rear section of frame and floor only if the arms are leading.

[Andrew Gibbens]

The principle also applies to cars - when you apply the brakes the nose goes down & helps w/tire contact.

This seems to be mixing up two related phenomenons - weight transfer when braking makes the nose of a car go down and the same weight transfer increases the load on the front tyres. The nose going down doesn't provide any benefit at all.

Trailing arm suspension does not help with tyre contact - it reduces tyre contact when the brakes are first applied.

Andrew

[Byron Kinnaman]

Your point of view seems resonable, but ALL trailer mfgs. have gone to trailing arms. Just call one & ask the engr, dept why they have done this. The principle also applies to cars - when you apply the brakes the nose goes down & helps w/tire contact.

If you get more info please report back to us........Don Meyer, mech engr.

The reason the nose goes down is that center of gravity is above the center of wheels and between the front and back wheels. When the brakes are applied the center of the front wheels become the moment piviot point. The CG attempts to continue going forward but can't so it rises forcing the front of the car down.

In the case of a two wheel trailer the CG is in front of the wheels and behind the coupler. The couple becomes the piviot point. The CG again doesn't want to stop so it attempts to piviot over the coupler putting downward force on the hitch.

If the trailer is properly balanced the CG is in the same realtionship with wheels and the coupler in both cases. It appears to me in both cases the tires will have a tendency to unload, thus no gain in either case.

This is where somebody with a Finite Element Analysis program could if there is a differences between leading and trailing arms.

[Roy in TO]

In the case of a two wheel trailer the CG is in front of the wheels and behind the coupler. The couple becomes the piviot point. The CG again doesn't want to stop so it attempts to piviot over the coupler putting downward force on the hitch.

This is where somebody with a Finite Element Analysis program could if there is a differences between leading and trailing arms.

Byron,
Does your '06 S13 have a leading or trailing axle? If leading that makes at least 2 manufactures with leading arms.

The forward rotation of the TV will cause the hitch to lift upwards. I think we might need the Finite Element Analysis program to explain it since Don seems a little tight lipped ( or fingered in this case) with his professional knowledge. {light fingered just does not sound right thought, since it usually means something else}

Roy

[Byron Kinnaman]

Byron,
Does your '06 S13 have a leading or trailing axle? If leading that makes at least 2 manufactures with leading arms.

The forward rotation of the TV will cause the hitch to lift upwards. I think we might need the Finite Element Analysis program to explain it since Don seems a little tight lipped ( or fingered in this case) with his professional knowledge. {light fingered just does not sound right thought, since it usually means something else}

Roy

I just took a quick look and it appears to be a trailing arm.

The only reason I can think of at the moment for trailing vs leading is that the tortional forces created during braking would have a tendency to decrease the life of the axel. Trailing arm isn't going to put a lot of tortional stress on the axel, where as leading arm with force the arm to it's maximum downward rotation. I suspect that those tortional forces would overload the axel.

Interesting topic, eh?

[Andrew Gibbens]

Trailing arm isn't going to put a lot of tortional stress on the axel, where as leading arm with force the arm to it's maximum downward rotation.

I can't see much logic in this. The torque applied to the leading arm is likely to be lower since most leading arms are used with low ride heights (eg, 'up' axle start angles), so the lever (ground to axle centre) of the braking force is less.

The leading arm isn't going to be forced to its maximum downward rotation, any more than the trailing arm isn't forced to its maximum upward rotation.

Andrew

[Don Meyer]

When I ordered my new axle I told Jim Tuthill (Engr Dept @Dexter axel, that my Scamp has leading arms. He recommenged to go w/trailing arms. I have since then ordered the axel & will place it under the dropped box w/the arms facing rearward. The axle will have a o degree angle vs. the current 22.5 Degree down angle.

On the passenger side I had to lower the mounting point 4 1/2". I did this by adding a 5' pc. of 1 1/2" square tubing from the axel area forward past the bend. To this I welded a pc. of 2' x 3" x 1 1/2" tubing to the area above where the axel will go. The overall effect will be lowering the axel 4 1/2" which will raise the trailer 2 1/2"( I got a 2" drop by going to o degree angle vs. 22.5 degree down). I would have not gone to all this work if I had not been advised by 2 axle mfgs. to use a trailing arm axle.

I am now waiting for the axle to arrive.(pictures to folow)

I also talked to Redneck trailer in Tampa Fl. & they refused to make a leading arm axle.

I am just telling my story......My Engineering expertise is not in axle design, however Jim Tuthill, The Engr at Dexterthat I talked to , should be able to give those that want more info ......Dexter axle (574)295-1900
Don Meyer

[Byron Kinnaman]

I can't see much logic in this. The torque applied to the leading arm is likely to be lower since most leading arms are used with low ride heights (eg, 'up' axle start angles), so the lever (ground to axle centre) of the braking force is less.

The leading arm isn't going to be forced to its maximum downward rotation, any more than the trailing arm isn't forced to its maximum upward rotation.

Andrew

Can you imagine a long stick with a short stick attached with a piviot. The short stick is then pointed toward the other end of the long stick. The short stick has a wheel attached at the end of it. (leading arm). You pull on the long stick and then stop the wheel from turning. What's it going to do?

It's going to reverse become a trailing arm if there are no forces to prevent it.