Downside to air trailer brakes?

Scrap · September 5, 2015

The advanced trailer ABS units will do your axle unweighting for you automatically. So if you are doing air the feature is already in it (with the premium version) so all you have to do is enable it. This is usally done on the tag whose whole point in life is to add pin weight, but I'm sure the right balance could be figured out for whatever you are building.

But with air brakes you still need to fit a 4" shoe (5" for 12K) in there. So even if you figured out a single wheel setup you are going to have to make enough tub clearance for that shoe. I'd be willing to bet that it is going to end up being the same basic envelope as a set of duals. Add to it the real long camshaft tube that trailers have and your floor envelope has to go up a fair amount as well. And it is an air brake - you've got to get on your belly in the mud every morning and check the thing out. Not fun.

phoenix2013 · September 5, 2015

The lifting third axle was already done on fifths, actually long time ago in 2006. I attached a short section from a very comprehensive article I wrote on an incredible custom Teton built in 2006, Enjoy.

VegasFlyer · September 5, 2015

Post #8 discusses why an air lift would work for low speed maneuvering, thus making a spread axle feasible even in a campground.

Yes, we're way off topic, but it sure is interesting.

Lifting a spread axle on a loaded trailer is not the wisest idea, especially on a wet unpaved surface.

The idea of spread axles trailers is great, I owned a 53' spread axle flatbed and absolutely loved it, for the purpose that I used it and would not hesitate to buy another. Wouldn't even consider it for an RV build.

The biggest benefit and or purpose to a spread axle trailer is weight distribution, not ride.

Just like the OP, I am planning a build for a trailer and do plan to use air brakes and suspension.

G&K · September 5, 2015

The advanced trailer ABS units will do your axle unweighting for you automatically. So if you are doing air the feature is already in it (with the premium version) so all you have to do is enable it. This is usally done on the tag whose whole point in life is to add pin weight, but I'm sure the right balance could be figured out for whatever you are building.

But with air brakes you still need to fit a 4" shoe (5" for 12K) in there. So even if you figured out a single wheel setup you are going to have to make enough tub clearance for that shoe. I'd be willing to bet that it is going to end up being the same basic envelope as a set of duals. Add to it the real long camshaft tube that trailers have and your floor envelope has to go up a fair amount as well. And it is an air brake - you've got to get on your belly in the mud every morning and check the thing out. Not fun.

Scrap, is there a more compact air disc setup on the market? I'm thinking that if you are going air, might as well go for the most modern configuration if it will work...?

Geo

G&K · September 5, 2015

I'm looking at this from a wheelbase management point of view. If building from scratch, I would overbuild contact patch anyway to gain some flotation, so overloading an axle wouldn't be much of an issue. It sure would be interesting to be able to effectively shorten both the tractor and trailer wheelbases by unloading an axle though.

Geo

Lifting a spread axle on a loaded trailer is not the wisest idea, especially on a wet unpaved surface.

The idea of spread axles trailers is great, I owned a 53' spread axle flatbed and absolutely loved it, for the purpose that I used it and would not hesitate to buy another. Wouldn't even consider it for an RV build.

The biggest benefit and or purpose to a spread axle trailer is weight distribution, not ride.

Just like the OP, I am planning a build for a trailer and do plan to use air brakes and suspension.

peety3 · September 5, 2015

Peety, I'm kinda slow, but couldn't we unweight the back axle in the tandem config on my 780 to enhance parking at low speeds?

I really like your idea. The mind boggles.

Geo

Yep. Go back to the basic idea. Make sure the leveling valve is on the back axle. Two 12V solenoid air valves to decide which pipe feeds your power divider axle air bags - make sure they're "normally closed", which means they open if they receive 12V. Valve #1 feeds leveler-valve air to the power divider axle (aka "normal driving" - it's sharing the load with the aft axle. Valve #2 feeds direct 120psi air (or perhaps regulator it down to 100psi - check the pressure limits on your air bags) to the power divider axle air bags. SPDT switch (single pole dual throw, which means you can "throw" the switch into position A or position so you "can't" get yourself in trouble.

Unless you've got a heavy bed with a heavy Smart car, I'd either not use the magic switch without a trailer, or I'd get the truck weighed and figure out how much drive weight you've got without a trailer. If your drive weight is less than 17k, you might end up raising the rear to max height if you run direct 100psi/120psi air into the bags. In that case, you may want to consider a third valve on a regulator set to an appropriate pressure for bobtail configurations. We can work through the numbers if it comes to that.