Lift axles

[angelo7]

By what I see in this image lift axles are steerable, but how do they steer?

And would the steering rod be facing to the back or to the front? I'm trying to make one from scratch for one of my model trucks.

Edited April 15, 2015 by angelo7

[Fat Brian]

I always thought they were powered by the steering system somehow but after some reading most seem to work like casters and just follow the angle between the front and rear tires. Hendrickson makes a system that uses some air pressure from the bags to re-center the wheels but they don't "steer" as we think of it. All of the Hendrickson systems say to lift the axle in reverse because it can't follow correct going backwards.

[Muncie]

steerable - yes and no...

The example in the picture steers by just tracking where the rubber meets the road and is not connected to the steering gear or the front axle. A steerable lift axle is generally located about midway in the wheelbase. The steerable function helps with tire wear and allows the truck to turn easier.

not steerable - If the lift axle is located just ahead of the drive axles it would be a pusher axle - they are not steerable - X_______LDD

same deal, not steerable if it's a tag axle aft of the drive axles - X_______DDL

yes, steerable - If the lift axle is located further forward, about midway in the wheelbase - X____L____DD - this would be a steerable lfit axle

Edited April 15, 2015 by Muncie

[angelo7]

Great information! Thank you guys.

[tbill]

thanks for bringing this up, as I had no idea how these worked, between the picture and the following explanations, I have now been able to grasp the concept.

thanks again

[angelo7]

So, Steve (Muncie), according to your explanation this set up would be inaccurate, right? The steering lift axle is too close to the rear wheels., right?

[Truck parts]

Thank's for the tip and that's a cool build

[Muncie]

I kind of generalized and simplified a bit... However, given the shorter wheelbase, which puts the lift axle closer to the steer (front) axle, the steerable lift axle is appropriate to reduce tire scrub - better steering control and longer tire life. It could be non-steerable, but the driver would have to lift the axle to make a tight turn.

BTW that's a great looking truck.

Let's add someting about fifthwheel position - The fifthwheel position needs to be forward of the center of the drive axles to ditribute weight forward onto the lfit axle.

Edited April 17, 2015 by Muncie

[angelo7]

Thanks Steve. I appreciate your input.

[angelo7]

The finished truck is here: http://www.modelcarsmag.com/forums/index.php?showtopic=101253#entry1410776