F53 Softer Leaf Spring Match Found?

[rvfigs]

Check out a potential softer F53 front leaf spring that seems like a direct bolt on!

From springs from an F53 (1994 to 1997) actually look like they may work.

Any thoughts?

[l1v3fr33ord1]

rvfigs-

Have you weighed your coach in loaded condition to determine the weight on the axles?

At a given load, a softer spring will deflect more. This changes the geometry of the suspension. I should think one result would be the axle would hit the bump stops more often.

In contrast, the Kelderman suspension typically combines a softer spring with an airbag. This maintains the geometry, while allowing a more comfortable ride.

[rvfigs]

Originally Posted by l1v3fr33ord1

rvfigs-

Have you weighed your coach in loaded condition to determine the weight on the axles?

At a given load, a softer spring will deflect more. This changes the geometry of the suspension. I should think one result would be the axle would hit the bump stops more often.

In contrast, the Kelderman suspension typically combines a softer spring with an airbag. This maintains the geometry, while allowing a more comfortable ride.

If we add SUMO springs...then we have essentially what Kelderman has...

This idea surfaced in the past by other members. The difficult part was tracking down an actual leaf spring that would fit.

As per Kelderman, the leaf springs they use have a spring capacity of 4400 (2200 each spring).

SUMO springs for the F53 18K chassis have a spring capacity of 2600lbs...I'm not sure if this is combined...

[aauummm]

Originally Posted by rvfigs

If we add SUMO springs...then we have essentially what Kelderman has...

This idea surfaced in the past by other members. The difficult part was tracking down an actual leaf spring that would fit.

As per Kelderman, the leaf springs they use have a spring capacity of 4400 (2200 each spring).

SUMO springs for the F53 18K chassis have a spring capacity of 2600lbs...I'm not sure if this is combined...

The difference between the 22K chassis Kelderman front spring and the 22K chassis OEM spring is that the Kelderman spring has 7 leaves that are of varying length and each leaf is thinner than each leaf of the OEM spring.

This gives a progressive rate spring but has the same total load capacity as the OEM. The OEM spring has 2 leaves that are full length, thicker, carry the full load, and are very stiff.

The Kelderman design is a combination of the new progressive rate springs, air bags and softer shocks.

Top picture is Kelderman, the second is OEM.

[spyderRV]

What about these. https://www.sdtrucksprings.com/index...oducts_id=7933

[rvfigs]

Originally Posted by aauummm

The difference between the 22K chassis Kelderman front spring and the 22K chassis OEM spring is that the Kelderman spring has 7 leaves that are of varying length and each leaf is thinner than each leaf of the OEM spring.

This gives a progressive rate spring but has the same total load capacity as the OEM. The OEM spring has 2 leaves that are full length, thicker, carry the full load, and are very stiff.

The Kelderman design is a combination of the new progressive rate springs, air bags and softer shocks.

Top picture is Kelderman, the second is OEM.

Thanks for the comparison...

There have been many conversations about this, but it helps a lot to look at apples to apples comparison data.

According to Kelderman, the leaf springs they use have a spring capacity of 4400lbs (2200 each spring).

[rvfigs]

Originally Posted by spyderRV

What about these. https://www.sdtrucksprings.com/index...oducts_id=7933

I studied those...at 3500lbs each spring...this would be OEM stock. No change here.

I'm not sure about your rig, but my OEM spring capacity is 7000lbs (3500 each spring) as per Ford cutaway chassis specs.

Check out the factory Class A brochure from Ford:

https://www.fleet.ford.com/resources...2018_ARLSD.pdf

[Campering]

Originally Posted by rvfigs

If we add SUMO springs...then we have essentially what Kelderman has...

This idea surfaced in the past by other members. The difficult part was tracking down an actual leaf spring that would fit.

As per Kelderman, the leaf springs they use have a spring capacity of 4400 (2200 each spring).

SUMO springs for the F53 18K chassis have a spring capacity of 2600lbs...I'm not sure if this is combined...

I am not sure if I am understanding what you are stating. If you add sumo springs to the stock leaf springs in front it will be very firm. If you are saying what I think you might be, that is finding softer, lower rate leaf springs and then supplementing them with Sumo Springs you would be approaching the suspension in a similar fashion as Kelderman. New soft multi leaf, leaf springs and Sumo Springs will get you into a similar cost situation with the hope that it will work, and without the same compliant dampening as an air bag like Kelderman uses and without the ability to adjust for correct ride height or changing load.

[spyderRV]

Originally Posted by rvfigs

I studied those...at 3500lbs each spring...this would be OEM stock. No change here.

I'm not sure about your rig, but my OEM spring capacity is 7000lbs (3500 each spring) as per Ford cutaway chassis specs.

Check out the factory Class A brochure from Ford:

https://www.fleet.ford.com/resources...2018_ARLSD.pdf

Yes but there are 6 leafs in this one for a more progressive stiffness on compression versus my current two thick leafs!?

[rvfigs]

Originally Posted by Campering

I am not sure if I am understanding what you are stating. If you add sumo springs to the stock leaf springs in front it will be very firm. If you are saying what I think you might be, that is finding softer, lower rate leaf springs and then supplementing them with Sumo Springs you would be approaching the suspension in a similar fashion as Kelderman. New soft multi leaf, leaf springs and Sumo Springs will get you into a similar cost situation with the hope that it will work, and without the same compliant dampening as an air bag like Kelderman uses and without the ability to adjust for correct ride height or changing load.

I think the firmness of the SUMO springs depends on the durometer (stiffness). The blue SUMOs are "softer" than the yellow SUMOs.

Yes, I'm trying to see if a "poor mans" version of Kelderman can work.

If we can figure this out and make it work, then we can help a lot of folks who are looking to improve the comfort of their rigs without spending a fortune

[rvfigs]

Originally Posted by spyderRV

Yes but there are 6 leafs in this one for a more progressive stiffness on compression versus my current two thick leafs!?

Honestly, this is the part that I don't understand...

Kelderman uses more leafs and less spring capacity?

So, if we want the leaf springs to be softer we need to look at both spring rate and spring capacity?

Am I understanding this correctly?


https://www.eatondetroitspring.com/s...-vs-load-rate/

[aauummm]

Originally Posted by rvfigs

Honestly, this is the part that I don't understand...

Kelderman uses more leafs and less spring capacity?

So, if we want the leaf springs to be softer we need to look at both spring rate and spring capacity?

Am I understanding this correctly?

https://www.eatondetroitspring.com/s...-vs-load-rate/

I don't believe that Kelderman would use a spring with less design capacity than OEM. The liability implications would be massive. What if an airbag goes flat (it happened to me once). Then the springs would have to carry most of the OEM design load, which on my unit would be 8000 lb.

As I see it, the softer ride comes from the progressive rate spring that Kelderman uses and not from a reduced spring capacity. I would have to confirm that with Kelderman.

[rgmiller32]

We added the Sumo springs to our unit after the first long trip. The difference was night and day. I don't think the main springs are to stiff if the coach is loaded properly. To me it felt like the axle was hitting the bump stop. The Sumo springs helped to cushion that movement.

[rvfigs]

Originally Posted by aauummm

I don't believe that Kelderman would use a spring with less design capacity than OEM. The liability implications would be massive. What if an airbag goes flat (it happened to me once). Then the springs would have to carry most of the OEM design load, which on my unit would be 8000 lb.

As I see it, the softer ride comes from the progressive rate spring that Kelderman uses and not from a reduced spring capacity. I would have to confirm that with Kelderman.

This makes sense to me as well.

The kid I spoke with on the phone a few days ago said: "We cut spring capacity in half...yeah...about 4400lb spring capacity."

I can only assume the following: (a) the kid is correct because he is selling the product (b) the kid is incorrect and doesn't know the product (c) the kid made up some random number to get me off the phone after a long day of work

He also said: "This is why we call it a two stage system because the air bags make up the rest of the capacity..."

Or...perhaps I didn't ask the right questions:

What is the your spring capacity?
What is your spring rate?

Hopefully we can get more folks to search for real specs on the Kelderman leaf springs