V/Modified B codes, step-by-step
MMNC (SS)(Ret)
Joined: Mar 2004
Posts: 11,602
Likes: 148
From: SE Georgia
Measure the individual leafs and plug the results into a spring calculator
Leaf Spring Calculator | Suspension Maxx
Leaf Spring Calculator | Suspension Maxx
Tensile strength alone discounts that. Quality of steel, and the annealing process is another huge factor.
Heck, my butt dyno disproved that last time I did it. Modded B's are significantly higher rated than G's
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
Specifically to our leaf springs Ford used SAE-AISI 5160 steel with a Elastic Modulus of 210 GPa and a Ultimate Tensile strength of 110,000 PSI
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
Fords specs on the Excursion rear spring list a spring rate of 410 lbs. in.
https://www.fleet.ford.com/truckbbas...1/excursCD.pdf
https://www.fleet.ford.com/truckbbas...1/excursCD.pdf
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
Fords data puts Spring rate for the f-250 f350 SRW rear spring without the overload at 320 lbs in.
The popular B mod spring removes the overload and adds the 2 bottom springs off the Ex pack which is how the B mods get a stock Excursion like spring rate of 410 lbs in.
https://www.fleet.ford.com/truckbbas...1/fsersdcd.pdf
If you modified your differently and want to know your spring rate the calculator I linked to above is a handy tool.
The popular B mod spring removes the overload and adds the 2 bottom springs off the Ex pack which is how the B mods get a stock Excursion like spring rate of 410 lbs in.
https://www.fleet.ford.com/truckbbas...1/fsersdcd.pdf
If you modified your differently and want to know your spring rate the calculator I linked to above is a handy tool.
FTE Chapter Leader
Joined: Nov 2010
Posts: 30,591
Likes: 1,236
From: N. IL
Thx for all the charts Pirate! 
In my case, I took the:
5 leaves from an F350 SRW pickup (no overloads) plus;
3 leaves from the G rear Excursion plus;
1 slapper bar.
That gives me:
5 @ 320/670 plus;
3 @ 410 plus;
1 slapper leaf which has ? impact.
In the photo below, F350 leaves are black; G leaves are dusty.
Not sure on the math, but those 8 leaves + slapper sure feel stiffer than the original G's she came from the factory with.
In my case, I took the:
5 leaves from an F350 SRW pickup (no overloads) plus;
3 leaves from the G rear Excursion plus;
1 slapper bar.
That gives me:
5 @ 320/670 plus;
3 @ 410 plus;
1 slapper leaf which has ? impact.
In the photo below, F350 leaves are black; G leaves are dusty.
Not sure on the math, but those 8 leaves + slapper sure feel stiffer than the original G's she came from the factory with.
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
Thx for all the charts Pirate!
, I took the:
5 leaves from an F350 SRW pickup (no overloads) plus;
3 leaves from the G rear Excursion plus;
1 slapper bar.
That gives me:
5 @ 320/670 plus;
3 @ 410 plus;
1 slapper leaf which has ? impact.
In the photo below, F350 leaves are black; G leaves are dusty.
Not sure on the math, but those 8 leaves + slapper sure feel stiffer than the original G's she came from the factory with.
, I took the:
5 leaves from an F350 SRW pickup (no overloads) plus;
3 leaves from the G rear Excursion plus;
1 slapper bar.
That gives me:
5 @ 320/670 plus;
3 @ 410 plus;
1 slapper leaf which has ? impact.
In the photo below, F350 leaves are black; G leaves are dusty.
Not sure on the math, but those 8 leaves + slapper sure feel stiffer than the original G's she came from the factory with.
That said, if you used 3 leafs off the Ex and not 2, then yes you will have a slightly higher spring rate. not likely enough to notice seat of the pants though.
And no, the anti-wrap bar does not add to spring rate.
MMNC (SS)(Ret)
Joined: Mar 2004
Posts: 11,602
Likes: 148
From: SE Georgia
G Codes
rated for 5250 lbs combined at the ground
rated for 2275 lbs individually
410 lbs/inch
B Codesrated for 2275 lbs individually
410 lbs/inch
rated for 6084 lbs combined at the ground
rated for 2670 lbs individually
320 lbs/inch
The B codes are more progressive and give a better ride. It's an early attempt at capacity and smoother ride (ie: see the 2008+ leafs). Sure they deflect more per inch with weight, but they are overall rated 800lbs higher combined, and 400lbs more individually. That's a 15% increase in weight capacity over G codes before messing with themrated for 2670 lbs individually
320 lbs/inch
essentially G codes will deflect less with 1,000 lbs on the rear compared to a B code. But the B codes will handle that 1,000 lbs better as they are rated higher.
now take the common "Modded B" leafs that contain 2 of the G leafs on bottom of B pack.You are taking the 2 strongest leafs from the G codes at 410 lbs/inch rating. These will take the load before the 320 leafs see loading. Not to mention the extra capacity of ???? they add to the already beefy 6,084 lbs B codes have
All that being said, there is no way you can say that "Modded B" codes are the same as G codes. No way shape or manner.Just like I said earlier: tensile strength, heat annealing, steel quality...all of these are important factors. You can plug and chug into your calculator, but it doesn't compute those variables. I put the G code specs in (6 leafs only since the slapper doesn't affect spring rate) and it calculated over 500 lbs/inch. Ford says they are 410 lbs/inch. Who to believe?
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
The springs rated capacity is travel x spring rate
The Excursion rear spring has about 5.5" of arch.
5.5" of travel x 410 lbs inch = 2255 lbs needed to fully deflect the spring.
The F-truck spring has about 8" of total travel however the bottom overload spring only comes into play for about the last 1/4 inch. ( hense your "progressive" spring rate. "
I will reiterate:
The common method of building a Mod B spring pack (4+2) has the same spring rate as the stock Excursion G pack.
However, if you build a 8" travel spring that has a spring rate of 410 lbs in then your "rating at the pad" would be 8x410 = 3280 lbs
The Excursion rear spring has about 5.5" of arch.
5.5" of travel x 410 lbs inch = 2255 lbs needed to fully deflect the spring.
The F-truck spring has about 8" of total travel however the bottom overload spring only comes into play for about the last 1/4 inch. ( hense your "progressive" spring rate. "
I will reiterate:
The common method of building a Mod B spring pack (4+2) has the same spring rate as the stock Excursion G pack.
However, if you build a 8" travel spring that has a spring rate of 410 lbs in then your "rating at the pad" would be 8x410 = 3280 lbs
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Mountain Pass
Joined: Apr 2017
Posts: 180
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From: Central Ohio
OK, I have read through most of the suspension and wander threads and I want to see if this is correct, so I can start to make some decisions about spring replacement. My 01 x 4x4 PSD shows spring code D G (which would be spring codes specific to the Excursion line). If I want to upgrade my springs I would need to go to V or X on the front and B, B-modded or C on the back (V, X, B, and C are SD spring codes).
Thanks
Thanks
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
properties of SAE 5160 steel
Tensile Strength
ultimate tensile strength = 105,000 psi
yield tensile strength = 39,900 psi
Hardening
springs are not annealed as that would make them soft, springs are hardened and tempered.
in the case of the SAE 5160 Ford uses for leaf springs it comes as Brinell hardness 197 and is then Tempered to ford spec at 415-461 Brinell hardness
Steel Quality
SHE 5160 quantifies the mechanical and chemical properties of the steel ford specs. additionally ford calls for "continuously cast steel."
So while these and a few other details are critical important from an engineering and production standpoint I fail to see how they relate to our spring rate comparison.
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
OK, I have read through most of the suspension and wander threads and I want to see if this is correct, so I can start to make some decisions about spring replacement. My 01 x 4x4 PSD shows spring code D G (which would be spring codes specific to the Excursion line). If I want to upgrade my springs I would need to go to V or X on the front and B, B-modded or C on the back (V, X, B, and C are SD spring codes).
Thanks
Thanks
FTE Chapter Leader
Joined: Nov 2010
Posts: 30,591
Likes: 1,236
From: N. IL
Or really go out on a limb and do the C-mod'd.
Whatever you do 92, share lotsa pics
.
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
I'll play.
The top 4 leafs from the F-350 DRW have a spring rate of 350 lbs in.
aside from 20 lbs in difference in the base leaf pack ( minus the Top Auxiliary and bottom overload ) the C-mod would be fine. Just use a leaf from the excursion that has a spring rate of 60 lbs in. to finish the pack.
The top 4 leafs from the F-350 DRW have a spring rate of 350 lbs in.
aside from 20 lbs in difference in the base leaf pack ( minus the Top Auxiliary and bottom overload ) the C-mod would be fine. Just use a leaf from the excursion that has a spring rate of 60 lbs in. to finish the pack.
Tuned
Joined: Jul 2011
Posts: 316
Likes: 8
From: chambersburg, PA
So i have an ex with v/mod B codes. springs. I added 2 of the excursion springs to the B code pack. I am wanting to add airlift air bags to the rear to help with some squat and porpoising. Will the excursion kit still bolt up with the B codes?
Lead Driver
Joined: Apr 2011
Posts: 8,259
Likes: 346
From: Northern California
Airbag adds the ability to in increase spring rate, so if your proposing is bouncing then the would be a problem with shocks not spring rate.