From what I've read a flatter spring is supposed to make for a smoother ride but the tradeoff is load capability. So I guess nothing would be wrong with a flat spring as long as it's doing it's job to your satisfaction.

 

i didn't go into detail when i said his spring went flat or that he felt his springs went flat. i didn't think that i needed to as the term " went flat" to myself meant they wore quickly, weren't what they were, sagged, front end dropped etc etc what ever description you want to apply, that means, no longer were what they were when installed. he swapped out the fronts because from 100k miles to 250k miles of service, the front had begun to get bouncy when loaded with a toyhauler camper. it's the same toyhauler he has hauled long distances, loaded for thousands of miles over the years, with the same toys loaded inside.

at 250k miles, not only was the front end weak, worn and yes a slight concave shape to the oem leaf pack but lets say apprx 2" lower then it did at 100k miles. i say apprx as this was a couple years ago and i don't remember the exact number i was told. once the sd springs were installed the truck sat apprx 1" higher then it did at apprx 100k miles and no longer looked like an '80s 2wd unloaded and firmed the ride back up. well by the end of the year, the front end was back to sitting low and bouncy. again, i simply call that " went flat " but use what ever term you want. he then replaced them from a different shop, using a different brand and after a year in service, they have, at the absolute most, dipped, flattened, lost some shape, sagged, weakened, broke in, settled down maybe .3/8". he's happy, front leaf spring packs work as he wants/wanted/expected/pre-fers. bottom line is, the sd springs went flat, develped ED , were in need of viagra and cialis and needed to be replaced 1 year later. as stated above, clearly not all customers have had the same experience with sd springs. i chose not to use them as i too wouldn't be happy with those results and do not need practice changing leaf springs.

so that is when i came across some info referencing parabolic spring packs and began looking into them. i couldn't find the info I wanted so i gave up and called ats for a stock replacement set for my rears. i replaced my rears because the thickest bottom leaf had cracked clear through on one side. my fronts are flat to my eye, and have looked like that since i bought it 60k miles ago. the front is definitely weak but i have not changed them yet. i have not had time to deal with that yet. i say there weak at 141k miles because with the camper on the bumper, the front end starts trying to hop ( with out leaving the ground or breaking traction more of hopping like motion) on sagging or poorly leveled sections of roads. yes i replaced the front shocks. barely a noticeable difference, so i will change them when i get time. it isn't bad enough to loose control or at a point i think its dangerous but bad enough when you find a stretch of road like that ( like the last 20 miles heading north to hermosa SD) you'll be glad you haven't eaten anything in a while! the truck has not done that since i bought it with 80k miles on it. so no, that isn't the way its supposed to ride. it has gradually gotten worse in the last 20k to 25k miles of towing a toyhauler camper or trailers of similar. it is only bad or what i call bad with a trailer on the back. recently felt a tad bit of it empty on a similar stretch of road. i say all of this because this is similar to what my friend was experiencing as well. he drives a 1997 4x4 srw pds where mine is an '99 4x4 drw but, we live 30 mins apart, drive the same roads, the same time of year to the same offroad events. my front end does look like its nose down a bit and i notice this when i get in truck, even my wife has noticed she doesn't need the running boards as she did when we bought it. she hasn't gotten any taller either. now that the rear has been replaced i really notice the front sitting lower for obvious reasons. when i have time i will purchase from ats again as i have had a great experience with there products as well as staff. i will not purchase from sd springs, based on what i have seen in person, i don't want the practice. again, clearly not everyone has had that same experience with sd springs.

 

That is a big IF, and not a probable one, IMHO.

How were these leaf thickness dimensions determined? (By mic'ing your ATS springs if you have them? By eyeballing the photos? By ATS specs?)

Where were these leaf thickness dimensions measured or estimated? (At the spring seat over the axle? At the eyelet and shackle ends?)

Is the range in thickness cited (i.e. "between 3/8 and 5/8") intended to reflect the range of taper of the spring? Or the range of possible thicknesses by your estimation, if estimated?

Does ATS provide leaf thickness in their specifications? (I couldn't find that spec on their website)

Would such a thin spring be "tougher" at the eyelet?

It was a straight forward Job 1 model year change. 2005 and up coil springs on 4WD. 2004 and earlier leaf springs on 4WD (within the Super Duty models).

Spring arch is not the determining factor of load capability. The F-650/750 models with 10,000 lb front GAWRs have "flat" front springs (when installed). consisting of only two leaves.

 

So looking at ats’s webpage they have multiple weight ratings, does anyone know what a stock f250 springs are rated for front and back

 

open your drivers door and look for this sticker on the lower jamb. What I have circled in blue will give you the front spring rating. How many leaves on your rear leaf packs?

 

The leaf thicknesses are listed in the description in thousandths. I roughly converted those listed thicknesses for simplicity. I didn't think the absolute accuracy of those measurements would be necessary given the heart of the question.

https://www.autoandtrucksprings.com/...-leaf-springs/

 

Thanks @udsuth78 . I had looked at that very same page, prior to posting, and my eyes apparently glossed right over the thickness specs.

Painted OEM front springs (each leaf tapered) for the F-250 (2002) are .592 at the spring seat as determined by my physical measurement (not necessarily accurate as the springs were installed), so it appears that the ATS 43-812 matches the dimension of the OEM springs (not X codes).

Knowing how you arrived at the thickness measurements that you posted earlier (via ATS spec info) helped in making the comparison.

 

Here is a question: what was the stance of these SDs when new?

​Nearly every 99-03 SD I have seen is raked forward/rear-end higher. If so, what was the design diff in height front to back?

​​​​​​My old e99 f250 was pretty low up front. Previous owner used it for hauling a 5th wheel. My new 02 f350 is low upfront, but not as much as the 99 was. Given the rake I always see - and that these trucks are nominally 20+ years old - I assumed it was because the front springs were tired.

 

There is not enough detail about your Early 1999 F-250 or your 2002 F-350 in your post or signature to be able to provide an exact answer, because that answer depends on bed length, engine, 2WD or 4WD, SRW or DRW, trim packages, weights of options, etc.

Let's assume you have a 2002 F-350 Super Cab Long Bed 4x4 SRW, with stock wheels and tires (LT265/75R16E), a 9,900 LB GVWR, and only standard equipment, no options.

To measure difference in vehicle height between front and rear axles, and between empty and loaded states, we need a reference point, or a horizon line, common to both front and rear axle, and parallel to the ground.

Ford calls this reference line the "Z" axis, which is also referred to as the frame datum line, which in the 2002 Ford Super Duty passes just beneath the bottom flange of the frame directly above the front and rear axles.

Note that the frame itself undulates above (at engine) and below (at cab) the frame datum line, while the Z axis datum line is a horizontally flat plane... which is the reference line we need to compare OEM stance and spring compression between empty and loaded states.

All measurements below are between flat ground and the Z axis datum line.

2002 Ford Super Duty F-350 Super Cab 4x4 Long Bed SRW 9,900 GVWR Base / Standard Configuration, with Standard Springs, with No Options and with Stock LT265/75R16E tires inflated per Federal Certification Label

Front Frame Height at Datum Line at Curb Weight: 24.4 inches
Front Frame Height at Datum Line Loaded to GVWR: 23.8 inches

Rear Frame Height at Datum Line at Curb Weight: 28.6 inches
Front Frame Height at Datum Line Loaded to GVWR: 23.8 inches

Therefore, in answer to your question, the "forward rake / rear end higher design difference in height front to back" for this example truck is 4.2 inches in an unloaded state at curb weight, and 0 (zero) inches difference between front and rear (leveled) when in the fully loaded state. This design difference is indicative of what is generally applicable to all Super Duty pickups of this era, but which differs in specifics from vehicle to vehicle depending on how configured and equipped.

 

Ok so now I'm curious. How much variation are we talking about figuring in options and trims? We can keep it simple and at least stick to either 2x4 or 4x4.

 

This question is not possible to answer accurately, as Ford acknowledges variations in production tolerances.

Base vehicle configurations have average "rear height" differences (as defined in my post above) between empty and loaded ranging between 4" to 5".

However, "Load Height" differences appear more amplified, as the pitch angle telegraphs to the end of the bed. So in the truck example application above, the load height difference at the end of the bed would be about 5.8" between empty and loaded to GVWR.

Since we can't "see" the imaginary datum line, but we can see the actual pickup bed, our visual perception of muscle car rake is greater when looking at the side of the truck and comparing the end of the pickup bed with the front bumper.

 

They say a picture is worth a thousand words

 

Maybe it's me but that looks like a negative arch there, right at the block.

 

yep they really kind of snake up and down on either side of the block. I just really think worn springs are a big part of my problem

 

Awesome Y2KW57, that is some solid info. The example 2002 actually is nearly what I have, crew cab and 235/85s instead. Either way, it answers a two basic questions: right out of the box, these rigs had a pretty decent rake to them. Second, thinking that new front springs are required to get things to "level" may be misplaced. The truck was never level to begin with, so trying to do so with springs alone isnt going to get you there. There might be a small gain over and above what you get with a replacement set (of fronts), but it isnt going to amount to much and you will still be raked forward. I guess this is why there is a healthy selection of lift kits.

I took a time out from installing my onboard batt tender/charger and fiddled around with a level and ruler. Ironically I quickly estimated a 4" "rake" with my crude approach.