Favorite Spring Rate?

[Goatman]

I've run both the Rancho ZJ coils and the RE ZJ coils, which supposedly are the highest spring rate out there......whatever we decide the rates actually are. With a winch and heavy bumper, I wouldn't mind a little more spring rate than these springs provide. I currently have the RE's, and the ride is very good, not harsh at all. I like the stability of a strong coil, plus it's better for the whoops.

 

[MDMIKE]

My buddy just got off the phone with the spring manufacturer and things are looking good. Some EARLY #s which are open for debate. The # following the spring rate is the projected lift height on a 6cyl 4wd stock bumper no winch. As you can see that # grows over advertised lift height to allow for different bumper/winch combos. I figure someone running a 3" kit might add a brushguard so .25" of free height coil compensation was added. I figure someone running a 4.5" kit would add a HD bumper and someone running 6"/8" would most likely be running HD bumper and winch. What do you think?

XJ 3" Coil 165 lbs/in 3.25
XJ 4.5" Coil 180 lbs/in 5.00
XJ 6" Coil 215 lbs/in 6.75
XJ 8" Coil ?????? 8.75 (pending more 7.5"/8" coil tests)

 

[ChuckD]

My buddy just got off the phone with the spring manufacturer and things are looking good. Some EARLY #s which are open for debate. The # following the spring rate is the projected lift height on a 6cyl 4wd stock bumper no winch. As you can see that # grows over advertised lift height to allow for different bumper/winch combos. I figure someone running a 3" kit might add a brushguard so .25" of free height coil compensation was added. I figure someone running a 4.5" kit would add a HD bumper and someone running 6"/8" would most likely be running HD bumper and winch. What do you think?

XJ 3" Coil 165 lbs/in 3.25
XJ 4.5" Coil 180 lbs/in 5.00
XJ 6" Coil 215 lbs/in 6.75
XJ 8" Coil ?????? 8.75 (pending more 7.5"/8" coil tests)

I have rusty's 4.5" with 2" spacers. They have always given me a solid 5" from the springs. No winch, just a HD bumper. I would prefer a stiffer spring, for that I going with some RE ZJ 4.5" springs. HTH

 

[Ed A. Stevens]

For anyone that wants to setup their own spreadsheet to calculate this, the formula is:

spring rate (lbs/in) = (1,440,000*wire dia^4) / (qty active coils * mean spring dia^3)
or

=(1440000*A1^4)/(B1*(C1-A2)^3)
where A1 = wire dia, B1 = # coils & C1 = mean spring dia

using this formula with MDMikes example returns 204.33lbs/in

I'll mostly keep out of the discussion (you Guy's seem to do OK without me), but note the difference between "mean spring diameter" and "outside spring diameter" when comparing calculations.

The typical 5/8 spring stock (the stock used in the 200 to 250 #/in rates you are working with) will alter the two measurements up to the 5/8" (0.625") in the diameter used for the calculation (entering more error than the difference in Youngs Modulus). Keep the calculation to the "mean spring diameter" measurement (subtract the spring diameter from the outside diameter measurement, before entering it into the calculation).

The springs in series rate calculation is dependent on the block load travel of the springs as much as the basic spring choice (there is a spreadsheet calculator to use if needed, or if you want to optimize).

FWIW, my preference has been for XJ front coil spring rates in the 220 to 250#/in range (for a single spring, stock mount). It's stiff for many, but I also try to stay away from the steep control arm angles and anti-dive typical of tall lifts (I keep the lift height low).

Keep up the research and revise the calculations. The results can make a good reference.

 

[MDMIKE]

I believe we have the correct calculations. The calculator Im using asks for the outer coil diameter while MaXJohnsons equation uses the mean coil diameter. Im sure the different equations compensate for the 2 different input measurements. I believe the approx. 2% in variance is in the material rigidity standard.

 

[Ed A. Stevens]

I believe we have the correct calculations. The calculator Im using asks for the outer coil diameter while MaXJohnsons equation uses the mean coil diameter. Im sure the different equations compensate for the 2 different input measurements. I believe the approx. 2% in variance is in the material rigidity standard.

No problem.

What are you using for the equation?

On the coils you have modeled: what are the wire diameters, coil OD, and lengths (both total and active coils, and unloaded heights)?

The information can help build a more complete reference.

 

[MaXJohnson]

For anyone that wants to setup their own spreadsheet to calculate this, the formula is:

spring rate (lbs/in) = (1,440,000*wire dia^4) / (qty active coils * mean spring dia^3)
or

=(1440000*A1^4)/(B1*(C1-A2)^3)
where A1 = wire dia, B1 = # coils & C1 = mean spring dia

Cool, now I'm quoting myself :wstupid:

What Ed is pointing out, is that the first formula correctly calls for the "mean" coil diameter, but in the conversion to an Excel formula, C1 should be the outside coil diameter since "(C1-A2)" returns the "mean" diameter as required.

=(1440000*A1^4)/(B1*(C1-A2)^3)
where A1 = wire dia, B1 = # coils & C1 = outside spring dia
Clear as mud

 

[MDMIKE]

Spring rate calculator. http://www.cswnet.com/~carother/coil_spring_calculator.htm

Crash did you check how many active or total coils in RE 7.5 coil?

Wire Dia, active coils, and coil dia are the factors.

http://www.stockcarproducts.com/pstech10.htm

These are the 2 equations I used to determine the coil rates. MaXJohnson came in with a 3rd independent equation which proved the 2 equations were accurate within 2.5%. I believe the calculators I use subtract the wire dia. from the outside coil dia. before inputing into a similar equation. 6 or 1/2 dozen which ever you want. Im sure the 2 calculators would be way off if they didnt.

As far as specs they are all on paper and cant justify transfering them. I will give any specs you need if you want to double check me. I just think that we have established an acceptable calculator that simply plug and play so why bother beating a dead horse.

As for spring rates Im very interested in the amount of lift and springs you are running on your XJ. All knowledge is appreciated.

 

[Ed A. Stevens]

As far as specs they are all on paper and cant justify transfering them. I will give any specs you need if you want to double check me. I just think that we have established an acceptable calculator that simply plug and play so why bother beating a dead horse.

As for spring rates Im very interested in the amount of lift and springs you are running on your XJ. All knowledge is appreciated.

The specs I requested are important, not to justify (or even double check) the math, but to identify how the lift height gain is derived. I would hope you are kind enough to provide the specs for this purpose?

An Example (to why the specs are important):

The factory XJ coil is ~18 inches tall unloaded, and is reported to have a rate of ~150#/in (having the other specs will help confirm the rate).

If you wanted an easy 3-inch lift coil just fit a similar ~150#/in coil that is three inches taller when unloaded (find a 21 inch coil of the same wire and coil diameter, something like one of Rusty's older 3" coils).

You could also find and fit an 18" tall unloaded coil that provides ~450# more resistance at the ride height deflection (something like the old RANCHO 240#/in coil).

Both coils provide ~3-inch lift, but through different methods. The height may be similar, but the ride is significantly different with these two coils.

The various XJ-lift coils use a combination of unloaded length change and a change in spring rate to gain lift. Knowing the advantage of what method to exploit (how it will work for your need) will provide a better solution than simply changing the wire diameter and rate.

 

[jjvande]

i dont think that adding 3" to the free length will add 3" to the lift height......you should add 3" to the compressed height..so take the force in the spring into account.

 

[MDMIKE]

Factory 6 cyl AT XJ Coil
Wire dia: .5"
Total Coils: 9 Active: ~8
Coil OD: 5.0"
Calc Spring Rate: 120 lb/in
Tested Spring Rate: 125 lb/in
Unloaded Height: 18.0"

I am not looking for a specific coil just what coil rates people like to run for different lift heights. My buddy is seriously considering manufacturing his own springs to sell. I posted some EARLY estimates as far as spring rates and lift heights. I didnt post the the free height of the coils because that will be determined later. I did post projected lift heights that each of these springs will give on a stock XJ.

I feel we are caught up in a sidenote of the intended issue of the thread. I appreciate the concern in determining spring rates but I think I have a good understanding of engineering the correct spring using the feedback from this thread and specs on other manufacturers springs. My buddy is not interested in making some easy springs but the correct springs for the right applications. I think there is a lot of beneficial input on this board and am trying to get feedback from all types of XJers.

Could you post what coils you are running and how you like them.

 

[jjvande]

4.5" xj RE coils.about 7 years old...theyre a nice rate and ride great. im not sure what rate they were using back then. I like low spring rates and high damping.

 

[Ed A. Stevens]

I am not looking for a specific coil just what coil rates people like to run for different lift heights. My buddy is seriously considering manufacturing his own springs to sell. I posted some EARLY estimates as far as spring rates and lift heights. I didnt post the the free height of the coils because that will be determined later. I did post projected lift heights that each of these springs will give on a stock XJ.

I feel we are caught up in a sidenote of the intended issue of the thread. I appreciate the concern in determining spring rates but I think I have a good understanding of engineering the correct spring using the feedback from this thread and specs on other manufacturers springs. My buddy is not interested in making some easy springs but the correct springs for the right applications. I think there is a lot of beneficial input on this board and am trying to get feedback from all types of XJers.

Could you post what coils you are running and how you like them.

Fair enough, you intend to Engineer the coils without regard to the unloaded height, or block load, or coil pitch, but solely on coil and wire diameter. My goal was to help, but I'll offer what you want.

I run the ~240#/in RANCHO 2.5" lift coils: 5" OD, 0.625 wire, 11 active coils, 18" free length, ~7.8" block height, ~10.2" travel ... and I run it with a 1.75" spacer and 5/8" cushion. The net is ~4" lift over stock. The coils unseat ~1.5" with the ~9.5" travel shocks extended, and I leave ~1"+ of unused travel before block loading the coils (when hard on the stops, with ~1/4" on the shock shaft remaining).

Travel Rate Force
0.0 0 0
0.5 0 0
1.0 0 0
1.5 0 0
2.0 238 119
2.5 238 238
3.0 238 357
3.5 238 476
4.0 238 595
4.5 238 714 ~ ride height
5.0 238 833
5.5 238 952
6.0 238 1071
6.5 238 1190
7.0 238 1309
7.5 238 1428
8.0 238 1547
8.5 238 1666
9.0 238 1785
9.5 238 1904 ~ travel stop
10.0 238 2023

I prefer the rigid spring rate to achieve better handling at the desired ride height, and maintain the ~1900# resistance on the stops. I have run these coils for almost 15 years without sag or significant loss in height, over rocks and endurance race pre-run/chase speeds.

I would prefer a taller coil with a similar rate but a reasonable block load height (good travel performance). My wish list (ignoring physics) would to be able to achieve ~15 inches of travel performance and not exceed 21 inches total free length to fit in the factory XJ mounts, with a spring rate between 220 and 240#/in at ride height. I do not wish to run more than 5.5" lift, but prefer to run 14" travel shocks without unseating the coils and maintain a reasonable resistance to body roll.

I would expect most of the higher lift guys would like a slightly higher rate and a taller coil?

I will probably end up with a dual (or triple) coil setup on a coilover shockbody to achieve the performance I want (it's just not a priority at this time).

I hope this helps (I'll return to lurk mode, as I have nothing else of worth to offer)?

 

[RCP Phx]

I think that everyone here has there own opinion on ride heights and spring rates.More important is the balance between front/rear!Is this guy going to develop rear leaves also to match the fronts?The bottom line here is that he will have to develop and test his product on his own!Wire size,wire material,coil rates(single or multi),and all of the metal finishing/heat treating will all play in the finished products ability to be marketed!"Can you say$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$"

 

[ChuckD]

I think that everyone here has there own opinion on ride heights and spring rates.More important is the balance between front/rear!Is this guy going to develop rear leaves also to match the fronts?The bottom line here is that he will have to develop and test his product on his own!Wire size,wire material,coil rates(single or multi),and all of the metal finishing/heat treating will all play in the finished products ability to be marketed!"Can you say$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$"

Man, you are always the party pooper!

 

[jeepinmike]

Before I confuse anybody Im the owner of the 4wd shop that is undergoing this information quest. My buddy and I have been batting around this idea for years and are finally slowly moving into it because of 2nd rate suspension companies offering either horrible service or poor products (no names will be mentioned Im not here to bash). We feel we understand for the most part what people want and feel we can supply the public directly with high quality parts at a very affordable price (no middle men to deal with, customer service that will call back and no magic 8 balls for spring rates). I have not mentioned the shop name because Im not here to step on toes just share information. I believe the people buying the parts should have a part in designing them so feel free to tell me what you want. I understand the design and manufacturing will take lots of $$$$$ and thats my problem. As far as testing goes we will be testing first then maybe Ill donate a test set or 2 to a member(s) for unbiased opinions. I greatly appreciate all info that has been posted and encourage all to speak freely.

PS Ed A Stevens I dont want to deter you from offering info and believe me we will be using the block height, unloaded weight, and coil pitch in the final design. I would like to figure coil rates first then figure block height and coil pitch then finally unloaded height. I think we are on the same track just you are a car ahead.

 

[MDMIKE]

Could I get the RE 7.5" coil specs?
Wire dia:
Total coils:
Coil OD:

Thanks again.

 

[Mike L]

Did anyone get the info for MDMIKE to figure the spring rate of the 7.5 XJ springs from RE?

-Mike

 

[jeep_87_cherokee]

does any one know about PORC's springs they have i think like 6" lift springs for like $90, not a bad price but dont know about quality??

 

[xj92]

I run 3" Skyjacker coils and I like them. I don't have the specs on them but I like how they ride. I'd rather have to slow down for speed bumps than around corners.