Favorite Spring Rate?

[MDMIKE]

Im surprised at the low interest of this thread. This is a good opportunity for the real wheeler to give real feedback on what you want out of a coil spring. I have seen a few good pieces of info but not as much as I expected. Isnt there anybody out there that loves the way your cherokee springs ride. All info is welcomed and greatly appreciated. My buddy posted the coil spring rate equation so if you are curious about your rate you can check it.

Crash I appreciate your time and interest.

 

[Nay]

I'll make it simple and tell you what I want for a 7.5" coil:

The RE 7.5" spring rate, whatever it is, plus about another 10-15 lb/in. The RE's are the best I've had so far...but just a bit stiffer would be nice. Mass market coils are still biased to this concept of a nice onroad ride. Whatever, give me handling and the ability to run at speed on unpaved surfaces.

Nay

 

[MDMIKE]

Thanks Nay thats what Im looking for.

 

[CRASH]

I'll make it simple and tell you what I want for a 7.5" coil:

The RE 7.5" spring rate, whatever it is, plus about another 10-15 lb/in. The RE's are the best I've had so far...but just a bit stiffer would be nice. Mass market coils are still biased to this concept of a nice onroad ride. Whatever, give me handling and the ability to run at speed on unpaved surfaces.

Nay

Exactly!

A wide range of rates will work in the rocks, anything from 200 to 240 depending on winch, bumper, etc. But running at speed in the desert or fire roads is a whole different matter.

For your friends manufacturing process questions, I think it would be cool to offer 4 different lift height coils for various apps, with various associated spring rates. For instance:

3" w/ stock bumper
3" w/ winch and HD bumper

4.5 w/ stock bumper
4.5" w/ winch and HD bumper

6" w/ stock bumper
6" w/ winch and HD bumper

8" w/ stock bumper
8" w/ winch and HD bumper

Maybe even offer a Jeep Speed special spring with a nice 275# rate and 5" of lift.

Spring and damping rates are about my favourite subjects to discuss.

Andy
CRASH

 

[MDMIKE]

Now we are getting somewhere.

 

[Big Red]

I put my 8" skyjacker coil on my 91' xj with a warn 8000i winch and heavy bumper and it seems to be sitting a little lower than my 4.5 re zj coils with 2" spacers. When I compared my re springs to the sj coils they looked to be the same length, but it looks like the sj coils are thicker and will not compress as much. I have a 5.5 extreme duty re kit with 2" blocks in the back and want to level my xj up with the heavy bumper and winch up front and an aftermarket rear bumper with my 35" tire hanging off the back. Does anyone know the spring rate of the 8" skyjacker coil? I have mine installed and wasn't able to compress them to check for the spring rate? Are re's 7.5" coil for an xj specifically? Are they out yet? Re is right down the street from me, but I got a good deal on the sj springs and they are practically brand new.

 

[Redcbr007]

That is correct if Im running a dual spring rate in a dual spring rate style. (there's a primarty and a tender) Im not, Im running them in series, there is no 'seat adjustment'. Fox is about 1 mile from my house and they set it up for me. When your not running them in a typical 'dual-stage'format you basically take the 2 add them together and divide by 2 because now they have become 1.

-Red

Based on Sway-a-Ways dual spring rate calculator, you have a primary spring rate of 95 lbs/in.......not 219. You don't calculate a dual spring rate by adding together and then dividing in half the two spring rates. The reason the primary rate is lower than the tender spring rate is because while the tender spring is compressing the main spring is also compressing to some degree, so the overall rate is less than if the tender spring is working on it's own. Now, once the tender spring is fully compressed, the spring rate jumps up to 300 lbs/in which is the rate of the main spring. The length of each coil is a factor here, plus you are preloading the springs to set ride height, but that's the basic spring rate calculation.

 

[MDMIKE]

All you need to know to calculate spring rate is diameter of wire, outside coil diameter, and # of active coils ( I usually count all coils and subtract 1 coil for # of active coils because about 1/2 of the top coil and 1/2 of the bottom are inactive). My buddy posted the calculator link.

 

[MDMIKE]

Calculated some springs.

All rates are Approximates

SJ RR TJ 6" 200
RE FT ZJ 4.5" 200
RE FT TJ 5.5" 185
RE RR TJ 5.5" 215
Wn FT TJ 3" 125
Wn RR TJ 3" 120

 

[Nay]

I'll tell you one other thing: copy what OME does for the passenger side coils.

OME has a different passenger side coil to keep side to side balance - taller lifts tend to lean more to the passenger side and this is irritating. If somebody came up with a 3"/6"/8" coil series that was designed to provide this balance, along with stiffer than typical spring rates...you'd have a sweet product on your hands and one that nobody else offers.

Nay

 

[CRASH]

Calculated some springs.

All rates are Approximates

SJ RR TJ 6" 200
RE FT ZJ 4.5" 200
RE FT TJ 5.5" 185
RE RR TJ 5.5" 215
Wn FT TJ 3" 125
Wn RR TJ 3" 120

What wire diameter did you measure for the RE ZJ? The 7.5" RE's are about .0625" thicker than the RE ZJ's.

I don't believe that RE TJ rears are stiffer than RE TJ fronts.........does that make sense to anyone?

CRASH

 

[Eagle]

Spring and damping rates are about my favourite subjects to discuss.

Both are of interest to me, as well, but I still think it can get like discussing religion or politics at a cocktail party.

I know that my brother and I have never agreed on either. We both drove, autocrossed and hillclimbed 2-seat AMXs, so you might think we would tend to have them set up the same. If you thought that, you couldn't be more wrong. At one time he was running an AMX with factory "rallye" suspension and he was using Monroe Load-Leveler rear shocks. Those are the shocks with the integral coil-over, for trailer towing. He thought they were great. I followed his car on a twisty, hilly country road one day, and every time he crested a hill you could see that the rear springs were literally launching the tail of the car, and the rear wheels were leaving the ground at each crest. When I mentioned it to him later, he didn't have a clue what I was talking about.

It's my unsupported view that spring rate and shock damping rate (or proportion) should be roughly inversely proportional. In simple terms, if you have stiff springs you don't need stiff shocks, and if you have wimpy springs you need more shock to control compression.

On a more technical level, what would be ideal would be the ability to adjust shock rebound and compression independently. A stiff spring resists compression fine, but needs the shock to resist extension. A soft spring doesn't require as much resistance to extension, but needs the shock to be better able to dampen compression. However, the shock manufacturers don't publish or release the damping characteristics of their shocks. In general, I think they are mostly engineered to be about 50/50 -- equally resistant (or equally not resistant) to both compression and extension. That's probably okay for stock suspensions, but when you move into the realm of enthusiasts who are trying to optimize and fine-tune a suspension for particular performance parameters and personal preferences, it's not helpful. Knowing the spring rate is helpful, but unless you can also select an appropriate shock absorber to match the performance curve of the springs, you really haven't accomplished very much.

 

[MDMIKE]

I measured wire dia. .625 in, 13 total coils (12 active) with OD coil dia 5.1" anybody double check for me.

 

[CRASH]

Both are of interest to me, as well, but I still think it can get like discussing religion or politics at a cocktail party.

I know that my brother and I have never agreed on either. We both drove, autocrossed and hillclimbed 2-seat AMXs, so you might think we would tend to have them set up the same. If you thought that, you couldn't be more wrong. At one time he was running an AMX with factory "rallye" suspension and he was using Monroe Load-Leveler rear shocks. Those are the shocks with the integral coil-over, for trailer towing. He thought they were great. I followed his car on a twisty, hilly country road one day, and every time he crested a hill you could see that the rear springs were literally launching the tail of the car, and the rear wheels were leaving the ground at each crest. When I mentioned it to him later, he didn't have a clue what I was talking about.

It's my unsupported view that spring rate and shock damping rate (or proportion) should be roughly inversely proportional. In simple terms, if you have stiff springs you don't need stiff shocks, and if you have wimpy springs you need more shock to control compression.

On a more technical level, what would be ideal would be the ability to adjust shock rebound and compression independently. A stiff spring resists compression fine, but needs the shock to resist extension. A soft spring doesn't require as much resistance to extension, but needs the shock to be better able to dampen compression. However, the shock manufacturers don't publish or release the damping characteristics of their shocks. In general, I think they are mostly engineered to be about 50/50 -- equally resistant (or equally not resistant) to both compression and extension. That's probably okay for stock suspensions, but when you move into the realm of enthusiasts who are trying to optimize and fine-tune a suspension for particular performance parameters and personal preferences, it's not helpful. Knowing the spring rate is helpful, but unless you can also select an appropriate shock absorber to match the performance curve of the springs, you really haven't accomplished very much.

You're not looking at the right shocks.
7100 series:

9100 series:

Both of these units are available with a mind numbing array of compression and rebound rates, measured in newton-meters of force. In addition the 9100 series can be had with bypass modes to garner position sensitive valving. The new rig is going to run 275/78 front and rear (compression/rebound) as a baseline, and I may stiffen the front rebound rate as necessary. That's the beauty of rebuildable/tunable shocks.

CRASH

 

[MaXJohnson]

MDMike:
All you need to know to calculate spring rate is diameter of wire, outside coil diameter, and # of active coils ( I usually count all coils and subtract 1 coil for # of active coils because about 1/2 of the top coil and 1/2 of the bottom are inactive). My buddy posted the calculator link.

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

Redcbr007:
That is correct if Im running a dual spring rate in a dual spring rate style. (there's a primarty and a tender) Im not, Im running them in series, there is no 'seat adjustment'. Fox is about 1 mile from my house and they set it up for me. When your not running them in a typical 'dual-stage'format you basically take the 2 add them together and divide by 2 because now they have become 1.

The formula for springs in series is:
1 / Ktotal = (1 / lower spring rate) + (1 / upper spring rate)
using this formula will return the rate Goatman provided. How do your "springs in series" differ from other "springs in series"

Eagle:
Use your sample numbers of a 125 lb/in spring, and an added weight of 125 pounds. That extra weight will drop the static ride height 1" but the rate after that will still be 125 lbs/inch. Of course the added weight adds mass, so the ride quality can't be exactly the same, but it'll be in the same ballpark.

Adding 125 pounds to the front should drop the height by ~1/2" since it is compressing two springs in parallel. In general, increased sprung weight should dictate an increase in spring rate to maintain the same ride quality based on suspension frequency.

 

[MDMIKE]

That equation seems right but the material rigidity standard you are using must be slightly different from the calculators I have found. Both calculators give me a rate of 199.536 for the same numbers.

 

[MaXJohnson]

That equation seems right but the material rigidity standard you are using must be slightly different from the calculators I have found. Both calculators give me a rate of 199.536 for the same numbers.

I've seen variations in the value for Youngs modulus (for steel). Usually 11.5X10^6 or 12X10^6. I used 11.5X10^6 which is divided by 8 for calculating coil spring rate. Plus, I rounded the product; 1.4375X10^6 to 1.44X10^6 for simplicity.

 

[olympic4x4tech]

Id like something with around a 250 spring rate with about 6-7" of lift.

 

[MDMIKE]

Does anyone have the RE 7.5 XJ specs(wire dia, coils, coil OD) handy I know crash was going to check later

 

[CRASH]

Give me two hours......got to fight traffic home and I can give you an answer.

CRASH