[santak]

Ok, all you guys with experience in suspension techs, maybe you have some comments that'll get me a little further:

I understand there are suspension kits out for the 1/2, 3/4 and 1 ton trucks, gas as well as diesel powered. It makes sense that springs for a diesel truck would be stiffer than e.g. for a SB due to the weight factor. So far so good. Now, I was talking to Rocky Mountain Suspension a little while ago and was asking for some stuff with regards to my application, which is:

clear 35s, carry around weight: about 335# - stock bumper on the front and on the rear axle probably plus 270-350# as well, so about a total of 600+lbs. And the whole thing without providing a stiffer than stiff suspension setup, but rather something with good street manners that doesn't sweat a couple of trail runs. I'm not intending a trail rig build up, but rather something like a Earth Roamer in XXS (if anyone has followed that project online or in Four Wheeler mag).

now the guy at Rocky Mountain (can't even remember his name) at that point was: sorry don't have anything for you. All springs will get tired and sag, basically a lift kit is not built haul weight. Ok, I get it so far no spring lives forever, but I was wondering: wouldn't a diesel kit be built for more weight than I have with my SB now, so those 300 additional pounds would basically just smoothen out the ride again? Does anyone know if the rear spring rate for 3/4 trucks, gas and diesel powered, are different or if they're the same? Anybody see any trouble with a 3/4 ton diesel suspension fitting on a 1/2 ton SB RC?

I'd prefer an off-the-shelf solution at that point that having a custom suspension setup. Though I haven't contacted national springs for their pricing information, some of the "kits" I found run as high as 3.5K, and I'm not talking about Canadian $ or Yens.

Any helpful comment is appreciated.

 

[Sam Simpson]

usually the 3/4 and 1/2 tons springs will be the same. There isn't a lot of companies that make a true diesel lift, I think I only found 1 company in my search that made a seperate lift just for the cummins compared to a gas engine 1 ton. I don't remember who that was, it was a long time ago

Now, you 335#'s, are you saying the stock bumpers weigh that much? Or do you mean about 335#'s out front extra weight and 270-350# extra weight out back?

Those weights aren't too bad. If you used the cummins lift that is made for only a cummins then that would work.

Another alternative is using the 1/2 ton / 3/4 ton lift and something that assists the spring rate, like helper springs, adjustable coilover load shocks, or an extra capacity air bag setup.

Or maybe just takeing the 1/2 ton / 3/4 lift and adding some sort of add a leaf to it might work as well.

 

[santak]

The weight ratings I mentioned above are additional weights, minus the stock bumper, which is negligible. Come to think about that the rear probably will be more around 600-650 additional lbs (I mixed the kilograms and lbs, my bad).
I want to build the whole thing as light as possible for 2 main reasons

• I don't want to necessarily max out the payload, and so far I will probably be close to a curb weight of about 6400# when it's all done, which is my GVWR.
• the light the vehicle the less stress overall in operation: recovery, driving, weight limitations etc etc

I'm guessing at this point that the frame has something to do with the payload also, but in case it's only the axles, they will be swapped anyways for a set of D60s....

I know that Skyjacker advertises a 1/2& 3/4 ton lift and a separate 1 ton lift for gas powered trucks as well as a 3/4 & 1 ton lift for diesel powered trucks. Superlift only "suggests" you use their HD springs when having a winch or diesel engine. Tuff Country is basically the same as Superlift. Was also looking at BDS, since they're supposedly are also pretty good, the problem I'm having is, they don't give out any information about spring rates, even if asked specifically. Also with pricing, everywhere you look it's: please call for pricing...strange.

I figured I would need about 5" to clear those 35s on a 16x10 rim (so it will be something like a 315/75R16), so if Skyjacker nets 6", one inch more or less doesn't bother me, the geometry of the driveshafts or steering doesn't change by that much due to that 1". Don't know if I want a 4" and body lift the rest, heard both pro and cons about it and haven't settled that argument for myself.

I was alos looking at the airbag systems and it seems to be a nice alternative to take some load off the springs, and the rear is where the main stuff will be. But I haven't looked into that technology too much.

Good ideas so far Sam. Thanks.

 

[Sam Simpson]

If I was going to do this, I would go with a 4" suspension and maybe 1 or 2" body lift. With the 4" suspension lift your steering geometry won't be as bad and you won't have to lengthen drivehsafts or any other serious mods.

 

[santak]

You know, I was thinking the same, but then I came to think of how much this whole thing will cost me and then I was like: ok, what's another 2 driveshaft and a crossover steering? After I'm done I think the only thing that I haven't changed on that truck will be the frame and body, just to give some scale of what I have sketched out for the year(s) to come.

 

[Sam Simpson]

lol, I know what you mean. My RC only has the orginal body and frame, but severe body mods are coming soon

 

[RXT]

Basically what you are asking is about spring rates.

Spring rate is the amount a spring will compress under a given weight. For example a spring rate of 250lb-in, will take 250 lb to compress one inch.

Now if you have 250lb-in springs with your 335 lb estimated weight, a single spring would compress alittle over one inch. However keep in mind that suspension manufacturers already figured in how long the springs must be when installed.

If you were to add a Cummins with its 980lb dry weight divide the weight by 2 (You have two springs up front) you would only lose slightly less than two inches of height.

Remeber that based on spring rate you always divide by the number of springs carrying the load. In your case carrying an additional 335 lbs on both front springs will compress them alittle more than 1/2 an inch

Heres a helpful site to calculate spring rates;

http://www.efunda.com/DesignStandards/springs/calc_comp_k.cfm

Ed

 

[santak]

thanks Ed. You hit the nail on the head: I am looking for spring rates, but nobody tells me and I only found a table with spring rates for 4" lifts for the Blazers and Jimmys over at ck5. All I get from the companies when asked specifically for spring rates is: they are a little stiffer than stock, to make up for the extra weight of bigger tires. Not exactly what I was looking for

However, another question comes to mind. Did I get that correctly that when you say

However keep in mind that suspension manufacturers already figured in how long the springs must be when installed.

does that mean that, taking your example from above, a 4" lift 1/2 & 3/4 ton spring with 250lbs rating would require an additional 250lbs to compress this spring 1 inch? Additional meaning that the weight of the front end of the truck is already factored into the 4" lift, i.e. engine, front clip etc. and doesn't compress the spring already by x inches. Additional = winch, other than stock bumper etc.

 

[Evildriver-3]

Yeah follow what RXT said, however just a word of caution with 1 ton springs, i have had well over 600 lbs in my truck and it didn't compress a damned thing and it took another 500 lbs for it to ride nice, it still didn't compress a damned thing though, the tires were the only thing giving away that there was weight in the truck

 

[santak]

that's what I'm afraid of: a very harsh ride. Looking at the info in this thread I'd say the rear is pretty much covered: put in some 3/4ton springs (diesel or gas should have the same spring rate for the rear, don't you think?) and then add an airbag system, like the Firestone rite-ride.

The only thing I'm not so perfectly clear about yet is the front end. I know that some of you run HD bumpers and a winch, how does it look like? Lost a lot of clearance? Any? I just want the minimum amount of lift to clear those 35s and have enough clearance to allow for some compression. I don't need any high RTI ramp ratings on that truck, it's not a rock buggy, it's a travel truck build up.

 

[Evildriver-3]

Well for the rear if you are thinking of running air bags to suplement wieght carrying then use a normal spring, as for the front in my truck i had 1 220 lb guy 1 250 lb guy and 1 180 lb guy standing on my front bumper and it didn't compress at all, the 1 ton stuff needs alot of weight to feel comfortable, to compress god only knows, i had my 30 foot boat behind it on a trailer with alot of tounge weight on it maybe more than the 1100 pounds in the bed i still haven't seen those springs compress, we look all the time and it's always the tires just flattening out, we wonder what it takes to flatten those springs out even alittle, i would recommend stay away from the 1 ton stuff

 

[santak]

That doesn't sound like something I would want in my truck I'll try to get in touch with Skyjacker again and get some spring rates...maybe they are willing to give out that info this time...

 

[RXT]

....does that mean that, taking your example from above, a 4" lift 1/2 & 3/4 ton spring with 250lbs rating would require an additional 250lbs to compress this spring 1 inch? Additional meaning that the weight of the front end of the truck is already factored into the 4" lift, i.e. engine, front clip etc. and doesn't compress the spring already by x inches. Additional = winch, other than stock bumper etc.

Thats about right. When I bought my 6 inch lift springs, the unloaded springs were 10 inches tall. After the weight it sat right at 6 inches. They compressed 4 inches.

Also keep in mind that by their nature of running multiple leaves, leaf springs can also have progressive rates, meaning that the first few inches of compression maybe at say 250lbs per inch but increase to 300lbs in the next inches and 350lbs the next inch after that.

Ed

 

[santak]

cool, thanks Ed. Learned a lot about this stuff again. Now I'll need to get me some real numbers about those springs

 

[santak]

So, now I'm digging around and hey, lift kit manufacturers do have spring rates, just gotta make them dig through their books

These are the spring rates I got when asking lift for a 88 Dodge Ramcharger.

Manufacturer	Lift	Spring Rate f	Spring Rate r	Free Arch f	Free Arch r	# of Leafs f	# of Leafs r
Skyjacker​	4"​	500 lbs/inch​	500 lbs/inch​	4 3/4"​	9 1/4"​	5​	5​
Skyjacker​	6"​	535 lbs/inch​	500 lbs/inch​	6 1/2"​	11 1/2"​	5​	5​
Superlift*​	5"​	318 lbs/inch​	318 lbs/inch​	5.5"​	9 3/4"​	5​	5​
Tuff Country​	4"​	495 lbs/inch​	495 lbs/inch​	6 1/8"​	10 7/8"​	6​	6​
Tuff Country​	6"​	595 lbs/inch​	595 lbs/inch​	6 7/8"​	10 7/8"​	6​	6​
BDS​	5"​	15% over OE​	15% over OE​	5.5"​	9.875"​	5​	5​
Rough Country​	4"​	499 lbs/inch​	499 lbs/inch​	4"​	4"​	?​	?​

* I need to verify the Superlift data again, because after 2 calls I had basically 3 different answers.

Also, if anyone wants to add to this list, please feel free to IM me the info and I'll paste it in here.

I will be adding to that list as I get the information from a couple more manufacturers myself.

 

[awyseguy]

Need to ask them for the rates for the 3/4 & 1T pickup as well as the diesel packages.. For comparisons. I for one am figuring that when I order a kit for my RC It'll be for a 3/4T diesel.. To carry the weight better; I'm working on a bumper for the front end.. that I fear would be taking my lift away.
Aaron Wyse

 

[santak]

Almost every company has one package for 1/2 & 3/4 ton gasoline powered trucks. That is what I list above. Some companies don't even care about diesel trucks, or 1 tons. But from what I gathered so far is, that 1 ton springs will be really stiff, so I tried to get spring rates for the normal lift kits first and then see what I might actually lose with 350 additional pounds up front. Loss is in the neighborhood of around 1/2", depending on the kit (I don't really believe the 318 lbs/inch from Superlift).

So anyway, I will try to get that info on the diesels and 1 ton as well, but I have no idea what you plan on building as your bumper. The cummins weighs in about 500 lbs more than the SB mopar. That's a lot of weight!! The bumper I'm looking at is around 200-230 lbs, plus a winch with around 100-110 lbs = approx. 350 lbs.