[BigBlueBurban]

Think of it this way. By raising the resting ride height, the lower control arms angle down further than stock. However, this alone does not increase spring rate. What does, causing the "harsher" ride, is when the suspension compresses. Since there is now more room for upward travel, the bars twist farther than they did at the stock height. The farther they twist, the stiffer the spring rate becomes (in theory). I don't have the time right now - maybe later - but a diagram would really help with what I'm trying to say. LMM Guy - the torsion and coil comparison has one flaw, being that eventually coils compress to the point that all of the coils come into contact and they can no longer compress (extreme compression situations where no other factors such as bumpstops come into play) whereas the only limiting factor in how much a torsion bar can "compress" are other suspension components, ie bump stops, fenders, etc. or until the metal deforms. However for all intensive purposes your comparison helps put into laymans terms what is usually considered "PhD" material to most.

 

[EDS_5_OH]

If the t-bars are not up against the bump stops, you are not pre-loading them. If you look at a coil over from a dirt bike, it has a fixed length.Therefore you can preload that type of suspension. By simply "raisng" your t-bars does not preload them, unless you crank them beyond there amount of travel. Does installing a lift block under a leaf spring preload it? I think not.

I'm do not agree with you. If you crank the back of the torsion bar in relationship to the front, your are "pre-loading" that bar. It is the same if you had a coil-spring and compressed it some at install so the spring is pre-loaded when the vehicle is at rest.

 

[mmangels22]

great write up I totally agree no need to crank t bars. Just get a leveling kit or a mild lift and forget it.

 

[LMM_Guy]

Our torsion bars are NOT progressive rate... they are linear. It is very hard to make a torsion bar that is progressive, to do so you have to tapper the bar. Ours are strait....so the rate is strait. You'll add XXX lb's of force for every degree it's twisted.

You will not increase the resulting force or the rate of a spring by putting a spacer on the end. You will increase the rate if you put a spacer between the coils....which is not what I'm talking about. Coil springs do have the downfall of being able to stack coils effectively giving up the ability to be a spring. Torsion bars or leaf springs will not do this, you can bend them untill you go outside of their yeild point then they stay bent.

Lets simplify this further......take a spring with a rate of 10 lb/in, put a 20 lb weight on top of the spring and it is going to compress 2" You agree? Now put a 1" spacer that weights nothing between the weight and the spring.......will that spring compress any?

Pre-load: Lets better explain what is going on here. Say we take a 10" coil spring with a rate of 100 lb/in and compress it 2" to fit on our shock. We will effectively have 200 lb of "pre-load" on the spring. Then we crank down the spring seat another 1" and end up with 300 lb's of pre-load. Now lets take this shock and put it on a bike that will put 400 lb's of force on it. The bike will compress the shock 1"......it will take 300 lb's to overcome the preload then there should be 100 lb's left to compress the shock. You could adjust the spring seat down another inch and the bike would set 1" higher, but the force of the spring would be the same, it won't change untill you either add more weight or run out of travel.

To relate this to our trucks, we already have met the equilibreum point when we set the truck on the ground. All we are doing is changing the installed "height" of the spring. By cranking down the spring collar on our coil over or our bolts on our torsion bar all you are doing is changing the height of the point of which the spring acts on the chassis. The spring will not compress any more untill you bottom out the upper arm on the stop.

P.S. I'll have more time to dig up our actuall spring rates and find my torsion calculations later tonight.

 

[EDS_5_OH]

To relate this to our trucks, we already have met the equilibreum point when we set the truck on the ground.

I see what your saying, with this information, I retract my statement that by cranking the bars we are "pre-loading" them further than if we don't. I hadn't considered the fact that the truck is twisting them addtionally as it sits at rest on it's wheels. Assuming the additional crank at the keys is less than the final amount of twist when at rest, we have not changed the pre-load at all. Good info here...

 

[EDS_5_OH]

great write up I totally agree no need to crank t bars. Just get a leveling kit or a mild lift and forget it.

A leveling kit will be the same as cranking the t-bars.

 

[ryeguy]

LMM_Guy is pretty much right.

The "pre-load" on our torsion bars is the weight of the vehicle. And that's it. It doesn't matter if you rotate them 5 degrees or 10 degrees or turn them a whole "notch" with the same spring height, the "pre-load" is the static load placed on the spring regardless of ride height of the vehicle. Think about it from the torsion bar's perspective: it doesn't know if it's on a stock height truck or modified height or lifted, or green or brown or purple keys, or on a Ford or a Dodge or a HMMV or a Nissan. It just knows about load. And it's being asked to hold X lbs of load off a lever (the A-arm) and given its diameter, it twists Y degrees. It's no more complicated than that. If you disagree with this idea, I suggest reading a book like "Chassis Engineering", by Herb Adams. It's a well written book with good example, equations, and diagrams.

The way to change the pre-load is to change the amount of load on them. That can be done a few ways such as by transferring load to another item (like the spring jouncers that look like the bump stops). Or by adding a heavy front bumper - that will increase the preload. Or (effectively) by changing the geometries in the front A-arm suspension design.

I, too, believe that we are not going to introduce spring fatigue by raising the pre-load height of the vehicle, then repeatedly forcing them to the original compressed height defined by the jouncer.

The concerns about accelerated wear on certain parts like CV joints and tie rod ends and ball joints are warranted. The amount of load on these parts goes up exponentially, something like the chart presented earlier.

Another concern is handling - by changing the static angles on the A-arms we have introduced changes in how the vehicle will handle - things like anti-squat, anti-roll and a simple alignment cannot correct for these items. I believe we are putting more load on our anti-sway bar by turning up our keys, but again not enough to be concerned. Now, I have raised my LMM's front profile by 1.5 inches. To compensate (not correct) for these handling concerns, I'll be also putting a slight spacer between the jouncer and its mount to correct for that to make it more-like-stock again. The jouncer does play an important part in the vehicle's handling, and I believe that correcting for it after lifting with green keys is an often overlooked item.

On my LB7, we swapped to green keys. On my LMM, we simply re-adjusted the stock keys. The effects are the same, and thus were the results. I believe that Nick has also correctly identified a primary issue with turning the keys too far - limiting suspension droop.

'nuff for now, this post is long enough.

--Rob

 

[EDS_5_OH]

Another concern is handling - by changing the static angles on the A-arms we have introduced changes in how the vehicle will handle - things like anti-squat, anti-roll and a simple alignment cannot correct for these items. I believe we are putting more load on our anti-sway bar by turning up our keys, but again not enough to be concerned. Now, I have raised my LMM's front profile by 1.5 inches. To compensate (not correct) for these handling concerns, I'll be also putting a slight spacer between the jouncer and its mount to correct for that to make it more-like-stock again. The jouncer does play an important part in the vehicle's handling, and I believe that correcting for it after lifting with green keys is an often overlooked item.

You're talking about putting a spacer underneath the yellow compression bumper on the lower A-arm to restore it's relationship to travel when at stock height? My truck actually sat on the jounce stop when stock and rode terrible. I cranked it slightly at first just to lift it off the jounce stop and it rode much better.
My ride now with green keys and Cognito UCA's is as good as it was when slightly cranked (better than stock). Cornering might be reduced but with the wider tires, the stability feels the same.

 

[Reiter284]

Correct me if I'm wrong but isn't tightening the torsion bars is like twisting a coil spring tighter or compressing it more.

If you tighten the torsion bars more it puts downforce on the A-arm and lifts the truck up more.

 

[kilo6490]

really in depth info. Hard to understand at first, but it's right. I actually thought it was the other way around, but after reading this, I understand, and it makes perfect sense.

 

[ryeguy]

You're talking about putting a spacer underneath the yellow compression bumper on the lower A-arm to restore it's relationship to travel when at stock height? My truck actually sat on the jounce stop when stock and rode terrible. I cranked it slightly at first just to lift it off the jounce stop and it rode much better.
My ride now with green keys and Cognito UCA's is as good as it was when slightly cranked (better than stock). Cornering might be reduced but with the wider tires, the stability feels the same.

Yeah, this is what I'm suggesting - have it *just* make contact at static ride height.

--Rob

 

[EDS_5_OH]

Okay, the *just* will be key to a decent ride. Mine stock sat on the jounce bumper too much.

 

[LMM_Guy]

Ok the two BIG idea's I've seen come out of these discussions that I would like to dive into more are:

1. The added "twist" for lack of a better term at full compression because of us lifting the truck. I don't think it's enough to matter at all, but I want to prove it with math.

2. The effect that bump stops have on ride, this next to the lack of droop travel is really the key to a good ride......lets discuss further.

 

[ryeguy]

Bump stops: are really called jounce bumpers for our trucks. I remember being concerned about this for my LB7. There was also discussion on another diesel board about this some time ago. The dealer told me the suspension is supposed to "rest" on them - i.e. no clearance at normal ride height, like you would see on a normal bump stop. After doing some measuring, I was able to basically confirm this based on info in the factory service manual. They are really like variable-rate springs, and act as a supplement to the regular (torsion bar) spring rate.

So...by raising off of those, you get just the torsion bar spring rate until you contact those bumpers. So you'll have a softer spring rate until you use up that extra travel. If the truck was basically sitting all of its weight on them, then your effective spring rate will then be dictated by the jounce bumper. Based on posts here, I seem to like a firmer ride than others, which is why I want to compensate for that new clearance.

--Rob

 

[MB1]

Ok the two BIG idea's I've seen come out of these discussions that I would like to dive into more are:

1. The added "twist" for lack of a better term at full compression because of us lifting the truck. I don't think it's enough to matter at all, but I want to prove it with math.

2. The effect that bump stops have on ride, this next to the lack of droop travel is really the key to a good ride......lets discuss further.

Good. I like this.

Our torsion bars are NOT progressive rate... they are linear. It is very hard to make a torsion bar that is progressive, to do so you have to tapper the bar. Ours are strait....so the rate is strait. You'll add XXX lb's of force for every degree it's twisted.

False. The opposite is true. The best example is a fishing rod. The end of it is thin, and responds to a small load. The thicker part of the rod only starts to bend under a larger load - hence a progressive rate.

The TB is uniform thickness front to back, therefore it will have an increasing # load necessary for each degree rotation.

I doubt if cranking them up will cause them to fail - like you said earlier, they can take a huge amount of stress before they will permanently deform.


2) I agree 100%. Look at a trophy truck. 2' travel, and they have roughly half of that in sag? Our trucks only have 7" to work with, so when you crank up the TB's you will upset the balance.

My observation when tuning my TB's was this. When the bars were low, I had a rough compression when hitting a bump, and since the suspension was already touching the bumpstops I think it's safe to say that there was so little travel left that I needed to go higher.

I raised them up - guessing 6 turns? and the ride was pretty good. I went two turns higher, and it was harsh again. I think this was the point that I was too close to the top-out stops. I started coming back down 1/2 turn at a time and settled at the point where it felt the best.

As I sit now, on one side the bumpstop is barely touching, and theres about 1/4" clearance on the other side. I know it sounds bad.

Even when I jack the truck up off the ground there's only about 1" of clearance. pic below.

 

[MB1]

Bump stops: are really called jounce bumpers for our trucks. I remember being concerned about this for my LB7. There was also discussion on another diesel board about this some time ago. The dealer told me the suspension is supposed to "rest" on them - i.e. no clearance at normal ride height, like you would see on a normal bump stop. After doing some measuring, I was able to basically confirm this based on info in the factory service manual. They are really like variable-rate springs, and act as a supplement to the regular (torsion bar) spring rate.



--Rob

Thanks, I feel better about mine now. See my post above this one.

 

[Reiter284]

I think it's going to be very difficult (not impossible) to "prove" with math the effect of the spring rate on the ride. There are a lot more variables that come into play. The dampening of the shock, the rotation of the a-arm changes the moment of the force to the ground, and the length/speed of the motion (what size of bump you hit and how fast).

There is a lot going on there besides a slight increase in spring rate. I think it would be relatively easy to calculate the increase in beginning/ending spring force. However the effects of this on the ride would be much more complicated.

For example, you may calculate 1100lbs of force before cranking at rest and 1150lbs after cranking at rest. This doesn't tell us the whole story.....

 

[BigBlueBurban]

What it does tell us is there's a reason GM employs so many engineers .... Or is it so few? Hard to tell sometimes.

 

[Nick.V70]

I was "approached" in another thread about WHY torsion bar lifts cause rough rides. It was stated that "the keys let you raise the front w/o added stress " which is completely not true. My goal with this thread is not to "call anyone out" but to simply make my case and participate in a CIVIL conversation about the technical aspects of lifting with torsion bars. Let me state that I am NOT the creator of torsion bar lifts...hell I've only owned my LMM for 8 months. Most of my knowledge came from this site along with my own observations of my own truck. I am a weekend racer and an engineer by day. I've designed suspension systems from the ground up. My experience is mostly with road race cars.

I have to start by giving Nor-Cal Nick the most credit as he states perfectly WHY torsion bar lifts cause a rough ride in the thread below. Read it....understand it.

http://www.dieselplace.com/forum/showpost.php?p=1641068&postcount=7

To summarize, the "rough ride" everyone complains about is from the shocks and/or upper control arms running out of droop travel...... .

I have to start by giving credit back to LMM_Guy for giving credit to my post I did on the "fly" sparked from a thread debate a while back. My post is not the best and can use a clean up to help better explain the GM front ends. LMM_Guy is posting from a more in depth direction that is hard to grab if you are not on top of the terms compared to mine being more "la mens terms". LMM_Guy is pretty dead on the money of what he is putting out on the table. I myself am not or hold a engineer degree but I have spent a long time chasing issue's with these front ends over the years of being in the suspension lift business.

LMM_GUY GREAT thread :bow:

If I may put a few words in off of my knowledge with the GM front end..:beerchug:

has anyone taken out the bumpstops???

Been looked at but cutting the OE bump stop off would fix only a small percentage of the overall issue if not add to the problems.

made a crude chart to help me with my point.

You are in the right idea and it make complete sense but over the years I have not so much seen this happen. Maybe 1 in or there but not a direct common reflection seen.

Our torsion bars are NOT progressive rate... they are linear. It is very hard to make a torsion bar that is progressive, to do so you have to tapper the bar. Ours are strait....so the rate is strait. You'll add XXX lb's of force for every degree it's twisted.
.....
......
To relate this to our trucks, we already have met the equilibreum point when we set the truck on the ground. All we are doing is changing the installed "height" of the spring. By cranking down the spring collar on our coil over or our bolts on our torsion bar all you are doing is changing the height of the point of which the spring acts on the chassis. The spring will not compress any more untill you bottom out the upper arm on the stop.

Very true. The torsion bar is not getting twisted when cranking rather than one end turns and the other end follows and pushes down on the control arm witch lifts the truck.

LMM_Guy is pretty much right.
....
.....
I, too, believe that we are not going to introduce spring fatigue by raising the pre-load height of the vehicle, then repeatedly forcing them to the original compressed height defined by the jouncer.

The concerns about accelerated wear on certain parts like CV joints and tie rod ends and ball joints are warranted. The amount of load on these parts goes up exponentially, something like the chart presented earlier.

Another concern is handling - by changing the static angles on the A-arms we have introduced changes in how the vehicle will handle - things like anti-squat, anti-roll and a simple alignment cannot correct for these items. I believe we are putting more load on our anti-sway bar by turning up our keys, but again not enough to be concerned. Now, I have raised my LMM's front profile by 1.5 inches. To compensate (not correct) for these handling concerns, I'll be also putting a slight spacer between the jouncer and its mount to correct for that to make it more-like-stock again. The jouncer does play an important part in the vehicle's handling, and I believe that correcting for it after lifting with green keys is an often overlooked item.

On my LB7, we swapped to green keys. On my LMM, we simply re-adjusted the stock keys. The effects are the same, and thus were the results. I believe that Nick has also correctly identified a primary issue with turning the keys too far - limiting suspension droop.

'nuff for now, this post is long enough.
--Rob

Wear on,

CV Shafts- Most of the failures are do to end users using there trucks in a way that is best or more suited for a true lift kit that drops the front diff. Guys that are Sled pulling, 4wd boost launching or off roading in ways where the suspension is dropped out and you are using the torq of the truck to crawl over obstacles need to stay away from any style of "cranking" the torsion bars and taking the suspension working angles higher. This goes for stock or lifted trucks that have a suspension package.

Tie Rods & Idler/Pitman Arms- So as you increase the front end hight you also increase the tie rod working angle that directly increases the load to the Idler and Pitman arms. The GM front end was designed to have the tie rods working in a close to flat push and pull motion to the center link. The center link has a "S" bend on the end so as you increase the working angle your tie rods now push and pull on the center link that puts it in a twisting motion working the Idler and Pitman arms in a higher percentage than designed decreasing the life drastically. Also your tie rods not must work at a increase leverage rate and they tend to fail as well.

Thinks of this....ever arm wrestled? Would you want to square up with your opponent to offer the "Most" strength you have to win the match. Yea will your tie rods are the guy that looses because he was not squared up and could not stand a chance.

Ball joints- The factory UCA has the OE ball joints angled to best suit the factory stance. Now increase that stance hight and the ball joint is riding on a angle not designed for longest lasting and strongest position.

Handling- Now that the truck is at a higher pre-load/stance in the factory suspension yes you will have off setting feed back. The biggest is the shock (too short to start with) and it's OEM valving that was designed to suit the factory travel points of how the truck sits off the show room floor. The shock is and was not developed to slow the travel down so the truck doesn't top out so fast.

Now after all of this that is just talking about the hight changed from factory stance, add the extra weight and taller leverage and load of the new wheel and tire combo you will be looking to add after lifting the front end up higher

Really all this talk we are going over relates directly to ANY IFS GM owner, lift kit or not. It all works the same. A lifted suspension package truck has the same suspension travel as a factory truck so it relates.




When it comes down to it there are many factors that play a roll in the GM IFS suspension design and really leveling your truck is just as much a suspension package of product that off sets all the little things that get taking out of premium working angles. Those the need for the many products that are commonly sold every day. The funny thing is that when most people buy suspension lift kits non of these upgraded products to help the steering and ball joint are sold or even said to the buyer but he we are talking about all this just over the leveling discussion, makes you think huh....

 

[BLT2WRK]

Cause and affect. Said I would consider larger tires & small lift when I was due for new treads. Time has come. Was about to pull the trigger on a set of keys but something really bugged me. How it is that re-keying is not the same as turning the TB's? As others write (to include key mfg's/suppliers) that turning gives a rough ride, re-keying does not. I asked a local 4x shop. He said the same. When I Q'd how a rekey can lift but is not the same as turning my OEM keys? He said he wasn’t sure but it just works that way. Hum? As I came across this thread earlier today, the timing could not have been better. LMM_GUY, nice topic. This amount of data was way more than I bargained for. Although very interesting, I am simply looking at forecasting the adverse effects of any mods I am considering. Ya'll's threads are very insightful. At my start, my basic objectives were: new 16” wheels, slightly larger tires with small lift as I have had clearance issues and the ‘look’ will improve. All this, without causing damage or premature failure and voiding warranty on components.
My '05 3500 single w/ utility bed weighs in a 9k and has since new. Yes, plenty of tools in the bins. In the rear I am just tapping the overload springs. When I say tap, I mean it. They TAP and tap. I know I am adding bags to get 'some' load off the leafs. The front? Well I was hoping for 285 tires on 16" rims all around. After all this TB reading, I am not doing 285's since another common sense topic came about in a thread. The oversize tire can and will travel back to where it didn’t fit in the first place. Thought about twisting the TB's just a tad to lift for looks. Now I am not so sure about that as it will effect the geometry. I am not doing keys after seeing and reading Nicks stuff. Again, geometry ‘cause and affect’. Then thought about 275's but I can't seem to get those in E load. So then I decided new wheels and OEM size 265's in E load and no level kit lift. I don’t scare easy but I am afraid of 3 things here. Wasting money, breaking my truck and adding more unexpected projects on my overloaded to-do list.
Nick, tonight I viewed your recent post and project pics. Besides the cost, I have Q’s: How does your mild lift with those component changes effect the Mfg Warranty? (I have the GM 5/72). What are the new weak spots? And, as this string started, how did the ride change? Rougher, same, softer?