Zr2 front suspension

[kylant]

well, i removed most of the parts I put on the truck and traded it for a ZR2. basically went back to gas. way to many potential issues with the diesel.

 

interesting tid bit. the truck rode much better with the stock suspension parts (shocks, torsion bars, leafs) back on it. 

i left the torsion bars cranked slightly. but the ride was much smoother, absorbed bumps, cracks, etc... in the road better. i was actually quite surprised. i do remember that truck being the best riding stock hd truck i have had. 

 

i had fox reservoir accutune valved shocks, cognito comfort ride torsion bars, and cognito comfort ride leaf springs on the truck. 

 

food for thought.

accutune did tell me that the softest riding shock would be a rancho 5000.

 

on this truck, i think i will swap the torsion bars and leafs, but leave the mutlimatic shocks. will see

 

i measured the torsion bars, and the cognito ones are definitely smaller diameter. not much

[Chuck FB]

2 hours ago, kylant said:

well, i removed most of the parts I put on the truck and traded it for a ZR2. basically went back to gas. way to many potential issues with the diesel.

 

interesting tid bit. the truck rode much better with the stock suspension parts (shocks, torsion bars, leafs) back on it. 

i left the torsion bars cranked slightly. but the ride was much smoother, absorbed bumps, cracks, etc... in the road better. i was actually quite surprised. i do remember that truck being the best riding stock hd truck i have had. 

 

i had fox reservoir accutune valved shocks, cognito comfort ride torsion bars, and cognito comfort ride leaf springs on the truck. 

 

food for thought.

accutune did tell me that the softest riding shock would be a rancho 5000.

 

on this truck, i think i will swap the torsion bars and leafs, but leave the mutlimatic shocks. will see

 

i measured the torsion bars, and the cognito ones are definitely smaller diameter. not much

I couldn't recall which engine you had in your truck you had been working with and so it was the diesel and did that come with the 5600 rated torsion bars ?. This new gas truck, did it come with the standard 4800 rated bars ?

 

I was watching a video of a youtuber who recently took a new AT4X ( I believe its the diesel but not 100% sure ) and had a McGaughy's 4" lift installed but that would be a 4" lift compared to a stock non X truck so the actual gain in height was only the height difference between the X model and his lift. Why he went through all that expense was that he claimed the 4X has less droop travel over a stock suspension and he claimed with this "true" 4 inch lift that the ride quality improved and also it put the half shafts and tie rods at a better angle than what the 4X does along with 3 inches or so of droop. He claimed the 4X only has 2 inches of droop and was wondering before you touch your truck, to do some measuring from the under side of the fender to the hub center with the truck on its wheels and then jack the truck up and measure again to see how far your factory ZR2 suspension is able to droop. Oh and he did keep his multimatic shocks with the lift kit but a small extender is incorporated to make the shocks work with the lift. Part of why he went through all that was so he could stuff 38" tires under it with some slight inner fender liner mods. He claimed his ride improved noticeably because of the angles and the extra droop gained the way he set it up but of course tires being changed would play into that as well. 

 

And speaking of the diesel, did you have any issues pop up or was it the experience of pouring in DEF and noting the DPF regens and all of that lovely un needed garbage to have to live with ? 

[kylant]

my truck was diesel. 5600 lb torsion bars. 

i don't have a need for diesel other than the "cool" factor . not towing, not hauling 

my truck had 13.8mpg economy for the life of it. not much better than gas. gas is anywhere from .50 to $1 less a gallon here. 

no issues, but only a matter of time. i am seeing more and more issues with these new duramax trucks right around the 20k mile mark. didn't want to deal with it if they arose. 

for me, gas just makes more sense. i should have gone gas in the first place.

 

i know who you are talking about. 

cognito claims the same. they say adding a shock spacer will add about 1" of droop. it that is true, that tells me the shock is the limiting factor.

i will measure droop travel before i change anything. 

 

this truck has 5200 lb bars. it does ride better than the duramax. the rear is the issue

Edited November 13, 2025 by kylant

[Chuck FB]

Everyone's use case for what they will generally do with their truck can be different and I too was tempted to buy the diesel because I know its certainly more capable for towing and they are very popular if for some reason I had to sell it in the area I am located. But I knew that would come with the potential negatives and dealing with cold weather for half the year and the diesel typically takes quite a bit longer to warm up. I just wasn't as gung hoe anymore to deal with the downsides and yes these days diesel fuel as I figured out locally would be about 95 cents CAD more per US gallon, very different from years ago when diesel was quite a bit less than gas. Of course the rig pigs up here, I don't know if they can get away with it now but years ago that was the huge incentive to have a diesel pickup as they were basically stealing diesel from the oil rig they worked on site at and the all did it and imagine the company knew it and just let it happen. I had thought of getting the 3.0 mini duramax had I gone the half ton route but I have an uneasy feeling about that engine long term, great fuel economy but ... 

 

However if one planned on lifting a truck to the sky, the diesel has a lot more going for it to drive that billboard sized frontal area on large tires down the highway. 

 

I am guessing that the extra weigh of the front bumper and skid plates and potential for mounting a winch may have a roll in GM putting the 5200 bars in the front, but you do still have those other bars if you ever want to swap them in for an experiment. 

 

I could not tell as it was too dark under that guys truck when he was showing the factory suspension in droop without the tire on but it almost looked to me that the upper A arm was not resting down on the steel pad that stops the droop travel. Something you should look closely at when you do your droop measuring test and you could at that point take the tire off for access ( using jack stands for safety ) unbolt the bottom end of the shock and see what additional travel the hub would droop to. That is "if" the droop stop is not being rested on with the shock bolted up. 

 

The guy I referred to, I looked at a few other recent videos of him using a prior modified 2020 half ton with the 6.2 and when he gets something modded on his truck, does he ever as that is quite the rig with that long arm front suspension lift with the various shocks and the rear end cut through the box with taller shock towers to turn the truck into a longer travel desert pre runner and the fiberglass widened body panels, $$$ was put into that truck and then being able to fit 40's on it, that guy likes his toys !. 

[kylant]

did some measuring. 100% stock ZR2 (other than reducing rear tire pressure) and Chevy rubber bed mat

 

front ground to fender: 42 1/2" 

hub to fender: 26"

full droop hub to fender: 28 1/4"

droop: 2 1/4"

1 finger width gap between UCA and service perch 

 

rear ground to fender lip: 43 3/4"

 

rake: 1 1/4"

 

Edited November 19, 2025 by kylant

[Chuck FB]

3 minutes ago, kylant said:

did some measuring. 100% stock ZR2 (other than reducing rear tire pressure)

 

front ground to fender: 42 1/2" 

hub to fender: 26"

full droop hub to fender: 28 1/4"

droop: 2 1/4"

1 finger width gap between UCA and service perch 

 

rear ground to fender lip: 43 3/4"

 

rake: 1 1/4"

 

Interesting, so my chev stock before I did some re adjusting of the torsion bar keys "averaged" between the two sides to be 24.5 inches from hub center to fender and averaged 40.5 from the ground to fender on the front with the stock 20" wheel/tire combo. Droop, that I never recorded but did that experiment after I had reset both sides to 25" and from memory I am going to say I had around 2  7/8 droop or just under that as one side was slightly different then the other by an 1/8, so that would be somewhere around 27  7/8 or just under in total droop going off of memory. My total droop distance would of course not changed with my adjustment of the torsion bars but my actual droop would have by around a 1/2 inch more before I touched the torsion keys so again a little speculation that my average factory keys setting droop would have been around 3 1/4 or a bit more. What I don't believe I had done though was actually look to see if the UCA were resting on the frame perches, I "assumed" they would be. 

 

My rear, again the average between the two sides was 25  1/8 to the hub and 41  5/16 or so to the ground and I already had a bak flip cover, mud flaps and the Chev accessory rubber mat in the back by then which would make a slight difference to the rear weight and keep in mind I have the factory spray in liner and the fifth wheel prep as those items would add up as well. 

 

Oh and I had reduced the front tires down to 40 pounds and the rear to 35 before this measuring was done so the fender to ground height would have dropped a bit accordingly from fresh out of the factory measurements. 

 

So definitely its not bs about the ZR2/AT4X having less droop than a stock truck and "maybe" as much as an inch less it would appear like. That is not exactly what I would have expected GM to do, I would take a wild guess it was not what a suspension engineer was hoping for as there are always compromises made when it comes to big business and take the Allison transmission name, marketing vs substance. 

[Epsilon Plus]

ZR2s have MORE not less droop. Some pages back where I'm doing the swap I posted a pic with driver side ZR2 and pass still stock and you can see the difference. 1.75" more for ZR2/AT4X

Edited November 19, 2025 by Epsilon Plus

[Epsilon Plus]

On 3/30/2024 at 5:35 PM, Epsilon Plus said:

A look at the increased droop travel stock passenger side vs ZR2 driver side (both ZR2 diff drop brackets in). No torsion bars in. Stock is 8.25" from lower ball joint nut to ground. ZR2 6.5"

 

 

[Chuck FB]

25 minutes ago, Epsilon Plus said:

 

 

What you picture there, wouldn't that just be the assembly itself able to hang down further due to the different knuckle that the ZR2 has which equates to the raise in the trucks height when all said and done, either the parts added as you did or if one bought a ZR2 off the lot ?. Put another way, taking a stock ZR2 from the show room floor and how the factory adjusted the torsion bars, measuring the fender to hub center and then lifting it with a jack or shop lift to allow the tires to hang in mid air, then remeasure the fender to hub distance. 

 

The only item I came across lately and wasn't even looking for such information but was watching a youtuber that had just recently bought a AT4X and his claim was that the droop travel from factory on his truck was reduced over a non X truck, I believe he talked about it being around 2 inches of droop they measured. I was surprised at that as I assumed it would have had the same droop travel. But then again there is only so much that can be done with the same length A arms and why race trucks ( and often were two wheel drive ) have wide A arms to increase that stroke distance. The only way one would gain more over all travel is to do like some have done and hack the UCA droop travel stop off and rely on the shocks stroke to extend to its limit I assume with a shock that had a long enough travel but also did not bottom out on the up stroke. 

 

In fact see where your truck is at now by doing that droop test measurement, full weight on the front and driven to the level flat spot you would do the measuring, then lift up the front and remeasure. It would depend on how you set up your torsion key adjustment as to what droop your truck has as you could very well have more than a factory set up truck, hard to say until one measured. 

Edited November 19, 2025 by Chuck FB

[Epsilon Plus]

That is with both torsion bars out. That eliminates the torsion lift. It's simply the front end droop at its maximum point against the LCA stop.

 

I wouldn't trust fender to hub. Fenders vary. Different flares on standard vs ZR2 and different plastic "squish" variations of how well it attached to the metal.

[kylant]

the shock limits the droop on the ZR2. the UCA was not even touching the service perch at full droop.

i added a shock spacer (5/8") and now the truck has near full droop. the UCA is still about 1/16" off the perch

Edited November 22, 2025 by kylant

[Epsilon Plus]

Needless to say the shocks weren't on either even though ZR2 shocks are longer than stock.

 

If y'all can't see the increased travel in ZR2 vs stock I dunno what to tell ya. 

[kylant]

17 minutes ago, Epsilon Plus said:

Needless to say the shocks weren't on either even though ZR2 shocks are longer than stock.

 

If y'all can't see the increased travel in ZR2 vs stock I dunno what to tell ya. 

not arguing about travel. just stating facts. the increased travel on the ZR2 comes from the increased clearance on the UCA and the slightly taller knuckle. the arm doesn't hit the perch as soon as a standard UCA,  but the travel is limited by the shock extension. it gives up 1/2" + before the UCA hits the perch

[Chuck FB]

2 hours ago, Epsilon Plus said:

Needless to say the shocks weren't on either even though ZR2 shocks are longer than stock.

 

If y'all can't see the increased travel in ZR2 vs stock I dunno what to tell ya. 

 

I don't think you caught what I was trying to explain as I was not referring to the added truck height that the ZR2 has over a stock truck as that certainly is evident and the knuckle is creating a portion or perhaps all of that additional height. What I am referring to and for this measurement and it would not matter if the fenders were uneven on the truck as its being used as a reference point only to measure off of, is the difference in distance between the hub center and fender with the full weight of the truck allowed to settle on the suspension / vs the remeasured distance from hub center to fender with the front of the truck lifted off the ground so the tires are dangling in the air. That difference is the "droop travel" of the suspension and with a torsion front suspension that is going to vary with how the keys were set. 

 

So for example with a stock LTZ for example it may be around 3 1/4 inches of droop travel give or take depending on how the factory set the keys. With a ZR2/AT4X it was stated in a video I watched that he found there was only 2 1/4 inches of droop travel on his AT4X and again I expect that could vary slightly from truck to truck as well due to the hands that were on it at the factory. That owner of his AT4X was finding that his truck was not riding as well as he felt it could due to the reduced droop travel over a basic stock truck and decided to spend the big money and put a lift on it so he would not lose total height while at the same time backing off the torsion keys to create the 3+ inches of droop travel he was striving for. 

 

All I was inquiring about was what have others found with their ZR2/AT4X as per how much droop travel there was from the original factory setting and if similar or not to that finding of that individual. 

 

And the ZR2 could have its torsion keys adjusted differently to create more or less droop travel much like a standard non off road truck. 

[OS RR]

 

 

You can see "Leveled" next to an AT4X. What I can't figure out is why the front wheels are sucked in more (in relation to the rear) on the leveled truck while sitting practically at the same height as the AT4X. Is the something inherently different with the ZR2/AT4x suspension parts that causes this difference?

 

Price wise, a decent leveling kit and the ZR2 kit work out similarly. AEV has figured out how to fit 37x13.50 (w/ 18+ offset wheels) on these trucks with some minor trimming and fender liner brackets.