Suspension : Stock spring replacement for softer ride

Yondu · November 16, 2020

Lucas287 isn't the only internet sleuth here. Using car-part.com I found a wrecked 2015 Tahoe LT, confirmed 4x4. In the pics, was the RPO tag. Zw7 - Premium smooth ride suspension

Then head over to Rockauto.com and look up coil spings for a 2015 Tahoe and you'll see about 20 choices, but this one has the same 7ZH and 6ZH code as the RPO sticker of the Tahoe above. $61 a spring.

GM GENUINE 22845791 Info

FitsFront Right; Suspension Code (7B4), Suspension Code (7CP), Suspension Code (7PF), Suspension Code (7RS), Suspension Code (7RW), Suspension Code (7WS), Suspension Code (7ZH), Suspension Code (7YU)
orFront Left; Suspension Code (6B4), Suspension Code (6CP), Suspension Code (6PF), Suspension Code (6RS), Suspension Code (6RW), Suspension Code (6WS), Suspension Code (6ZH), Suspension Code (6YU)

2 Day Delay

lucas287 · November 16, 2020

1 hour ago, Yondu said:

Lucas287 isn't the only internet sleuth here. Using car-part.com I found a wrecked 2015 Tahoe LT, confirmed 4x4. In the pics, was the RPO tag. Zw7 - Premium smooth ride suspension

Then head over to Rockauto.com and look up coil spings for a 2015 Tahoe and you'll see about 20 choices, but this one has the same 7ZH and 6ZH code as the RPO sticker of the Tahoe above. $61 a spring.

GM GENUINE 22845791 Info

FitsFront Right; Suspension Code (7B4), Suspension Code (7CP), Suspension Code (7PF), Suspension Code (7RS), Suspension Code (7RW), Suspension Code (7WS), Suspension Code (7ZH), Suspension Code (7YU)
orFront Left; Suspension Code (6B4), Suspension Code (6CP), Suspension Code (6PF), Suspension Code (6RS), Suspension Code (6RW), Suspension Code (6WS), Suspension Code (6ZH), Suspension Code (6YU)

2 Day Delay

DANG! Look at you go! Nice work.

I bet that a dealer could source them a lot cheaper if you have any connections. I, personally, don't though.

lucas287 · November 16, 2020

2 hours ago, Yondu said:

Thanks for the detailed response. If we could find the right spring that comes on the Suburban 2wd or Tahoe 4wd that would be a cheap option...my brother had one too, but sold it a few months ago. Would have been easy to find out.

I'm disappointed to hear about the Michelins, I've always heard the opposite but not used them myself. Can you tell me what size yours were? LT load range? My biggest draw I was told they were super smooth. I don't off-road my truck and don't want aggressive tires anymore. I need road tires that work well in MN winters.

Same here. Michelin has a following just like Bilstein does. Tried them out and couldn't be more disappointed. The Ms2's on my truck are the previous generation of what is now called the "Defender". I bought them off a owner of a 2019 F150 that drove it off the lot next door to a tire shop and had mudders put on. They were brand new. Size is 275/55/20 and they are just P series, not LT. My thought process was:

*significant discount on a brand new tire

*manufacturers get the smoothest tires before retailers

WRONG. I'll never do that again. Ended up paying within $100 what a set of Falken HT02 in 275/60/20 would've cost. And then I could've fought with Discount to get all 4 tires under 10 lb of RFV. I can't do with my pre-owned tires I have now, which is why I've resorted to lengthy smoky burnouts in hopes that it makes the tires more round BTW these Falkens look like a good tire. Noticeable sidewall with a highway tread pattern and a 70,000 warranty. Plus the sidewall increase from a 55-series to a 60-series is .55" or 1.1" total. That should help with absorbing small bumps.

Yondu · November 16, 2020

I'll keep it in mind. The tire I'm looking at from Michelin is actually the Primacy XC, which is OEM on the F150. 275/65r18. Discount has them for $175 each and with Black Friday I'd be able to get them all for $550 plus install/tax. They have a lower mileage rating than the defender so I think they'll be a little softer. I buy a lot of tires from Discount Tire and I think I'll just tell them I need them all to be road force balanced to 15 or less. I had the Cooper AT3 4s in 275/60r20 and they were perfectly smooth, just wanted a bigger tire/smaller wheel and so I went with the same tire in 285/70r17. They just aren't as smooth, but they're not on OEM wheels. The wheels are lug centric Methods and I think that's why they're only 97% smooth after about 65mph.

I think I'll go with either the Primacy XC or the Terraincontact HT, depending if I can find a Black Friday sale. After that's done and I sell my Method wheels I look the suspension.

Yondu · November 19, 2020

I decided to go for it. Ordered the Tahoe 4wd springs specified above, Koni front and rear dampers and a 1" Motofab lower strut spacer. My thought is the Tahoe springs will lower the truck maybe 3/8"-1/2" over stock, so this will give me a very slight front lift.

Currently I have Bilstein 5100's at 1.2" lift, rear 2" block (over 1.25" stock block). So I'm hoping to go from a 1.2 / .75" lift to a .5" front lift.

Doing this for ride quality. It will be next week when everything arrives and I won't be able to get to it Thankgiving weekend, but I hope the weekend after. Having a young lad at 18 months, working full time and going to school keeps me busy.

Edited November 19, 2020 by Yondu

Grumpy Bear · November 19, 2020

14 hours ago, Yondu said:

I decided to go for it. Ordered the Tahoe 4wd springs specified above, Koni front and rear dampers and a 1" Motofab lower strut spacer. My thought is the Tahoe springs will lower the truck maybe 3/8"-1/2" over stock, so this will give me a very slight front lift.

Currently I have Bilstein 5100's at 1.2" lift, rear 2" block (over 1.25" stock block). So I'm hoping to go from a 1.2 / .75" lift to a .5" front lift.

Doing this for ride quality. It will be next week when everything arrives and I won't be able to get to it Thankgiving weekend, but I hope the weekend after. Having a young lad at 18 months, working full time and going to school keeps me busy.

:lurk:

lucas287 · November 19, 2020

17 hours ago, Yondu said:

I decided to go for it. Ordered the Tahoe 4wd springs specified above, Koni front and rear dampers and a 1" Motofab lower strut spacer. My thought is the Tahoe springs will lower the truck maybe 3/8"-1/2" over stock, so this will give me a very slight front lift.

Currently I have Bilstein 5100's at 1.2" lift, rear 2" block (over 1.25" stock block). So I'm hoping to go from a 1.2 / .75" lift to a .5" front lift.

Doing this for ride quality. It will be next week when everything arrives and I won't be able to get to it Thankgiving weekend, but I hope the weekend after. Having a young lad at 18 months, working full time and going to school keeps me busy.

Hell yeah, I'm pumped for this. You'll really like those Koni dampers compared to the Bilsteins. With the rears side by side you'll realize just how stiff the Bilsteins are. The fronts are good, don't get me wrong, but the rear was dramatic.

If this works for you, this might be a better alternative to the direction I've been heading: https://atomicfabandperformance.com/product/07-18-gmt900-front-coilover-package/ $900 for a custom spec'd true coilover package that has dual adjustable Viking shocks might be a pretty trick setup.

Also, heard that with your young lad, my little man just turned 1 a couple weeks ago. What a year lol.

Edited November 19, 2020 by lucas287

Yondu · December 1, 2020

Hey guys, just a small update.

Still waiting on the front struts, but I got everything else. I haven't taken anything off my truck yet, but comparing the new front springs to the existing ones and it appears the coil is the same length (longer / more coils would mean softer) as the coil starts and stops in the same spot. Could be a different free standing height, but I doubt it. My truck also has almost less than 10k miles on it, so I don't think they will have sagged much and I'll compare when I take them off.

What I did notice is my stock spring coil has a diameter of 20mm, the Tahoe coil is 19mm. This is an area of 314.16 vs 283.56mm, which is approx 10% less. What that means (I believe, correct me if I'm wrong) is that IF the stock spring is 750lbs, this should be 677lbs.

Grumpy Bear · December 1, 2020

17 hours ago, Yondu said:

Hey guys, just a small update.

Still waiting on the front struts, but I got everything else. I haven't taken anything off my truck yet, but comparing the new front springs to the existing ones and it appears the coil is the same length (longer / more coils would mean softer) as the coil starts and stops in the same spot. Could be a different free standing height, but I doubt it. My truck also has almost less than 10k miles on it, so I don't think they will have sagged much and I'll compare when I take them off.

What I did notice is my stock spring coil has a diameter of 20mm, the Tahoe coil is 19mm. This is an area of 314.16 vs 283.56mm, which is approx 10% less. What that means (I believe, correct me if I'm wrong) is that IF the stock spring is 750lbs, this should be 677lbs.

https://www.newcombspring.com/springulator/compression-spring-calculator

Use CS for material type. Use the dimensional calculator.

Edited December 1, 2020 by Grumpy Bear

lucas287 · December 2, 2020

Excited to see how this works out! I wish calculating spring rate was that easy it's quite complex though especially when trying to compare a coilover setup that has more shock stroke/travel.

For example:

Corner weight = 1000 lbs

Shock stroke = 4"

Ideal Spring rate (to achieve a 50% compressed ride height where the shock is exactly in the middle of the stroke): 500 pounds/inch rate.

Corner weight = 1000 lbs

Shock stroke = 6"

Ideal Spring rate: 333 pounds/inch rate.

This is just a crude example to illustrate that you can't compare one vehicle's spring rate to anothers without knowing the other factors. Now, in this scenario, it's the same shock body! So stroke stays the same! Since there's less weight to support, the spring rate will be lower (i think).

But the more I research this topic the more I'm realizing the impact that valving has on ride comfort. I'd argue that it actually has a bigger influence! The problem is that most aftermarket companies use overly firm valving specs and we have no way of changing that unless we have custom spec'd Kings or Fox. Enter Viking Double Adjustables. You can now independently adjust rebound and compression damping to YOUR liking. Done. Choose a spring rate by doing some math and having your truck weighed properly at a speed shop and then dial in your valving settings. Bam - should be a fantastic riding truck.

Grumpy Bear · December 2, 2020

9 minutes ago, lucas287 said:

Excited to see how this works out! I wish calculating spring rate was that easy

Calculating spring rate is that easy. It's rate is independent of it's installed height. It has a rate sitting on a shelf.

A KING OEM uses a 750# spring that is 13 inches long on the shelf. Installed on the coil over at zero additional preload it has a 10" length. It's installed preload is than 2250 pounds. Now lets put it in the truck. The truck has a arm leverage ratio of 2:1. The truck in my case weights 5000 pounds. It has a bias of 52/42 so on the front corner it weights 1300 pounds which is multipiled by the arm ratio thus 2600 pounds. The difference is 350 pounds so the shock will compress an addtional .466 inches. The shock has a stroke of 4.5" so sits at 4.034" or (4.034/4.5)*100 = 89.6% of stroke. And that is how it worked out in the real world as well.

I refit the truck with 600# springs. Installed preload is now 1800 with the same 2600 pound corner weight. The difference was then 800 pounds thus compressed an additional 1.33 inches or a stroke height of 3.17 or 70% of the stroke. Still not ideal but got it to a point I have some rebound distance.

500# spring 1500 installed preload. 2600 - 1500 = 1100 delta / 500 = 2.2 inches or a stroke height of 2.3 inches or 51% of stroke. Could now add a half inch or so of perch preload to arrive at 55/60".

lucas287 · December 2, 2020

2 minutes ago, Grumpy Bear said:

Calculating spring rate is that easy. It's rate is independent of it's installed height. It has a rate sitting on a shelf.

...I was referring to Yondu's calculation whereby only referencing wire diameter wasn't calling you out.

The rest of your post is some good stuff!! Definitely sounds like you need some 500# springs.

Question, would you need to have that much preload on them? Could a shorter spring be used thereby reducing how much preload is needed?

Grumpy Bear · December 3, 2020

5 hours ago, lucas287 said:

...I was referring to Yondu's calculation whereby only referencing wire diameter wasn't calling you out.

The rest of your post is some good stuff!! Definitely sounds like you need some 500# springs.

Question, would you need to have that much preload on them? Could a shorter spring be used thereby reducing how much preload is needed?

Didn't take it as a call out so no worries.

Spring needs to have some preload so it doesn't rattle around in there Is 3" to much? :dunno:

Yes I could load 500# springs but if I did then I haven't any haul capacity. We see this with the trucks back half where it takes 2000 pounds over the axle to get the truck level and the shock at mid stroke. Now if ride is my ONLY goal then yea....500# it is plus a much softer back leaf system.

Yondu · December 9, 2020

Hey guys, an update.

My truck is a 2018 z71 crew cab LT. 5'8 box. The front coils have a diameter of 20.22mm and the Tahoe coils are 19.17mm. If someone had a loaded up crew 6'5 box truck, you'd probably want the the suburban 4wd springs if you were looking for something softer.

I swapped my bilstein 1.25" front lift for the Konis with a 1" lower strut spacer. I knew going into this it would lower the truck more than that .25" and I am good with that. I just don't want a level /small lift anymore. After installing the front setup and taking out my rear 2" block for the stock 1.25" block the front dropped 3/4" to 7/8", which means 1/2 to 5/8" drop from the spring itself. That was the measurement I got tonight and I've put about 15 miles on the truck. In my experience coils don't really settle after the first few days, but I guess I'll find out.

Right now the front of my truck is 3/8" to 1/2" higher in the front, which is where I want to be.

I hesitate to mention ride quality changes because I just haven't driven much. I have a work vehicle and with Covid....well my 26 month old truck has 9950 miles, so that shows you how much I drive it! It is softer in the front of course and I still have the Bilsteins in the back. Partially because I want to evaluate this setup first, partially because I ran out of time. I do have the Koni rear shocks and will most likely install them.

I will update some more hopefully next week when I have some more miles on it.

Yondu · December 9, 2020

On 12/2/2020 at 11:55 AM, Grumpy Bear said:

Calculating spring rate is that easy. It's rate is independent of it's installed height. It has a rate sitting on a shelf.

A KING OEM uses a 750# spring that is 13 inches long on the shelf. Installed on the coil over at zero additional preload it has a 10" length. It's installed preload is than 2250 pounds. Now lets put it in the truck. The truck has a arm leverage ratio of 2:1. The truck in my case weights 5000 pounds. It has a bias of 52/42 so on the front corner it weights 1300 pounds which is multipiled by the arm ratio thus 2600 pounds. The difference is 350 pounds so the shock will compress an addtional .466 inches. The shock has a stroke of 4.5" so sits at 4.034" or (4.034/4.5)*100 = 89.6% of stroke. And that is how it worked out in the real world as well.

I refit the truck with 600# springs. Installed preload is now 1800 with the same 2600 pound corner weight. The difference was then 800 pounds thus compressed an additional 1.33 inches or a stroke height of 3.17 or 70% of the stroke. Still not ideal but got it to a point I have some rebound distance.

500# spring 1500 installed preload. 2600 - 1500 = 1100 delta / 500 = 2.2 inches or a stroke height of 2.3 inches or 51% of stroke. Could now add a half inch or so of perch preload to arrive at 55/60".

I understand what you're writing here, but that's just a whole lot of math. I will add my 1" front leveling spacer is closer to 5/8 thick, so if it is 1" it's not a 2:1 ratio.

Another random factoid is CST makes double adjustable coilovers for our trucks that use 650lb springs for the crew cab 4wd, 600 for the 2wd. I believe you have a regular cab 2wd v6? I assume my truck would be quite a bit heavier. Most coilovers for our truck are 700lb. I'm hoping my springs are 650-675 now but I'm not smart enough to figure it out. Free standing height and coil length appeared to be identical to the stock spring I pulled off.