2020 GMC SIERRA AT4 with Readylift 2" SST

Chay Dommeti · May 6, 2020

I am getting my truck lifted today by 2" using Readylift 2" SST kit on my AT4 and i am planning to upgrade my tires for now. Currently i am running 275/65/R18. Anyone here who did the same lift Can tell me what size tire i can use on my stock wheels and also looking to see what others did with upgrades on their 18" or 20"

Supercup · May 6, 2020

I have the same lift - I stayed with 275/65/18 Duratrak wranglers that came on truck - but swapped out wheels to Method.

Be aware that Ready Lift does not recommend you use auto 4WD with this level kit - from website "NOTE: Use of Auto 4 HI feature not recommended" - due to having customers who have damaged their front diff using it.

they say you can fit "AT4 - Max tire 305/55-20, 20x9 0 offset wheelTrail Boss - Max tire 295/65-20, 20x9 0 offset wheel"

As you can see they make no statements for 18" wheels - here are some photos of clearance to my upper control arm - about a finger width - so you can't go much wider than 275, without getting a spacer or wheels with different offset than stock.

Note in my last photo the angle of cv axel - not ideal.

Do a search on AT4 and TB and there a lot of threads on this topic and many have gone larger - but the wheel well is tight and the spacing as well to the upper control arm.

Edited May 6, 2020 by Supercup

Supercup · May 6, 2020

Here is a photo of my truck with stock wheels and then with Methods (same 9x18 and same offset as stock) - after leveled.

Chay Dommeti · May 7, 2020

2 hours ago, Supercup said:

3 hours ago, Supercup said:

I have the same lift - I stayed with 275/65/18 Duratrak wranglers that came on truck - but swapped out wheels to Method.

Be aware that Ready Lift does not recommend you use auto 4WD with this level kit - from website "NOTE: Use of Auto 4 HI feature not recommended" - due to having customers who have damaged their front diff using it.

they say you can fit "AT4 - Max tire 305/55-20, 20x9 0 offset wheelTrail Boss - Max tire 295/65-20, 20x9 0 offset wheel"

As you can see they make no statements for 18" wheels - here are some photos of clearance to my upper control arm - about a finger width - so you can't go much wider than 275, without getting a spacer or wheels with different offset than stock.

Note in my last photo the angle of cv axel - not ideal.

Do a search on AT4 and TB and there a lot of threads on this topic and many have gone larger - but the wheel well is tight and the spacing as well to the upper control arm.

Got it , So my only option now will be either to swap the wheels or stay with existing wheels. I like the wheels anyway so may be i will leave the stock wheels and tires for now. Thanks for clearly explaining

Supercup · May 7, 2020

You can probably fit a 285 or 295 tire - I would go to your local tire guy and see what they think.

truck will look great with level!

bgweed · May 7, 2020

4 hours ago, Supercup said:

Be aware that Ready Lift does not recommend you use auto 4WD with this level kit - from website "NOTE: Use of Auto 4 HI feature not recommended" - due to having customers who have damaged their front diff using it.

Any idea why this could be? How could you damage your front diff using a spacer kit?

Supercup · May 7, 2020

You can probably fit a 285 or 295 tire - I would go to your local tire guy and see what they think.

truck will look great with level!

check out this thread for tire size and trimming information - good info.

Edited May 8, 2020 by Supercup

Supercup · May 7, 2020

29 minutes ago, bgweed said:

Any idea why this could be? How could you damage your front diff using a spacer kit?

The issue is the angle of the cv axel is out of OEM spec range and it puts added torque on the unit. 2" of lift is about the max you can lift, without lowering the diff to keep the factory geometry in line - so for a normal truck a level kit is fine - goes from stock to 2" - Problem for the AT4 and Trail Boss, is they go from 2" of factory lift + 2" of level - so 4" of lift with level kit - so now too much angle on cv axels. - Ready Lift had complaints about loud grinding noises when shifting into auto 4wd on the fly - and there is a post on this forum from someone who shifted into auto 4wd on the fly and heard all kinds of bad noised - limped to the dealer and dealer had to replace, no warranty due to 2" of added lift for ready lift level kit.

That is why all the 4" and 6" lift kits you see, have brackets to lower the front diff, to maintain the geometry angles of the cv axels into the front diff. If you look at the last photo in my prior post - you can see the cv axel in the background and see the angle up and down at both ends is pretty extreme for the truck being level on the ground.

Had I known this, I would have not done this kit, which is a nice kit - good quality - just has this issue for AT4 and TB that is not good. My truck is leased, have 2 more years, so I am debating if I go with correct level or just leave as is and roll the dice. I have used my truck offroad in 4WD high and had no issues, but it will always be in the back of my mind.

sweatandsteel · May 7, 2020

I am considering the readylift kit for my AT4 as well. Has anyone out there come out with brackets to drop the differential that can be bought separately? It seems there is a pretty good market for this if the product is out there......

bgweed · May 7, 2020

I'm familiar with CV angles, but the point of the split spacer is to try to alleviate that somewhat. The photos people are posting of the motofab 1.5" don't look bad, and I don't think the Rough Country sounded bad from verbal description. Yours looks significatly worse... glad you clarified that was on level ground! Also, I was curious as to why onl the 4WD Auto being the issue... seems like that angle should be a major issue under power for other modes.

Anyway, I think I'll skip this one and maybe go with Motofab or Rough Country.

sweatandsteel · May 8, 2020

Unless I'm missing something, no matter where the spacer is located (top mount, bottom mount, or split) the CV angle is still increased by the amount of the leveling kit. The Motofab kit is obviously a 1/2" shorter which will help on the angles and the split spacer style is meant to try to keep the strut from getting too close to the CV boot and therefor preventing boot damage. While I tend to lean toward the top mount style spacer to keep from boot damage, I don't see how you can help the CV Angle without installing some sort of differential drop bracket. I will probably be using the Rough Country Top mount leveling kit for AT4 while also swapping out the upper control arms to help the ball joint angle. I don't have to use 4WD often but when I do it will be 4WD HI and not auto.

Edited May 8, 2020 by sweatandsteel

Roy Hutchinson · May 8, 2020

On 5/6/2020 at 3:47 PM, Chay Dommeti said:

I am getting my truck lifted today by 2" using Readylift 2" SST kit on my AT4 and i am planning to upgrade my tires for now. Currently i am running 275/65/R18. Anyone here who did the same lift Can tell me what size tire i can use on my stock wheels and also looking to see what others did with upgrades on their 18" or 20"

I got a 2020 RST Z71 with a trail boss suspension. The truck came from the dealer with 35x12.5x22 and an OEM +28 wheel...The GM dealer installed a 2" level kit to eliminate the rub on the upper control arms. Although there is minimal rub on the mud flaps it did eliminate the rub on the UCA's....I too were concerned about my CV Axles, however everything on my truck is dealer/factory installed so it want cost me anything if things go south. So far no issues but i haven't utilized 4H or 4L since the level kit so that will happen today to see what happens.

Supercup · May 8, 2020

Truck looks good! But be clear you won't have issus, so long as the dealer who installed it backs it up. GM will not back it up, they will push it off to the dealer who installed it. As long as you are comfortable with that, you are good to go. from my discussion with Ready Lift - their primary concern is the torque put down when "shifting on the fly" at speed - the other issue is, if you go offroad and are in 4WD the geometry is off, so if you have extreme articulation, we may suffer issues.

Do you have any idea how much those tires with 22's weigh vs stock - I drove one with same 22's and the ride was compromised to what I have quite a bit. I picked a 22" wheel up in the part department and I was surprised what a lead brick it was, sucker was heavy - that will put further load on your cv axels under off road conditions.

Supercup · May 8, 2020

6 hours ago, sweatandsteel said:

Unless I'm missing something, no matter where the spacer is located (top mount, bottom mount, or split) the CV angle is still increased by the amount of the leveling kit.

I don't see how you can help the CV Angle without installing some sort of differential drop bracket.

You are not missing a thing - no drop brackets with 4" lift, you will have bad cv axel geometry - potential for issues exists - user beware! Whatever you do don't "shift on the fly" into or out of 4WD (per Ready Lift in phone conversation).

Roy Hutchinson · May 9, 2020

13 hours ago, Supercup said:

Truck looks good! But be clear you won't have issus, so long as the dealer who installed it backs it up. GM will not back it up, they will push it off to the dealer who installed it. As long as you are comfortable with that, you are good to go. from my discussion with Ready Lift - their primary concern is the torque put down when "shifting on the fly" at speed - the other issue is, if you go offroad and are in 4WD the geometry is off, so if you have extreme articulation, we may suffer issues.

Do you have any idea how much those tires with 22's weigh vs stock - I drove one with same 22's and the ride was compromised to what I have quite a bit. I picked a 22" wheel up in the part department and I was surprised what a lead brick it was, sucker was heavy - that will put further load on your cv axels under off road conditions.

Yeah I would agree, GM in no way will take responsibility for any of the dealer upgrades. Long story short, this Chevrolet dealer has been selling these trail boss suspension packages with level kits long before I showed up so at least I'm not the test monkey. Luckily for me and my application I very seldom run 4H or 4L. Living in South Mississippi we dont have to deal with snow and honestly these damn trucks are too damn expensive to off-road. At least in my opinion. As far as the tire/wheel weight. I really dont know the difference as compared to stock. What I do know is I've run trail grapplers before and they are a very heavy tire. I would also imagine the 22 inch stock wheels weigh about the same as boat anchors. However, this truck with its suspension upgrades and tire/wheel combination, rides extremely softer/smoother than my recent 2017 GMC Sierra Denali with leveled suspension and 33 inch Toyos and 22 inch stock wheels. Not sure if it's because of the Rancho coil/overs or what but my 2020 is night and day as compared to my previous Denali.