Ass sag during acceleration

[daytonaviolet]

I’m having this strange issue where the front of the truck seems to get higher and the rear seems to get lower during acceleration. I see my headlights pointing higher during acceleration at night.

i have kings 600lb spring rate fronts set to 3.5” lift and unknown spring rate icons (158506) 2” lift on the rears.

im thinking the sag may be related to the icon springs. Perhaps the spring rate is too soft ? I’m thinking of switching to icon (52700). This seems to be the standard for icon 2” rear springs.

Any thoughts or recommendations will be appreciated.

 

[fkheath]

I’m having this strange issue where the front of the truck seems to get higher and the rear seems to get lower during acceleration. I see my headlights pointing higher during acceleration at night.

i have kings 600lb spring rate fronts set to 3.5” lift and unknown spring rate icons (158506) 2” lift on the rears.

im thinking the sag may be related to the icon springs. Perhaps the spring rate is too soft ? I’m thinking of switching to icon (52700). This seems to be the standard for icon 2” rear springs.

Any thoughts or recommendations will be appreciated.

.

"Ass sag" during acceleration and nose dive during braking is common. It is not caused by the springs. Sometimes stiffer shocks can help, but is not a cure.

Think of it this way (laws of physics): when you accelerate, there is a rotational force (torque) applied to the tires. This caused a counter rotational force to the axle, i.e. the axle wants to turn in the opposite direction to the tires. This counter rotation transfers to the vehicle chassis/body, causing it it rotate in the opposite directions from the tire rotation, that is lift the nose.

 

[daytonaviolet]

.

"Ass sag" during acceleration and nose dive during braking is common. It is not caused by the springs. Sometimes stiffer shocks can help, but is not a cure.

Think of it this way (laws of physics): when you accelerate, there is a rotational force (torque) applied to the tires. This caused a counter rotational force to the axle, i.e. the axle wants to turn in the opposite direction to the tires. This counter rotation transfers to the vehicle chassis/body, causing it it rotate in the opposite directions from the tire rotation, that is lift the nose.

Thanks for the detailed information. Prior to this suspension setup, I had trd pro Bilsteins with Cornfed spacers. But I didn’t have this much sag. Seems the issue started when swapping to kings and icons.

 

[Kamalani Mahie]

Sounds like normal physics to me.....

In all seriousness though was the difference noticed when you swapped suspension setups? What suspension setups did you have in the rear prior to and after you noticed the higher sag? The fronts won't really affect rear sag much; they'll only change the front lift/feel/nosedive. So since you changed the front to stiffer suspension, it can definitely contribute to feeling as though your ass is sagging more, but it's actually not affecting it that much. Your rear setup is what will be the main contributor. So what were your setups exactly?

 

[BigGy]

What's this you say....you can get your 4Runner to accelerate hard enough to actually shift the weight! :jk:

Higher up in the air it is (your lift), the more it would be noticed as well.

 

[ahtoxa11]

OP, if your lift specs are 3.5" up front and 2" rear, this will probably make you feel like your butt sags, because it does. Did the previous setup have the same amount of lift font and back?

Based on those specs, you've pretty much eliminated the factory rake, and I'm betting that if you measured at the frame, you're likely sagging in the back even when parked, or just about close to it. When you accelerate, this gets exacerbated and you feel like it's sagging.

 

[daytonaviolet]

Sounds like normal physics to me.....

In all seriousness though was the difference noticed when you swapped suspension setups? What suspension setups did you have in the rear prior to and after you noticed the higher sag? The fronts won't really affect rear sag much; they'll only change the front lift/feel/nosedive. So since you changed the front to stiffer suspension, it can definitely contribute to feeling as though your ass is sagging more, but it's actually not affecting it that much. Your rear setup is what will be the main contributor. So what were your setups exactly?

I waited 3 weeks longer for the rear kings to arrive. So the fronts had the kings 600# and rears has the icons 158506 and trd Bilsteins. At this point the fronts felt stiffer but rears started to have a sag feeling.

When the rear kings arrived, I felt more sag. That’s when I started to 2nd guess the icon springs that I’m using.

i question. What’s the difference between 2” icon 158506 vs 52700. All the icon kits stages 1 thru 7 use 52700 as the rear 2” lift. But I’m using 158506. I can’t seem to find info on 158506 other then it’s a 2” lift.

 

[daytonaviolet]

What's this you say....you can get your 4Runner to accelerate hard enough to actually shift the weight! :jk:

Higher up in the air it is (your lift), the more it would be noticed as well.

Yes I got leveled. Here are the spaces

Current lift kings/icons springs
23.5” fronts
24” rears

Stock springs
20” fronts
22” rears

I may lower the front to 23” to have 3” lift and see if the sag reduces.

 

[daytonaviolet]

OP, if your lift specs are 3.5" up front and 2" rear, this will probably make you feel like your butt sags, because it does. Did the previous setup have the same amount of lift font and back?

Based on those specs, you've pretty much eliminated the factory rake, and I'm betting that if you measured at the frame, you're likely sagging in the back even when parked, or just about close to it. When you accelerate, this gets exacerbated and you feel like it's sagging.

Previously I was leveled with trd pro Bilsteins and 2/1.5” Cornfed spacers. It was similar heights and rake as I have now.

If I remember correctly previous lift was ~
23.25” fronts
23” rears

 

[llDemonll]

The front of your car is 1.5" higher than the rear, that's going to exacerbate any sag you're seeing. It's not surprising. Also it's a large heavy brick.

 

[ahtoxa11]

Previously I was leveled with trd pro Bilsteins and 2/1.5” Cornfed spacers. It was similar heights and rake as I have now.

If I remember correctly previous lift was ~
23.25” fronts
23” rears

IMO, that looks like reverse rake (sag) already, so when accelerating it gets exacerbated. Your previous set up looks to be less aggressive on the front lift, too, even if we factor in an extra 1" in the front due to taller PRO springs.

If you don't see any obvious coil issues (you'd know a broken coil if you saw one) and you don't have any side-to-side sag that's more than a quarter inch or so, then probably what remains is your perception and not a mechanical issues.

I'm still thinking that the way you have your rig set up affects your perception of sag.

 

[daytonaviolet]

IMO, that looks like reverse rake (sag) already, so when accelerating it gets exacerbated. Your previous set up looks to be less aggressive on the front lift, too, even if we factor in an extra 1" in the front due to taller PRO springs.

If you don't see any obvious coil issues (you'd know a broken coil if you saw one) and you don't have any side-to-side sag that's more than a quarter inch or so, then probably what remains is your perception and not a mechanical issues.

I'm still thinking that the way you have your rig set up affects your perception of sag.

This is my previous setup with cf spacers and Bilsteins trd pro springs. This setup had less sag.

It’s the current kings with icons rears 158506 which sags more :-(

 

[ahtoxa11]

This is my previous setup with cf spacers and Bilsteins trd pro springs. This setup had less sag.

It’s the current kings with icons rears 158506 which sags more :-(

Try a different spring in the rear. My 2" Superflex have given me an actual lift of 2.75" initially, which settled in a few months down to around 2.25-2.35" of overall lift. I don't carry much gear with me day-to-day. They are around 10-13% stiffer than stock.

 

[Kamalani Mahie]

I waited 3 weeks longer for the rear kings to arrive. So the fronts had the kings 600# and rears has the icons 158506 and trd Bilsteins. At this point the fronts felt stiffer but rears started to have a sag feeling.

When the rear kings arrived, I felt more sag. That’s when I started to 2nd guess the icon springs that I’m using.

i question. What’s the difference between 2” icon 158506 vs 52700. All the icon kits stages 1 thru 7 use 52700 as the rear 2” lift. But I’m using 158506. I can’t seem to find info on 158506 other then it’s a 2” lift.

This is all I could find on those springs from other forum posts back in 2014 and 2016:
Icon 158506 rear 2" lift coils are 400mm, 220lb

It sounds like they are an old part number that probably got replaced with the new ICON rear 2" coils. I know some guys that have said they decided to go to a heavier duty rear spring because the ICONs weren't cutting it, but that's unique to everyone's setup. It sounds like maybe lowering your front a bit would help the overall perception of sag. Looks like overall the fronts are 1.5" higher than they were before compared to the rear so I'd lower the front 0.5" or 1" and see if that helps you.

 

[daytonaviolet]

This is all I could find on those springs from other forum posts back in 2014 and 2016:
Icon 158506 rear 2" lift coils are 400mm, 220lb

It sounds like they are an old part number that probably got replaced with the new ICON rear 2" coils. I know some guys that have said they decided to go to a heavier duty rear spring because the ICONs weren't cutting it, but that's unique to everyone's setup. It sounds like maybe lowering your front a bit would help the overall perception of sag. Looks like overall the fronts are 1.5" higher than they were before compared to the rear so I'd lower the front 0.5" or 1" and see if that helps you.

Thanks for finding the spring rate. I think at this point I’m going to reduce the front lift from 3.5” to 3” and see if the sag reduces. If it does not, my next step is to replace the rear shocks with another 2” spring.

Now I know to find something stiffer then 220lbs.

 

[Kamalani Mahie]

Thanks for finding the spring rate. I think at this point I’m going to reduce the front lift from 3.5” to 3” and see if the sag reduces. If it does not, my next step is to replace the rear shocks with another 2” spring.

Now I know to find something stiffer then 220lbs.

I believe the OME 895 and 895e are 260lbs. I'm running OME 895.
895 is a 2" lift and 895e is a 1.5" lift. But due to the higher spring rate than the ICONs, you will get a little more lift out of them than 2" or 1.5".