Some stock suspension calculations and measurements

[87-Z28]

just wanted to post some real world front shock maximum extension data for a wider audience. A lot of this stuff is kinda hidden.

from @BigMeatsBronco

I run spacers and 1.5"diff drop....highly recommend this for any lift above 1 inch.

the data from AccuTune Off-road to back this up. @AccuTune Offroad

Fox 2-door and 4-door part numbers are the same:
FRONT Compressed Lengths: 18.79 Extended Lengths: 24.26 Travel: 5.47
REAR Compressed Lengths: 19.24 Extended Lengths: 27.21 Travel: 7.97

King:
FRONT Compressed Lengths: 18.50 Extended Lengths: 24.60 Travel: 6.10
REAR Compressed Lengths: 18.50 Extended Lengths: 27.00 Travel: 8.50

*These measurements, are going from the top of the top hat to center of lower bolt, or to mounting surface of bar pin.

DON'T let the longer travel fool you. More travel/droop is not a good thing in this case. We've been testing and tuning both Fox and King in the last few weeks and the Kings really are a bit too long in front causing the CV axles to bind, even with aftermarket axles they bind. This will lead to premature wear or worse. We will be addressing this. Fox lengths are not an issue.

We are also working on a Fox vs King comparison article. Quite a few big difference between these shocks.

data on the factory SAS shock max extension

Extended rear: 26.125" Front: 23.3125"

binding has been observed in front CV joints at 24.6” extension, no binding at 24.3” with stock SAS running at 23.3”.


Updated with chart posted by @Merc4x4

Make	F Compressed	F Extended	F Travel	R Compressed	R Extended	R Travel
Sas Bilstein	17.0625​	23.3125​	6.2500​	18.6250​	26.1250​	7.5000​
ADS	18.0000​	24.6440​	6.6440​	17.7190​	27.7230​	10.0040​
King	18.5000​	24.6000​	6.1000​	18.5000​	27.0000​	8.5000​
Fox	18.7900​	24.2600​	5.4700​	19.2400​	27.2100​	7.9700​
Eibach 2.0	17.7700​	24.2000​	6.4300​			0.0000​
Icon	17.6000​	24.5300​	6.9300​	18.3600​	28.9000​	10.5400​

Sponsored

 

[AccuTune Offroad]

Although the shock lengths seems very minor, these are shocks are on a motion ratio, so actual wheel travel would be greater which would be more of what the CV angles see.

@87-Z28 may be worth adding the ADS lengths here too.

 

[Bikeric]

Excellent 1st thread Andy!!
FYI, I owned a 1986 Iroc-Z back in the day. Wish I still had it.

 

[87-Z28]

Mine was black and not an iroc. Bought it straight out of college. Loaned it to my brother for a few months when I moved out of town. He trashed it. Brothers.

 

[87-Z28]

Mine was black and not an iroc. Bought it straight out of college. Loaned it to my brother for a few months when I moved out of town. He trashed it. Brothers.

 

[87-Z28]

Although the shock lengths seems very minor, these are shocks are on a motion ratio, so actual wheel travel would be greater which would be more of what the CV angles see.

@87-Z28 may be worth adding the ADS lengths here too.

understood. the shocks attach onto the LCA at a distance closer to its pivot point than the wheel does. So linear motion from the shock pivoting the LCA is amplified at the wheel. The correlation to shock length is not linear wrt wheel motion. I believe this is correct? Please explain if not. And do you have numbers as to this ratio of amplification. For example, a 1/2” spacer lift moves the wheel x inches relative to the frame. And therefore provides an x inch lift.

 

[AccuTune Offroad]

understood. the shocks attach onto the LCA at a distance closer to its pivot point than the wheel does. So linear motion from the shock pivoting the LCA is amplified at the wheel. The correlation to shock length is not linear wrt wheel motion. I believe this is correct? Please explain if not. And do you have numbers as to this ratio of amplification. For example, a 1/2” spacer lift moves the wheel x inches relative to the frame. And therefore provides an x inch lift.

Motion ratio numbers won't mean much to most. There wont be an exact formula to reach a specific lift height, unfortunately its not that simple. In general, its pretty close to being 1/2" top hat spacer = 1" lift at the wheel for the front, but don't hold me to that. We always make adjustments based on shock lengths not specific lift heights.

 

[87-Z28]

Sure. Shock length is precisely controllable. You kinda get what you get at the wheel. Thanks for all the info. Very useful to put some numbers to this.

 

[87-Z28]

I believe the amplification of spacer height at the wheel can be estimated from trigonometry. The shock acts on the LCA by rotating it about its pivot point at the inner bolts. Since the LCA is rigid the pivot angle is the same for the wheel and shock. So I believe the amplification ratio should be the radial length from pivot point to wheel (zero offset location) divided by radial length from pivot point to lower shock mount.

This amplifies wheel motion. 6” shock travel >6” wheel motion. It seems this ratio for stock geometries maybe 2:1. Would be nice to get a good number for this. That way a spacer length can be correlated better with wheel motion and lift.

The above may be oversimplified since shocks are not perfectly vertical and other angles exist in the IFS. Alternatively the total spacer height of a 1” level kit might be more useful to estimate from. 1” level divided by total spacer height is amplification factor.

someone has worked out the exact numbers. None the less it seems like total spacer heights <1” are safe and will amplify lift >1” maybe even close to 2”.

 

[NORCALGXP]

Excellent 1st thread Andy!!
FYI, I owned a 1986 Iroc-Z back in the day. Wish I still had it.

Are we old or what I to had 86 loved the handling drifted nicely.

 

[87-Z28]

Are we old or what I to had 86 loved the handling drifted nicely.

indeed. I had a manual, 5 speed I think. It was hard to keep the backend from going sideways. Especially when you’re 20 years old. That was a fun car.

 

[87-Z28]

Has anyone measured the total height of the spacers provided in a 1”” level kit? I would be interested in estimating the amplification factor at the wheel.

 

[Merc4x4]

Watching for more Iroc photos...

I put all the numbers from that other thread into a grid. Copying it here.

Make	F Compressed	F Extended	F Travel	R Compressed	R Extended	R Travel
Sas Bilstein	17.0625​	23.3125​	6.2500​	18.6250​	26.1250​	7.5000​
ADS	18.0000​	24.6440​	6.6440​	17.7190​	27.7230​	10.0040​
King	18.5000​	24.6000​	6.1000​	18.5000​	27.0000​	8.5000​
Fox	18.7900​	24.2600​	5.4700​	19.2400​	27.2100​	7.9700​
Eibach 2.0	17.7700​	24.2000​	6.4300​			0.0000​

 

[87-Z28]

Yeah, the best part of this thread are the IROCs. I will dig out a 3x5 glossy of mine and post it. If I can find it. I think I took it with this camera.

 

[87-Z28]

On the front you will gain about 1.5 times the thickness of a spacer ie 1" thick spacer gets you about 1.5 " lift. On the rear you'll get about the thickness of the spacer 1" will gain you about 1"..

I think RC has determined that max droop CV is pretty much met with the 2 inch kit (Base,BB,OBX). In order to get to 3.5" on the kit with the diff drop they added a spring pre-laod. But, they didn't want to overdo the preload (0.75" preload x 1.47 ratio = 1.1 preload lift). So the front spacer is bigger than the 2" kit (1.8" vs 1.6"). The added lift from the bigger spacer is 0.2" x 1.47 = 0.3".

I estimated it as about 1.5. the ratio of radial length of the LCA at the knuckle where it meets the wheel to the lower shock mount, both with respect to pivot point, should provide amplification at wheel. Rough numbers seem to be 15”/10” or 1.5. Was wondering how accurate this is. I don’t have a spacer lift to measure and can’t find the spacer thicknesses for a 1” level kit anywhere.

it seems a good number for lift amplification at the wheel on the stock front end is about 1.5. Meaning any linear increase along shock axis, by either spacers or spring compression, will amplify at the wheel by 1.5.

of course for spacers this should be direct correlation as long as spring is not additionally compressed. For spring compression it all depends on final static equilibrium position at ride height. Force in spring and weight it is supporting. Much harder to estimate increased axial shock length without knowing spring stiffness. However amplification at wheel should remain 1.5 since this is tied to shock orientation and location it mounts on LCA. This causes pivot about inner LCA bolts to produce amplification.

Those with more experience, please add or correct and improve. Just trying to quantify things in the front end.

Sponsored