Control arm length question

[fiatslug87]

I came across the attached control arm length list, why would lifting 2-3” require shorter upper control arms? Just trying to make sense of things.

 

[motownXJdad]

maybe to correct caster angle on the alignment

[ghetdjc320]

 

Assuming you have adjustable uppers and lowers, just use the lowers and center the axle. Then use the uppers to set the caster angle. 

[75sv1]

Another list I have has :

 

 

	With stock Control Arm Mounts			With RE Drop Brackets			Rough Country Brackets
Lift Height	LCA	UCA		LCA	UCA		LCA	UCA
Stock	15.75"	15"		N/A			N/A
2"	16"	15"		N/A			N/A
3"	16"	15"		N/A			N/A
4"	16.33"	15"		15.75	15"		N/A
4.5"	16.5"	15"		15.875"	15"		15.75"	15"
5"	16.6"	15.25"			15.25"		N/A
6"	17"	15.5"		16"	15.5"		15.875"	15.125"
7"	17.36"	15.75"		16"	15.75"		N/A
8"	17.75"	16"		16.33"	16"		16.25"	15.524"
9"	18.25"	16.25"		16.6"	16.25"		N/A
10"	18.75"	17"		17"	17"		N/A

I'd take it as get it in the ball park. 

[fiatslug87]

Thanks for the replies. I just looked at my other truck, at stock height the upper control arm is higher at the axle than the frame. As the axle is initially dropped straight down (to keep it centered) the arm length decreases then increases as it’s lowered more. I thought it was level to start with.

[Andy in Pa]

6 hours ago, 75sv1 said:

Another list I have has :

 

 

	With stock Control Arm Mounts			With RE Drop Brackets			Rough Country Brackets
Lift Height	LCA	UCA		LCA	UCA		LCA	UCA
Stock	15.75"	15"		N/A			N/A
2"	16"	15"		N/A			N/A
3"	16"	15"		N/A			N/A
4"	16.33"	15"		15.75	15"		N/A
4.5"	16.5"	15"		15.875"	15"		15.75"	15"
5"	16.6"	15.25"			15.25"		N/A
6"	17"	15.5"		16"	15.5"		15.875"	15.125"
7"	17.36"	15.75"		16"	15.75"		N/A
8"	17.75"	16"		16.33"	16"		16.25"	15.524"
9"	18.25"	16.25"		16.6"	16.25"		N/A
10"	18.75"	17"		17"	17"		N/A

I'd take it as get it in the ball park. 

Yes, this is much more achievable and makes more sense.  Keep in mind that first chart is changing the length of the uppers by less than 3/16's" from stock to 4".  This can't be more than a 1* difference in castor, probably less.  It becomes more critical when the lowers are extended past the recommended dimensions (to push the axle forward slightly).  But as long as everything moves forward the same amount it works fine.