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First post here and pretty new to jeeps. Had mine for about 6 months now. 09 jku with 80k miles. Just got some rubi shocks for $80 on eBay and it included the springs as well. I looked at the tags on my current springs and they are the same as the ones im getting but I noticed something funny and haven't been able to find any info anywhere online about it so I figured I would ask. My rear springs are 58 but my front driver side is 17 and passenger is 18. Why is this? If it had to do with the gas tank or something shouldn't the front and rear on that side be a number higher?
 

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First post here and pretty new to jeeps. Had mine for about 6 months now. 09 jku with 80k miles. Just got some rubi shocks for $80 on eBay and it included the springs as well. I looked at the tags on my current springs and they are the same as the ones im getting but I noticed something funny and haven't been able to find any info anywhere online about it so I figured I would ask. My rear springs are 58 but my front driver side is 17 and passenger is 18. Why is this? If it had to do with the gas tank or something shouldn't the front and rear on that side be a number higher?
Driver weight
 

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That would make sense but the stiffer spring (18) is on the passenger side not driver side so with my 200+ pound ass it would make it worse I would think lol
 

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The reason is not weight, it is suspension geometry. The higher the part number the higher the spring rate of the coils. 5-link suspensions are not symmetric. The Track Bar is mounted to the frame on the driver side and to the axle on the passenger side. Consider the case when both wheels hit a bump, the passenger wheels compresses directly with minimum effect from the TB. However, when the passenger side compresses it has some leverage from the TB so in order for the axle to move equally the spring rate of the passenger side needs to be slightly higher. More importantly the same difference in applied load happens during a turn. This will also eliminate the famous JK lean that not all JK's have.

The same principal applies to the rear except that is not as noticeable and does not impact ride dynamics as much as the front.
 
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