When installing an aftermarket long travel kit on any machine the springs need to be upgraded. We have built a spring kit for the 64 inch wide Turbo and Pro Xp.  This kit is engineered to counter the extra leverage from the LT suspension install. When you add length past the lower shock eyelet you add leverage. So, our kit is rated heavier to counter that leverage.  By countering the added leverage the machine will be back to factory height and factory ride but with the quality of the ATU spring.
The kit includes
Half set options
2 Front main lower springs rated for long travel suspension
2 Front tender springs rated heavier for long travel suspension
 
The full set option adds
2 Rear Tender Springs
 
You may ask the question, why only upgrade the front? We are sure that the rear lower spring is sufficient. Simply because you have not made the trailing arm longer, you have only made the trailing arm wider. Wider does not create leverage. So the rear is fine with OE lowers and ATU tenders.