This is normal and I would suggest that it is due to any one or all of the following reasons: Your husband is A) a bigger stronger rider, B) has ridden his Slider more and or C) is more aggressive of a rider. In any case, the ‘Action Springs’ on his U8 have broken in and have lost some of their static preload making it easier to get the ‘Action Decks’ moving.

You have the option of switching units for a while or swap out the 'Action Springs'. As riders develop their strength, most will want to move the springs to the second position provided on the frame brackets to return the Action Springs’ preload and performance. Over time and again depending on many factors, the Action Springs' yield (spring's ability to maintain it's length preload) may diminish and require relplacement.