How to cut the seat foam and add extra padding to the stock ZRX seat. This mod removes the forward slant.
Cover removal / Staple removal
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Remove the seat, turn it over, and remove the cover.
Give the staples a little lift with a screwdriver. This makes it easier to grab them with some pliers. Grip the staples tightly and yank 'em out.

It's best to leave a few staples in at the back edge of the seat, and the cover attached, so alignment is not a problem after you are finished cutting the foam.
Foam Bottom
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Mark an area with guide lines. Removing foam from this area on the bottom of the seat makes the seat more level on top.
Slice that turkey!
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It's as simple as slicing a turkey...
Don't take too much on the first cut - never more than 1/4" at a time. Take a little off, put the seat base and foam on the ZRX, and try it out. Make a few thin cuts, and test it each time.
Cutting more off is much easier than putting it back on.
Seconds, anyone?
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After 2 or 3 thin cuts toward the back of the rider's seating area, remove a little from the front of the seat. These cuts help level the seat from left-to-right.
Do a friend a favor.
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Mark an area under the passenger seat and trim the foam to make the seat more level.
Add a little foam.
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Add a piece of foam to the top-front of the seat. This helps make the seat top level.
Top foam location.
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Put the foam in this area before re-installing the seat cover and seat base.