Go to change the deck belt on my Z248F and the new belt absolutely will not fit the deck.  It's the correct part number belt and it looks to be too short by maybe a few inches.  The old one was toast, so can't compare the length.  Anyway, I fought with this thing for 45 minutes and thought to myself this cannot be this hard.  Jacks shows the belt as 539109243 at 135" long.  I can tell you now that a 135" belt is too short.  The other part number that Husqvarna shows is 582558001 which is what I bought and is said to be 147.5" but seems a couple inches too short.
 
I'm at a loss.  The routing of the belt is correct and really can't go any other way.

Looking into this further, the Jacks listed 539109243 belt looks to be for lawn tractors with the same deck as the Z248F.  I'm finding more and more there's a lot of confusion about what fits what with these things.  I also needed a new set of mulching blades since my 248F has a mulch kit.  The dealer wasn't really sure of which blades were meant for use with the mulch kit.  Said he had to order them.  That's been almost 2 weeks ago and haven't heard back.  I'm told the ClearCut decks are a whole nuther animal when it comes to parts and you have to be careful to make sure you get parts for that deck or it won't work as designed.

There are apparently several sub models of the Z248F:
 
https://www.partstree.com/models/z-248-f-husqvarna-48-zero-turn-mower-parts/ 
 
I would look up your SPECIFIC model # from above to see if that helps.
 
Also, even thou the belt is shredded, you SHOULD be able to lay it out on the floor, 
like a puzzle, (where frazzled end meets frazzled end) to get an idea of the length.
 
You can also use a roughly 1/2"- 5/8" piece of rope. Set your tensioner (W/O the spring)
about midway thru it's arc.  Now, run/put the rope around idlers, pulleys, etc bringing both ends back together.  With a magic marker, mark the un-cut length of the rope.
 
You now now the approximate length of the belt needed (give or take 2" tops)....
 
 
.
 
.

After thinking about it I figured out my mistake was that I had the deck off to clean it up and change a few toasted bearing idlers and didn't put the lift arms back on quite yet.  Put the lift arms on and lifted it and had enough slack to walk the belt over one of the spindle pulleys.  After all was said and done, the tensioner pulley ended up not quite halfway through it's travel, which by the way ain't much with the belt on.  While it's on and runs smoothly, I still think these belts should be maybe another half to inch longer, but I guess it will stretch very slightly.
 
Tip for those that are doing this by themselves and want to save some potential grief.  On the engine end of the belt, put a thin rubber band around the belt before putting it on the engine pulley and chinch it up to keep the belt from falling off the pulley as you work on threading it on the deck end.  No need to cut the band since it will in short order meet the end of it's life as soon as you engage the deck.