As it is widely known in this forum, the GP4000 28mm tire size bloated up much bigger than 28mm. I have the GP4000 in various sizes for different bikes and found only the 28mm to have the bloating scenario. Bigger = more volume, so in general a nice feature. However...
On our road tandem the rims are just over 19mm interior width (the width that counts the most). On these rims, the GP4000 28mm tires measure closer to 29.8mm on install and after a year or so (very long wearing) more like 34mm. We run them at only 93-95psi due to all the air volume there is - higher psi not needed. I finally had to take off the front tire because it ran out of room under the fork crown - funny you might think that as a tire wears it would have more room but no, this bloated more than it wore down. We have a supply of new GP4000 28mm tires, so I mounted new treads front and rear, long before the old rubber had given up its life. Now there is a good 3mm clearance under the fork crown again, at least for the time being.
So the question... does the new GP5000 28mm tire maintain close to its advertised size, or bloat / grow like the 4000 does?