Even though the wheels are 25.5 mm the 26mm tires will fit fine.
I have been using Ofna wheels,you can buy an 8 pack for $8.00 the wheels are made of nylon not plastic and they are very strong. they also measure 25.5 mm but seem to be fine.
When I first got my Impulse, I test fitted the V33 tires (26mm) on the HobbyTech Pinzetti's, and they fit fine. I also tried mounting 24mm tires on them and thery do nt fit very well. .5mm is not a big deal, but 1.5mm is.
The only problem I feel there is with that is that most competition tires are 24mm.