Hard to slide window
Thank you for your patience during this busy season. I don't think adding more rollers would necessarily make the window roll more easily. It's entirely possible your old wheels were just worn down. Try replacing just the two you have now and see if that works out.
Replacing did not work. Maybe they installed the wrong wheels to begin with? Are there wheels specifically designed for heavy windows?
If the 87-208 is identical for your original roller assemblies, then I think that's what you should stick with. That said, it's possible that whoever installed them may have gotten a little creative with it. It's possible that they altered the roller in some way to allow it to carry a heavier window. That's hard to predict, though.
Do you have a similar window in the house? That way you can see if the 87-208 is still a match across the board.
Adding an extra set won't hurt to see if that helps in the sliding sash. Like Tom said, it may not make a difference, but if you have no other options it could be worth trying.
You could also try using something like our 75-077 track lubricant or something similar to help in the operation of the sash.
I installed the new ones and it is still very hard to move.
Are there other wheels that are the same width? I get the sense that I could have something taller if needed when I remove the window.
I'm sorry to hear you're still having trouble. We have wheels with a greater diameter, but the problem is if they're too tall then the axle won't install in the slot where they need to go. There's not really that much clearance in the housing for a larger wheel.
I'm not sure if the rollers are the problem at this point. There could be damage to the window track itself, or an issue with the frame being warped in such a way that you have too much friction. There could be a ton of other explanations, honestly. You may want to have a professional come out and look at your windows.