I'm worried that my hamster's wheel may be too small?

He's a fully grown male Syrian, and he has an 8 inch Wodent Wheel. I'm a little worried that it might be too small (just looking at him and then looking at it- the fact that the wheel is enclosed makes it difficult to see him clearly on it, but I'll try to take a look tomorrow night). His cage, a 20 gallon long, is simply not tall enough for a larger wheel. If his wheel is too small, is there a wheel available that's the right size? The lack of 9-10 inch wheels (that I've been able to find) really baffles me- they're exactly the right size, surely someone makes them. He's in my room, so silence is a must. That's another issue with the Wodent Wheel- it started out really silent, and it still isn't keeping me up (much) but it's gotten a lot louder over the months I've had it. I'll try oiling it again, but it's not squeaking... They're really expensive, so I don't want to have to buy another possible too small one if this one breaks completely, and the next size up is too tall for the cage. I can't get a cage topper for less than $80, and even that's on the cheap end. I don't trust my hamster around things he can climb (he gets just high enough to be dangerous, then loses his balance and falls) anyway.

Anyway, that was sort of long and ranty, can anyone help me?