I bought a 2014 Trek 7.3 today and the guy said it has a replacement rear wheel. This Trek is supposed to be a 9 speed cassette but they replaced it with a SRAM 8 speed on a hub of unknown origin. The rim is an Alexrims DA22, which Im reading is a low cost wheel. My question is, will a 9 speed cassette fit on this hub or should I track down the stock Bontrager Nebula wheel with Shimano RM30 hub that originally came on this bike? Any insight would be welcome(:

a 9sp. HG style "Shimano compatible" cassette will fit right on, after the dirt and greasy buildup is removed.
SRAM, SunRace, and a host of other companies also make the HG style cassettes...
i choose Shimano, SunRace, or SRAM, usually... good quality, and decent resistance to wear.
and yes, the more expensive ones shift better and last longer.

depending on your rear derailleur, you might be able to use a wide ratio cassette, or you might need to step down a few teeth on the biggest cog... what derailleur is on the bike, presently?

as an educated guess.. the hub is, most likely, from a company named Formula. Make sure it has good, fresh grease in it... neglect can ruin bearing surfaces in any hub.

The RM 30 is one of the crappiest hubs they ever produced I discovered after building 3 wheels using it.
I had assumed if it was Shimano, it was "good enough". Wrong!

Cones are oxide coated (rust browned) instead of polished.
The 2 wheels in use that I have access to had the DS cones noticeably pitted after about 500 miles.

oh dang. What do you recommend that would work better?

how about the one on the bike..

what's the rear O.L.D. of that frame?

Service the bearings on the one you have.
IF everything looks good, buy a 9 speed cassette and install.
Just because the rim is lower end, doesn't make the hub junk.

You've gotten good advice on the hub and cassette. My only comment/question - I'm assuming that the right shifter is 9 speed since you said the bike was originally 9 speed. How is that thing shifting with an 8 speed cassette? If they changed the shifter to match the 8 speed cassette, it won't work with a 9 speed cassette.

It is indeed a 9 speed shifter. It shifts ok, but skips.

Actually, there doesn’t seem to be anything really wrong with the current hub. I think that and the wheel are fine, really. I think I’ll just try and replace the cassette. The O.L.D. 135mm.

I know you didn't do this, so I'll just say it. How would putting an 8 speed cassette on that wheel make any sense at all. Maybe they just happened to have one on hand, or maybe ignorance. Just doesn't make sense to me.

I'm glad you're replacing it and it should be dead simple if you stick within the specs of the rear derailleur (maximum tooth for largest sprocket, and maximum take up range). You'll want to check and re-adjust the RD.

Thanks for the info! The rear derailleur is the stock Alivio that came on it.

As far as I can tell, the Alivio 9 speed RD can take a 36t large sprocket and 45T total capacity. You should be able to use an 11-36t 9 speeed cassette easily with almost any double or triple crank you might have.
SHIMANO ALIVIO REAR DERAILLEUR 9s

Sounds like they just replaced the wheel with something they could get for free and didn’t appreciate the very obvious 8/9 speed incompatibility.

Yup, as a whole, "seeking out a Bontrager wheel" is not something I would ever recommend.

Might be easier to just slap an eight speed shifter on the bike.

This is a 2014 bike, not a current Alivio RDER.
It appears to have been spec'd with an 11-32 cassette,
Without knowing the SPECIFIC MODEL Alivio, and able to actually research the largest cog size, I would stick with a 32T max cog.
Although a 34T would probably work, why take a chance?

5-10 minutes to change a cassette.
you aren't going to change a shifter that quick.

Look closely for an actual model#.
Something like RD-M430 or similar.
Knowing that, we can look up max cog size & chain wrap capacity.
The M-430 lists a 34T max cog & 45T chain wrap.

Apparently your rings are 26-36-48 for a 22T difference.
11-34 cassette = 23T difference for a total wrap capacity of 45T.

I just bought a 9-speed Alivio cassette 11-32. $11. Hope fully that should work.

That should work fine. Note that the chain should also be checked for wear, and replaced with the cassette if it’s worn.

That sounds a bit "too" inexpensive.

Haha! My mistake, it was $35.

Definitely. Im heading to the LBS today to get one and some new brake pads. I have to watch myself, I have a tendency to want to throw money at "fixer-uppers" that don't need it): The first irrational thought that came into my head when I bought it was "Hmmm, maybe Ill upgrade everything on this $100 bike to Ultegra components and convert it to a drop bar bike"...Doh!!!

Or as cheaply, probably.