Bicycle Mechanics - 7 speed cassettes

im getting a trek 820 because its the only thing they sell here and it come with a 7 speed cassette.

will i beable to up if i change out my wheel set.

will the crank and cassette line up

oh im changing the crank to

Huh?

Yeah, buying a bike because it has a 7 speed cassete is one of the craziest reasons I've ever heard.

But I see a small hint saying that you want to upgrade the wheels right away? Why buy a cheap bike so you can spend a lot of money on it right away? Just buy something better to start with that doesn't need upgrading.

IF you meant you want to upgrade to more speeds, BCRider is absolutely correct.
You don;t have to change the wheel set, but you would need a different Free Hub Body, cassette and SHIFTERS. IF 9 speed, add a new chain to the mix.
To get a reasonable quality upgrade, you're probably talking close to $200-300ish?
Much cheaper to buy a bike that already has more gears.

Hard to believe "that's the only thing they sell here", when you are that close to DC! LOOK at some other bike shops! The TREK site says there are 11 TREK dealers within 25 miles of you!

im in africa and thats all the Nex has.....im just going to order sette frame and start from there.

A Trek 820 will be spaced 135 mm so any current MTB wheel should fit. If you can only get 7-speed cassettes, a 4.5 mm spacer will allow them to be installed on 8 or 9-speed freehub bodies. If you do use an 8 or 9-speed cassette, you will have to change the shifters too.

BTW, telling us up front where you are actually located would have explained the situation and avoided some of the incredulous replies.

Can't you get a bike shipped out there from any of the MO places, Performance; Nashbar; bikesdirect; randal scott; ibex; ebay? It's way cheaper to buy a bike speced with what you want then to buy the parts and frame.

I would ask "what are you trying to accomplish by changing to a different cassette?" The 7 spd is a 13-34 which isn't really a bad range. It may be easier and certainly cheaper to look at you chain rings if you are only trying to get a different gear ratio.

im in africa and thats all the Nex has.....im just going to order sette frame and start from there.

Well, you show Dale City, VA on your info!

2nd bidaci's question: if only 7-speed stuff is available in your area, maybe you can make it fit your needs? That could also be handy, as replacement/repair parts would be locally available.

Ok, it appears that the poster is in the Navy or is a dependent of someone in the navy

Translation Nex= Navy exchange.

Been riding my bike with 7 cogs on my cassette for 18 1/2 years. They come in 9 now? Just kidding. I am just fine and have no problems. 3 Chainrings would be even better with 7 speeds in back.