need help

Since you say that you're only using you're top two gears now, what do you think that you'd gain by switching to a triple crankset? It looks to me like you'd be spending a lot of money to add a bunch of even lower gears that you'd never use.

Retro Grouch has a point. Instead of going to a 105, keep the crankset that you have. You know that you won't have to change out the bottom bracket and front derailleur. You can get an 8 Speed cassette but you will need to replace the freehub as the 7 speed will not accept an 8 speed cassette. This also means that you would need a new, longer axle. Also, most bike frames can be sprung enough to go up from a 7 to an 8, but you will want to make sure that yours is one of them. You will also need to make sure that your rear derailleur is compatible with an 8 speed cassette. In addition, you will need to check and see if your shift lever has an eight position. You may also need to buy a new chain if the gearing is way different from what you have now. You will also need to make sure that the 8 speed cassette gears are higher than what you have now. if not, then all of the above changes will have been for naught.

LOSTRIDER said:

I only use the top two gears on the current setup i have and can't afford to buy the bike that i want.
Thanks

Without meaning to sound rude, if you are only using your 2 top gears you need to spend a lot of time training yourself to spin and training yourself in the appropriate use of gears. I would do this before changing the bike.
Or did you mean that you only use the 2 bottom (easiest) gears?

LOSTRIDER said:

I am new to cycling and i have a 14sp road bike with shimano tiagra componets. Can i upgrade my crank to a shimano 105 triple with an 8sp cassette. I only use the top two gears on the current setup i have and can't afford to buy the bike that i want.
Thanks

I presume you want to have the 11t cog that is available with some 8-speed cassettes. You may be able to buy the cog & lockring OR you can buy the 8-speed LX cassette (it will come with the lockring) and you can simply use 7 of the cogs (the spacing is essentially the same).

LX (and, 105) cassettes have separate cogs -- the last (largest) several are "bolted" together. You can UN-bolt them with a 1mm (?) Allen wrench OR in some cases you have to grind off the head if they were riveted together OR you can simply exclude one of the intermediate cogs in the stack.

The smallest cog on most ROAD cassettes is only a 12t.

BTW. I'm presuming your rear hub is "fairly recent" and uses a standard Shimano lockring to hold the cogs in place.

As others have noted, there is no reason to change your crankset.

Thanks for the reply. I bent a chainring and was just wondering if going with a different setup would improve any performance in the bike. It sounds like i should just replace the bad part and keep on spinning. Like i said i am new to this and dont know much about cycling. Thanks again