crank questions
 

Hi I'm looking at getting a new pair of cranks for my bike and I found a good deal on a pair of fsa but they have 3 chainrings and my current cranks have 2 what do I have to do to make sure they're compatible with my bike or what would I have to replace to make them compatible. I'm only doing a few upgrades since I'm a newbie. Even though I love the sport its just an older bike and I am saving to get a better bike and don't want to invest a bunch of cash but the cranks flex on my fat a** so there a must to replace till I step up in quality.. Thanks everyone in advance you've all been very helpful with all my other newbie questions you guys rock

If your current bike is a double, and you want a triple, you'll need to get a new front shifter, and possibly a new front derailleur.

Changing an older bike's double to a triple involves changing the bottom bracket as well. If you have the integrated brake / shift units, then you'll need a new one of those as well (and they are shockingly expensive). Probably need to change the front derailleur as well.

I wasn't sure what you meant by the cranks flexing? Older crank arms at least are basically solid pieces of metal. They're not flexing a whole lot. The frame itself can be flexing (usually indicated by hearing the chain rub on the front derailleur while you're pedaling hard), but changing the cranks won't do anything to alleviate that.

What sort of bike do you have now?

I have an older specialized sirrus it has shimano 105 cranks now I never thought it could be the frame though there no rubbing going on just when I pedal hard up hill or stand up to pedal it feels like the cranks are weak. But I could be mistaken.

105 cranks will not flex unless you have very strong legs- the cranks/ bottom bracket are loose or you have a cracked frame.

To change from double to triple will be a new set of cranks along with the bottom bracket- probably a new front derailler and may require new shifters.

Check the bike out and unless you need lower gears- I would not bother changing. And if you do require lower gears- then changing the rear cassette or chainrings is a far cheaper alternative.