I have a giant defy 5, and I wanted to go to a double crankset

I got a good deal on a 105 5600 (39/53) crank (coming in the mail), and I was wondering if I could use it on my bike without much of a hassle.

Right now its got 8 speed rear cassette, and a triple FD.

I've done a bit of searching, and I found out that a lot of people have been using 10 speed cranks on 9 speed bikes no problem. But there's less information about people trying it on an 8 speed. Not sure if i'd need to get a 9 or 10 speed chain to make it work properly.

just curious if anyone here had experience with this and could chime in, thanks

I'm running an 8 spd SRAM cassette with 9 spd Ultegra RD, 10 spd 105 double FD and a 9/10 spd 53/39 crank. No problems. Chain is a Shimano HG50 8 speed.

Of course, YMMV. Some 8 speed chains are narrower than others. Go with a narrower model if you think clearance could be a concern with your crank.

I had no usable overlapping gears between rings due to chain rub on the big ring when I paired a FSA "9 and 10 speed compatible" crankset with a 9 speed Campagnolo chain until I shimmed the small ring inward back to 9 speed dimensions.

it won't work. looks like it's time to buy a new bike.

I just did something very similar and did a ton of research. Had a few hiccups but those seemed to be derailleur related and not a speed compatibility issue. currently running an 8 speed bike, 8 speed chain, with a triple ring crank, both the big and middle ring are 10 speed. From what Ive read about and discussed with shop mechanics, its fine to run chainrings that are a generation or two ahead of your rear cluster. hence, 8 speed rear, should run fine with 9/10 speed front rings. so, as long as your shifters are a double, your ten speed crank should work ok. if you have triple shifters/triple front fd, thats the only place where i might see an issue. you might be able to mess with the limit screws to stop the triple from going to the smallest postion (the third click) but optimally, you do want your shifters to match the number of rings in front.

from the sheldon brown site....

"New Chainrings, Old Chains
Going the other direction, using wider chains with chainrings intended for narrower chains is not generally a major problem if there's only a one- or two- generation difference. The only problem you might run into is that the chain will be more liable to rub on the inside of the bigger chainrings in the small/small crossover gears, gears you shouldn't be using in any case."

https://sheldonbrown.com/speeds.html

yeah, i just installed the crankset today.

it works just fine. however since the 10 speed crank has gear spacing smaller than an 8 speed, my eightspeed chain will actually rub on the 53cog a little bit, when im crosschaining a lot.

but it's perfectly rideable just not too good on 39 while on the smallest back 3 sprocketgears.

im going to try to get a 10 speed chain to see if that fixes the issue. if not i suppose i will have to shim the small chainring as drew stated.