9 speed crank 8 speed cassette
 

Ok gang, help educate me. This is the first time I have owned a good bike long enough to overhaul the drivetrain. I currently have a stock drivetrain on a 2005 Fuji Sagres: 52-42-30 cranks that need replacing, 8-speed cassette, which I just replaced last week along with the chain, Acera RD and whatever FD came with it.

I am interested in swapping out the cranks for an inexpensive compact double, as I am also converting this hybrid to a cross/commuter with drops and all. I also do not wish to upgrade to a 9 speed system as I have already spent money on 8 speed components.

That being said, I have found a compact double that is a 9 speed, as most seem to be. Assuming FD change to match this crankset, will I need to change anything else in the drivetrain to be sure of flawless operation? The only thing I can possibly see is the chain, to match the 9 speed crank. Is it important that the crank is rated at 9 speed with my 8 speed cassette, or is this crank '9 speed compatible'?

Thanks in advance.

In my experience an 8 speed chain on a 9 speed triple crankset can cause issues with the chain hitting the chainring ramps. A compact double will likely not have the same problem and several here have posted about successfully using 8 speed chains on 9 speed cranksets. You can always try it and see if it works. If not, a new 9 speed chain can be had for ~$15 and will work fine with the rest of your components.

I use 8 speed chains on so-called 9 speed cranks and have no issues. There really is no such thing as a 9 speed crankset anyways... they just get labeled that by the manufacturer.

I've used 8s chains on 9s cranks, 10s chains on 9s cranks, 9s chains on 8s cranks, etc. and rarely had any type of a problem. Those rare problems were probably due to needing a derailleur adjustment and not the crank itself.

There most certainly are differences. Whether or not they affect your particular set up depends on a lot of factors.

You probably won't need to change the FD either. I'd try changing the crank only and see how it goes.

if anything a compact double will be worse than a triple as far as chain hitting the ramps goes. 16t jump between the chainrings instead of 9-12 means the chain can't angle outwards as much. But if that happens you can fit it with thin chainring spacers.

My experience is you should match the FD with the chain, not the crankset. So use an 8 speed chain and keep the current FD, or 9 speed chain and change the FD.

on a side note, what type of brakes does this bike have? and what brake levers/shifters are you going to use on the drop bar?