Helderberg

I currently have an FSA 46-30 crankset and Shimano 105 front derailleur and shifter/brakes on my Topstone. I want to go to the same gearing but a 165mm crank arm so I have found two options. One is to stick with the FSA brand and the other is to switch to the GRX Shimano both set up for 11-speed cogs and the 165mm cranks I want. With the FSA I might be able to maintain the current BB and should be able to use my current FD and shifter/brake levers. If I go to the GRX I believe I would have a problem with the indexing of the FD and the shifters but I am not sure. I have not been able to find any information about the compatibility of my 105 to GRX but I am sure it is out there. Any help would be greatly appreciated. I would change the BB regardless of the FSA fitting the current BB as if I have it apart why not.
Thanks in advance, Frank.

Iride01 

GRX has a little more chainline than a typical road crank. Though you did say gravel bike, and GRX was specifically made for gravel bikes. But I don't knw what the chainline is on a Cannondale Topstone. So you might measure it from the center line of your seat tube to the centerline between your rings. Chain line of cranks can be a bugger to find, but often diligence does pay off in google searches.

I know you said it was FSA 46-30, but FSA makes a bunch of different model lines. Maybe a model number stamped inside under the pedal bolt holes?

Not certain why you'd think a 46-30 Shimano... if you can find it, will index differently. Unless perhaps you only have a 8 speed rear and are looking at a FDR for a 11 speed group. Even then, it might work.

Mostly the first part about the GRX is a lot of supposing on my part because I've only casually read about it. However it interest me because I might want that for a future bike or bike build. So double check if no one corrects my possible mistake.

70sSanO

What little I’ve read is the GRX outer chainring is positioned 2.5mm further out. This results is a hit or miss with a typical 11 speed road double FD.

Edit/Fix: The Tiagra FD-4703 triple might work with 11 speed 105 shifter. If the FD cable pull is the same, it might extend out far enough to reach the outer GRX ring.

John

Helderberg

If I understand what both of you are saying I should measure the existing chainring on my bike. Then find the centerline measurement on the GRX or the other FSA and that should tell me if the FD will work?
Frank.

deacon mark

I can tell you going all Shimano is the best option. This combination has the best front shifting and rear I don't care what anyone says. Shimano cranks, cassette, chain, and shifters still is the best option.

70sSanO

Yes, but this might help...

https://bike.shimano.com/en-EU/produ...0/FC-5800.html

https://bike.shimano.com/en-EU/produ.../FC-R7000.html

https://bike.shimano.com/en-EU/produ...-RX600-11.html

John

Edit: I'm not sure, but I think a GRX FD may work with your 105 11 speed shifters.