46-30 chainset 10 speed on CAAD 8, any drawbacks to take into consideration ?

[Guitars and Bikes]

Seems like the needing 19mm spindle is misinformation. Say I buy the 10 speed grx 46-30 crankset, will the 10 spd 105 5700 shifters work OK ? And what front derailleur do I need to buy due to chainline width ? Am I right thinking I don't have to change my 5700 rear derailleur ?

 

[Jameshow]

Seems like the needing 19mm spindle is misinformation. Say I buy the 10 speed grx 46-30 crankset, will the 10 spd 105 5700 shifters work OK ? And what front derailleur do I need to buy due to chainline width ? Am I right thinking I don't have to change my 5700 rear derailleur ?

Correct afaik suck it and see with current front mech it might work. Shimano tend to be conservative with specifications.

 

[wafter]

I expect that the grx would have a wider chain line tbh. Need to check with someone.

Yes, IIRC it's a whole 2.5mm further out.

The q factor with the grx is 51mm as opposed to the 105 which is 45mm, could this lead to knee niggles ?

Tbh it's chicken feed, and depending on your physiology it may be of benefit or hinderence. IIRC the total pedal centre-spacing on my fuji (MTB triple with flats) and CdF (road double with SPDs) is about 50mm. The narrower road setup destroys my knees and feet, while the wider MTB setup is lovely.

It says the usual hollowtech 11 bottom bracket won't fit due to grx needing 19mm spindle instead of 24mm. When I checked the shimano technical document it recommends a rs501 BB, when I checked its dimensions.....it says 24mm.....( bangs head off wall ) does a hollowtech ii BB for use with 19mm exist ?

All hollowtech cranks are 24mm IIRC. I don't know of any that are 19mm, I think this is an error.

Seems like the needing 19mm spindle is misinformation. Say I buy the 10 speed grx 46-30 crankset, will the 10 spd 105 5700 shifters work OK ? And what front derailleur do I need to buy due to chainline width ? Am I right thinking I don't have to change my 5700 rear derailleur ?

According to Shimano you need a dedicated GRX FD with the GRX crank on account of the slightly wider chainline. Anecdotal evidence suggests that in some cases you can get away with a road FD such as the 105 item. I think cable pull ratio is the same between later road and GRX, so there should be no issues here.

You shouldn't have to change the RD unless you're changing the cassette also.

 

[bobzmyunkle]

I was running the grx 46/30 with 5700 shifters for a while - no problems.
I did switch the front derailleur to grx400 due to the 5700 one being damaged, so not sure if the 5700 front derailleur would work with the slightly outset chainrings. Probably worth a try and if not the grx400 front derailleur isn't particularly expensive.