Cranks / Chainline / Q-Factor (Roadini)

[Jay]

I have a general understanding about topics above (scanned Sheldon Brown's site) but would appreciate some guidance for a future upgrade/replacement.

Currently on my Roadini I have DT friction shifters, GRX 2x crankset, GRX FD, 105 RD.  11sp

There are a few things I'm looking to change:

- shorter crank arms (probably 165mm)

- silver over black (as much as possible)

- maybe a narrower Q-factor of the crank, which may improve chainline (I may be mistaken)

I believe the GRX crank is a little wider than a traditional road double, but it's a rather small difference and may be something I should ignore.  Why I mention: for my bike fit, narrower is better, but what I'm more curious about is whether I can improve my chainline when in certain gears.  I know that when I'm in the larger chainring, I can only be in the 4 smallest sprockets without rub.  If I shift to the 5th or 6th sprocket, chain rubs inside of FD cage, if I trim it to move inside, it shifts down to smallest sprocket.  Whereas when I'm in the small chainring, I can use 8-9 sprockets before any rub (and easy to trim to avoid noise/rub, without going into the big chainring.  I realize this may not be about chainline, so please help me dial in my set-up so I can be in the large chainring and have more sprockets to use without rub (e.g., if a limit screw can move the FD inboard a couple mm, that may do it, but since the shop built this up I have not touched it, and it has always been like this).

Regarding part swap, I can ditch the hollowtech BB and put in the square-taper that came with the bike, and then add some nice cranks in a silver colour, or keep the hollowtech BB and find a crank in silver, with 165mm arms, that works with the frame/set-up.  I'm a bit lost here, but doing research.

Thanks

[Collin A]

If you are using the "modern" shimano FDs, they require a lot of setup initially to make work (great video here:  Shimano Ultegra R8000 Front Derailleur Set Up Tips) and the "limit screws" don't work like a traditional FD. It is really intended to be used with the current gen shimano shifters and not necessarily friction.

If you are looking for a narrow Q, short length, and silver (and the same BB standard), then this would be your best bet: alexscycle.com/products/dixna-la-crank-arm-set-130mm-to-170mm

BYOC(hainrings) though... and it has a standard road chainline, so in combination with the friction shifters, it might be worth getting a different FD that is more silver.

Collin in Oaktown

[Garth]

From here : https://www.ridecx.com/blogs/learn/understanding-chainline-shimano-grx-and-sram-wide-cranksets

In summary, Shimano gravel chainlines are 47mm, road doubles are 43.5mm. 

The GRX double has a tread width of 151mm, up from the 146-148mm of their Road(Dura Ace, Ultegra, etc) doubles. Sure the difference may be noticed, but it's neither here nor there as to making or breaking one's functional cycling experience. 

From one of the comments of the Dixna crankset @Alexscycle, the tread width of a double w/Ultegra BB 150mm rather than the stated 140-144mm. Bummer ! 

Since you're running a factory spec GRX drivetrain(minus the hub of unsaid origin), the chainline is what it is, as designed by Shimano. Trmming the FD as needed is normal. 

Look up all techy specs for Shimano here : https://productinfo.shimano.com/en#/com?cid=C-453&acid=C-454

For a 165mm road double 43.5 chainline and a 145mm tread width, the Sugino OX2-901D is an option. This price is better than the $500plus most retailers sell it for. https://www.amazon.com/Sugino-OX2-901D-Classic-Compatible-Shimano/dp/B09SL5TL8K/ (This is w/o their BB).

Lots of ring combos to choose from. 

[Will Boericke]

You can replicate the sub-compact chainring setup of the GRX crank with an older mtb triple (110/74 BCD).  Mount whatever 110 chainring you like on the inside of the big spider (with single speed chainring bolts), and whatever 74 BCD ring you want on the inside mounts.  I have this setup on a 90s era LX crank, 46/26, and it's great.  I'd probably go this route, as you have compromised gears with the GRX now.  Any front derailleur should shift that, unless the Riv seat tube angle is extreme.

Will

[John Hawrylak, Woodstown NJ]

Jay

If you want the narrowest Q in a modern crank, suggest you look at the Rene Herse double.   They quote a 142mm Q which is probably for the 107mm SKF BB and 43.5mm chain line.   It's expensive, but probably worth it.   Also, their 'downshift technology' seems to be useful, at least from their write ups

I'm using used Sugino AT cranks & 1st generation Dura Ace cranks to get narrow triple Q, but the RH may have worth the extra $$ to avoid the experimental development I had to do

John Hawrylak

Woodstown NJ