Technical FAQ: Shimano GRX chainline, substitution for GRX flat-mount calipers

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Dear Lennard,
I bought a Cervélo Áspero with Shimano GRX 800 2×11 mechanical groupset. Unfortunately, the bike comes with Easton EA90 cranks, which have a 45 mm chainline instead of the Shimano FC-RX810-2, which has a 46.9 mm chain line. Since the rest of the bike is GRX, which was designed around that wider chainline, I wonder if I have compromised drivetrain noise and wear. I currently get a fair amount of chain rub on the front derailleur when in the big ring and the third and fourth largest cogs regardless of trim. I also get the chain making a bit of noise as it sometimes slightly touches the big ring when in the small ring and the lower third of the cassette, but not enough that it wants to ghost shift to the big ring.

I am a former bike mechanic and am fairly experienced at proper derailleur setup and believe I have everything properly adjusted. I did have to deviate a bit from the standard setup instructions regarding the cable tension alignment line due to the different chainline. Unfortunately, I don’t have a full GRX bike to compare the shifting against.

So, my question is whether this is normal for GRX or if this is a function of using the incorrect chainline? Would replacing the crankset with the correct Shimano model eliminate the chain run on the derailleur and chainring? Or is this inevitable when cross-chaining?
— Erik

Dear Erik,
You either have to get a GRX crank, or you have to switch to an Ultegra front derailleur. Otherwise, that cross-chain rub won’t entirely go away. That’s because the GRX front derailleur sits outboard further than Ultegra, Dura-Ace, etc. in order to pair with the wider chainline of the GRX crankset.

Scroll down this pdf on the Shimano support web site to this statement, “To better accommodate wider tires for gravel riding we’ve pushed the chainline out 2.5mm. This means that the GRX double cranks and GRX front derailleur must be paired together.”
― Lennard

Dear Lennard,
I am looking to upgrade my 2017 Santa Cruz Stigmata to Shimano GRX Di2 groupset. There is a problem, however.

My bike has a 140mm post-mount frame/fork, so I could not use GRX flat-mount brake calipers. Instead, I would like to pair GRX Di2 levers with Shimano MTB brake calipers (preferably with XTR 9100 2-piston calipers, since they have a straight hose connection, not a banjo style).

Question is, will that combo work? Regarding to some mechanics rumors, it will. What do you think? Can you help me? It is next to impossible to have that question answered by Shimano.

A set of nice GRX post-mount calipers would have been nice…
— Jernej

Dear Jernej,
If I were you, I would instead seek out the Ultegra BR-RS785. It, too, attaches to post mounts and has a straight hose connection, rather than a banjo. Otherwise, I see no reason that you couldn’t use this straight-hose-connection XTR caliper.
― Lennard

Dear Lennard,
I was interested to read the recent post where you mentioned an older Salsa seatpost. Could you post/send a link to that older design? I wanted to look it up to perhaps track down a used one.

I had two thoughts. First, don’t modern micro-adjust seatposts manage the issue of separating leveling from fore and aft? These are the seatposts with bolts at the front and rear of the clamp that allows you to turn each separately and move the level.

Also, an older seatpost I enjoyed using and miss was the Easton CT2 model. It just used two bolts on either side and was much faster to adjust than some other seatpost designs.
—Corey

Dear Corey,
Here is a photo of the Salsa Shaft seatpost.

The vertical bolt tightens down on the rails. The rear horizontal bolt loosens the angular adjustment, and the forward horizontal bolt allows the cam to rotate. So, you can fully lock down the saddle rails into the cradle clamp while leaving the angular adjustment loose and then very precisely adjust the saddle angle while the saddle is secured fore-aft. Or, you can fully tighten down the angular adjustment at exactly the angle you want, and then you can loosen the vertical bolt and slide the saddle fore and aft without changing the angle adjustment.

While micro-adjust seatposts with two bolts do allow you to fine-tune the angular adjustment, they do not completely separate those adjustments. When you loosen the bolts enough to allow fore-aft saddle adjustment, you have also changed the angle adjustment. Of course, if you did have the angle dialed in with the bolts fully tightened, you can just loosen one of the two bolts, slide the saddle forward or back, and then tighten just that one bolt. You should end up at the same angular adjustment with the new fore-aft saddle position.
― Lennard

Dear Lennard,
I had — and loved — the Salsa Shaft seatpost you referred to in your July 21st column. It ultimately developed a circumferential crack in the adjusting cam. The symptom was a ticking sound under hard seated climbing that got progressively worse. The noise could be reproduced in the shop by rocking the saddle back and forth, nose-to-tail. I thought it was my Brooks saddle until I mounted a cheap plastic saddle, and the noise remained.

Both the Nitto S83 and the Paul Components Tall and Handsome are two-bolt designs that allow independent adjustment of saddle tilt and fore/aft position. They’re not the lightest posts on the market, so probably not attractive to a large number of riders. Also, Salsa now offers a seatpost called the Regulator Ti, which also claims independent adjustment.

I have the Nitto S83, and like all Nitto products, it’s as sexy as it is functional. Micro-adjustments to saddle tilt are a breeze, even on the side of the road while getting a new saddle dialed in.
— Greg

Dear Greg,
Perhaps that’s another reason the Salsa Shaft post went away.

The Nitto S83 is indeed elegant, and it is a shapely micro-adjust seatpost with bigger bolts than most tiny-bolt micro-adjust posts (like the Paul or the super-popular Thomson). It does not completely separate fore-aft and angular adjustments like the Salsa Shaft; it won’t allow you to move the seat back and forth without loosening the tilt adjustment like the Salsa Shaft post would. Again, like I said above, those posts like Nitto, Paul, Easton, and Thomson do allow precise angular adjustment, and to change fore-aft, you can just loosen one of the two bolts, slide the saddle forward or back, and then tighten just that one bolt.

The Salsa Regulator Ti post has a similar clamping system to many other titanium seatposts. When you loosen the clamp bolts, you have also freed the angular adjustment.
― Lennard

Dear Lennard,
I found this seatpost on local craigslist posting. I think it does the same as the Salsa one.
— Brad

Dear Brad,
Indeed, it does! I remember those RaceFace posts and loved them. Just like the Salsa Shaft, you can fully tighten the rails into the cradle and then separately work on precise angle adjustment. In this case, you loosen the bolt tightening the circular clamp around the post. Then, as you slide that clamp up and down, you change the saddle tilt via the linkage and can retighten it right where you want it, all without affecting saddle fore-aft.
― Lennard

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn