Lasue

Hi everyone,

I finally bit the bullet and upgraded my vintage Litespeed to have a 2x sram force axs on it. I am running a rotor crankset and used what I had, namely, dura ace hollowtech BB with 24 rotor axle. Now for the question...I am wondering about chainline. Technically the axle and the BB are setup for the shimano chainline of 43,5 and the sram force axs is 45mm (if I understand this). I have no spacers on the BB currently. Can I technically just put 1.5mm of spacers on both sides of the BB to get to that chainline and have a balanced out Q factor...or am I mixing things up here?

Please focus on the chainline question specifically, as I have read the Sheldon Brown stuff about chainlines but am not feeling 100% that my solution would be ok. Thanks!

Phil_gretz

Have you installed the SRAM crankset and measured the chainline? Do you have a photo of the spaces between the drive side crank and Shimano bearing, as well as the non-drive side space? Maybe an expert can enlighten me, but (in this setup, hollow spindle and external bearings) there normally aren't spacers to shift chainline, but only to better fit the fixed spindle-to-bearing alignment.

alcjphil

Is the 45mm chainline for the AXS crank the setup you would use for a disc brake equipped bike? Your bike has 130mm dropout spacing which would need a narrower chainline than a disc brake bike which has 142 mm through axle rear spacing. I wouldn't worry about your chainline and adding spacers might not even allow you to install your crank which probably has too short a spindle to permit that

Lasue

As mentioned in my post, I am not running an axs crankset. I am running a rotor crankset. The 45mm is the stated chainline that the axs crank has. I have a DA hollowtech BB and rotor 24mm spindle. That is the usual setup for shimano at 43.5mm. I have rim brakes.

I am concerned about the chainline because it seems to be a bit off and the tolerances for axs are super small so if something is 1-2mm off, it will not shift its best. I am doing more testing this wkend to see. Rotor makes spacers for the 24mm so I am not sure why spacers would prevent me from installing my crank.

https://rotorbike.com/catalog/defaul...cers-road.html

The question is still, if I want to have the exact same chainline as the axs crankset, would installing the above spacers of 1.5mm correct the chainline or how to you obtain this 45mm chainline?

Troul 

Recently I have dug thru the depths of the interwebz to find if such spacing is doable with a FSA PF BB. At this point in time I regret to inform you that no such accommodations exist for your desires.

Should a more in-depth research or some very recent innovation change the results that I could not uncover, I'd hope that information would be provided in your thread.

DaveSSS 

I have force axs on my bike, with the shimano 43.5 chainline and 142mm axles. It works fine. I use a shimano grx 46/30 crank that has a +2.5mm chainline, but corrected it with spacing washers. This is possible with the grx because the chain rings both mount behind the spider arms. I could have changed it to the sram chainline, but I'm more likely to use the larger sprockets than the 46/ 10-11-12.

I also used the GRX crank with it's +2.5mm chain line on my bike once and had no problem, other than the FD just barely had enough travel to clear the chain, in the big ring.

Lasue

Thank you for your reply. So you used washers behind the chainring bolts but found no problem with a bit off chainline? Good to know... my bigger test will be on the wkend but I have been a bit concerned.

jp911

I haven't personally worked with a Rotor crankset, but I adjust chainline for Easton and RaceFace cranksets using spacers on the spindle. Both of these products include a tensioning ring to allow for taking up any "slack" once the spacers are set and there's any residual play. If the Q-factor is off by more than a millimeter or two, I've used spacers between the crank arm and the pedal. With newer Shimano cranksets you can add a small amount of spacers at the spindle to increase chainline because the torque is more tension based and then the cransket system is secured using opposing bolts on the non-drive side arm.

In your case, I would try a few things: 1. try and add spacers between the BB and drive side at the spindle (increase in small increments and test until you're happy with the shifting), and 2. investigate BB options that are lower profile that will require spacers to get it perfect; more trial and error here, but you can probably get it dialed (I would contact Wheels Manufacturing to see if they have some options for you).

Retro Grouch 

You're only talking about 1.5mm difference on a derailleur bike that warps the chain sideways to shift. That's not very much difference.

My general philosophy is, if I already own parts, I'll bolt most anything together and see if I can get it to work to my satisfaction. If it was my bike, that's what I would do here. I wouldn't fret about fine tuning the chainline with spacers until I knew that what I had wasn't working.

Camilo

I agree with this. I think early in my second phase of amateur bike mechanic-ing (first: 1972-1985, second 2000-present), I read somewhere basically what he writes above. To my non-engineering mind, the rear derailleur spans so much lateral distance, The crank being a mm or two, or even a few, off is not going to make any noticeable difference. I do, as a courtesy to the mechanical gods, eyeball from between the chain rings back to the cassette and if it's at all close to being centered, it's good. Shifting has never been bad.

This is assuming there's no other reason to use spacers to shift the position of the crank arms vis-a-vis the bottom bracket.

Lasue

Update to everyone... I rode this wkend and no problems whatsoever! Guess I was just thinking about the absurdly small tolerances of sram axs and was concerned but everything was like butter! Thanks!

veganbikes

People love to freak out about chainline but it is probably pretty rarely an issue. The fixed gear community loves it especially. Honestly a few mm isn't going to make a huge difference and can probably be accounted for with good shifting practices and some derailleur tuning. If it is massively off then yes you could have a problem but that is a rare occurrence.

Park Tool made a Chainline gauge years ago and we have used it now twice and really only because a batch of frames we got had an issue and one of them was chainline as the thing was badly put together at the factory (not damaged in shipping) and the other had a chainring issue as they were not using a narrow wide and it was coming off and we didn't have more than a few before things got corrected.