Chainline value of 43.7mm is from SRAM's 2020 Frame Fit Specification document. Chainline values of 45.5mm and 47.5mm are from SRAM's crankset product webpage.
I am buying parts for an 11-speed build. I have the SRAM CX1 crankset and the SRAM BSA GXP 68mm BB, and my measurements are showing/predicting a 44mm chainline (with no BB spacers). I have not yet received the frame but it will have 68mm threaded bottom bracket.
I am attempting to have a 46mm (or close to it) chainline by replacing the spider and 50T chainring (that came with the CX1 crankset) with a direct mount 38T with the correct offset---which I think perhaps is 3mm. My measurements show that the SRAM spider and 50T chainring have a 6mm offset.
Do you think a 3mm offset for a new direct mount chainring will get me close to a 46mm chainline? (I cannot figure out why SRAM lists three different chainlines for this crankset.) Is 46mm the proper chainline target for an 11-speed speed build with a CX1 crankset?
Pretty sure it's right about 44 assuming you're talking about a non-mountain bike. Go with a 6 mm offset ring to get closer to 44 or go with a 3 mm offset if you think you need to be closer to 46 (and won't use any spacers). Or go with the 6 mm offset and add a 1 mm spacer on each side of your crank spindle.
Yes, I am talking about a non-mountain bike, i.e. a road bike frame with a 142mm rear end. I follow what you wrote and it makes sense to me. Your words are reassuring.
I guess the 45.5mm or 47.5mm chainlines listed on the SRAM webpage for my 50T crankset are maybe for OTHER versions of the spindle than the one that I have---maybe 30mm/DUB---as mine is the 24mm GXP with step to 22mm. That SRAM page NOT listing 43.7mm (of 44 mm) caused me to question my understanding.
I don't really know what those are referring to, so I could be wrong. SRAM doesn't like to make a bunch of tooling and extra parts, so there is a lot of crossover between stuff. I'm fairly sure there's only one spindle length outside of the BB30 non-removable spider cranks that seemed to only cover most RED cranks. So I'm not sure if 'different spindle lengths' answers the question there. The same 3 bolt pattern was used for both 30 mm spindles and GXP. They use the same spiders for 1x and 2x, it's just their 1x rings that are offset. If you put a non-SRAM 50 tooth on the spider, the chainline is going to be shifted to the outside by several mm.
I'm not sure why 46 mm is 'needed' here, but I think you're going to want to the ring option with the most offset. Talking about chainline without the actual frame, bottom bracket and spider/chainring involves a lot of guessing.
Yes, I am now beginning to accept that it is best and that I need to wait to have the frame in hand.
I do have the actual shop drawing of the frame now being built---but am new to the bike work. Being naive, I thought I could get this chainline value nailed down before I receive the frame
You have answered my questions. Thank you.
~~~ The following is just FYI and in response to your last post if you are curious. The 46 mm chainline target is from the "Tech Docs" section of Wolf Tooth Components where they state that the "ideal" chainline is about 2mm towards the outboard direction from the centerline of the cassette---and for an 11 speed cassette on a 142mm rear end that works out to a 46mm chainline. (So in reality, maybe I should first see if I have shifting issues---and if I do then measure the actual centerline of the installed cassette and then start adjusting the actual chainline---instead of adjusting it hypothetically.)
It is surprising to me the amount of guessing that is needed; I had thought it would have been easy to determine the chainline value from the paperwork.
Just for the record, I think I figured out the answer to part of my question. SRAM never published that the CHAINLINE is 43.7mm for the crank I bought. Looking more carefully at SRAM's 2020 Frame Fit Specification and the diagram shown, the 43.7mm is the distance between the frame centerline and the INSIDE of the chainring---I guess for a frame clearance consideration. The chainline would be about half the width of the chainring plus the 43.7mm. In other words, half the width of the ring does measure to 1.8mm---so the chainline of the CX1 crankset is 45.5mm.
I have decided that I am splitting hairs and think 45.5mm is close enough to Wolf Tooth's suggested 46mm chainline to have the hope that all will shift well.
(I still do not know where the 47.5mm chainline value is based upon, but that is a problem for another day.)
I don't think so. That 'frame clearance consideration' distance would change with every size chainring. I don't think this number you saw on the Wolf Tooth site means as much as you're making it to be here.
