2023 Santa Cruz Blur chain line

I am thoroughly confused after googling… I have a 2023 Santa Cruz Blur (V4) Carbon CC frame. I am planning a groupset upgrade for it. Either going SRAM transmission (mix of GX, X0, and XX parts) or Shimano 12 speed mechanical (mix of XT and XTR parts).

From what I read all SRAM transmission is built on 55 mm chain line and as many Blur’s comes spec’d with SRAM-T that must work? However, as spacing in the rear is Boost (148 mm) from what I read that means 52 mm chain line.

So will groupsets with either 52 or 55 chain lines work on latest generation Blur’s?

or put another way SRAM-T (55 mm chain line) will work? What about Shimano 12 speed mechanical? What chain line crank should I buy if I go Shimano? XT cranks appear to come in both 52 and 55 mm chain line varieties.

yes

Transmission allows you to select a zero offset chainring (55mm) or a 3mm offset (52mm) depending on what you want to run on your bike. Theoretically you could try both to see what works best, gives the best clearance, etc.

I have a blur with transmission and works perfectly fine with 55mm chainline with the correct amount of spacers as described in sram documentation, if you are using a dub bb it would be 3.5 NDS and 7.5 DS

Then if I go Shimano XT mechanical stick with 55 mm as well, and not 52 mm, even though rear spacing is 148mm?

if you go shimano you likely use the recommended spacers by shimano, the T-Type cassete is positioned a bit out compared that’s why sram recommends the 55 chain line. whatever drivetrain you decided to go I’d install according to the recommended by either sram or shimano with regards to their bb / crank spacers

Shimano steathily pushed their Boost chainline out to 55mm. Google “Sneaky Boost”

Ideally you run the narrowest chain line your frame and rear tire allow. If it’s 52, buy the 52 cranks whether it’s labelled boost or not.

I just put a full XX SL transmission group on my Blur replacing an older XO AXS group. I emailed Santa Cruz asking about this and they were super responsive and helpful. Here’s what I was told…

The new SRAM Transmission groupset you’re after should be purchased in the 55mm chainline option for your Blur 4.
You will want to get the SRAM DUB Wide Bottom Bracket as it comes with the necessary spacers to get the chainline optimized. You will want 3mm on the NDS and 7.5mm on the DS.

I later found that the spacers that come with the BB that are used when threading the BB in the frame are not needed, just the ones mentioned above. Hope that helps.

Thank you for the correction since I’ve said 3.5 nds and the correct is 3mm nds

So you need a new bottom bracket for sram transmission?

not really, the BB is exactly the same. but they have different part numbers that come with different spacers. the only thing you need is a 3mm NDS spacer and a 7.5 DS spacer for the dub BB

1 Like

Thanks for clarifying!