The repercussions of the SRAM 1x drivetrain system keep making changes in frame and component design. It’s even changing how we ride. For me, looking at building a few new narrow gauge dirt bikes, there is room opening up for larger tires and shorter stays. This is a good thing as long as the reduced gearing range isn’t an issue. Hopefully, GX12 is on the way.
With a lack of spider and chainring options on the market and a frame design in the works, I needed to make something happen in the range of what I call, BoostR. A 49mm chainline on road and cross bikes. This seemed to be the correct chainline for single chainring 135/142mm rear end bikes but it turns out that SRAM has tested large chainrings at 48mm. For 148mm rear ends, the chainline goes up to 52mm but that isn’t a concern for today.
The chainring mount face on these has been very carefully placed. The spider is designed to use the high quality SRAM Force x-sync and Rival x-sync chainrings in 110BCD. These are supplied in a 38 to 50 tooth range. That’s ample for most uses. The geometry of the SRAM rings is quite a bit different than other rings so being able to use these is something most other designs can’t offer. If a 34 or 36 tooth ring is required or rings from other manufacturers need to be used, some spacers can be used to get the 49mm or other chainlines.
For framebuilders, like me, these spiders don’t project past the chainring on the inside. This means that frame designs only have to clear the chain and not other useless projections. This means better power transmission within the frame and larger tire sizes.
A lot of engineering time went into getting a precision mate between the crank and spider interface. The diameter seat and drive lugs were quite an adventure in reverse engineering. Getting a sweet fit of the crank arm to the spider flange was interesting also. These are fits you won’t find elsewhere.
No matter who you are or who you ride for, if you’re racing cyclocross, you need this part and you don’t have it.
* 49mm 1x chainline
* For road Q145 cranks
* 5-bolt 110mm BCD
* Precision SRAM GXP interface.
* Designed for SRAM X-sync 110BCD chainrings but will work with all 110BCD rings.
Machine work was done by my favorite machinist, Devin Bodony of Lichen Bikes. Check him out.