Sram boost / dub cranks - help needed

[Yo-Yo]

Wondering if anyone can tell me if the ‘boost’ part in the SRAM boost crankset is a difference in the actual crank set up or just their boost chain ring with the different offset to the normal one (either 3 or 6mm)? I have a standard GC eagle set up that the chain ring is far too close on the chainstays and scratching the carbon. I’ve added dub spacers but there is a ticking on the higher gears that is apparently a thing with this.

 

I’ve been searching everywhere for info on this but the sram site doesn’t give much and there is o lot 1 forum I found with the same issue and that wasn’t resolved.

 

I have found out the difference in chainlines is 49 to 52 between the cranks on CRC. Recommended chainline in my bike is 51.

[MORNE]

boost literally just moves the chainring 3mm out on the drive side (tomatch the rear cassette's 3mm outward spacing of course)...if it is a direct mount ring and the spline is the same as as the new rings..just get the appropriate offset chainring and you are golden.

 

its more difficult with the 104 BCD stuff ala shimano etc but still possible. Using my saint non boost cranks on a boost frame no issues.

 

You mentioned, it differs frame to frame in the chainstay area regarding clearance. 

 

good read on the topic.

 

https://www.wolftoothcomponents.com/pages/boost-chainline-and-chainrings

 

Edit: non boost crank on boost frame with 32T front ring

 

 

[DieselnDust]

Wondering if anyone can tell me if the ‘boost’ part in the SRAM boost crankset is a difference in the actual crank set up or just their boost chain ring with the different offset to the normal one (either 3 or 6mm)? I have a standard GC eagle set up that the chain ring is far too close on the chainstays and scratching the carbon. I’ve added dub spacers but there is a ticking on the higher gears that is apparently a thing with this.

 

I’ve been searching everywhere for info on this but the sram site doesn’t give much and there is o lot 1 forum I found with the same issue and that wasn’t resolved.

 

I have found out the difference in chainlines is 49 to 52 between the cranks on CRC. Recommended chainline in my bike is 51.

 

 

 

Boost vs Std in SRAM cranks is just the chainring offset the crankset is supplied with and Q168mm.

 

If Qfactor is 156mm then its non boost.

so....

Boost chainring = 3mm offset on a Q168mm crankarm

std chainring = 6mm offset on a Q156 or Q168mm crankarm

[MORNE]

with shimano stuff the q-factor does not change at all though...the chainlines are also closer to the 51-53mm ranges of boost.

 

example:

 

Saint non boost Q factor = 178mm, 50.4mm chainline

 

m8000 non boost 176mm... 50.4mm chainline

m8000 BOOST 176mm....53.4mm chainline (3mm out)

[Eddy Gordo]

I am using a 0mm offset ring, but thats because the rear wheel had to be dished 3mm to one side

[DieselnDust]

I am using a 0mm offset ring, but thats because the rear wheel had to be dished 3mm to one side

 

 

on which bike is this??

[DieselnDust]

boost literally just moves the chainring 3mm out on the drive side (tomatch the rear cassette's 3mm outward spacing of course)...if it is a direct mount ring and the spline is the same as as the new rings..just get the appropriate offset chainring and you are golden.

 

its more difficult with the 104 BCD stuff ala shimano etc but still possible. Using my saint non boost cranks on a boost frame no issues.

 

You mentioned, it differs frame to frame in the chainstay area regarding clearance. 

 

good read on the topic.

 

https://www.wolftoothcomponents.com/pages/boost-chainline-and-chainrings

 

Edit: non boost crank on boost frame with 32T front ring

 

 

 

 

104 BCD is simple. The Chainring either has the spacers built onto the ring itself or not. If not then the rings are 0mm offset and the offset is achieved via the spider.

If the spider is a std chainline i.e. every bike since before BOOST then its not possible to make it BOOST. You would need a Boost crank.

IF the spider is BOOST you can space the chainring inward 3mm to meet std chainline requirements.

Chances are good that if your crank has a spider and is pre 2017 it won't be BOOST

[Yo-Yo]

Thanks for the info everyone. That has helped alot but not 100% on if I need a dedicated SRAM boost crankset. I know that there are 6mm and 3mm offset chain rings for the Eagle GX but wasn't sure if the QFactor changes or if it's a combination of Spider and chainring.

 

I've found a cheap(ish) SRAM Boost chainset that I was considering buying but do you think It would be better to get the different offset chain ring rather. The GX was bought in January and at the time I thought I'd ordered the dub / boost version but apparently I didn't I got the Dub / standard version. 

 

Shame Sram doesn't have more supporting documentation on this. Just frustrating as the bike shop that built the bike up from new didn't give any in diction that there was an issue and I took it back twice to say it was damaging the chain stays and each time they just added a random spacer. Most of the time it's fine but under power or climbing on the 50 it sounds like I've got a loose BB and that the barrings are grinding to dust. 

[MORNE]

Thanks for the info everyone. That has helped alot but not 100% on if I need a dedicated SRAM boost crankset. I know that there are 6mm and 3mm offset chain rings for the Eagle GX but wasn't sure if the QFactor changes or if it's a combination of Spider and chainring.

 

I've found a cheap(ish) SRAM Boost chainset that I was considering buying but do you think It would be better to get the different offset chain ring rather. The GX was bought in January and at the time I thought I'd ordered the dub / boost version but apparently I didn't I got the Dub / standard version. 

 

Shame Sram doesn't have more supporting documentation on this. Just frustrating as the bike shop that built the bike up from new didn't give any in diction that there was an issue and I took it back twice to say it was damaging the chain stays and each time they just added a random spacer. Most of the time it's fine but under power or climbing on the 50 it sounds like I've got a loose BB and that the barrings are grinding to dust. 

if the crank arms don't hit the chainstays at the back, just take the spacers out and try a different offset chainring and see. The q-factor is only a problem if the frame is too wide at the stays in the rear...and thats usually just if the bike can take proper plus sized rubber in either 650b or 29" (2,8" - 3,2" tires). some will argue minute wheel stiffness gains but that is a side extra imo.

They dreamt up boost for- tire/chain clearance...it's all over the internet.

[DieselnDust]

Thanks for the info everyone. That has helped alot but not 100% on if I need a dedicated SRAM boost crankset. I know that there are 6mm and 3mm offset chain rings for the Eagle GX but wasn't sure if the QFactor changes or if it's a combination of Spider and chainring.

 

I've found a cheap(ish) SRAM Boost chainset that I was considering buying but do you think It would be better to get the different offset chain ring rather. The GX was bought in January and at the time I thought I'd ordered the dub / boost version but apparently I didn't I got the Dub / standard version. 

 

Shame Sram doesn't have more supporting documentation on this. Just frustrating as the bike shop that built the bike up from new didn't give any in diction that there was an issue and I took it back twice to say it was damaging the chain stays and each time they just added a random spacer. Most of the time it's fine but under power or climbing on the 50 it sounds like I've got a loose BB and that the barrings are grinding to dust. 

 

 

 

IF its a cheapish SRAM crank then it will be Q168. Only the XX1 is available in Q156mm

If it has a direct mount chainring then just swap that out with a 3mm offset direct mount chainring and flog the 6mm to a Cannondale Scapel /FSi Ai rider.

If it has a Spider then remove it and fit a 3mm direct mount chainring.

If the spider is forged into the crack arms then flog the crank as is and start again

 

sorry for my post reading like BASIC programming

 

can you also post a pic of crank and bike. I'm not sure what models of hardware we're talking about here

[Eddy Gordo]

on which bike is this??

Its on a guerrilla gravity, but if you need to locate you chain ring 3mm more outwards, then you most likely need the 0mm offset ring. Csixx has them available.

[Eddy Gordo]

Thanks for the info everyone. That has helped alot but not 100% on if I need a dedicated SRAM boost crankset. I know that there are 6mm and 3mm offset chain rings for the Eagle GX but wasn't sure if the QFactor changes or if it's a combination of Spider and chainring.

 

I've found a cheap(ish) SRAM Boost chainset that I was considering buying but do you think It would be better to get the different offset chain ring rather. The GX was bought in January and at the time I thought I'd ordered the dub / boost version but apparently I didn't I got the Dub / standard version. 

 

Shame Sram doesn't have more supporting documentation on this. Just frustrating as the bike shop that built the bike up from new didn't give any in diction that there was an issue and I took it back twice to say it was damaging the chain stays and each time they just added a random spacer. Most of the time it's fine but under power or climbing on the 50 it sounds like I've got a loose BB and that the barrings are grinding to dust. 

I see you mentioned using spacers. As far as I understand, you shouldnt use any spacers with sram boost. Also most if not all sram DM cranks are boost compatible. Its just a matter of using a 3mm or 0mm offset chain ring.

If you using a 3mm chainring and its rubbing the stays, then chances are you will need to use a 0mm offset ring. 

Also as the above grinding, have you adjusted the B screw out far enough to get the puller away from the cassette and is the tension screw adjusted enough so that the chain is more or less smooth on all the rings of the cassette

[T-Bob]

Interesting subject for me as I've had similar issues with my Ibis Ripmo. I replaced my NX Dub crank with a boost one as I didn't know any different. It's solved the issue. 

 

I see you mentioned using spacers. As far as I understand, you shouldnt use any spacers with sram boost. 

 

 

The Dub system comes with a variety of spacers as part of the set up but I think they are for converting to different BB standards rather than adjusting the offset. 



 

[T-Bob]

This might help the OP. 

 

https://forums.mtbr.com/ibis/question-ripmo-chainring-rub-1091940.html

[T-Bob]

[Yo-Yo]

This might help the OP. 

 

https://forums.mtbr.com/ibis/question-ripmo-chainring-rub-1091940.html

 

That is almost exactly what is happening to mine.