Hi, finding myself a bit confused with the whole boost thing…

Brought a new Cotic Solaris Max frame which has a boost rear at 148mm. New wheels too so that solved that. Forks are non boost & all was working well.
Moved my SLX drive chain over & hope BB but knew there wasn’t much life left in the chain & cassette… I know you should change it regularly but I never have…
& decided to change it all. New chainring has about a 2mm gap from the chainstay & cant use a 34T as that clips the chainstay all a bit too close.
So not quite sure what to do. I know everything is wider to accommodate fatter tyres but it’s all a bit tight.
So is there a boost crank to move everything out a bit or am I just being a bit naive that most things should fit & work…

Yep. If it’s that close you should use a Boost crank.

I’ve got a Santa Cruz Bronson with a 148 rear. I changed my chainring and had the same questions as you. It depends on frame design. I found that my bike would work best with a non-boost chainring. The boost chainring would have moved the chain line further away from the bike and caused problems for the lower gears. Have a look to see if moving you chain line out by 3mm would cause a problem. If not, you need likely need boost. The next problem is i don’t think you can get a boost ring for a Shimano crank – But they do make boost cranks. I changed from Shimano to a raceface cinch setup and found out that raceface have one crank design and you get boost and non-boost rings. Saying all that, I’d just stick a bb cup spacer in behind the Drive side cup and see how it goes

I’ve got a Vitus Sentier and even with a boost chainring (with stam the varying offsets are e chainring rather than crank spacing) the clearance to the chainstay with a 32t chainring is very tight – like a couple of mm tops. It’s been fine so far – even in claggy mud it’s not jammed or scratched the paint. I think with the Sentier the gap is so small because of the flared chainstays to fit plus tyres in it.

Tempted to put a 28t chainring on my fs bike and move the 30t to the Vitus which should slightly improve the clearance.

Cotic specify non-boost chainring up to 32t (non oval) on the Solaris Max. Anything bigger definitely needs a boost crankset. 11 speed SLX Boost crankset is £68.50 on Chain Reaction at the moment…

It’s just a little bit tight at the moment & already scratched… not so fussed about that as it’s there to be ridden.
If I got a boost crank would I need a new BB or do you put a spacer between the chainring & the bearing cup? If that makes sense.

Concrete24 has it right, pretty sure I remember reading once in one of Cy’s emails that non-boost chainset are fine for up to 32t but if you need bigger then you have to go boost (I’m running 34t oval on my soul with a boost chainset). For 11s Shimano cranks, the offset is in the arms so you don’t need to change anything else, assuming you already have the 2.5mm spacer on the drive side.

Try what I suggested earlier, stick an extra spacer behind the drive side bb cup. Given a raceface cinch crank only uses the dish in the ring to create the offset I can’t see worries about q-factor being legit (which feels like the only argument for not doing it). All a boost ring or chain set does is shunt the chain line out 3mm after all. see https://www.wolftoothcomponents.com/pages/boost-chainline-and-chainrings

@sheepdip71 it’s not just you.

I’ve just built my Solaris Max up with a Boost crankset and 32t chainring along with a DUB bottom bracket and the crank arm has very little clearance from the chainstay. Not sure if it’s normal as I’m new to the world of Boost and DUB cranks.

hi all thanks for the info, i have a 2.5mm spacer on the drive side at the mo, spoke with a friend who explained a bit more about it (bike mechanic by trade) luckily i think BBs havent changed size yet… i am sure lots of stuff will to keep us spending more money.
the plan is to buy a SLX boost crank & take it from there & that should solve any problem. Sticking with shimano as i like the way the cranks tighten & difficult to get wrong. @notmyrealname crank arm clearance is fine.
I dont know if its my age but i am sure everything is getting more complex never had this problem with my Bmx’s in the 80s
Happy cycling everyone

@notmyname, what do you think of your Solaris Max? enjoying it?

You may also be able to space the ring out on the crank arms.

SLX chainrings attach from the inside if that makes sense so no option tp space.

Ah it’s that sort of bullshit. Yep, less shortcuts then

Long and short of it seems to be even with a boost back end a non boost crank works better.
Crank wise some cranks are boost via the crank and some via the chainring
Examples I’ve had
Santacruz Hightower. Came with a boost back end and a boost crank. Smashed the crank so fitted a spare non boost crank. Worked better, less grinding in 1st and 2nd, chain didn’t drop when back pedaling in 1st,2nd.
Geometron G13
Boost back end recommended non boost crank everything worked well from the off.

Last fastforward
135x10mm bolt in back end with 6mm offset on the rear wheel set to give boost chain line.
Won’t take a non boost crank as the chainring hits the chainstay
Not great in 1st and drops the chain when back pedaling in 1st
All bikes on same drivetrain.
If you have clearance for a non boost crank/ chainring run one with a boost back end as it works so much better.

Dropped Cotic an email & the reply was….

You will need a Boost chainset which has a 53mm chainline to make the 32t and 34t chainrings work on the new SolarisMAX. It wasn’t critical on the older SolarisMAX frames as the chainstays didn’t bend out so much.

On Sram chainsets the cranks are all the same and the chainrings are Boost and non Boost, but with Shimano the crank arms are different to give the different chainlines.

A boost has been ordered….

Should of brought a complete bike I think. Been a bit of a learning curve

^^ Can be a learning curve building a frame up from scratch but it’s honestly so, so satisfying once you’ve built up your own bike and overcome the niggles along the way.

Makes future maintenance easier too as you know how it all goes together… and comes apart.👍

Quick update…
SLX Boost cranks arrived today… snaggletooth chainring fitted. Plenty of room all sorted… ready for a wobble at the weekend.