I’m looking for an off the shelf wheelset for my Cannondale Scapel Si.

The thing is that the rear is built with “Ai (Asymmetric Integration)” – https://cannondale.zendesk.com/hc/en-us/articles/219101107-Ai-Asymmetric-Integration-

Essentially it means the rear drivetrain is shifted 6mm outwards to allow for the wheel to have even spoke length, angle, tension. Basically a normally dished wheel wont fit.

Anyone know of any off the shelf wheels that would be suitable? Or would i always need to plump for a built to order wheel?

Just needs them to be re-dished – any LBS worth their salt should be able to do it for you.

Mavic did Ai versions of some of their wheel sets

Would the spoke length need changing for it to be re-dished?

I think it will depend on the wheel, but 6mm is quite a bit to move a rim over.

Generally for similar situations, like when you need to re-dish is using certain boostinator kits for non boost rear wheels in boost frames, that’s only 2.5mm of a dish, so most wheels will cope.
6mm may prove difficult, but saying that, highly tensioned off the shelf wheels with fewer spokes may shift the rim over with fewer nipple turns than a traditional wheel.

If it’s a traditional looking wheel, I’d respoke it.

I couldn’t find any wheelsets for mine or anyone who would make a set up. I ended up buying Hope Enduro’s and redishing them myself.

I’ve got a set of Mavic Crossmax on mine, which seem to do the job well!

Quite a few options for MTBs (a lot less for SuperX)

Mavic do rear wheels like this
https://www.probikeshop.com/en/gb/mavic-crossmax-pro-29-rear-wheel-offset-9-12×135-12×142-mm-axle/155956.html

Actionsports website lets you choose 6mm offset in their custom builder (and get a Lefty front if you need one)
https://www.actionsports.de/en/wheels/custom-wheels/mtb-disc-29/

And Cannondale make it sound easy to re-dish anything (although I hesitate to try this myself)

Would the spoke length need changing for it to be re-dished?

No

I had a play around with the DT calculator whilst choosing rims for my cross bike and again when considering different variations of ‘boost’ converter. It makes almost no difference, 1mm at most.

It would only be a problem if the spokes have seized into the nipples. Absolute catastrophic worst case scenario, swap the nipples for longer or shorter ones. But that won’t be the case. And TBH you would only know in a few thousand miles if/when nipples cracked (and personally i’ve never had nipples crack as a result of undersized spokes so suspect there’s more to it than just that).

AI is really just a more sensible implementation of “boost” that didn’t need a whole new hub. Specialized did the same thing for years with their rear wheels, but didn’t give it an acronym.