So I'm looking to finally upgrade my 26" hard tail to a 29er but I need some help picking out a frame.
My number one requirement is that it can fit a 2.35" Maxxis Ikon in the rear. This is not negotiable.
Other desires are for a slack head angle (70 or less?), a 30.9 or 31.6mm seatpost and obviously on this forum - light.

Sifting through through the net the Scott Scale fits all my other desires with a 69.5 deg head angle but anyone know if it can fit a 2.35 Ikon in the back? Any other good frames that are known to have really good tire clearance?

Have a look at the Planet X Dirty Harry, On-One Lurcher/Race frames.

The Scott Scale 29er will not fit "bigger than normal" tires IMHO. I had a Scale 26", and the chainstays had rub on the insides from using a Schwalbe Rocket Ron 2.25 (maybe due to flexy ZTR Alpine wheels? I don't know. I weigh around 70 kgs). I borrowed a Scale 29er for a test ride, and noticed there wasn't more tire clearance than with the 26" Scale...

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Cannondale F-Si Team 2015
Cannondale F29 Team 2014
Cannondale F29 Carbon 1 2013

i've got a 2013 Superfly running 2.2's front and rear. No clearance issues at all (could probably fit 2.5's there, too).

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Madone 9 https://goo.gl/7UwZpV

Crockett https://goo.gl/f5PdCN

Madone 5 https://goo.gl/cMdyFo

Madone 4, SpeedConcept, Cobia

I own a lot of Treks.

Anyone know how much room the Santa cruz Highball has in back?

Why is your rear tire size so non negotiable?

Sounds to me like you want a carbon Trek Stache

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Probably want to use Surly Knard tire?

Message removed: I didn't read the carbon part!

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Campagnolo; because I ride a bicycle, not a fishing rod.
M∆SON Definition / Camapgnolo endurance & bikepacking build - ~8.4kg

No heaps likely, the Knard on a proper rim is too big to fit in most production XC-ish frames. One of the older 2.4 Racing Ralph's is basically the next biggest tyre - for example, it's bigger than a 2.55 Weirwolf despite the stated size and the casing volume is bigger than the Continental 2.4 tyres. On a nice & wide rim, all of these are already too big for many frames, let alone a Knard which is much bigger.

Canyon 29 CF SLX - have a 2.25 rocket ron on back currently and clears the frame 10mm each side

Not very much, looking at this photo (with 2.1 Crossmark):



Apparently the alloy bike has a lot more room.