There've been a few recent threads about bodged 96ers (for want of a better expression) that have got me thinking about trying this on my Soul but despite a fair bit of reading I'm still a bit hazy on exactly how the geometry would be affected.

How much difference would there be between a 26" wheel with suspension forks (approx 480mm A-C) and a 29" with some On-One or similar carbon rigids (440mm A-C)? My back of an envelope doodling suggests not that much, but has anyone actually done the sums?

No sums but don't forget you don't need to use a 29er rigid fork, a 26 rigid fork works fine and gives another thing to consider when you are thinking of your geometry…

Plus the 29er wheel adds another 1 1/2" to fork length.

Yes, was definitely planning on the 26" version of the fork, plenty of people seem to be using them with 29" wheels with no clearance issues.

Now thats taken me on another line of thought. whats the total diametre of a 29er wheels with, say a 2.1 tyre?

Singular make (made?) a 69'er fork, specifically for converting a frame to the big-wheel front… it's what I've used on this build:

Took it for it's for 'shakedown' ride today, around the Surrey Hills… was good, handled well, climbed brilliantly, though I can't say with complete honesty that the big-wheel made the rigid setup any more comfortable! the best compliment I can say is that I completely forgot there was a 29" wheel up front, really didn't notice it, which to me is a good thing 🙂 Next step will be to set it up as a standard rigid 26" front and see if it feels any different…

I'm running a Ti456 with On One 440mm 26er fork and 29er wheel with Racing Ralph 2.4" tyre. No clearance issues at all, rides fantastically but that is as a commuter (on & off road).

Advice (from Brant) when I started was that it'd be good with rigid forks but a barge with short travel 29er forks. Yet to try this out as it'd be an expensive experiment.