29er fork on 27.5 frame?
 

I'm looking to build a new mountain bike in the near future, and the number of options available are staggering. I already have a RockShox Reba RLT 100mm 29er fork with a tapered headset, but no other parts. I'm a fan of steel bikes, and am intrigued by the On One 45650B (On-One 45650B Frame | Planet X). It says it is designed around a 120-140mm 27.5 fork.

I am open to both a 29er or a 650b bike, but it appears there are not many 29er options in my price range (which is fairly low, admittedly) that will accept a tapered steer tube, or that is designed for 100mm forks.


The 45650B would work with a 120mm fork, and the Reba 27.5 fork has an axle-to-crown of ~507mm, whereas the A-C on my Reba 29" fork is 506mm. In theory, would this work? I would be using a 27.5 wheelset. I understand that the travel would still only be 100mm, which I think is more than enough for my local trails.

From my research, it seems like these are the facts:

-Axle to crown measurement is close enough to where the two should be interchangeable
-The 45650B accepts a tapered steer tube, whereas other options (such as the Inbred 29) doesn't.
-There will only be 100mm travel, and some extra room between the fork bridge and the tire (which will be 27.5)
-Brakes are not an issue since they are both disc brake setups

Am I missing anything? Is there any reason not to do this? Ideally I would buy a 27.5 fork, or a 29er frame, but both are very much over my budget (and I got the Reba in a trade, so it hasn't cost me much).

Alternatively, any suggestions for a 29er frame (under 300 shipped, the cheaper the better) that accepts a tapered steer tube and has a derailleur hanger would be appreciated. I am looking locally for complete bikes as well, but haven't found anything I particularly like yet. If anyone has a steel 29 frame, size small or medium (I'm 5'8", 31" inseam) they are looking to unload, please PM me.

Thanks in advance!

I think it would probably work fine. with the 29 fork you would also have the option of running a 29 front or a 27.5+ front for different trails. The plus or 29 would raise the front a little and give you a degree or two of slack from stock on the head angle.