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I've seen that I can buy a boost 29er lower leg for about £100. If I swapped over the seals to the new leg from my 27.5 forks would I end up with a 46offset 29er fork?
Boost Pikes use the same air spring for both sizes - am I missing something?
Are the stanchion lengths the same for 27.5" & 29"❓
Bushing fit / sizing❓
Same 35mm stanchions.
I'd be running them at 140mm so loads of overlap compared to them at 160mm. The same air spring which sets travel is used in both.
This thread seems to suggest it works but you loose 20mm of travel if swapping to 29er legs. But I think the thread is old enough that they are talking about A1 Pikes.
https://forums.mtbr.com/shocks-suspension/swapping-650b-uppers-29er-lowers-1065589.html
But that was the case with A1-A2 Pikes as you used 160mm 27.5 airshaft gave you 140mm in a 29er fork using the same airshaft. B1 forks use the same airshaft regardless of wheel size
Anybody else done this or have any more info?
I'd double check that the new lowers include bushings, but I think it will work, yes.
Edit - just thinking more on this - Rockshox 29er offsets are 51 and 42, their 27.5 offsets are 37 and 46. That to me suggests they might be using different CSUs for different wheel sizes - so they may not be the same length.
Thanks - I am presuming that the CSUs are different lengths - 20mm different length i think. With the 27.5 CSU being shorter
The 29er a-t-c is 20mm different for the same travel fork, i think previously that the CSUs were the same (bar offset) but in boost Pikes that changed.
Its the only way that they can use the same airspring for the same travel in a 27.5 fork as in a 29er fork (previously the same air spring gave different travel depending on wheel size).
Pike max out at 160mm in both wheel sizes, but i'm planning on using the re-legged changed fork at 140mm, so even if the 27.5 CSU is 20mm shorter than the 29er CSU, i'll still end up with the same amount of bushing overlap. So they 'should' be fully useable and safe. I think if i intended to use the fork at 160mm with the 27.5 CSU i'd end up with too little bushing overlap. Which is not a good idea.
I've asked the question about the bushing being included to the german website. But looking at the exploded diagram in the SRAM parts manual the bushing is not listed as a separate item only the seals and foam rings are.
I'm 99.9% sure that I read somewhere, part of the fork offset is in the crown (i.e. how far its sticks forward from the steerer). It's not all in the lowers. The 27.5 crown is different to the 29er crown. They will fit, but the fork offset will be messed up.
further to previous post, I've just done more research.
It was for X-Fusion forks that I had seen this advice. But it possibly also applies to other brands. For X-Fusion it's mechanically possible, but not recomended due to messing with tyre clearance and offset.