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Is this possible: Converting 27.5 to 29 with lower leg swap?

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jon123

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Discussion starter · #1 ·
Basically as the title says -- is it possible to convert a 27.5 fork (2017 Fox 34 in my case) to a 29er by swapping out just the lower legs?

I really haven't been able to find anything online about this so guessing it's far from common, or even not possible. BUT in theory it looks so doable -- the internals are the same, I'd reuse my 15x110 axle, and have spare crush washers/seals/foam rings.

I have a 140mm 27.5 and would want a 120mm 29 so in that way it's an ideal swap, from what I can tell. Air shaft is the same for these two I believe.

Biggest issue seems to be finding lower legs for sale. I haven't been able to find them anywhere.

Thoughts?
 
Discussion starter · #5 ·
Bringing this back up from last summer. Thought I'd ask this again since a lot of the new 29er forks are coming with 44mm offset. And that seemed to be the one sticking point here.

So ... any reason this can't be done? Stock offset on the 27.5 is also 44mm
 
#6 ·
jon123 said:
Bringing this back up from last summer. Thought I'd ask this again since a lot of the new 29er forks are coming with 44mm offset. And that seemed to be the one sticking point here.

So ... any reason this can't be done? Stock offset on the 27.5 is also 44mm
Click to expand...
Yes this can be done with no issues. I was about convert my Diamonds from 27.5 to 29er by doing a lower leg swap but ended up sticking with the Fox 29 so I could fit the push kit.
 
#8 ·
Hi, sorry to necro an older thread. Do you guys know whether installing a 27.5" upper in a 29" fork is possible, and if so, does it affect travel?

Replacement Rock Shox uppers in the 27.5" size are easily obtainable, but 29" are hard to find.

Thanks!
 
Discussion starter · #10 ·
Pmrmusic26 said:
I've been having this same questions lately. The CSU are the same, so are the 29er lowers longer than the 27.5? on the 2021 the airshafts are the same.
Click to expand...
No issues doing this. Especially with the shorter 29er offsets. I did this conversion for several months before buying a new 29 fork

For Fox, the air shafts are wheel-sized specific. So if it's for a Fox fork you'll need a new air shaft too.

I believe RockShox the air shafts are interchangeable - so a 140mm 27.5 air shaft is equivalent to a 120mm 29 air shaft
 
#11 ·
jon123 said:
No issues doing this. Especially with the shorter 29er offsets. I did this conversion for several months before buying a new 29 fork

For Fox, the air shafts are wheel-sized specific. So if it's for a Fox fork you'll need a new air shaft too.

I believe RockShox the air shafts are interchangeable - so a 140mm 27.5 air shaft is equivalent to a 120mm 29 air shaft
Click to expand...
Rockshox a 140mm 27.5 airshaft is a 140mm 29 airshaft. The 27.5 vs 29 wheel size is catered for by the position of the axle dropouts on the lowers.
 
#12 ·
rete said:
Rockshox a 140mm 27.5 airshaft is a 140mm 29 airshaft. The 27.5 vs 29 wheel size is catered for by the position of the axle dropouts on the lowers.
Click to expand...
Yeah so the 2021 Fox is the same deal. I took a tape measure to our bikes in the garage. CSU are the same, Airshafts are the same, Only differences is the offset and length in the lower drop outs.
 
#15 · (Edited)
Anyone know if it would it be possible to put a 2020 Fox 36 27.5 lower leg on a 2006 Fox 36 Talas 26 to "mullet" the bike and just keep the same internals?

The stanchions are the same diameter and distance apart, and I figure because the Talas has adjustable travel you could alter it to accommodate the bigger wheel without having to get a new air spring. I guess my real questions is: would the Talas air spring and dampener connect properly to the ports at the bottom of the new lower leg correctly and might there be anything else I should be concerned with besides the slightly altered geo of the potentially new bike set-up?

Thanks!
 
#16 ·
Thinking about trying this. I'll look up fork specs on my fox 34 and see if airshafts are different. I have a Mojo 4 I'm wanting to make a mullet. I was going to put a 44 offset 130 on it, but then I thought I could keep it a 140 if I can change out the lowers with the 37 offset upper.
 
#17 ·
kvbikes said:
Thinking about trying this. I'll look up fork specs on my fox 34 and see if airshafts are different. I have a Mojo 4 I'm wanting to make a mullet. I was going to put a 44 offset 130 on it, but then I thought I could keep it a 140 if I can change out the lowers with the 37 offset upper.
Click to expand...
Hey, did that work? I know with a Mezzer you can just swap the lowers, but you get +7mm offset. I had a 44os 275 so ended up with 51os 29er. If I had the 37os 275 I'd get a 44os 29er. They sell two CSUs, 'long' and 'short'. Is it the same with Fox?
 
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