Recently I set up a category called "11-Speed Compatibility Talk".
In the comments I've gotten questions about whether Shimano components work with Campagnolo sprockets, or vice versa,
and for that sort of thing (→check this out)
and that should pretty much answer it.
This kind of thing tends to get contentious, so I don't really want to write about it,
but like it says in the linked article, being a workshop that isn't exactly a proper bike shop
might be exactly the place where I can say this stuff.
So, topic number two that's likely to ruffle some feathers.
Can you swap out the freebody from a 7900
with one from a 9000? That's the question.
Well, the freebody length is obviously different.
The spacer thickness fitted into the hub body is the same.
These spacers often get stuck to the hub body with grease,
and sometimes they don't even look removable,
so there's a possibility of stacking two of them when swapping freebodies.
You'd probably notice that, but when doing freebody maintenance and such,
you could easily not realize you've dropped one, so watch out for that.
The freebody fixing bolt is aluminum, apparently for weight savings.
It has an extremely fine thread pitch and thin walls,
and you're supposed to tighten it properly with a 14mm Allen key,
so this bolt has a service life of "one tightening only".
Once you remove it, you have to buy a new one each time—you can't reuse the old one.
↑Left: 7900 Right: 9000
↑7900
↑9000
To cut to the chase: the spline shape is different, so
you can't swap them.
Most third-party manufacturers making Shimano-compatible freebodies
have made provisions so that existing 10-speed users can keep using
their wheels.
Campagnolo, Mavic, Easton, DT, Novatec, American Classic and others do this.
Fulcrum is covered under Campagnolo, Reynolds is covered under DT,
PowerTap and TN are covered under Novatec, and so on—
basically all the major manufacturers are covered.
As for Mavic, back in the 9-speed days there was a time when they
only had Shimano freebodies in their lineup,
and at that time the company came out with "Campagnolo-compatible gears for Shimano freebodies"
(CC9 and CC10).
They added a 2mm spacer deep in the freebody to allow for this flexibility,
and it happened by coincidence that the 10-speed to 11-speed difference was about 1.85mm,
so by removing it you could kind of make it work.
The main exception among the big makers would be around ZIPP.
But given that there's definitely a structural problem preventing 11-speed conversion
in the hub-to-shaft relationship,
I don't think their intention is "just buy new wheels".
And practically speaking, Shimano themselves—the original manufacturer—seem to be the only ones
showing reluctance to enable 11-speed conversion on their existing hubs and wheels.
But if you're being charitable, there is some justification.
The right flange on a 7900 hub sits further outward than on a 9000 hub,
so with an 11-speed 7900 wheel, when you shift to the low gear (especially outer ring × low),
there's a possibility of the rear derailleur and spokes interfering.
But from what I can see, it's pretty much the same on complete wheels…
After all, the fact that they bothered to change the spline means:
"They're reluctant to enable 10-speed hubs to go 11-speed,
and very eager to prevent 10-speed hubs from going 11-speed"
is the only conclusion I can draw.
But it's a shame to be unable to use such excellent (←something you can only say "today") Shimano wheels because of this.
Maybe the very idea of trying to get by with a freebody swap—this cheap, penny-pinching way of thinking—
shows insufficient devotion as a disciple.
That's right: you're being tested. When you upgrade your components to 11-speed,
only those who can throw 10-speed wheels—now utterly useless forever and ever—
into the trash are true 11-speed users.
(Otherwise you'd be offering existing "customers" 11-speed compatibility through compatible parts)
So abandon all selfish thoughts and
happily upgrade to 11-speed compatible wheels!
A major price increase is coming soon, so
right now is exactly your chance to get your hands on wonderful Shimano wheels!
Huh, who's calling at this hour?
In the comments I've gotten questions about whether Shimano components work with Campagnolo sprockets, or vice versa,
and for that sort of thing (→check this out)
and that should pretty much answer it.
This kind of thing tends to get contentious, so I don't really want to write about it,
but like it says in the linked article, being a workshop that isn't exactly a proper bike shop
might be exactly the place where I can say this stuff.
So, topic number two that's likely to ruffle some feathers.
Can you swap out the freebody from a 7900
with one from a 9000? That's the question.
Well, the freebody length is obviously different.
The spacer thickness fitted into the hub body is the same.
These spacers often get stuck to the hub body with grease,
and sometimes they don't even look removable,
so there's a possibility of stacking two of them when swapping freebodies.
You'd probably notice that, but when doing freebody maintenance and such,
you could easily not realize you've dropped one, so watch out for that.
The freebody fixing bolt is aluminum, apparently for weight savings.
It has an extremely fine thread pitch and thin walls,
and you're supposed to tighten it properly with a 14mm Allen key,
so this bolt has a service life of "one tightening only".
Once you remove it, you have to buy a new one each time—you can't reuse the old one.
↑Left: 7900 Right: 9000
↑7900
↑9000
To cut to the chase: the spline shape is different, so
you can't swap them.
Most third-party manufacturers making Shimano-compatible freebodies
have made provisions so that existing 10-speed users can keep using
their wheels.
Campagnolo, Mavic, Easton, DT, Novatec, American Classic and others do this.
Fulcrum is covered under Campagnolo, Reynolds is covered under DT,
PowerTap and TN are covered under Novatec, and so on—
basically all the major manufacturers are covered.
As for Mavic, back in the 9-speed days there was a time when they
only had Shimano freebodies in their lineup,
and at that time the company came out with "Campagnolo-compatible gears for Shimano freebodies"
(CC9 and CC10).
They added a 2mm spacer deep in the freebody to allow for this flexibility,
and it happened by coincidence that the 10-speed to 11-speed difference was about 1.85mm,
so by removing it you could kind of make it work.
The main exception among the big makers would be around ZIPP.
But given that there's definitely a structural problem preventing 11-speed conversion
in the hub-to-shaft relationship,
I don't think their intention is "just buy new wheels".
And practically speaking, Shimano themselves—the original manufacturer—seem to be the only ones
showing reluctance to enable 11-speed conversion on their existing hubs and wheels.
But if you're being charitable, there is some justification.
The right flange on a 7900 hub sits further outward than on a 9000 hub,
so with an 11-speed 7900 wheel, when you shift to the low gear (especially outer ring × low),
there's a possibility of the rear derailleur and spokes interfering.
But from what I can see, it's pretty much the same on complete wheels…
After all, the fact that they bothered to change the spline means:
"They're reluctant to enable 10-speed hubs to go 11-speed,
and very eager to prevent 10-speed hubs from going 11-speed"
is the only conclusion I can draw.
But it's a shame to be unable to use such excellent (←something you can only say "today") Shimano wheels because of this.
Maybe the very idea of trying to get by with a freebody swap—this cheap, penny-pinching way of thinking—
shows insufficient devotion as a disciple.
That's right: you're being tested. When you upgrade your components to 11-speed,
only those who can throw 10-speed wheels—now utterly useless forever and ever—
into the trash are true 11-speed users.
(Otherwise you'd be offering existing "customers" 11-speed compatibility through compatible parts)
So abandon all selfish thoughts and
happily upgrade to 11-speed compatible wheels!
A major price increase is coming soon, so
right now is exactly your chance to get your hands on wonderful Shimano wheels!
Huh, who's calling at this hour?