Chain ring Sora to 105

[justinmg]

My wife has a sora road bike which I would like to move to 105 using spare bits I have and some 2nd hand bits off my road bike.
both bikes appear to use chain rings with 5 hole 110bcd. Can I buy fresh chain rings for my bike and install my cast off rings onto her sora bike. I am presuming the fact that mine is a gxp set up is irrelevant as the cranks and spindle stay on the original bike.

 

[Ajax Bay]

Probably
https://www.wiggle.com/p/sram-force-22-gxp-compact-chainset
Be aware that the large ring will have a pin on the outside to stop the chain if it overshifts dropping down and getting well and truly stuck 'tween crank and ring. The GXP bolt pattern is 5-bolt and 110mm BCD but one bolt is directly behind the crank whereas the Shimano 5-bolt is 'offset' iyswim, so this pin will be in the 'wrong' place for her crankset.
https://www.tredz.co.uk/.Shimano-105-FC-5800-Double-Chainring_239037.htm
Maybe cosmetic issues (colour and).
Swapping her rings for 105 is, to be frank, not 'moving to 105' it's just changing the rings, in your case on both bikes. If you want new rings on your bike fit them. Leave her rings be.
Such fun and HTH

 

[boydj]

Not sure what benefit there is in changing chainrings, unless they are worn or there is some technical improvement in the 105. A chainring is a chainring. Sounds like you just want a justification for changing rings on our own bike - though my first point still holds.

 

[Dogtrousers]

Swapping her rings for 105 is, to be frank, not 'moving to 105' it's just changing the rings, in your case on both bikes.

TBF the OP refers to "spare bits I have and some 2nd hand bits off my bike" So for all we know those bits could include shifters, mechs, brakes and so on

Or maybe not.

 

[justinmg]

I was hoping to do this with only new chainrings. I will have a close look at the bolt patterns on the rings, but they looked evenly spaced (72 degrees) at first glance on both.
My wife's bike is currently a flat bar and she wants it to be drop. As I have spare bars, shifters and derraileurs from when I converted my bike to Di2 a few years ago, I hoped I could get her on a road bike with just some chainrings, with the added benefit of me getting slightly newer rings.
Im now thinking if my GXP praxis 105 chaining won't go onto her Sora crankset, perhaps a new Shimano 105 chainring would fit her sora crankset, and I'll stick with my old ones.

 

[vickster]

I was hoping to do this with only new chainrings. I will have a close look at the bolt patterns on the rings, but they looked evenly spaced (72 degrees) at first glance on both.
My wife's bike is currently a flat bar and she wants it to be drop. As I have spare bars, shifters and derraileurs from when I converted my bike to Di2 a few years ago, I hoped I could get her on a road bike with just some chainrings, with the added benefit of me getting slightly newer rings.
Im now thinking if my GXP praxis 105 chaining won't go onto her Sora crankset, perhaps a new Shimano 105 chainring would fit her sora crankset, and I'll stick with my old ones.

Have you checked the geometry? She may find the reach too great if converting, or need a very short, potentially twitchy stem. What bike is it?
Do the right thing and just buy her a new Di2 bike

 

[Ajax Bay]

My wife's bike is currently a flat bar and she wants it to be drop. As I have spare bars, shifters and derraileurs

What sort of brake calipers are on her bike?

 

[justinmg]

From a stem point of view I have a spare 70mm from when I went to redshift. But good suggestion…. I can put the drop bars on in 5 mins to make sure she’s happy with the reach.
The brakes are one minor downside. They are currently hydraulic and the shifters are mechanical. I do however have spare TRP HYROAD Hybrid callipers which are pretty good.
As for getting her Di2, if she comes riding with me more often, I’ll change up to some 6870 or 8050 derallieurs ( as I already have some unused Di2 shifters).
I really do have too many spare bits kicking around and this upgrade path uses them all up, but only if I can get an 11 speed chain ring turning!

 

[Ajax Bay]

So you want to change her bike to 11sp everything, but use the current crankset, and swap the current hydraulics to hybrid (to allow use of mechanical (brake and gear) STIs. Implies an 11sp chain (which wasn't clear to me from the OP).
The Sora crankset with your (ex GXP) 11sp rings fitted will, I think, allow an 11sp chain to fit nicely into the gap between the rings: needs checking which you could do before any serious swapping. As well as the earlier issue wrt the outer pin on the large ring being misaligned with the crank (see post #2 above).
Other thing to check is the freehub: will likely be a 8/9/10 one and the 11sp cassette won't fit.

 

[justinmg]

Thanks Ajax you have thought through to the next problem that I had missed!!!
The chain ring came off in 5 mins and looks like it will just swap over. The sora ring on my wife’s bike seems to be an oem ring which is 5 hole not the 4 hole shimano type.
HOWEVER I missed the free hub size issue. It looks like I’m going to have a more complex wheel project to get a cassette to fit….
Thanks

 

[Ajax Bay]

You can swap the 8-9-10 freehub for an 11sp one. Large allen key required.
A 5-bolt 110mm BCD ring is a long time Shimano standard. OEM indeed: Shimano.

 

[Dogtrousers]

Other thing to check is the freehub: will likely be a 8/9/10 one and the 11sp cassette won't fit.

You probably know more about this than me, and I've probably mis-remembered anyway but ...

I'm pretty sure that when I changed from 10S to 11S a few years ago it was a case of using a spacer with the 11S cassette, and used the same freehub. I remember I thought it weird because I would have expected the 11S to be the one that didn't need the spacer.

Maybe my freehub when I was using 10S was a 10/11 compatible one or something. It's all so confusing and I've lost track of wheels and such like. Or maybe I did change the freehub at the time. I don't remember doing that though.

Edit I've just done a bit of googling and it may be a peculiarity of the 105 R700 34T cassette. Or something like that.

 

[justinmg]

I’ve measured with the callipers and certainly the current hub is about 4 mm too short to accept an 11sp cassette.

 

[Ajax Bay]

Actually it's 1.85mm too short

 

[iluvmybike]

From a stem point of view I have a spare 70mm from when I went to redshift. But good suggestion…. I can put the drop bars on in 5 mins to make sure she’s happy with the reach.
The brakes are one minor downside. They are currently hydraulic and the shifters are mechanical. I do however have spare TRP HYROAD Hybrid callipers which are pretty good.
As for getting her Di2, if she comes riding with me more often, I’ll change up to some 6870 or 8050 derallieurs ( as I already have some unused Di2 shifters).
I really do have too many spare bits kicking around and this upgrade path uses them all up, but only if I can get an 11 speed chain ring turning!

Perhaps if you got her Di2 she WOULD go out with you more often!