Will GRX work with Ultegra? (BB90 road-bike)

TGD

I'm looking for a way to lower the gearing for bikepacking on a Trek which has a BB90 press-fit bearings for Shimano Ultegra.

I've looked at Praxis Works Alba M30 48/32 but this would need a different bearing which would practically rule out switching with 50-34 again.

I've also looked at Absolute Black oval rings but opinions differ.

So, Shimano GRX 810 (48-31T) work? I might have an issue with the deraileur not coming down far enough - what distance would I get away with?

Mefistofelino

As a further complication, GRX chainsets have a slightly (2.5mm IIRC) wider chainline that the road chainsets, so the rings are 2.5mm further out from the bottom bracket. The GRX front mechs are built to reach slightly further out.

TBH I don't know if a road front mech will refuse to play with the GRX chainset at all or if it is just sub-optimal.

CramCycle

These rings should fit I think: https://www.bike24.com/p2249322.html

Give you 46/36

Mefistofelino

What sized cassette is currently fitted? The new Shimano road mechs are specced to 30T and can be pushed to at least 32 without issue (IME). The new 105 long cage will go to at least 34T officially and costs under €50. An 11-34 cassette would also be under €50.

The 48/31 GRX chainset is over €220

TGD

CramCycle wrote: »

These rings should fit I think: https://www.bike24.com/p2249322.html

Give you 46/36

But that’s going up all the inner ring. The problem is that with the standard 110 BCD spider/crank, 32 is the lowest ‘standard’ ring to fit.

TGD

Mefistofelino wrote: »

What sized cassette is currently fitted? The new Shimano road mechs are specced to 30T and can be pushed to at least 32 without issue (IME). The new 105 long cage will go to at least 34T officially and costs under €50. An 11-34 cassette would also be under €50.

The 48/31 GRX chainset is over €220

I can get a 34 on it no bother, but that’s not enough for multi-day trips, with steep gradients, with a load, when you are over 60. Ya, I know, I ‘should’ have another bike but I’m not going there.

TGD

Mefistofelino wrote: »

As a further complication, GRX chainsets have a slightly (2.5mm IIRC) wider chainline that the road chainsets, so the rings are 2.5mm further out from the bottom bracket. The GRX front mechs are built to reach slightly further out.

TBH I don't know if a road front mech will refuse to play with the GRX chainset at all or if it is just sub-optimal.

Thanks, I guessed it couldn’t just be that simple

Mefistofelino

Is it 10 or 11 speed?
10 speed road shifters will operate a 9 speed Shimano MTB mech so you can get access to some large cassette sizes.

Will a shimano MTB chainset fit the BB90?

CramCycle

TGD wrote: »

But that’s going up all the inner ring. The problem is that with the standard 110 BCD spider/crank, 32 is the lowest ‘standard’ ring to fit.

You can do 46/34, its not optimised but will work absolutely fine, you can fit a 34 on the back. That is a 1:1 ratio, if you need lower you may as well walk.

TGD

CramCycle wrote: »

You can do 46/34, its not optimised but will work absolutely fine, you can fit a 34 on the back. That is a 1:1 ratio, if you need lower you may as well walk.

34 x 34 x 28” wheel = 12 kph @ 90 rpm.
Obviously I don’t walk uphill with a loaded bike as quick as you, but thanks for the advice anyway.

Borderfox

Absolute black do a 30-46 for four arm shimano that fits 110bcd, i had a set up for sale a while ago

TGD

Borderfox wrote: »

Absolute black do a 30-46 for four arm shimano that fits 110bcd, i had a set up for sale a while ago

I looked into those as an option - they are expensive just for rings! (about same price as GRX chainset). Someone made the point that, because they are oval, a '30-ring' is wider at the 'power' part of the circle, than a round 30-ring, so in effect it's a higher gear than a standard 30. It's a moot point but interesting.

Borderfox

Ill do my set for €80 if your interested?

gman2k

I've Doval sub compact 30/46 chainrings on a DA chainset.
R8000 SGS rear mech with an 11-34 cassette.

TGD

gman2k wrote: »

I've Doval sub compact 30/46 chainrings on a DA chainset.
R8000 SGS rear mech with an 11-34 cassette.

Is ‘DA’ dura-ace or something else. What length are the cranks?

TGD

Borderfox wrote: »

Ill do my set for €80 if your interested?

That’s very tempting. Good condition? I’d probably need a ‘long reach’ derailleur as well as I’m near the bottom of the hanger as is. Let me look into it.

gman2k

TGD wrote:

Is ‘DA’ dura-ace or something else. What length are the cranks?

Yeah Dura-Ace, sorry not for sale.

TGD

gman2k wrote: »

Yeah Dura-Ace, sorry not for sale.

Ok, sorry I misunderstood. By 'Doval' do you mean 'oval' - I have been Googling 'Doval chainrings'. If they are Absolute Black, how much gap approx have you between big ring and deraileur?

gman2k

TGD wrote:

Ok, sorry I misunderstood. By 'Doval' do you mean 'oval' - I have been Googling 'Doval chainrings'. If they are Absolute Black, how much gap approx have you between big ring and deraileur?

By Doval I mean Doval...
They are a South Korean brand which make chainrings which are Oval!
You'll find them on eBay.

TGD

Borderfox wrote: »

Ill do my set for €80 if your interested?

Will take them thanks - have PM’d you.