GRX chainset.

[Barry and Janet wil]

My wife's road bike has a 34/50 11-32 Ultegra 8000 drive train. The smallest gear is still too big for her so I'm wondering about changing to a GRX 30/46 chainset. Also from 25mph and upwards she freewheels so a reduced biggest gear will not be an issue. How compatible is the GRX chainset with Ultegra?

I'm a trendy consumer. Just look at my SM-G950F using hovercraft full of eels.

[slowster]

If a 34 x 32 bottom gear is not low enough, will 30 x 32 be low enough? Moreover, if she freewheels above 25mph, that suggests she not only does not make much use of 50 x 11, but also that she does not make much use either of 50 x 12, and possibly 50 x 13 as well (unless she has a low cadence and tends to push big gears). Why are you considering 46/30, other than for the reason that Shimano is not offering anything else?

Fit a Spa Super Compact chainset, and she can choose from 46/30, 44/28, 42/26 and 40/24. For example, a 24 tooth inner ring would give three lower gears than 34 x 32, and a 40, 42 or 44 tooth outer might give her a more usable top gear and a better range of cruising gears than a 46 tooth outer.

Comparison of 50/34 with 46/30

Comparison of 50/34 with 40/24

Comparison of 46/30 with 40/24

[Valbrona]

Can the FD be lowered? Bracket type usually allows this.

[Geoffroid]

I think the GRX 2x chainset sits 2.5mm further out than a Shimano road chainset (to allow for wide rear tyres). It needs a GRX front mech, that will move out the extra 2.5mm.

[NetworkMan]

Strange how Mr. Shimano persists in offering chainsets that won't take small enough rings. This new GRX one looks like a re-cooked 4 arm one. Another lost opportunity - you'd thing that a 'gravel bike' would at last be a reason for having a wide range double or a triple. Perhaps it's intended for flat gravel!

[pwa]

Any chance that Barry and Janet could simply put a 36 tooth max cassette on it? It is 11 speed and it looks like Shimano already provide 34t, and often you can go a couple more than they specify.... That, along with a longer chain, would be simplest if it were possible.

[NetworkMan]

Any chance that Barry and Janet could simply put a 36 tooth max cassette on it? It is 11 speed and it looks like Shimano already provide 34t, and often you can go a couple more than they specify.... That, along with a longer chain, would be simplest if it were possible.

I'm sure that this "compact double doesn't offer low enough gears" issue has been addressed on this forum more than once before. Anyone an expert with the search tool? - I don't ever get on very well with it.

[pwa]

Having had a brief glance at this GRX stuff, it does seem to dangle the prospect of a cassette going up to 40t with a new derailleur. If this were compatible with the existing Utlegra levers it would (not cheaply) make a difference.

[slowster]

Having had a brief glance at this GRX stuff, it does seem to dangle the prospect of a cassette going up to 40t with a new derailleur. If this were compatible with the existing Utlegra levers it would (not cheaply) make a difference.

I think the 40 tooth cassette can only be used with a single front chainring in a 1 x 12 set up. The rear derailleur designed for use with the extra large cassettes has a maximum capacity of 31 teeth, i.e. there is not enough capacity for a double chainset as well.

[pwa]

Having had a brief glance at this GRX stuff, it does seem to dangle the prospect of a cassette going up to 40t with a new derailleur. If this were compatible with the existing Utlegra levers it would (not cheaply) make a difference.

I think the 40 tooth cassette can only be used with a single front chainring in a 1 x 12 set up. The rear derailleur designed for use with the extra large cassettes has a maximum capacity of 31 teeth, i.e. there is not enough capacity for a double chainset as well.

Makes sense, unfortunately.

[geocycle]

I’m having reasonable success with a spa sub compact 44/28 matched with 11-32. All 11 speed 105 which is not far from Ultegra. The two smallest sprockets are a bit noisy but I’m much more interested in the low gears. Importantly also the cruising range appropriate to your landscape without lots of front shifting. The spa chain set seems to be a modified triple with a chain guard replacing the big ring. I’ve set the height of the derailleur to 2mm above the chain guard (ie the faux big ring), I tried to use the 3mm above the actual big ring but it fouled the chain guard even when restricting the lateral movement as much as possible. Seems to work ok.

[pwa]

I’m having reasonable success with a spa sub compact 44/28 matched with 11-32. All 11 speed 105 which is not far from Ultegra. The two smallest sprockets are a bit noisy but I’m much more interested in the low gears. Importantly also the cruising range appropriate to your landscape without lots of front shifting. The spa chain set seems to be a modified triple with a chain guard replacing the big ring. I’ve set the height of the derailleur to 2mm above the chain guard (ie the faux big ring), I tried to use the 3mm above the actual big ring but it fouled the chain guard even when restricting the lateral movement as much as possible. Seems to work ok.

I have put a variation on that (modified triple) Spa extra compact double chainset on two bikes for family members and it works really well with their 8 speed set-ups. 44t is a big enough ring for reasonably fast progress over rolling hills, and the 28t smaller ring is well worth having. If it also works with 11 speed Shimano stuff, that is great. Different bottom bracket as well, of course.

[slowster]

I'm using a 40/24 Spa compact chainset. The bike came supplied with a 46/36 chainset and 11-28 10 speed cassette, which was just too high for my level of fitness and because I use it mostly for off road tracks. I had to replace the front derailleur because it fouled the chainstay when lowered to within 2mm of the 40 tooth ring. However, that derailleur was a Microshift Arsis, which looked to me like it has a longer cage than, say, Shimano Ultegra, so a standard Shimano front derailleur might not need to be replaced depending upon the choice of outer ring size, seat tube angle, and the shape and size of the chainstay. I fitted a CX70 front derailleur, and having anticpated that I could have some problems getting the shifting to work with such small non-standard size chainrings, I was very pleasantly surprised at how well it shifts.

Eventually I want to replace the 11-28 cassette with 11-32 or 11-34, not so much for the lower gears but rather to increase the gaps between cruising gears. The 11-28 has one tooth jumps from 11t to 15t which would be fine for fast riding on the road, but for off road riding the gaps are too small and I always seem to have to shift at least two sprockets at a time.

[Barry and Janet wil]

I've fitted 46/30 chsinrings and a 11-34 cassette and it works fine with the rest of the 8000 groupset.

I'm a trendy consumer. Just look at my SM-G950F using hovercraft full of eels.

[Lookrider]

I've fitted 46/30 chsinrings and a 11-34 cassette and it works fine with the rest of the 8000 groupset.

I'm a trendy consumer. Just look at my SM-G950F using hovercraft full of eels.

To be a little more specific
Did you fit the chain rings to your existing cranks and bottom bracket etc and manage to have tbe spider and Bolt circle diameter all compatible ?? .or was it a full new front drive .
.thanks