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Ultegra to GRX.. yeah, another thread

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Ultegra to GRX.. yeah, another thread

Old 03-20-23, 09:52 AM
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Zaskar
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Ultegra to GRX.. yeah, another thread

I figured, why not a 64th thread on the topic (kidding, there are probably more). I even started a thread a while back asking for suggestions on how to upgrade to get more gear, and can't even find my own thread. But this question is more specific... I think.

I have an Ultegra 8000 2x - 50/34; 11-34 drivetrain. That's just not enough gear. Example: this weekend's ride - 50 miles, 6,000' of climbing had me in the 30-40 RPM cadence a few (okay, several) times.

I know I can push Shimano's conservative limit and run an 11-36 cassette.

What, if any, benefit will I gain just swapping the rear derailleur for a GRX? Will that allow me to run a 40t?

Thanks!
(and sorry for another version of a familiar thread)
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Old 03-20-23, 09:59 AM
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Have you considered going to a GRX 46-30 crank instead? Cost might be close to what you would pay for a new RD and cassette.
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Old 03-20-23, 10:04 AM
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Originally Posted by shelbyfv View Post
Have you considered going to a GRX 46-30 crank instead? Cost might be close to what you would pay for a new RD and cassette.
Yep. I believe there is a 46-30 and a 48-31. But they require the use of the GRX front derailleur which is designed to work with the cranks, which sit outboard a few millimeters further than other Shimano cranksets.
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Old 03-20-23, 10:52 AM
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Originally Posted by Zaskar View Post
I figured, why not a 64th thread on the topic (kidding, there are probably more). I even started a thread a while back asking for suggestions on how to upgrade to get more gear, and can't even find my own thread. But this question is more specific... I think.

I have an Ultegra 8000 2x - 50/34; 11-34 drivetrain. That's just not enough gear. Example: this weekend's ride - 50 miles, 6,000' of climbing had me in the 30-40 RPM cadence a few (okay, several) times.

I know I can push Shimano's conservative limit and run an 11-36 cassette.

What, if any, benefit will I gain just swapping the rear derailleur for a GRX? Will that allow me to run a 40t?

Thanks!
(and sorry for another version of a familiar thread)
The GRX RX810 rear derailleur is a 2x RD with a 34t max large sprocket. It can handle 36t though.
This has a total capacity of 40t, and your hypothetical setup of 50-34 and 11-40 has a total capacity of 45t, which is too much(even when considering Shimano's known conservative numbers).

The GRX RX812 rear derailleur is a 1x RD with a 42t max large sprocket.
It is 1x and not 2x. And it only have a total capacity of 31t, which helps confirm it is not designed to handle a 2x drivetrain like what you have.



Others have suggested using one of Shimano's GRX cranksets since they have smaller chainrings. This would help solve your issue(and you could pair it with an 11-36 cassette to help even more). As mentioned though, the GRX cranksets sit further out from the centerline of the bike frame and so you need a GRX FD too.

Alternative options to the GRX crank are offered by Easton, Paul, FSA, Praxis, and others.
I will suggest Praxis specifically since that is what I have on my main road bike, one of my secondary road bikes, and my gravel bike. I really like the look, easy setup, and performance of the Zayante and Alba cranks.
Praxis makes a 48/32 crankset option and it is designed with a traditional road Q-factor so it doesnt sit further out from the centerline. This means you would keep your current front derailleur and you would not have a wider crankset.

Rolling on 40mm tires...
Your current setup of a 50/34 crank with 11/34 cassette gives you a gear inch high of 125.75GI and a gear inch low of 27.64GI
Your suggested 50/34 crank with 11-40 cassette(which wouldnt work due to the 1x RD) would give you a gear inch high of 125.75GI and a gear inch low of 23.49GI.
A 48/32 Praxis crank with 11-36 cassette would give you a gear inch high of 120.50GI and a gear inch low of 24.60GI.


So looking at those numbers...
- A 125 GI on the high end is really quite large(what you currently have). For context, a road bike with 28mm tires and a 50-11 combo is only 121.45GI. So you are currently rocking a setup that has a high end ratio that is larger(tougher relative to cadence) than a commonly set up paved road bike. You could easily drop down to a 48t large ring and not give up anything at the high end since it gives you basically the same high end as a typically geared road bike rolling on 28mm tires.
- A 32/36 low is quite low. Is it low enough for you and where/how you ride? No idea. But it is over 4 gear inches smaller than your current set up, and that is significant at the low end.

For what its worth, my gravel bike has a 48/32 crank with 11-36 cassette. The Ultegra RX RD and 105 FD shift it all just fine.
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Old 03-20-23, 11:11 AM
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damn guys (mstateglfr!) this is awesome!

On the big end, I totally agree - I don't need more. The only time I'm in the 50/11 is on noticeable downhills - and a tuck is imminent. I like the idea of the Praxis (or other) crank - 48/32 - to start and probably an 11-36 when the current cassette is toast... or if the 32t small ring still doesn't feel like enough.

Time to start shopping for parts!

Related question: any idea why Praxis (are they alone?) doesn't go longer than 172.5mm on the gravel cranks?

Last edited by Zaskar; 03-20-23 at 11:16 AM.
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Old 03-20-23, 11:39 AM
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A couple of additional points as you begin shopping. A GRX crank can use your existing bottom bracket but you'll likely need a different one with another brand. Also, check the chainline. Some may be extended like the GRX (47mm) some may be more standard like your Ultegra (44.5mm.) If extended you'll probably want the GRX FD, regardless of crank brand. Folks have reported using standard FDs with GRX cranks but there are bike specific variables so trial and error. FWIW, my new Cannondale was spec'd with a GRX crank but showed up with an FSA. Has a GRX FD. I Googled the crank and found it has the same chainline as the GRX. Works fine, just a little disappointing. I guess C'dale saved a buck or two.
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Old 03-20-23, 01:27 PM
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Absolute Black makes 48/32 and 46/30 oval chainrings that fit standard shimano road cranks like yours and you don't need a GRX FD. They aren't cheap though. I'm running the 46/30 on my 5800 cranks on my road/gravel bike because I wanted to keep the tighter 11-32 cassette for road but needed the 30 up front for the super steep gravel/mtn bike climbs around here. The GRX setup wasn't around when I did it, today I'd go 48/31 GRX crank for a better mix of both high and low gearing.
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Old 03-20-23, 07:02 PM
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Originally Posted by Zaskar View Post
Related question: any idea why Praxis (are they alone?) doesn't go longer than 172.5mm on the gravel cranks?
https://praxiscycles.com/product/alba/
This lists 175mm 48/32 as an option.
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Old 03-20-23, 09:19 PM
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I use a GRX 46/30T crankset on my otherwise Ultegra (Di2) drivetrain (including front derailleur). It works (at least in my case, might be worth a try in yours).

I also have a GRX mechanical front derailleur on an otherwise non-GRX drivetrain on my touring bike. Nothing exploded.
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Old 03-20-23, 09:22 PM
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Originally Posted by mstateglfr View Post
https://praxiscycles.com/product/alba/
This lists 175mm 48/32 as an option.
Ironically, the gearing on that is too high for me to ride up Alba Road. (Also, it burned in 2020, including the little red school-house).
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Old 03-21-23, 06:14 AM
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Originally Posted by mstateglfr View Post
https://praxiscycles.com/product/alba/
This lists 175mm 48/32 as an option.
I saw that under the Road category. Gravel stops at 172.5. BUT, the Alba GR is made specifically for GRX and is wider. So, it's not relevant. The Road version is the right one for my application.
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Old 03-21-23, 07:25 PM
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I run a GRX 812 rear derailleur with 46/30 crank and 11-42t cassette. I swapped out the GRX derailleur cage for a XT SGS (long cage). The low end gives me 19GI on 650b x 40 tires . . .
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Old 03-21-23, 10:15 PM
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I think the Ultegra RD-R8000 will actually work with an 11-40 cassette in most cases (though adding a RoadLink may sometimes be necessary). Swapping to a 46/30 crank is also appealing, but the adjustment range of braze-on FD's on many road bikes isn't enough enough to work with chain rings this small.
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Old 03-21-23, 10:27 PM
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Originally Posted by sdimattia View Post
I run a GRX 812 rear derailleur with 46/30 crank and 11-42t cassette. I swapped out the GRX derailleur cage for a XT SGS (long cage). The low end gives me 19GI on 650b x 40 tires . . .
I am running the similar set up on my adventure/touring bike except I am running the 810 and using a road link as well. Not sure I needed it but it works perfectly.

Swapping cages within Shimano is a game changer and reasonably cheap. I also put a Ultegra cage on my Di2 R9150 rear derailleur and run 11-36 perfectly.

Last edited by Atlas Shrugged; 03-21-23 at 10:36 PM.
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Old 03-23-23, 01:40 PM
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I landed on a blend of the suggestions:
  • GRX Crank - 48/31
  • GRX FD
  • 11-36 cassette
I recognize this is a massive change - from 34/34 to 31/36. But, assuming all works out - derailleurs play nicely with all the changes - that range - 48/11 on the big end - will be nice. And yeah, I know I'm giving up more 1 and 2 tooth shifting for some big jumps. I have road bikes for all that smoothness. I'll give up some of that for a cadence north of 40 on long steep climbs.
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Old 03-23-23, 01:44 PM
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Originally Posted by Zaskar View Post
I landed on a blend of the suggestions:
  • GRX Crank - 48/31
  • GRX FD
  • 11-36 cassette
I recognize this is a massive change - from 34/34 to 31/36. But, assuming all works out - derailleurs play nicely with all the changes - that range - 48/11 on the big end - will be nice. And yeah, I know I'm giving up more 1 and 2 tooth shifting for some big jumps. I have road bikes for all that smoothness. I'll give up some of that for a cadence north of 40 on long steep climbs.
If it makes sense for the terrain you ride, it's all good.
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Old 03-23-23, 05:46 PM
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I don’t think you’re too far off. You might not want to get extreme.

I began “gravel” with 28mm road tires and 50/34x12-29. I definitely bogged down a bit but not as often as you’d guess.

Over the years I’ve experimented with some other ratios on purpose built bikes, always right around 40mm tires.

40x11-36 seemed nice but flat out kicked my ass on the White Rim. Probably added a literal hour or more to my day.

40x11-42 seemed okay (roughly equivalent on the low side of you getting an 11-36) but I did spin out with a tailwind, a problem your setup won’t have.

On my new bike I went to 40x10-44 with a contraption from Wolftooth. I’ve literally never wanted more. I’m not bike packing but I’m not avoiding anything steep, between Colorado, Utah, and Central Oregon. 2 more teeth and the suddenly I’m in a sweet spot.

Realize that this bike purchase was pretty close to when I got my mountain bike, so I stopped riding hard single track on the gravel bike at around the same time.

Then, just as an experiment, I swapped to an oval chainring, 42t. Due to all the purported benefits, I actually haven’t noticed any difference between it and the round 40. Two free teeth, science!!

All that said. Given your current drivetrain, I’d get the Absolute Black 46/30 rings and ride them for a couple rides. If you’re still lacking, an 11-36 is very easy to add.
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Old 03-29-23, 06:55 AM
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Parts arrived and swapped over. I did go with the GRX 48/31 and 11-36 cassette. I haven't hit the trail yet, but did spin around my neighborhood - very hilly neighborhood. On the steepest hill, I was pleasantly surprised that the 31/36 was definitely low but not that chain's-off spinning kinda low. It felt like a great bailout option for those rides where you bit off more than anticipated and you just need to get over that last peak to get to the car.
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Old 03-29-23, 10:50 AM
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Originally Posted by Zaskar View Post
I haven't hit the trail yet, but did spin around my neighborhood - very hilly neighborhood. On the steepest hill, I was pleasantly surprised that the 31/36 was definitely low but not that chain's-off spinning kinda low.
Near where I live there is one steep paved MUP with an adjacent gravel track, so they have essentially the same slope. On my (105) road bike I can make it up on its lowest 34:28 ratio but on my (GRX) gravel bike I need its 31:30 and sometimes even 31:34. My conclusion is that I am weak as heck and I definitely need lower gearing for gravel than for road.
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Old 03-29-23, 10:21 PM
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When I installed my 46/30 chainrings I figured I wouldn't use my lowest gears on the road anymore, I was wrong lol. I use my 30f/32r pretty much every ride. Just allows me to get up the hills at the same speeds as my 34 chain ring but now I can do it at a higher cadence and my legs aren't dead at the top.
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Old 03-30-23, 05:30 PM
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We have one customer running a GRX rear derailleur with a double crank and Ultegra front derailleur and a 40-tooth cassette with a Wolftooth link to lower the derailleur to accommodate the bigger sprocket. This is on an older Warbird and may not work on every bike, but it works perfectly on his bike. This is one of those things you have to try to see if it will work or not on your own bike.
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Old 03-31-23, 06:45 AM
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I like to post a link to this video on GRX threads. I used the advice given on my own bike and had very good results. I'm currently running GRX Di2 with a 48/31 crankset and 11-40 XTR cassette and using the wolftooth10 link. Check it out...

https://bikepacking.com/gear/wide-range-grx-2x11/
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Old 04-02-23, 01:44 PM
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I purposely went with GRX 48/31 crank an 11-34 cassette on my road bike since I am a senior citizen. I do not regret it one bit. I may not use the lowest gear all the time but its there when I need it. Glad I did...
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Old 04-02-23, 01:59 PM
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Originally Posted by RockiesDad View Post
I purposely went with GRX 48/31 crank an 11-34 cassette on my road bike since I am a senior citizen. I do not regret it one bit. I may not use the lowest gear all the time but its there when I need it. Glad I did...
I have this exact GRX drive train on my gravel bike and it works fine on gravel, but for road riding the gaps between adjacent cogs in the smaller half of an 11-speed 11-34 cassette are too big for my meager and narrow power band.

When I become a senior citizen, I think I will go for a 14-28 junior cassette and if necessary, the cheaper GRX 46/30 chain rings.
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Old 04-12-23, 12:17 PM
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Originally Posted by Zaskar View Post
I landed on a blend of the suggestions:
  • GRX Crank - 48/31
  • GRX FD
  • 11-36 cassette
I recognize this is a massive change - from 34/34 to 31/36. But, assuming all works out - derailleurs play nicely with all the changes - that range - 48/11 on the big end - will be nice. And yeah, I know I'm giving up more 1 and 2 tooth shifting for some big jumps. I have road bikes for all that smoothness. I'll give up some of that for a cadence north of 40 on long steep climbs.
Thatís what I have on my Norco, with a SRAM 11-36 cassette. I highly recommend the SRAM cassette. It has much better spacing than the Ultegra 11-32 it replaced. Also, donít ignore the fact that you can go with 650b wheels and gain better gearing reduction as well. I just put 650bís on my bike and the ratio Shane just in wheelset alone is pretty noticeable.
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