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Cannondale Topstone 105 - Shimano 11-42 Cassette Possible?

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Cannondale Topstone 105 - Shimano 11-42 Cassette Possible?

Old 06-19-19, 06:32 PM
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996
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Cannondale Topstone 105 - Shimano 11-42 Cassette Possible?

Hi All,

Looking at purchasing a Cannondale Topstone 105. The bike is an 11 speed and comes with Shimano 105 7020 hydro discs/hydro brakes, and a Shimano 105 7000 GS rear derailleur. Would it be possible to substitute this derailleur with the Shimano RD-RX812 (GRX) derailleur with the same shifters? This specific RD model allows up to 42T on the low gear.

Any help or suggestion would be greatly appreciated!

Thanks.
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Old 06-19-19, 07:06 PM
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Originally Posted by 996
Hi All,

Looking at purchasing a Cannondale Topstone 105. The bike is an 11 speed and comes with Shimano 105 7020 hydro discs/hydro brakes, and a Shimano 105 7000 GS rear derailleur. Would it be possible to substitute this derailleur with the Shimano RD-RX812 (GRX) derailleur with the same shifters? This specific RD model allows up to 42T on the low gear.

Any help or suggestion would be greatly appreciated!

Thanks.
The RX812 is for 1x only. The RX810 is the equivalent model for 2x. Its range is the same as the 105 R7000 GS rear derailleur, which allows for a maximum 34 tooth in the back. However, some people have found that in practice, you can easily run an 11-36 or in some cases, an 11-40.
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Old 06-19-19, 07:17 PM
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Originally Posted by raisinberry777
The RX812 is for 1x only. The RX810 is the equivalent model for 2x. Its range is the same as the 105 R7000 GS rear derailleur, which allows for a maximum 34 tooth in the back. However, some people have found that in practice, you can easily run an 11-36 or in some cases, an 11-40.
Thanks for the response. This is the info that Shimano provides below:

"RD-RX810/RD-RX812
  • SHIMANO SHADOW RD+ stabilization
  • Compatible with existing 11-speed mechanical DUAL CONTROL levers
  • Max. cassette range:
    • RX810 (30-34T low)
    • RX812 (40-42T low)
  • Max. front chainring range: 17T (RX810 only)
  • Capacity
    • RX810 - 38T
    • RX812 - 31T
  • 251/264 g "


Not sure if the RD will be compatible with the 105 hydro shifters. If so... then I might bite the bullet and install an bigger cassette and run this RD. Chainline would be something else I would be worried about.
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Old 06-19-19, 07:25 PM
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Originally Posted by 996
Not sure if the RD will be compatible with the 105 hydro shifters. If so... then I might bite the bullet and install an bigger cassette and run this RD. Chainline would be something else I would be worried about.

The GRX 810 RD is compatible with your R7020 shifters, but it won't provide any more range than you currently have. You are not changing your chainline, so there's no need to be concerned about the chainline. That would only happen if you changed the crankset.

Given that the Topstone comes with a 46/30 crankset, an 11-34 cassette will get you up very steep climbs - even 15% gradients shouldn't be too much of an issue. If you're standing and going at a cadence of 60rpm, you'll be going at 7 km/h.
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Old 06-19-19, 07:31 PM
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Originally Posted by raisinberry777
The GRX 810 RD is compatible with your R7020 shifters, but it won't provide any more range than you currently have. You are not changing your chainline, so there's no need to be concerned about the chainline. That would only happen if you changed the crankset.

Given that the Topstone comes with a 46/30 crankset, an 11-34 cassette will get you up very steep climbs - even 15% gradients shouldn't be too much of an issue. If you're standing and going at a cadence of 60rpm, you'll be going at 7 km/h.
Thanks for the response. My goal is to have the Topstone with an 11-40 or 42 in the rear, but stick with the 105 model given the Shimano components I want. I kind of want to avoid the Apex 1 model.

So the RX812 RD won't fit with the stock cranks on the 105 Topstone?

Thanks again for the help.
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Old 06-19-19, 07:42 PM
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Originally Posted by 996
Thanks for the response. My goal is to have the Topstone with an 11-40 or 42 in the rear, but stick with the 105 model given the Shimano components I want. I kind of want to avoid the Apex 1 model.

So the RX812 RD won't fit with the stock cranks on the 105 Topstone?

Thanks again for the help.
No, because the RX812 is for 1x only. The Topstone has two chainrings at the front, a 46 tooth and a 30 tooth. This is to provide a wider range of gearing over a narrower cassette, like an 11-34. On the other hand, 1x gravel drivetrains have a front chainring of 40 teeth or 42 teeth. The range is made up for by having a wider cassette in the back, such as an 11-40 or 11-42.

Combining the 46-30 chainrings with an 11-42 cassette gives you lowest gear of 30-42, which at a cadence of 60rpm, gives a speed of about 5.7km/h. For most people, that's slower than walking pace. If you're regularly encountering territory that requires that kind of gearing, then a mountain bike would be much better suited to the task as it maintains stability significantly better at slower speeds.

There's not much you won't be able to get up with a 46/30 and 11-34 combination. Try it first.
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Old 06-20-19, 09:33 AM
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Originally Posted by raisinberry777
No, because the RX812 is for 1x only. The Topstone has two chainrings at the front, a 46 tooth and a 30 tooth. This is to provide a wider range of gearing over a narrower cassette, like an 11-34. On the other hand, 1x gravel drivetrains have a front chainring of 40 teeth or 42 teeth. The range is made up for by having a wider cassette in the back, such as an 11-40 or 11-42.

Combining the 46-30 chainrings with an 11-42 cassette gives you lowest gear of 30-42, which at a cadence of 60rpm, gives a speed of about 5.7km/h. For most people, that's slower than walking pace. If you're regularly encountering territory that requires that kind of gearing, then a mountain bike would be much better suited to the task as it maintains stability significantly better at slower speeds.

There's not much you won't be able to get up with a 46/30 and 11-34 combination. Try it first.
Thanks for this. You're right, I gotta go ride one. The goal is to have a capable gravel bike that I can take on the fire roads around Los Angeles, which get quite steep at times. I was considering a 1x setup with a 30 or 32 in the front combined with the 11-40/42 in the rear as well.

Best,
996
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Old 06-20-19, 10:02 AM
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Originally Posted by 996
Thanks for this. You're right, I gotta go ride one. The goal is to have a capable gravel bike that I can take on the fire roads around Los Angeles, which get quite steep at times. I was considering a 1x setup with a 30 or 32 in the front combined with the 11-40/42 in the rear as well.

Best,
996
If you want a 1x setup like you describe, you wouldnt want the 105 Topstone. They are totally different drivetrains.
What you describe wanting is a pretty common/modern MTB drivetrain setup.

30x34 gearing at 70rpm with 40mm tires is 5mph and 24.3 gear inches.
What you describe, a 30x42 bailout, is 19,6 gear inches. Thats super low for riding unloaded on gravel roads. Everyone is different and we all climb differently(i am certainly not fast), but the proposed setup is really really low gearing. There is no clear line for when a bike isnt good to use for a certain task, but that sure seems like its squarely in the 1x MTB wheelhouse.
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Old 06-20-19, 10:29 PM
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https://www.wolftoothcomponents.com/products/roadlink
There now you can just do it with your stock RD well 11-40. So what if it is basically the same gearing I have on my mountain bike? Some of us do stupid stuff with our gravel bikes and that kind of gearing comes in handy in those situations.
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Old 06-21-19, 05:36 AM
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Originally Posted by raisinberry777
No, because the RX812 is for 1x only.
I'm not so sure that is actually the case. I think shimano is just being conservative since it wont have the take up capacity to handle the full range that a 48/31 11-42 would need to work in every gear but geometry is the same as the xtr which is 2x compatible
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Old 06-21-19, 05:53 AM
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Originally Posted by redlude97
I'm not so sure that is actually the case.
Well, it is.

https://www.cxmagazine.com/shimano-u...00-rx600-rx400

The mechanical GRX RX800 series follows with RX810 (2x) and RX812 (1x) rear derailleurs, RX810 mechanical STI levers, and the RX810 front derailleur.
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Old 06-21-19, 06:42 AM
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Originally Posted by raisinberry777
again, that is what shimano says but just look at the 812 vs xtr rd and they look essentially the same and use the same clutch design. Shimano regularly claims things wont work because they are conservative with the claims
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Old 06-21-19, 07:06 AM
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I don't know about GRX compatibility but an 11-42 cassette will work with 7000 and 8000 series GS rear derailleurs if 46/30 rings are used up front. I'm running this exact setup now.

A 1.85 mm spacer is required behind the mountain bike cassette so that it fits a road freehub. An entire 116 link chain is needed. No Wolftooth is used. Low gear with 38 mm tires is 19.5 inches.

I was running an 11/36 cassette with Ultegra 50/36 compact road cranks. That was fine for racing but not for bikepacking where the bike has 25 to 35 lb extra gear.

Even apart from bikepacking, my legs are happier now. North Georgia is very rugged terrain and every ride has climbs 10% or more. I regularly do climbs up to 16%. Sometimes I'll be climbing for an hour straight. The lower gearing of the 11/42 cassette allows me to use the middle range of gears where I would have been in the lowest gear grinding it out with the previous or stock setup.

There are at least two others I ride with in North Georgia who run gravel bikes with 11-42 XT cassettes and 46/30 rings. On just completed Dirty Kanza with this setup.

Stability at low speeds isn't an issue. On the contrary. 45 minutes into a 1.5 hour long climb and the lower gears are a Godsend.


-Tim-
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Old 06-21-19, 08:10 AM
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Originally Posted by TimothyH
I don't know about GRX compatibility but an 11-42 cassette will work with 7000 and 8000 series GS rear derailleurs if 46/30 rings are used up front. I'm running this exact setup now.

A 1.85 mm spacer is required behind the mountain bike cassette so that it fits a road freehub. An entire 116 link chain is needed. No Wolftooth is used. Low gear with 38 mm tires is 19.5 inches.

I was running an 11/36 cassette with Ultegra 50/36 compact road cranks. That was fine for racing but not for bikepacking where the bike has 25 to 35 lb extra gear.

Even apart from bikepacking, my legs are happier now. North Georgia is very rugged terrain and every ride has climbs 10% or more. I regularly do climbs up to 16%. Sometimes I'll be climbing for an hour straight. The lower gearing of the 11/42 cassette allows me to use the middle range of gears where I would have been in the lowest gear grinding it out with the previous or stock setup.

There are at least two others I ride with in North Georgia who run gravel bikes with 11-42 XT cassettes and 46/30 rings. On just completed Dirty Kanza with this setup.

Stability at low speeds isn't an issue. On the contrary. 45 minutes into a 1.5 hour long climb and the lower gears are a Godsend.


-Tim-
Currently running 34×36 low with an rx700 with the bscrew about halfway in. I'm sure a 40t would work and a 42t could work with the screw flipped around. My guess is both grx rds will work
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Old 06-21-19, 10:35 AM
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Thank you all for the informative replies. Doing some more research on this topic.

Originally Posted by TimothyH
I don't know about GRX compatibility but an 11-42 cassette will work with 7000 and 8000 series GS rear derailleurs if 46/30 rings are used up front. I'm running this exact setup now.

A 1.85 mm spacer is required behind the mountain bike cassette so that it fits a road freehub. An entire 116 link chain is needed. No Wolftooth is used. Low gear with 38 mm tires is 19.5 inches.

I was running an 11/36 cassette with Ultegra 50/36 compact road cranks. That was fine for racing but not for bikepacking where the bike has 25 to 35 lb extra gear.

Even apart from bikepacking, my legs are happier now. North Georgia is very rugged terrain and every ride has climbs 10% or more. I regularly do climbs up to 16%. Sometimes I'll be climbing for an hour straight. The lower gearing of the 11/42 cassette allows me to use the middle range of gears where I would have been in the lowest gear grinding it out with the previous or stock setup.

There are at least two others I ride with in North Georgia who run gravel bikes with 11-42 XT cassettes and 46/30 rings. On just completed Dirty Kanza with this setup.

Stability at low speeds isn't an issue. On the contrary. 45 minutes into a 1.5 hour long climb and the lower gears are a Godsend.


-Tim-
Wow that's good to know. Does the RD stretch to concerning lengths at all given certain gearing positions? Would you happen to have a picture of your setup? In theory if I have an MTB hub, I won't need the spacer correct?

Thanks a bunch for this information. Just want to pull this off and have a reliable setup. The stock hubs on the Topstone 105 are: Formula RX-512 12x100 front, RX-142 12x142 rear.

Best,
996
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Old 06-21-19, 12:35 PM
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Originally Posted by 996
Thanks a bunch for this information. Just want to pull this off and have a reliable setup.
I'm happy to help and hope it works out for you. Keep us posted. Ultimately it is trial and error and what works for one won't necessarily work for everyone. The best advice I can give is to try it. Several guys here are using this setup.

Below is the CS-M8000 11-42 cassette on an Industry Nine Torch road hub with the 1.85 mm spacer. The B screw was reversed.

The biggest concern is crosschaining 46 front and 42 rear. It does stretch the derailleur, yes, but I run it that way on occasion and nothing bad happens. I'll see if I can get a photo of it that way.

Keep in mind that it is Di2 running an RX-805 rear derailleur and firmware prevents using the two smallest sprockets in the rear when on the small ring in the front. There is physically no way to shift into the 30/11 or 30/13 combinations. Those gear combinations are simply locked out by software. A mechanical system could shift into the small/small combinations but I don't know what would happen - maybe the chain would be too loose?

19.5 gear inches is ridiculously low when riding around town unloaded. Strap 30 lb of gear on the bike, head up a 15% grade or do a 2500 ft climb however, and it comes in handy.










-Tim-

Last edited by TimothyH; 06-21-19 at 12:42 PM.
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Old 06-21-19, 04:16 PM
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Originally Posted by TimothyH
I'm happy to help and hope it works out for you. Keep us posted. Ultimately it is trial and error and what works for one won't necessarily work for everyone. The best advice I can give is to try it. Several guys here are using this setup.

Below is the CS-M8000 11-42 cassette on an Industry Nine Torch road hub with the 1.85 mm spacer. The B screw was reversed.

The biggest concern is crosschaining 46 front and 42 rear. It does stretch the derailleur, yes, but I run it that way on occasion and nothing bad happens. I'll see if I can get a photo of it that way.

Keep in mind that it is Di2 running an RX-805 rear derailleur and firmware prevents using the two smallest sprockets in the rear when on the small ring in the front. There is physically no way to shift into the 30/11 or 30/13 combinations. Those gear combinations are simply locked out by software. A mechanical system could shift into the small/small combinations but I don't know what would happen - maybe the chain would be too loose?

19.5 gear inches is ridiculously low when riding around town unloaded. Strap 30 lb of gear on the bike, head up a 15% grade or do a 2500 ft climb however, and it comes in handy.

-Tim-
Appreciate it. Nice bike! So if I were to put the wolftooth adapter on my frame, in theory the results would be the same but maybe less stress on the rear derailleur?

Also what do you mean by the "B screw was reversed?"

Thanks,
996
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