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Gravel cassette upgrade

Old 06-03-20, 11:27 PM
  #1  
nickthedangerou
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Gravel cassette upgrade

Hi all, please bear with me as DIY bike improvements are new for me... I'll try to not sound too stupid. I bought this funky Slingshot gravel bike and want to replace my cassette and I assume, RD . It has Dura Ace 7801 shifters, crankset is a 50/34 with a FD 7800, and currently riding a CS 6700, I believe it's only a 11-28.

As these are all 10 speed components, If I were to upgrade my cassette, I've read I could put on a Shimano Deore M6000 CS-HG500 Cassette - 10 Speed, 11-42t - is that correct? And, if so, then I imagine my current SS RD is too short, so I'd need the Ultegra GS RD. That said - I was reading on Shimano's website and they recommended the GRX RD-RX400. Any advice there?

And - do any of these specs not work, once I've made the cassette and RD adjustments?

Lastly, in general, is this a wise upgrade? My legs are getting torched w/ my Los Angeles fire road climbs, so that's the reason for my tinkering.

Thanks in advance.

best,
Nick
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Old 06-04-20, 05:21 AM
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dsaul
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There is no rear derailleur with enough chain wrap capacity to shift an 11/42 cassette with a 50/34 crankset. That cassette was meant for 1x use only. The biggest cassette you could use is probably an 11/36 by using a 9 speed MTB rear derailleur.like the Alivio RD-M4000 or Deore RD-M591 or 592.(I know the 9 speed thing makes it confusing, but it works with the 10 speed road shifters and will shift all 10 gears)

The GRX RD-RX400 is not compatible with your shifters and is also only rated to a 36t max cog.
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Old 06-04-20, 10:42 AM
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or you swap your chainrings for subcompact 46/30 and change your cassette to something wider
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Old 06-04-20, 11:21 AM
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Originally Posted by dsaul View Post
There is no rear derailleur with enough chain wrap capacity to shift an 11/42 cassette with a 50/34 crankset. That cassette was meant for 1x use only. The biggest cassette you could use is probably an 11/36 by using a 9 speed MTB rear derailleur.like the Alivio RD-M4000 or Deore RD-M591 or 592.(I know the 9 speed thing makes it confusing, but it works with the 10 speed road shifters and will shift all 10 gears)


The GRX RD-RX400 is not compatible with your shifters and is also only rated to a 36t max cog.

thanks for the note - I was reading this article: road. cc/ content /feature/246424-how-get-ultra-low-gearing-gravel-bike-adventures - (sorry for the extra spaces, I haven't posted enough in this form to be able to include links) that if I did a Shimano road cage GS (either ultegra or 105) - then an 11/40 (and they claim 11/42) would work. If I did update my crankset to a 11/36 which I don't hate the idea of anyway, wondering if you support the idea of the Shimano 105 or Ultera GS RD sufficing. Apparently this writer suggested putting a 11 speed chain on so it clears the 50.
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Old 06-04-20, 11:40 AM
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Would the GRX FC-RX6000 46/30 be compatible with my ultegra shifters? You're saying, if I did that, then I could also add a 11/42 in the back? I read if I expanded like that, I'd add a 11speed chain even though the rest of my bike is set up for 10 speed (including shifters).
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Old 06-04-20, 02:02 PM
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In that article, he uses 11 speed components, which are not compatible with your 10 speed shifters. Shimano is conservative with their max cassette cog ratings and it probably does shift an 11/40 cassette OK. The 11/42 is probably pushing it too far. I suspect that he can not shift into the small/small gear combo without the chain drooping completely slack due to exceeding the chain wrap capacity of the derailleur.

Lets look at the only currently produced 10 speed road rear derailleur that is compatible, the Tiagra 4600 (Tiagra 4700 uses 11 speed cable pull and is not compatible)
=The GS version is rated for a 32T max cog and a 37t total capacity(chain wrap) when used with a double crankset.
=The chain wrap capacity is important, because that is what allows you to have a long enough chain to use the large chainring/large cog combo and still be able to take up the slack in the chain when you shift into the small chainring/small cog combo.
=50/34 crankset has a 16 tooth difference
=11/42 cassette has a 31 tooth difference
=those two numbers added together (47t) make the total chain wrap necessary for the system to work properly.
=the 37t capacity of the GS road derailleur is nowhere near enough to work with a 50/34 crankset and an 11/42 cassette.

The Alivio 9 speed RD-M3100-SGS has a total capacity of 45t, which is close enough that it should work fine if it can shift to the 42t cog. An 11/40 cassette should work with no problems with this derailleur.

The GRX crankset will work fine, but you will have to adjust the front derailleur limit screws since the chainrings are spaced 2.5mm further out than a road double.
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Old 06-04-20, 02:38 PM
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Originally Posted by dsaul View Post
In that article, he uses 11 speed components, which are not compatible with your 10 speed shifters. Shimano is conservative with their max cassette cog ratings and it probably does shift an 11/40 cassette OK. The 11/42 is probably pushing it too far. I suspect that he can not shift into the small/small gear combo without the chain drooping completely slack due to exceeding the chain wrap capacity of the derailleur.

Lets look at the only currently produced 10 speed road rear derailleur that is compatible, the Tiagra 4600 (Tiagra 4700 uses 11 speed cable pull and is not compatible)
=The GS version is rated for a 32T max cog and a 37t total capacity(chain wrap) when used with a double crankset.
=The chain wrap capacity is important, because that is what allows you to have a long enough chain to use the large chainring/large cog combo and still be able to take up the slack in the chain when you shift into the small chainring/small cog combo.
=50/34 crankset has a 16 tooth difference
=11/42 cassette has a 31 tooth difference
=those two numbers added together (47t) make the total chain wrap necessary for the system to work properly.
=the 37t capacity of the GS road derailleur is nowhere near enough to work with a 50/34 crankset and an 11/42 cassette.

The Alivio 9 speed RD-M3100-SGS has a total capacity of 45t, which is close enough that it should work fine if it can shift to the 42t cog. An 11/40 cassette should work with no problems with this derailleur.

The GRX crankset will work fine, but you will have to adjust the front derailleur limit screws since the chainrings are spaced 2.5mm further out than a road double.
Thanks so much - this is incredibly helpful and educational. thanks for bearing w/ my lack of understanding. I'm going to dig into all of this. Thanks again!
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Old 06-04-20, 03:29 PM
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Thanks again - I'm going to keep my shifters the same, the front 50/34 crankset and FD the same, and buy the Shimano Alivio RD-M4000-SGS 9-Speed Shadow Rear Derailleur(Long Cage) and theSUNRACE MX3 10 SPEED 11/40. I read about the RoadLink, but idea is that this RD will be long enough to handle the 11/40, yah?
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Old 06-06-20, 10:20 PM
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One last question - chain

Originally Posted by nickthedangerou View Post
Thanks again - I'm going to keep my shifters the same, the front 50/34 crankset and FD the same, and buy the Shimano Alivio RD-M4000-SGS 9-Speed Shadow Rear Derailleur(Long Cage) and theSUNRACE MX3 10 SPEED 11/40. I read about the RoadLink, but idea is that this RD will be long enough to handle the 11/40, yah?
just realizing I should ask - should I still be using 10 speed chain or consider this spread, I should get an 11 speed?
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Old 06-07-20, 11:27 AM
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Originally Posted by nickthedangerou View Post
Hi all, please bear with me as DIY bike improvements are new for me... I'll try to not sound too stupid. I bought this funky Slingshot gravel bike and want to replace my cassette and I assume, RD . It has Dura Ace 7801 shifters, crankset is a 50/34 with a FD 7800, and currently riding a CS 6700, I believe it's only a 11-28.

As these are all 10 speed components, If I were to upgrade my cassette, I've read I could put on a Shimano Deore M6000 CS-HG500 Cassette - 10 Speed, 11-42t - is that correct? And, if so, then I imagine my current SS RD is too short, so I'd need the Ultegra GS RD. That said - I was reading on Shimano's website and they recommended the GRX RD-RX400. Any advice there?

And - do any of these specs not work, once I've made the cassette and RD adjustments?

Lastly, in general, is this a wise upgrade? My legs are getting torched w/ my Los Angeles fire road climbs, so that's the reason for my tinkering.

Thanks in advance.

best,
Nick
You could.

There are people who use short cage with 11-42 and a road crankset (i can't remember what size). Neverthless longer is safer.

Try it. There are even people who have done 28-38-48x11-42. "Cannot" on paper but can in real life.

Wise. You don't need to help gravity. Excessively high gears are unneccessary. Low gears are very neccessary.

Some other combos to consider:

22-32-44 to 28-38-48 front. Or any combinations of these chainrings: 22, 24, 26, 28, 32, 34, 36, 38, 42, 44, 46, 48.

Some ideas from mine:

22-32-44x11-32. Top photo.
26-38x11-40. Bottom photo.
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Old 06-07-20, 12:37 PM
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Chain

Think i should stick with 10spd or do 11?
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Old 06-07-20, 06:23 PM
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Originally Posted by nickthedangerou View Post
Think i should stick with 10spd or do 11?
Stick with what you have. But if you want to spend more, it's up to you.

I have 8 speed and keeping it.
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