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I have a BMC Granfondo gf01 (Rim Brake version) that was bought second-hand and came equipped with Shimano Ultegra 6800 (11-speed). Just the Crankset is different, being a Shimano Ultegra FC-6700 (10-speed) with 53-39 tooth. Since I live in a hilly area and I want do to routes with some elevation (>1000m), I need to change the crankset and the cassette (I have an Ultegra CS-6800 with 11-28). With that in mind, I don't want to spend too much on changing the components, since I plan to eventually upgrade to a disc brake bike in ~1 year. Therefore, I thought about the following components:

  • Crankset: Shimano FC-RS510 50/34 (11-speed) [I have a good deal on this, for 60€ like new)
  • Cassette: Shimano 105 R7000 11-32 (11-speed) [I do have a medium cage rear derailleur - Ultegra RD-6800-GS, that supports the 32 tooth]
  • Chain: Shimano CN-HG601 105

Can you help me clarify the following questions:

  1. Do you know, for instance, that all of those (the RS510 crankset, especially) will be compatible with the rest of my Ultegra 6800 components (shifters Ultegra ST-6800, front derailleur FD-6800-B, rim brake BR-6800) ?
  2. Do you also think its necessary to change my bottom bracket when changing my crankset ?

Thanks in advance!

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  • Chain: Shimano CN-HG601 105 Don't spend extra for a Shimano chain over something like a KMC chain. I've never noticed any shifting difference between them. Mar 24, 2023 at 0:00
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    @AndrewHenle To add, the KMC ones usually come with a reusable quick link! I much prefer that to Shimano's pin system.
    – jayded-bee
    Mar 24, 2023 at 7:35
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    @jayded-bee I think Shimano may have given up on their pin-the-chain-back-together paradigm. I think their 11- and 12-speed chains come with quick links. But that's no reason to pay more for the Shimano brand name IMO. And FWIW, all quick links are reusable - IIRC it's just that someone (SRAM?) had a patent on reusable quick links, so everyone else just said "do not reuse", which everyone like me ignored and reused 'em anyway to no ill effect. Mar 24, 2023 at 13:24

2 Answers 2

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In the Shimano universe, their compatibility charts are very handy.

This chart only shows the 11 and 12 speed road groups, but the same collection of bottom brackets exist in the corresponding 10 speed chart, where your FC-6700 resides (I marked the FC-6800 on the chart, but these 10 and 11 speed groups all share the same 24 mm Hollowtech II axle). Your FC-RS510 crankset is compatible with the same bottom brackets that your FC-6700 currently has. Modern bottom brackets typically are low-maintenance items that last a long time, so usually you do not need to change them out when doing swap to a different compatible crankset.

The CN-HG601 chain you are selecting also is an 11 speed compatible chain.

Again, the chart shows that your shifters will work as well.

The only point where you may have an issue (and I stress the "may") is in the front derailleur. Your FD-6800 is not shown as compatible with your FC-RS510 crankset (indicated by the dashed red line). The reason Shimano does not show this as compatible is the inner chainring on the FC-RS510 (and the R7000, R8000, etc.) crankset is 0.4 mm closer to the outer chainring when compared to the older 11 speed models like the FC-6800 (I can't speak to your FC-6700 from personal knowledge). Just 0.4 mm. This was a change made between the first and second generation of Shimano's 11 speed cranksets. Getting to the front derailleur, that 0.4 mm difference is what is driving Shimano's lack of compatibility with the older front derailleurs. My suggestion is to first try it using your FD-6800 and see if it can be adjusted to work satisfactorily for you. 0.4 mm may not seem like much but it may be enough difference to not allow you to trim your front derailleur position to avoid chain rub in some rear cogs while on the inner chainring. Some have been successful with this even without Shimano's blessing. Fortunately, front derailleurs are not horribly expensive and you can still ride your bike with the older front derailleur if you feel the need to upgrade that as well.

If you are not changing your brake lever/shifters (brifters) your brake calipers are perfectly fine.

Compatibility chart Link

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    I can confirm: After my Ultegra FC-6800 cranks gave up I exchanged them for 105 FC-R7000. It worked, but I wasn't super happy with the shifting and the inline barrel adjuster of the 6800 had always been a bit finicky. So I swapped the front dereilleur to a 105 FD-R7000 (tension adjuster directly on the dereilleur and newer/better mechanism). I'm happy now! But honestly, if I hadn't looked at the chart beforehand I probably wouldn't really have noticed that it's not optimal ...
    – linac
    Mar 24, 2023 at 9:22
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Yes, the parts will be compatible. You will unify everything to road 11-speed. With Shimano, everything is compatible here. The Ultegra vs. 105 cassettes only differ in weight. For cranksets it is similar. Select the crank length according to your fit.

No, you do not need to change the bottom bracket as all the mentioned parts use the Hollowtech II type of bottom bracket with the same 24 mm spindles.

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