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I'm rehabilitating a cheap gravel bike. I'd like to alter a Shimano Claris 2400 groupset so I have at least a 1x1 lowest gear or preferably a bit better. I'm somewhat inexperienced, having replaced most bike parts at some point but having never figured out compatibility issues.

Here's the current status: The bike started with a Shimano Claris 2400 2x8 speed groupset that had 50/34t chainrings and a 11--32t cassette. The bottom bracket, the crankset, the front derailleur, and the rear derailleur need replacement. I'd like to put on a crankset with has something like 46/30t chainrings. I found something that appeals to me: SHIMANO GRX FC-RX600 CRANKSET (2 X 10 SPEED) (HOLLOWTECH II) (46/30T). Will this crankset work with my setup if I just use the current shifters and replace the front and rear derailleurs with the same models as were on there before (Claris FD2400 and RD2400)? (I'm not sure if the fact that the GRX crankset is advertised as 2x10 speed matters or not...)

I read that using a wolf tooth product can enable usage of cassettes with bigger cogs. But the alternative of making the chainrings smaller appeals more to me at this point.

I'm certainly open to other suggestions for meeting my lowest gear desire without forking out much cash.

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  • There's a 46/30 8-speed in the Tourney MTB range (FC-TY501-2), that would require the matching front derailleur, but not sure about compatibility (I'd think that yes, but not 100% sure). There's also a 46/30 in the Acera range (MT201-2 with a FD-T3000-2 front derailleur), 9-speed so less of a stretch and is a Hollowtech II crank.
    – Rеnаud
    Commented Apr 25 at 15:07
  • @Renaud Probably compatible with 2400, quite surely not with R2000. Commented Apr 25 at 15:16
  • Thanks, @Renaud. After reading Vladimir F's answer, I appreciate that chainline length is important. Since the Claris has a 43.5 chainline and the Acera MT201-2 has a 48.8mm chainline, wouldn't the Acera be incompatible?
    – Maple
    Commented Apr 25 at 15:30
  • @Maple that's why I wrote that the front derailleur needs to be changed, MTB crank and MTB front derailleur are no issue - and entry level MTBs/hybrids are also using 135mm rear hubs, so that wouldn't be an issue.
    – Rеnаud
    Commented Apr 25 at 15:32
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    But just thinking about it: Shimano recently release a new 8-speed range (Essa, and it is said to be compatible with existing 8-speed systems). It's based on a 11-45 8-speed cassette, a clutch derailleur and there's a 40T crankset. That could work for a gravel bike, although the steps between gears may be a bit big and removing the front derailleur would simplify the set up.
    – Rеnаud
    Commented Apr 25 at 15:42

3 Answers 3

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No, the crankset is completely incompatible. The chainline is different together with the number of speeds being also too different, albeit by itself probably somehow workable.

That has nothing to do with the cassette, BTW. The 10-speed cassette also cannot work with an 8-speed shifter. You wouldn't even have enough positions so no pull ratio modification device can change that. Or if you want bigger 8-speed cassettes you will find out that there actually aren't any. The biggest you would normally find is 11-34. Once I did buy an extension device (cheap from Asia) for my Claris, but there aren't actually many bigger cassettes available.

For lower gear, search for subcompact cranksets compatible with the rest of your drivetrain. However, there are not too many for 8-speed either.

Anyway, what you proposed would not be very cost-effective. You would get some horrible bike, and it would not be too cheap. Think about getting a new bike. You can also look for second-hand ones.

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  • Thanks @Vladimir F. How tight do you think the tolerance needs to be on chainline for things to work decently? +-1mm? +-2mm?
    – Maple
    Commented Apr 25 at 15:31
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Yes, the chainset can work.

The chainline is outboard by 2.5mm but if your derailleur struggles to shift to the outer ring on max. adjustment, thanks to the design of the spider, you can use 2mm shims/washers between the spider and the rings to correct the chainline. You would require 8 if this was necessary (usually it is not). Slightly longer chainring bolts may be sensible though not essential.

The rings are very slightly closer together on a 10sp chainset than an 8sp. Typically this does not give a problem but again, can be corrected with microshims if necessary.

It may sound like alot of work and messing around but really it's quite straightforward when you understand what's going on.

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    Thanks! Let me just make sure I understand what's going on. You're talking about the front derailleur struggling to shift to the outer ring, right? And so the fix is to move this closer to the bike frame to correct the chainline so I can still use the Claris front derailleur?
    – Maple
    Commented Apr 26 at 1:26
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    Also, I found this exploded view of the GRX FC-RX600 crankset. Are you suggesting adding spacers/washers between the spider and the larger chainring? And when you say "longer chainring bolts," do you mean the bolts labelled 10 in, for example, the bottom left image of the linked page?
    – Maple
    Commented Apr 26 at 1:27
  • both chainrings are bolted from the inside, you would have to space both rings equally for the effect to work. There are 8 chainring bolts total (4 each ring) so eight spacers and eight chainring bolts would be required (the thread is usual so there are plenty of types available. @Maple
    – Noise
    Commented Apr 26 at 7:42
  • @Maple regarding your first question: Yes
    – Noise
    Commented Apr 26 at 7:42
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    @DanGao I have fitted this chainset to an ultegra 6800 di2 equipped machine (temporarily while waiting for warranty chainset) and it worked with no issue BUT the front derailleur was set literally to its adjustment limit. I can see a case being possible where on certain frames, the reach to the outer ring is too far, but i don't think it will be a frequently occurring problem in the total population
    – Noise
    Commented Apr 27 at 17:13
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Especially if you're inexperienced, i'd suggest to keep working within the range of the official compatibility chart of Shimano:

For Road/Gravel Groupset use these diagrams: https://productinfo.shimano.com/en/compatibility/C-454 https://productinfo.shimano.com/en/compatibility/C-455

Sure, with a little bit of fiddling, you might be able to make something work outside of this chart, but this should only be done if you know what you are doing.

As you can see from the chart, Claris is the only 8 speed left in Shimano's line-up, so it isn't compatible with any other groupset. You probably have to replace the shifters and cassette as well, or replace the parts that need replacements with compatible parts from the Claris groupset.

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  • Boo!! Boring!!!
    – Noise
    Commented Apr 27 at 17:13

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