Hello everybody.. I have this bike ===> https://archiv.cube.eu/2021/403100 and I want to add a bit more speed by adding the FC-RX600 crank thus making something of a mountain/gravel hybrid, i.e. mountain bike with gravel gearing. There is a 10 speed version of the FC-RX600 to match the existing 10 speed 11-42 cassette on the bike, the chainline of the FC-RX600 is 1.8mm smaller than the existing crank so may have to add a spacer for better shifting and to help clear the chainstay (46t is 20mm longer radius than existing 36t), I may have to change the front derailleur, and will probably need a longer chain.
I'd appreciate advice on what else I should be looking for and I will keep you posted, many thanks
It's not likely to fit: your MTB most likely has a BB shell that is too wide (73mm) for the GRX crankset spindle. And even if it has a 68mm shell, installing a road BB would mess up your chainline even more and it's also quite likely you will touch the frame with your chainring.
In fact, when looking at the product page, the stock chainring seems to be very close to the chainstay already. Have a look if there is any space for a larger chainring. Also keep in mind larger than 36T chainring will be hard to source for a MTB 2x. If you can't find a 2x chainring but there is sufficient space, you consider converting it to 1x. Narrow wide 1x chainrings are easier to source. Since you want to go faster, you might not miss the small chain ring.
Or in the opposite direction: maybe a 3x would be a solution for you, if it can clear the chainstays, You will need a new front derailleur and a new left hand shifter for a 3x crankset.
Thank you for the replies, I use them to learn. I can see there are bb available that fit both 68/73, so if there is an issue I can get one of those. I have looked into the chainline already, there is a 1.8mm difference, and also looked into the clearance issue already, if the chainline was to remain unchanged there is enough clearance for the bigger 46t chainring, so worst case scenario I will need to use a spacer. I have thought of putting a triple crank, and this is what I will do if I'm not happy with the GRX component or if it turns out to be incompatible
It's the shell width that matters, not the BB width. Measure your BB shell width, it's likely 73mm and that will not work with the GRX crank as the spindle is not long enough. For the same reason it's likely you can't use a spacer to fix the chainline much: the spindle is not long enough to use (multiple or thick) spacers, even in a 68mm BB shell.
Current crank chainline is 48.8 mm and GRX crank chainline is 47mm so the chainline is slightly off by 1.8mm. I also carefully measured the clearance, the frame thankfully has enough clearance for a 46t chainring on either chainlines, so even without a spacer it will clear the GRX crank, but I guess even a tiny teeny spacer will do? Even 1mm wide? Correct me if I'm wrong.
Now the shell compatibility is an issue, I measured the shell to be 73mm, like you said.
I am going to read some more then, I was reading for the past hour and found one unusual solution i.e. ask the bike repair shop to shave 5mm off each side of the bb shell 😱 and I also found this http://bike.shimano.com/en-EU/product/component/alivio-m4000/FC-MT210-2.html which will fit perfectly but it is a 2x9 crank and I have no idea if that will cause any compatibility issues. If not, that would be the easiest, most straight forward solution, identical chainline, straight swap.
I think the 2x9 crank would be a good candidate, since you are confident that the chainring will fit.
As to compatibility: formally 9 speed crank is not compatible with 10 speed chain, but I think you will not notice significant impact on shifting. The reason it's not compatible: the 10 speed chain is slightly narrower than a 9 speed and your front derailleur might have issues pushing it from 1 chain ring to next. If you are planning to ride in the big ring mostly, it's not an issue at all.
The spindle length and q-factor of road and mtb cranks is totally different, and there's some very good reasons to not mess around with the BB spacing. One, safety, if you do some sort of bodge that results in the non-drive side arm falling off while cranking hard, or standing on the pedals over rough terrain, hospital. Two, if even if you don't care about safety, it will load the BB bearing wrong resulting in premature failure.
Having said that I kinda wanted to do the same thing with an older non-boost XC bike using a low maintenance 2x10 with like a 42/30 crank and and 11-42 or 11-45 cassette as a gravel rambler for terrible conditions. Didn't really find a lot of good options, and just decided on a modern XC frame with boost spacing and a chainstay cutout that can easily handle up to a 40T ring with the 1x12 Shimano setup that has a 10t small cog, which is enough for anything that bike will see. I still would have preferred a 2x, but it's too hard to find the right parts since 2x is very niche for mtb's now.
Sadly true, but if one doesn't mind low end, there are still 2x and 3x options.
If GRX 2x is not possible I can try the 2x9 crank mentioned above which is a perfect fit and possibly will be working without issues or an FC-T6010 48/36/26 3x crank, also compatible but more complicated to fit since I will need new deraileur, shifter etc.
Skylined wrote:Will definitely be using the full range, also realised that person made a mistake: the bike shop would need to shave 2.5mm off each side. Hm..
I realise my earlier post might have been confusing: formal Shimano specification shows 10 speed chain to be incompatible with 9 speed crankset. However the common thought is that "1 speed difference" doesn't impact the shifting much. So the 2x9 is probably an affordable solution that would work for you.
Best case scenario, fingers crossed, it will work and I won't have to change a single thing on the bike. Worth trying for sure. Thanks for the replies 😊😃
You just have to make sure the front derailleur has the correct chainline, or at least can be adjusted to the GRX chainline, and can shift 16T instead of 10T up.
GRX cranks are designed to work with a 2x 2.5mm offset, and thus work perfectly with 73m BB's: the crank spindle is long enough. It is being used like this in factory installs on several Salsa bikes and the Focus Atlas, which has 73mm BB and even boost wheel spacing.
Thijsvanderwal wrote:Looking at https://bike.shimano.com/en-EU/product/component/deore-m6000/FD-M6025-H.html the chain line of the Cube supplied FD is 48.8mm and has a 10T capacity. Those are both quite a bit off from the GRX specs (51mm & 17T) so I would not recommend combining this FD with a GRX crankset.
It is possible a different front derailleur will be required but for the record the FC-RX600 GRX crank I want to fit has 47mm chainline and 16T difference so the chainline is off by -1.8mm and that's why I was talking about using a little spacer.
Indeed you're right, I was looking at a different crankset, sorry. If the crank spindle allows it you could indeed try to add 1-2mm of spacers on the drive side, and ideally the same amount to the non-drive side. I'm especially curious if that deore FD with a 10T capacity has a long enough arm to do 16T, let us know how you get on!
Thijsvanderwal wrote:GRX cranks [...] work perfectly with 73m BB's: the crank spindle is long enough.
Are you very sure about this? Are these special GRX cranksets? I have a retail GRX810 crankset installed on 68mm BSA BB shell, and the spindle has absolutely no additional 5mm left... Also official specification of GRX lists as compatible with 68mm BSA only.
