So my Aspero came with GRX 810 cranks. My bike fitter is recommending 165mm as a better length, which Shimano doesn’t make in the 810, hence the switch.
Anyone here have experience making this switch, and did you encounter any issues?
Ideally, I’m looking to just switch the cranks, meaning, putting the 810 chainrings on the 600 cranks and keeping the rest of the setup exactly the same.
I’m sure Shimano won’t make it as easy of a switch as I’m hoping. A quick skim of related posts is suggesting that spacers may be necessary.
EDIT: the gearing of the 600 may be to my advantage. Are there any issues if you leave chainrings ‘as is’ and just swap out the cranks as they ship from the factory?
I can’t help on what you’re trying to do, but I will say that my last bike had 172.5mm GRX 610 cranks and I moved to 165mm. The 165mm was a huge improvement.
But, like you’ve noticed, they don’t offer this in an 810. I wanted to upgrade to an 810 and was pretty surprised and disappointed in Shimano to learn that they didn’t offer this..
Have you considered Rotor cranks? They are of impeccable quality and come in a variety of lengths. Their cheaper Vegast cranks are on sale. You can use an adapter to re-use your Shimano chain rings (a 110/80 BCD adapter) or use Rotor’s own chainrings (oval or round). You’d need the 24 mm spindle version and the matching spindle.
Edit: A complete crankset in 165 mm with 46/30 chainrings is on sale for $114, an absolute steal! It is specifically marketed for the GX groupset. I have ridden Rotor chainrings in the past, and their gear is top-shelf quality (think Ultegra/DuraAce or Force/Red). A buddy of mine had 2x Rotor chainrings and I thought they shifted just fine.
Their cranks are modular, so you can only change the crankarms or spindle. They also make more expensive cranks, a lighter aluminium version (Aldhu) and carbon cranks (Aldhu carbon). Another nice thing is that they make their own chainrings in more sizes, including e. g. 46/30 if that’s something you might be interested in.
I’m not 100% sure that the chainrings are compatible.
I put 600 chainrings on an 810 crankset a couple of years ago, and I believe I had to trim the post that stops the chain from dropping between the crank arm and the chainring.
Shimano has a history of engineering incompatibilities into chainrings to match them to specific cranksets. That makes it problematic if you want to buy genuine Shimano chainrings for “older” cranks.
I have an XTR M9000 1x crank and I cannot use XT or SLX chainrings. Plus, I have a hard time finding XTR chainrings in my locale that aren’t marked up to the bazoo. Not because the construction of them is fundamentally different, no, it is because of notches, cutouts and pins whose only job seems to be to make them non-interchangeable.
The Rotor oval chainrings I got for them were terrific, but they are out of production and not available where I am. I got some Garbaruk chainrings instead.
Strongly recommend this route, especially if you might ever want to add a power meter in future. Power2max or Sigeyi spider PMs are both excellent and available in compatible configurations.
Just remember to buy the gravel spacing (longer) axle and GRX compatible spider.
The deal I linked to is advertised specifically to work with GRX, so everything should be compatible. But good points.
One more thing: Rotor’s cranks are modular, so you can replace one axle with another axle (of the same size, here 24 mm) or you can just get new crank arms if you want an upgrade (to lighter aluminium or carbon cranks) or change crank length.
I really love this, because Shimano does the opposite here where e. g. you need to pair XTR chain rings with XTR cranks. If you have older cranks (I have an XTR M9000 crank on my mountain bike), then sourcing XTR parts is getting more difficult and/or a lot more expensive.
I swapped 48/31 chainrings onto 165 mm GRX 600 cranks without any issue so far.
Chainring bolts are very slightly different length and the 600 bolts use hex instead of torx.
The chain catch pin mentioned by eddiegrinwald is an issue with doing the reverse swap because the 600 cranks are concave on the back so the pin is longer. Now it will be slightly short in your case.
