I have short legs, and I want to change out my crank for a shorter one (165mm). This is kind of an experiment to see how much difference it makes, and whether I want to do this on all by bikes. The package arrived today, and I see I may have ordered the wrong thing. What I got is an HG-X 2x10s, 46-30t crankset. However, the bike has an 11 speed cassette. Is there really something about the front chainring that is going to make this not work, or work poorly, with an 11 speed cassette?

It does.

You can probably get away with it, but it will work better with the GRX 11-speed version. The chain may be more prone to wrapping on the sprocket, or skipping, because the teeth don't match the width of the spacing.

The 165mm ones are hard to get. I put myself on the alerts for all the major internet vendors, and one popped up and I grabbed it quickly.

I have a 29" inseam. It was worth the trouble.

Give yourself a month to get used to it. When I first got it, it felt a bit like riding a child's bike, and I thought I lost some torque climbing hills.

The maximum torque difference is about 5%.

My trail bike came with 165mm, and I think I like it, but it's obviously a very different kind of riding. When I researched this, the consensus was that the difference in torque is negligible, but the difference in knee/leg comfort enables a higher cadence. Going from 170mm to 165mm is less than 3% reduction in torque.

The FC-RX600-10 is shown as compatible with the same chains as the FC-4700 that is on my sons bike that is being used with a 11 speed chain and 11 speed rear.

What is your old chainset? The FC-RX600-11 and -10 share the same chain line of 47mm. However the FC-RX600-1 which is also 11 speed rear has a chainline of 49.7mm.

If your bike is a 11 speed road bike, then it's chain line is probably 43.5

FYI, I've got a 34.5" (87.6 cm) inseam and I've been riding 165 mm cranks for a long time. They do seem to help with maintaining a higher cadence and less range of knee motion so I can be more comfortable when low and in the drops.

As best I can measure it, assuming I didn't get my math wrong, the chainline is 49.10mm. Weirdly, the cassette is a Shimano 105 CS-HG700-11. The bike is a 2022 Trek Checkpoint SL 5.

Chainset = crankset. For some reason I thought I was talking to someone from the UK.

So I was asking what your current crankset is.

Oh. All my guesses were wrong It's a GRX FC-RX600 170mm 11S 46-30 NF.

There are two version of the 11 speed GRX FC-RX600. One is the FC-RX600-11 and the other is the FC-RX600-1. They have different chain lines. I'm betting you have the FC-RX600-11.

However to know for certain will require you to look for and read the part number stamped around the hole for the pedal on the inside of the crank arm.

Never mind, my blunder. The FC-RX600-1 is only a 1x crank. Duh.

Shimano FC-RX600 MALAYSIA VIA 170 TJ

You should be good. But if it was just a mistake in ordering and they have the 11 speed version, why not send it back and get the correct stuff?

Though like I said my son uses a 10 speed Tiagra 4700 crank on a 11 speed bike with 11 speed chain. And the FC-4700 is shown as compatible with the same chains as the FC-RX600-10.

So it's just a matter of do you want to try it or do you want to be certain. If you want to be certain, then send it back.

Yeah, I do want it to be right. If it ever misbehaves, I'll always have that doubt. It was my mistake in ordering. The retailer doesn't have the correct one in stock, but it's in stock elsewhere. I'm ordering it now. I'll figure out what to do with the wrong one later.

It's probably going to explode and kill you. Or nah...

It's not going to skate (it has pins)

The teeth will fit the chain just fine (the teeth are like .079 in / 2mm wide and have been since the 1970's, 9-12 speed chains have the same internal width of .086 in)

The difference is in the chain ring spacing. The 11-speed cassettes are wider and they go outboard a little more with the 135mm hubs for disc brakes, so Shimano changed the spacing a little to make sure the chain didn't rub on the 50 ring when you were in 34-11. Leonard Zinn went over this ad nauseum in his Velonews column at the time. On a gravel bike with smaller rings and longer chain stays and the wider chain line baked in from the start, it just shouldn't be a problem at all.

Are you able to check to see if what you received is what you actually ordered? Your cassette isn't the potential problem, the potential problem is if the space between the chainrings on the 10 speed version is wider than the space between chainrings on the 11 speed version. It is possible that there is no difference worth worrying about. E.G. I am using Campagnolo 11 speed Ultratorque cranks with my otherwise 10 speed cassette, shifters, and derailleurs. Campagnolo only produced Ultratorque 10 speed cranks for a very short period of time, about 1 year, so when I finally decided to swallow my pride and move to a compact crank to be able to do big climbs, it was too late to buy a 10 speed Ultratorque crank. However, after 4 years, my 10 speed drivetrain is happily and smoothly shifting on those 11 speed cranks. I suspect that your case will be similar, but before installing anything, check your order to see if the mistake was made by the vendor and not you

^ Much more informed than my answer.

Maybe, maybe not. To allow 11 speed cassettes on what were previously 10 speed free hubs, Shimano did nothing to change the position of the smallest cog. Rather, they changed the design of the inboard side of the cassette so that the biggest cog cantilevers over the inside of the free hub. Cog spacing isn't changed. This redesign only works for cassettes with large cogs with 34 or more teeth
Shimano couldn't do the same thing for road wheels of any kind because most road riders wanted much tighter gearing and hence smaller big cogs, so they had to redesign their wheels and hubs for road bikes

Well, if I were the OP, I would try it and see if it worked.

If not, order the 11-speed version, which is $150.

Then sell the other one or give it to the local bike co-op. (Or, be an idiot like me and keep the unused one in the garage.)

OK, but what if the OP actually ordered the actual crank that they needed and wasn't sent that item?. I am advocating for the OP

I really did order the wrong one. The retailer's web site clearly labeled it "(2 x 10 Speed)", and I assumed it was a meaningless designation on the retailer's part, so I ordered it. It wasn't until the product arrived that I saw Shimano's very clear labeling, which tipped me off that maybe it mattered. I should have done my research more carefully. (Shimano's web site is not exactly helpful in this regard, with its ambiguous part numbering and its useless organization.) I may contact the retailer, but I would expect to eat some shipping and pay a restocking fee. Or I might do as was suggested and donate it to the local bike rehab ministry.

Did I get it backward? Ah, well.

Even though a 10 speed crank would work just fine with an 11 speed cassette?

OMFG, now I have two of the wrong ones.

False alarm. It turned out to be mislabeling on Shimano's part. On a call with the retailer, we worked out that the barcoded number on the side was correct, and so we opened it up and verified the number printed on the chainring, which is also correct.

So you actually have two proper cranksets?

No. I have one 2x10 and one 2x11.