Crankarms awfully close to FD...

tepextate · #1 02-21-2021, 05:56 PM

I was looking for a power meter for my new gravel bike and decided on one of Power2Max's new "gravel" power meters.

It's advertised as maintaining GRX spacing (so the 47mm chain line), but a road Q factor. I liked the idea of the road Q factor, particularly for this bike which I'm going to be riding on a mix of tarmac and gravel.

I got the power meter and set it up, but now I'm realizing that the road Q factor causes the crank arms to get awfully close to the GRX FD (which matches the chainline of the crankset). I'm having trouble getting a 0.05 inch (1.27mm) hex key through, so I'm guessing it's around 1mm of clearance, if that (see photo below).

Do y'all think this will be an issue, or should I pedal away? The crankarms don't feel like they flex that much, but I'm not sure if I should be concerned about the crankset developing play over time and causing the crank arms to start hitting the FD.

Anybody seen this before?

BobbyJones · #2 02-21-2021, 06:02 PM

Personally, that's a little too close for comfort in my eyes.

However, your line "It's advertised as maintaining GRX spacing" makes me think they may know something that's not obvious.

If it were me, I'd get in touch with them and see what the official word is.

Spaghetti Legs · #3 02-21-2021, 06:03 PM

I have had bikes where that is an issue, but nothing modern like that. I’ll try to adjust the FD stops to bring in some if it doesn’t affect shifting. If it does and it’s not physically touching the crank, I don’t worry about it. One bike I have, with friction front shifting, will “tick, tick” on the crank, so that reminds me to feather it in a little!

tepextate · #4 02-21-2021, 06:06 PM

Thanks, guys. That's what I was worried about. The chain is already rubbing slightly on the FD in the smallest cog, so I don't think bringing the FD in is going to be a viable option.

I'll reach out to Power2Max and see what they say!

Blown Reek · #5 02-21-2021, 06:14 PM

Start from scratch setting the limit screws. Also, it sure seems that there's a bunch of space between the inner cage and the chain- you could probably move it in quite a bit. If that's your "overthrow" position, you could still back it in a bit. However, if that's the position of the front derailleur while it's in the big ring, it's way too far out.

Edit: from what I see. If that sideways black "v" thing is making contact and not the silver part of the cage, never mind.

SlowPokePete · #6 02-21-2021, 06:19 PM

My Shimano Ultegra (8000/8020) was like this before I switched to the Absolutel Black ovals which brought both chainrings in a couple mm's.

I didn't like it, but never had it cause a problem.

SPP

pbarry · #7 02-21-2021, 07:17 PM

Not to mess with your shifting, but, can the tail of the FD be rotated a couple of degrees outward? Looks like it’s currently a little inboard. That would get the front of the FD further away from the crank. Along with adjusting the limit screw, you might gain 1-2mm.

tepextate · #8 02-21-2021, 08:40 PM

Quote:

Originally Posted by Blown Reek

Start from scratch setting the limit screws. Also, it sure seems that there's a bunch of space between the inner cage and the chain- you could probably move it in quite a bit. If that's your "overthrow" position, you could still back it in a bit. However, if that's the position of the front derailleur while it's in the big ring, it's way too far out.

Edit: from what I see. If that sideways black "v" thing is making contact and not the silver part of the cage, never mind.

Yeah, that's exactly right - it's the sideways black "v" thing that's making contact in the big chainring / small cog combo.

@ pbarry, let me play around with it a little bit to see if I can move it inboard at all! Thanks for your feedback.

zzy · #9 02-21-2021, 08:49 PM

Your FD is not correctly set - in the big/small it should be as close as you can get it without rubbing on the outside of the chain. Check cage alignment. This is a thing for the long armed Shimano FDs but you can always make it work.

joevers · #10 02-21-2021, 08:54 PM

Derailleur looks a little high from this view also, mind if we get a shot of it from the side? These derailleurs are quite hard to set up and you're not working with a lot of clearance if you've got grx spacing and a narrow q factor so you've got to be super precise.

I'm thinking if you lower it you'll be able to get the front derailleur more inboard without it rubbing. I think it's too outboard now. I'm usually fine with very little clearance there but how you've got it right now is just too close for me. It will scrape up the inside of the crank.

tepextate · #11 02-21-2021, 10:33 PM

Quote:

Originally Posted by zzy

Your FD is not correctly set - in the big/small it should be as close as you can get it without rubbing on the outside of the chain. Check cage alignment. This is a thing for the long armed Shimano FDs but you can always make it work.

Can you clarify what you mean? The way I have it set up it's basically rubbing in the big/small combo (see where the arrow is pointing below):

Thanks!

tepextate · #12 02-21-2021, 10:37 PM

Quote:

Originally Posted by joevers

Derailleur looks a little high from this view also, mind if we get a shot of it from the side? These derailleurs are quite hard to set up and you're not working with a lot of clearance if you've got grx spacing and a narrow q factor so you've got to be super precise.

I'm thinking if you lower it you'll be able to get the front derailleur more inboard without it rubbing. I think it's too outboard now. I'm usually fine with very little clearance there but how you've got it right now is just too close for me. It will scrape up the inside of the crank.

Hey joevers - thank you!

I've been playing around with it this evening (following the Shimano manual and this Youtube video, but the results aren't better (in fact, a bit worse!).

Here's what it looks like from the side currently. I can just barely fit a 2mm hex key under the highest tooth. The manual says 1-3mm. Do you think it would help if I lowered the FD by 1mm or so?

jimoots · #13 02-22-2021, 04:57 AM

Looks like the FD needs to be rotated (tail away from frame). Height looks acceptable.

I’d get that rotation right and then set it up from scratch, you’ll find the shift is better and will correct any issues with chain strike.

madsciencenow · #14 02-22-2021, 06:33 AM

I had exactly the same issue and ended up selling the PM. One thing you can do is take off the drive side crank arm and insert a shim or two between the rings and the arm. The issue there is you will probably need to shim your non-drive side pedal out to match.

One other thing to check is the chain line which I presume you’ve done but thought I’d mention.

I’m now trying to decide if I should have 4iii do a factory install on my drive side grx crank or just go hog wild and get a pair of the SRM pedals when they are available.

Sent from my iPhone using Tapatalk

R3awak3n · #15 02-22-2021, 06:37 AM

height looks good but maybe do rotate it a bit, its hard to see from pictures.

I think it will be fine and it will not rub and be a huge problem but you could always move a few spacers around on the crank, not sure what system you have but looks like you have a few spacers on the BB, you could try to remove the bigger spacer and get smaller spacers there to let you at least take 1mm off that spacer and move it to the other side. It looks like a BB386 and you have to play with the spacers on those to get optimal chainline.