I broke a crank arm today on the trainer. I don’t currently have a powermeter on the bike and am thinking of just getting crank arms with power. I don’t trust the LBS to give me good advice or speedy part ordering so want to make a good decision on a part and then just take it in for them to install.
I have a few questions though. I am looking at this power meter:
Do I only need the crank arms? How do I know that it is compatible with my chain rings? There is a dropdown menu for BCD at 110 or 130 - what is BCD - do I need this?
I guess I could just replace the crank arms, but figure if I’m going to replace this part, it might be a good time to add a powermeter to my bike.
I don’t know anything about the new DUB cranksets and I believe its a whole different bottom bracket setup, but Ill leave that to others who know more about that then me. For your other questions:
You’ll only need to know the BCD if you just want to just replace the crank arms only and use your current chainrings. BCD (bolt circle diameter) is the measurement of the circle through the center of the chainring bolts. For the 5 bolt shimano cranksets, 130 BCD is normally the size for standard cranksets 53/39 and bigger while 110 BCD for mid-compact cranksets 52/36 and smaller. Also in your case, I think it could be a it hard to find new 5 bolt crank arms as shimano has moved to a 4 bolt pattern.
If you’re planning on going to a powermeter and buying a whole crankset you’ll just have to match your current crank arm length, chainring size and bottom bracket as long as you just want to match your current set up and not change anything.
Im sure others will offer more information as well.
I don’t know anything about the new DUB cranksets and I believe its a whole different bottom bracket setup
I’m sure you are right. It’s a different spindle diameter so you need the bottom bracket to match. But if you are buying a power crank then a new bottom bracket is a small part of the overall cost. They are consumable parts so need replacing eventually anyway. Just make sure there is a DUB bottom bracket to match what your frame needs.
After a little reading, the DUB bottom bracket uses a 28.99 spindle size. So in order to use it you as OddSlugg said, you’ll have to also get a new bottom bracket that corresponds and fits in your frame for that crankset.
There are lots of ways to can go for a power meter with the easiest being Shimano, since based on your pictures Im guessing you have a shimano 24mm BB, cranksets with stages power meters. They have both dual sided or just left sided power meters. https://www.racycles.com/…-8000-crankset-16002
Or if you want a Quarq as you posted above, you would have to look for one with a GXP crank like this.
Do you have a Shimano 10-speed drivetrain on that bike?
exactly what I was thinking. Looks like 6600 series
And, fwiw, all of these questions are what an LBS ‘should’ be for. Get the right thing, the right adaptor, the right spindle for your bike blah blah blah. If you need them to install it anyway best to get the right thing.
Can understand if you don’t trust them, if you have shops to choose from they will save you time.
Are you in Georgetown still (noting the Revolution sticker)
Do you have a Shimano 10-speed drivetrain on that bike?
exactly what I was thinking. Looks like 6600 series
And, fwiw, all of these questions are what an LBS ‘should’ be for. Get the right thing, the right adaptor, the right spindle for your bike blah blah blah. If you need them to install it anyway best to get the right thing.
Can understand if you don’t trust them, if you have shops to choose from they will save you time.
Are you in Georgetown still (noting the Revolution sticker)
Wow you don’t miss a thing! I bought the bike in Arlington about 13 years ago - I live in SC. It is a 10 speed drivetrain. I guess I could consult someone.
After a little reading, the DUB bottom bracket uses a 28.99 spindle size. So in order to use it you as OddSlugg said, you’ll have to also get a new bottom bracket that corresponds and fits in your frame for that crankset.
There are lots of ways to can go for a power meter with the easiest being Shimano, since based on your pictures Im guessing you have a shimano 24mm BB, cranksets with stages power meters. They have both dual sided or just left sided power meters. https://www.racycles.com/…-8000-crankset-16002
Or if you want a Quarq as you posted above, you would have to look for one with a GXP crank like this.
Well, if ST holds true, someone will tell you that whatever you replace it with should be shorter. With that in mind, drill and tap the remaining crank arm and you will have pleased the ST community.
Looking at the pictures you posted, particularly the second picture, I’d bet good money that your front derailleur is hitting the inside of the crank arm ever so slightly and scoring it a bit. It appears that the crank arm broke at exactly the same height as where the lower edge off the derailleur cage would hit it. I’ve seen this on a bunch of bikes and you don’t even know it’s doing it unless you look at the inside of the crank arm and see the mark from where it hits with each pedal revolution. Sometimes you don’t even see it hitting if you look a the bike in a work stand but when under load there can be just en9ugh flex in the frame for it to happen. Over time that “scoring†can become a weak point and in the right circumstances can cause the crank arm to fail under load. When you put a new crank on that bike take a close look at this. If the derailleur cage is angled out a bit at the bottom you may see it hitting very slightly. Check the crank arm periodically too see if a mark is showing up.
Looking at the pictures you posted, particularly the second picture, I’d bet good money that your front derailleur is hitting the inside of the crank arm ever so slightly and scoring it a bit. It appears that the crank arm broke at exactly the same height as where the lower edge off the derailleur cage would hit it. I’ve seen this on a bunch of bikes and you don’t even know it’s doing it unless you look at the inside of the crank arm and see the mark from where it hits with each pedal revolution. Sometimes you don’t even see it hitting if you look a the bike in a work stand but when under load there can be just en9ugh flex in the frame for it to happen. Over time that “scoring†can become a weak point and in the right circumstances can cause the crank arm to fail under load. When you put a new crank on that bike take a close look at this. If the derailleur cage is angled out a bit at the bottom you may see it hitting very slightly. Check the crank arm periodically too see if a mark is showing up.
Ok thanks for the insight - I’ll have to check this out on the new crank arm to make sure it’s not hitting.
