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Crank replacement question

Old 04-18-20, 07:15 PM
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Rocket5150
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Crank replacement question

Hey all. So I have a ://archive.harobikes.com/mtb/2016-mtb/aeras-2016

I am hearing differing opinions on if Shimano R7000's cranks would be able to be installed. I was told "no" because my stock bottom bracket is sealed and also the cranks are 11 speed, vs my stock are 7 speed.

Then I hit the local bike shop and dude say that they could install it easily. I was also told that I did NOT have to change out my rear derailer or rear cassettes. Is this correct I wont have to change derailers or back cassettes?

Then another bike shop tech told me contrary things from what I just stated. I frustrated and tired of hearing differing opinions. All I want is to order some R7000 cranks, arrive, and install without hassle. Does anyone have the correct answer and why? Swapping out cranks on my fixie was a breeze, why is this so hard to get on the correct page. Help
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Old 04-18-20, 07:45 PM
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You have a BB-UN26 square taper bottom bracket and a generic mountain triple crankset.

The R7000 crankset is a road crankset.

Road cranksets are designed around a 68mm bottom bracket shell.

Mountain cranksets are designed around a 73mm bottom bracket shell.

I mention the above because that may be where the confusion lies.

To use a 73mm hollowtech crankset in a 68mm bottom bracket it'll take some spacers & you are in business.

You can not go the other way though, putting a road hollowtech crankset in a 73mm designed bottom bracket shell. The spindle is not long enough.

Fortunately for you, all I see listed for BB-UN26 is 68mm shell width. Meaning the OEM put a mountain triple on a road square taper bottom bracket. Further meaning the 68mm Shimano 105 road crankset you want will fit the bike frame assuming you use the SM-BBR60 road bottom bracket (probably included with the crankset.)

Any interferance issues with crank arms or chain rings hitting the chainstays not withstanding you'll need to adjust the derailleur up a little bit to clear the larger rings & set the limit screw on the front derailleur to prevent shifting to the now non-existant 3rd (big) chainring. This may mean a new shift cable...~$5

Having said all that...Change your chain. The small/small combination is a lot bigger and your chain is will now be too short.

Easy job. Make sure you grease all the threads and the ParkTool BBT-9 will save you huge money over a bike shop that at this point doesn't sound like they even understand the basics.

Last edited by base2; 04-18-20 at 08:03 PM.
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Old 04-18-20, 07:59 PM
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Additional. Since you have a 7 speed cassette, it seems obvious you'd need a 7 speed chain. 7 & 8 speed chains are essentially interchangeable.

The 11 speed crankset, obviously would like to see an 11 speed chain. But 10 & 11 speed chains & chain rings at the crankset are more or less interchangeable.

If it were me, I'd split the difference & run a 9 speed chain. It'll be a touch wide at the crankset & may make a bit of a rubbing noise when cross-chained, but ought to work well enough. And so far as I know, it will work well enough at the cassette to not be an issue.

Your rear derailleur will not care what chain you run.
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My lights are obscenly bright because drivers are dim.

I shouldn't have to "make myself more visible;" Drivers should just stop running people over.
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Old 04-19-20, 12:34 PM
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Hey thanks for the clear info and also telling me what to expect in swapping parts beyond that. Best real facts I've heard in weeks not just "um"s and "i think" I found a site with new R7000 but BB not included but available at the same site for 12 bucks. Will I need to purchae a BB-UN26 as well? Sorry to pick ur brain but can I use my current trigger shift changers ?or a new ones required (which).

Biggest question probably is do you think this will be a worth while upgrade with better cranks, OR down grade since I get more gears total w/ stock(and leave as-is)? I almost always be in 2nd and 4-5 cruising and in 3/4 trying for top speed in flats. Thanks in advance, I appreciate your knowledge.
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Old 04-19-20, 06:26 PM
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Before you do anything, measure the bottom bracket shell width. It should be either 68mm or 73mm. You can only swap if it is 68mm.

The R7000 has an intigrated spindle that goes through the BBR60 bearings. $12 is a good price. They usually go for ~$20.

You do not need another BB-UN26 it is a different technology.

Upgrade/downgrade, it's not really either. It's just different, depending on what you are trying to accomplish.

For a lot of uses a 3x7 drivetrain is actually preferred because of the total range (~500% or more) of gears...able to carry heavy loads up steep grades, and still have reasonable speed on flats. Long life from beefy overbuilt components & multiple combinations to get the same ratios tends to make them wear well. You do not have 21 speeds. You have 21 combinations. Really, because of duplicates, you have 12-15 speeds or so depending on exactly what components you have. They do have a more complicated shift pattern to be fully utilized to it's full potential. Most people don't go utilize it's full potential. Hence the popularity of 2x systems.

2x7, has 14 total combinations, but fewer duplicates. Maybe your smallest ratios won't be as small, & your total range may not be as great at around 360-380% (because your smallest chainring is bigger) but your shifting will be simpler and you won't be carrying around a bunch of gears you are not using anyway.

I'm assuming you never use your granny ring & you frequently find yourself spun out in top gear. If this is the case, then yes, changing the crankset would be an upgrade in your case.

Your trigger shifter just operates the derailleur. The derailleur just moves x distance per click. The distance between rings is pretty universal. So set the 1 on the shifter to the smallest ring, & 2 will automatically be in the right place for the big ring. You'll never get a click into 3 at the shifter. The limit screw on the derailleur will prevent it from travelling far enough.
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My lights are obscenly bright because drivers are dim.

I shouldn't have to "make myself more visible;" Drivers should just stop running people over.
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Old 04-22-20, 06:36 PM
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Thanks for the information! You helped me out bigtime. I think I will move forward with the crankset now.
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Old 06-05-20, 03:25 AM
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Originally Posted by Rocket5150 View Post
Thanks for the information! You helped me out bigtime. I think I will move forward with the crankset now.
I'm curious, how did everything work out? No interference issues with the crank arms hitting the chain stays? How's the gearing working?
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My lights are obscenly bright because drivers are dim.

I shouldn't have to "make myself more visible;" Drivers should just stop running people over.
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Old 08-12-20, 03:29 PM
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I'll post soon and give you feedback. Been working like a mofo and it's hard to get outside and ride when most my energy is sapped and another 12 hour shift awaits six days a week.
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Old 08-13-20, 01:43 PM
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N+1 time So much is required to go from 80's 7 speeds to your latest 11 speed. just buy a new bike..
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