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Bottom Bracket Conversion Compatibility

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Bottom Bracket Conversion Compatibility

Old 08-02-14, 06:37 PM
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Steelcity80
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Bottom Bracket Conversion Compatibility

I have a 2014 Scott Sub 30, the bottom bracket is currently a Shimano BB UN26/ 68mm-122. It is a square tapered spindle. I am not happy with its performance and I am having trouble looking for a BB and Crankset to upgrade. Does anyone have an idea on what possibilities i have on compatibility and upgrade. Thank you, any insight is welcomed.
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Old 08-02-14, 07:19 PM
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check shimano's deore 590 crankset it comes with outboard bearings and shims for the bb length.
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Old 08-02-14, 07:27 PM
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Thank you i will check them out.
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Old 08-02-14, 08:26 PM
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In what way is your current BB or crankset lacking in performance? What would you like in an 'upgrade'?
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Old 08-02-14, 10:14 PM
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I had a square taper Acera crank on my bike and just changed it to a Deore LX hollow crank. It has outboard bearings and spacers to make it fit. It works great!
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Old 08-03-14, 06:01 AM
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the 9 speed 590 crankset is on sale now, the same place i purchased mine, delivery from the uk to usa was no problem. installation requires a special tool.
Shimano Deore M590 9 Speed Triple Chainset | Chain Reaction Cycles
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Old 08-03-14, 07:33 AM
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Well besides the creaking noise it just doesnt seem to be durable enough for the riding i do. I was also looking to get a lighter material.
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Old 08-03-14, 09:51 AM
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Originally Posted by simplybao View Post
I had a square taper Acera crank on my bike and just changed it to a Deore LX hollow crank. It has outboard bearings and spacers to make it fit. It works great!
Was there anything wrong with the Acera crank and what did you end up doing with it?
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Old 08-03-14, 10:59 AM
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Originally Posted by ColonelSanders View Post
Was there anything wrong with the Acera crank and what did you end up doing with it?
Nothing wrong with it. It had about 200 miles on it and I wanted something lighter and I wanted to try 175 mm arms instead of the stock 170. The new crank is a little over .5 LBS lighter. I was on a quest to shed weight. My bike started just a hair over 27 LBS and now it's 23.5.

Oh and I got the new crank for only $75 on eBay shipped so it was a low cost "upgrade". I can't tell if the new length affect anything because I modded just about everything at once. My bike now feels livelier and quicker than it was stock. And it fits me better now.
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Old 08-03-14, 02:30 PM
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Originally Posted by Steelcity80 View Post
Well besides the creaking noise it just doesnt seem to be durable enough for the riding i do. I was also looking to get a lighter material.
The creak may simply be movement at the interfaces of the BB threads or crank arms, and nothing reflecting the failure of a part. Any style of BB can originate noise, and it's not uncommon to remove and reinstall it to fix it. But an external bearing BB system (e.g., Shimano HollowtechII) is particularly simple to service in comparison to square taper. The bearings in an upgraded cartridge ST BB can be very durable and less susceptible to contamination than external cup bearings, and there are some other advantages of ST BBs that don't necessarily apply across the board. But external bearing crank systems get the nod for being [generally] simple to service, light in weight, and for having the greatest "stiffness." Most people would consider the move to Hollowtech a solid upgrade.
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Old 08-03-14, 06:49 PM
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Thanks for your input. as far as the external cup bearings go how would that affect the size of the bb. example i have a 68mm would that make it a 73mm? also would it change the spindle length?
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Old 08-03-14, 08:32 PM
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Originally Posted by Steelcity80 View Post
Thanks for your input. as far as the external cup bearings go how would that affect the size of the bb. example i have a 68mm would that make it a 73mm? also would it change the spindle length?
I don't know the answer to that question. I didn't measure it. If you get a Shimano crank, the instructions will tell you where to put the spacers (if needed) but I'm not sure what the final measurement will be. On mine, I didn't follow it exactly. The instructions said to put the A and B spacer on the drive side and the C spacer on the other side. With that configuration, the drive line was off slighlty and so I put the A (the biggest one) on the drive side and put C and B on the non-drive side. Go have a look at Sheldon Brown website for more info: Sheldon Brown's Bottom Bracket Size Database
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Old 08-03-14, 08:39 PM
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Originally Posted by Steelcity80 View Post
Thanks for your input. as far as the external cup bearings go how would that affect the size of the bb. example i have a 68mm would that make it a 73mm? also would it change the spindle length?
Cranksets that utilize external BB bearings are 2pc designs. The spindle is pressed into the back of the driveside crank arm; there is no separate spindle to worry about. On a 2pc road crank (e.g., Shimano Ultegra 6700), the spindle is just long enough to accommodate either English (68mm) or Italian (70) road frames. On a 2pc mountain crank (e.g., Deore), the spindle is wide enough for 73mm BB shells, since this is the modern standard for MTB frames. If you're installing a Deore Hollowtech crankset onto a 68mm BB shell, you install the additional spacers that are included with the crankset; these slip right onto the spindle between each crank arm and each bearing. So rather than installing just one 2.5mm spacer under the non-driveside crank arm, you would install two 2.5mm spacers under the non-driveside arm and another 2.5 spacer under the driveside arm.

Mountain bike cranksets typically mean you have a wider "Q-factor" than on road cranks. This is where some people see an advantage with square taper cranks, since you are free to use a narrower spindle to get a narrower q-factor. That option isn't available when the spindle is pressed into the right crank arm. The difference isn't especially great and shouldn't be annoying unless you're particularly sensitive. There's also the chance that the q-factor of a Deore wouldn't be any greater than the Acera you currently have.
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