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Replace MTB BB and crankset

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Replace MTB BB and crankset

Old 12-11-17, 11:06 AM
  #1  
mjtull
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Replace MTB BB and crankset

I have an older (2001) MTB with squared tapered BB that needs replacing. The current crankset is a Truvativ Trushift FiveD, 22/32/42
175mm crank
Centerline Measurement 48.5mm
8 x cassette

I use the bike for more road use than mountain bike riding, never use 22T chainring.
Several chainring teeth are worn. Have replacement cassette and chain already.

Is it feasible to replace current crankset with a road bike crankset?
Example: Shimano Claris 2400 3x8 crankset, Shimano Octalink V2 bottom bracket.

What issues do I need to consider (centerline measurement, etc) ?
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Old 12-11-17, 12:48 PM
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It’s very common on cranksets to make a few teeth lower by design. The ”gaps” are called shift gates, and makes it easier for the chain to move from one ring to another.
Are you sure what you’re seeing is actually wear, and not shift gates?
A full road bike crankset might not clear your chainstay.
And your front derailer might not play nice with a 50T ring.
42/11 on 26” wheels will take an average skilled rider to +25 mph.
If you spend a lot of time faster than that, you deserve a road bike.
If it was me, I’d look for a replacement square taper crank with maybe 44-46T and call it a day.
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Old 12-11-17, 12:51 PM
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road cranksets are engineered for the narrower frames use on the road. This will make correctly setting one up on your MTB very difficult, if not impossible.

there are older MTB triples for MTB use... Co-op bike shops keep a wide range of cranksets around....

sorry, but i can't say for sure which setup will fit your bike. Look for an older shimano deore lx or altus triple in the ratios you want, possibly...

another route would be re-ringing your present crank with ratios more suited to your use of the bike... 48-38-26, or something similar.... VUELTA sells a wide selection of rings in many BCD patterns...
your present crank set is a 104 BCD four... changeable rings, right?

Last edited by maddog34; 12-11-17 at 12:58 PM.
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Old 12-11-17, 01:04 PM
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https://www.ebay.com/itm/NOS-Shimano...gAAOSwySlaJhPZ

https://www.ebay.com/itm/Shimano-FC-...0AAOSwcdRY9kAr

https://www.ebay.com/itm/Shimano-SG-...gAAOSwz~paHWRe

and you'll need to swap on a larger radius, older MTB front derailleur
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Old 12-11-17, 03:17 PM
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After some more measuring and reading and then more reading, I've come to the same conclusions as maddog34 and dabac. The clearance between chainrings and frame won't allow larger diameters and I'd like to not have to replace the derailleur and all the troubles that can lead to. I think I'll go for a one-for-one replacement - maybe a better one with a good bottom bracket.
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Old 12-11-17, 03:22 PM
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Yeah, the BB bearings are shot, I was grinding metal on the last 3 miles. I must have 3000-4000 miles on it. I appreciate your advice. thanks
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Old 12-11-17, 07:26 PM
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It looks like the SRAM S600 8-Speed 3.0 Powerspline Crankset & Truvativ Power Spline Bottom Bracket are the way to go. Please comment if you disagree. thanks
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Old 12-12-17, 09:24 AM
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Originally Posted by mjtull View Post
It looks like the SRAM S600 8-Speed 3.0 Powerspline Crankset & Truvativ Power Spline Bottom Bracket are the way to go. Please comment if you disagree. thanks



Noooo! Don't back yourself into a single source item when that's also a wear item. And if you do decide to buy this mistake (my opinion) please keep the arm retaining bolts tight. We see too many Powersplines with augered out arms. Ever tried to find a replacement LH Powerspline crank arm? Andy
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Old 12-12-17, 11:44 AM
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Help me understand - are you saying square tapered is the better way to go? Just to be clear, my BB is completely shot and my 42T & 32T chainrings are very worn (as is my chain and cassette which I have already purchased but not installed). thanks
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Old 12-12-17, 05:05 PM
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this is a Shimano Deore Hollowtech II crankset... highly advised!
https://www.ebay.com/itm/SHIMANO-DEO...QAAOSw5adZpvFd

and i still think you could just re-ring your present crankset, but wth, it's xmas... get the deore.

the advantages of the shimano part is that BB's are EVERYWHERE, they have a nearly bullet-proof reputation, the rings don't wear as fast as other brands, and the BB bearings tend to last twice as long as other similar designs from other companies... Ya... BETTER.

the disadvantage of ANY "external bearing" hub? the cartridge type bearings are not rebuildable or regreaseable so you just buy a new BB assembly when the bearings get rough... 17 to 25 dollars, depending on where you buy them.... meh.

Last edited by maddog34; 12-12-17 at 05:24 PM.
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Old 12-12-17, 05:41 PM
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Please excuse if this is a stupid question but will the Deore 10-speed crankset require a 10-speed cassette and chain? Would you expect my hub can accept the 10speed cassette? thanks
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Old 12-12-17, 05:51 PM
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8-9-10 speed freehubs are the same... 7 speed is shorter, 11 speed is longer.

the SHIFTERS will of course, be different from 8 to 10 sp.... the derailleurs are the same, from 8 to 10 sp., since the cassettes are the same width.... and most 7 sp. ders. will work on 8-9-10 sp..... Shifters are specific to their designed gear counts..... just for knowledge-sake.
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Old 12-12-17, 05:54 PM
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just for knowledge... 7 sp. freehub is 132 mm... 8-9-10 is 35mm, and i've never measured an 11 sp. freehub, so you'll have to find that spec. yourself, eh?

measured from outer edge to the shoulder/step on the splines..... shimano compatible types... i don't see much, if any, campy hubs in my shop... mostly mtb and bmx riders out this way...
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Old 12-12-17, 07:26 PM
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So if I understand correctly, I could go with the Deore crankset, and use my new SRAM PG850 8x cassette and PC850 chain. Is there any advantage of going with a Shimano 8x cassette and Shimano chain?
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Old 12-14-17, 10:09 AM
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Originally Posted by mjtull View Post
So if I understand correctly, I could go with the Deore crankset, and use my new SRAM PG850 8x cassette and PC850 chain. Is there any advantage of going with a Shimano 8x cassette and Shimano chain?
None IMHO.
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Old 12-17-17, 09:25 AM
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Make sure you get the crank arm length you want, 175mm is prob the most common MTB.
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Old 12-17-17, 11:50 AM
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replace BB and chainrings, for larger tooth count, keep the crank arms, so that they still clear the chainstays..
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Old 12-17-17, 03:57 PM
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Truvativ Trushift Chainring | Jenson USA

A brand new crankset and BB are pretty cool but spendy. You could always use the link above to replace badly worn chain rings and replace your worn BB with the same style. Probably would cost 1/3 as much as new tech.
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Old 12-18-17, 07:13 AM
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mjtull
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I started off thinking the same, and after looking at the options (and learning a bit more), I believe you're right. thanks for your advice
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