Advice on Bottom Bracket Size for a Trek 1000 Road bike.



Ray1966

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Jun 2, 2011
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I have a Trek 1000 Road Bike with a Bontrager Triple front chain ring. The bike is a 2008 or 2009 model I believe. It's an 8 speed drive train. I'm going to change my Triple to a Compact double. My current BB is square tapered, the new crank uses ISIS. My question is on the size of the bottom bracket. The ISIS BB has 3 sizes 68 X108 / 68 X 113 / 68 X 118 : I'm not sure of the size I would need since my current Bottom Bracket is sized for a triple crank. I'm thinking the 108 or 113 Does any one have any suggestions? Thanks
 

alienator

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Jun 10, 2004
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Ray1966 said:
I have a Trek 1000 Road Bike with a Bontrager Triple front chain ring. The bike is a 2008 or 2009 model I believe. It's an 8 speed drive train. I'm going to change my Triple to a Compact double. My current BB is square tapered, the new crank uses ISIS. My question is on the size of the bottom bracket. The ISIS BB has 3 sizes 68 X108 / 68 X 113 / 68 X 118 : I'm not sure of the size I would need since my current Bottom Bracket is sized for a triple crank. I'm thinking the 108 or 113 Does any one have any suggestions? Thanks
68 x 108 is what you want. Note that you should do some surfing on Google (or your search engine of choice) on ways to maximize the life of your ISIS BB. ISIS was known for having a relatively short lifespan when compared to square taper BB's, Octolink BB's,......... The ISIS weakness is it's small bearings. With that said, many people have got a lot of miles out of ISIS. One thing you can do is have your BB shell checked to see if it is properly faced (i.e. the outside face of the shell on one side is parallel to the face on the other side). It doesn't cost much at all to have your BB faced, and proper facing has extended the life of many BB's. Likewise improper facing has killed a lot of BB's.
 

alfeng

Well-Known Member
Jul 23, 2005
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Originally Posted by Ray1966 .

I have a Trek 1000 Road Bike with a Bontrager Triple front chain ring. The bike is a 2008 or 2009 model I believe. It's an 8 speed drive train. I'm going to change my Triple to a Compact double. My current BB is square tapered, the new crank uses ISIS. My question is on the size of the bottom bracket. The ISIS BB has 3 sizes 68 X108 / 68 X 113 / 68 X 118 : I'm not sure of the size I would need since my current Bottom Bracket is sized for a triple crank. I'm thinking the 108 or 113 Does any one have any suggestions? Thanks
FWIW. If you have not bought your replacement crankset, yet, then you may want to consider choosing either an FSA MegaExo or Shimano Hollowtech II crankset instead of a crankset which uses an ISIS Bottom Bracket BECAUSE future BB replacements (bearings don't last forever) will be much easier to find ...

  • MegaExo & Hollowtech II are interchangeable, so you can use an FSA MegaExo crankset with a set of Hollowtech II BB cups, and vice versa ...
  • there ARE other crank-and-BB options
BUT, unless your crank has hard-tor-remove-riveted steel chainrings, another (¿temporary?) option would be to simply remove the Granny chainring & adjust the front derailleur's stops ...

If your current chainrings are held in place with chainring bolts & the current middle chainring is a 42t, then replacing it with a 38t-or-39t chainring may be a less expensive option which you may want to consider ...

  • 38t chainrings are less common and will probably cost more than the least expensive 39t 130BCD chainrings which are available
  • the least expensive 39t chainring will function as well as the most expensive 39t chainring, BTW, so check eBay for "replacement" chainrings
 

Ray1966

Member
Jun 2, 2011
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Hey Thanks guys for the help.

I think I'm going to dump the ISIS and go with a Compact Crank that already comes with a External bearing bottom bracket in one package. I found one on eBay for under hundred with free shipping. Changing out the Front and rear DER as well. I already have those ready to go. Just trying to get everything together so when I start it I can get it all done the same day.

The crank I found is: FSA GOSSAMER EXO Compact Road Bike Crankset and bottom bracket 50/34 170.0 MM

Thanks for taking the time to post, and the info on the ISIS Bottom bracket size. I may need that info in the future. So basically, a compact double on a road bike will use the size 108 in a cartridge style Bottom Bracket ?

My Cannondale has 170MM crank arms and they feel good to me because I'm not that tall:)


Ride safe

The G Man
 

alfeng

Well-Known Member
Jul 23, 2005
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Originally Posted by Ray1966 .

I think I'm going to dump the ISIS and go with a Compact Crank that already comes with a External bearing bottom bracket in one package. I found one on eBay for under hundred with free shipping. Changing out the Front and rear DER as well. I already have those ready to go.
FWIW. I guess this may be after the fact, but although many people use the front-and-rear derailleurs which are typically used with a normal Road crankset when they set up a bike with a "compact" crankset, 'I' prefer to use a long cage rear derailleur with a "compact" crankset + the front derailleur typically used for a Triple crankset with a "compact" crankset.