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I've got a Giant TCX SLR2 (2015) according to the spec sheet it has:-

Crankset: FSA Gossamer Pro Cross, 36/46

Bottom Bracket: FSA MegaExo

The other day I noticed the bottom bracket isn't sounding so great and needs replacing. Having read around I've seen a lot of issues with this BB so want to replace it with something better and possibly upgrade/change my crankset at the same time, possibly for a Shimano 105 HollowTech II 34/50.

The problem is I'm struggling to get my head around which bottom bracket I need. I think I understand the relationship between crank and bracket, it's which ones will fit my frame.

Any advice, suggestions or links to useful articles greatly appreciated.

To add to the confusion, the crank actually says 'For BBright BB386EVO'. Am I right in thinking this is not MegaExo as stated on the spec sheet?

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  • For the record, that's an external bearing BB, right?
    – Daniel R Hicks
    May 18, 2016 at 21:24
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    bikeradar.com/us/gear/article/… is a good starting point for reading.
    – Batman
    May 19, 2016 at 2:17
  • @Daniel R Hicks, not sure what you mean by "external". I know its a Press Fit. Need to get the crank off and see if I can find exactly what it is.
    – Nick Hall
    May 19, 2016 at 11:31
  • "External" means that the actual bearings are outside of the bottom bracket housing.
    – Daniel R Hicks
    May 19, 2016 at 11:34
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    i just went though the same exercise. In the end the LBS charge of $30 labour cheap compared to the time I wasted trying to figure the BB Standards Hell. I do not have tools tools to replace the press fit so that was another issue I avoided
    – mattnz
    May 19, 2016 at 21:21

2 Answers 2

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This frame either uses a BB386 Evo "standard" or a Pressfit 30 "standard". You can determine which by measuring the width of the frame at the BB shell. If 86.5mm it is BB386Evo. If 68mm it is Pressfit 30.

If it is a Pressfit 30(68mm shell) this BB is a direct fit for the Shimano crank without extra spacers. this is the PF30 version of the BB30 bottom bracket that @bikebum listed in his answer.

However, based on the markings on your existing crank, I believe it is BB386 Evo.

To add to the confusion, the crank actually says 'For BBright BB386EVO'

That means that it is a pressfit(non-threaded)frame, with a shell width of 86.5mm, and an outside bearing race(cup)diameter of 46mm. The inside diameter of that bearing cup is 30mm.

MegaExo is a brand of bottom bracket made by FSA, not a measurement standard.

Any Pressfit 30 BB kit, like the ones from SRAM or Wheels Manufacturing will fit the frame. Nothing else will fit.

To fit a crankset, you either need a BB386 Evo crank, as you have now (also known as the "long BB30"), or you need a spacer kit to adjust he diameter of your frame's required standard of 30mm to the crank you want to use.

Since the Shimano crankset is designed for an 86.5mm frame, you only need to adjust the ID of the bearing cup to 24mm Shimano standard.

A Wheels Manufacturing 24mm to BB386 Evo adaptor like this one does the trick.

FSA makes a good BB reference poster here.

enter image description here

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From what I can see the various "MegaExo" BB labels refer to the spindle size and crank fixing, rather than the size of the shell in your frame. There will be subtleties with frame clearance, but that's something for Giant rather than the BB or crankset people.

From that website I got this screenshot:

enter image description here

You will need a HollowTech II BB, or some that's compatible with that:

enter image description here

Someone on BikeForums thinks you could get it to fit if you're enthusiastic, while someone on RoadBikeReview says they're completely interchangeable.

Since you want a new BB anyway, it might be easier to just buy a new BB and crankset at the same time and buy matching ones. If you do want to test the match, in your position I'd be more inclined to buy a hollowtech BB and see if that works with the existing crankset. If it works you can delay buying a new crankset, if it doesn't you need to buy the crankset now. But you'd pay for two lots of shipping.

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    I can confirm that a shimano HollowTech II BB will work with FSA Gossamer Cranks that use the MegaExo BB, as I just did that swap few months ago on my commuter.
    – Rider_X
    May 19, 2016 at 3:34
  • @MÒŽ. Thank you I'll have a good read through the links. I think I will but the matching Crank and BB together. my real concern is whether the BB fitting the frame.
    – Nick Hall
    May 19, 2016 at 11:36
  • oh, also, it's Press Fit, if that makes any difference..
    – Nick Hall
    May 19, 2016 at 11:38
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    If it's press fit then a standard Shimano HT2 bb won't work as the frame itself won't have any threads to screw the BB into. If you've got a photo of the bike focusing on this area that would be the easiest way to clarify this.
    – Ryan Flaherty
    May 19, 2016 at 12:32
  • @NickHall - Weird every "MegaExo" branded BB I have seen have been threaded for a 24mm spindle axel. Yes, press-fit makes all the difference. You must have a BB30 crank then.
    – Rider_X
    May 19, 2016 at 18:25

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