Hollowtech II: chain line and Q-factor

Hollowtech II is a type of bicycle bottom bracket (BB) manufactured by Shimano. They are very easy to remove and replace, which meant it was also very easy to alter the chain line on my Ridgeback touring bike. It was simply a matter of fitting some spacers in different positions to those indicated in Shimano's instructions.

bb-before

Before: two spacers on the right and one on the left of the bottom bracket

Hollowtech II BBs have become very popular despite a traditional preference for the square taper type. Hollowtech has external bearings with smaller balls. They are sometimes alleged to be prone to premature failure due to the reduced ball size. I haven't experienced this, and I prefer the external bearings because they are further from the bike's centreline (more distance between the bearings – a good thing) and the circumference of the bearing surface is greater (must be a good thing too). True, you cannot maintain a Hollowtech BB – replacing the balls and greasing etc – but they are cheap, and easy to replace if they fail. Anyway, as mentioned, mine haven't failed so far after many thousands of miles.

My Ridgeback Panorama (fitted with Hollowtech II, although later models have apparently reverted to square taper) had two spacers – plastic rings – between the right-side bearing and the BB shell, and one on the left – pic above. This is how they should be, according to Shimano's tech docs, which also refer to four spacers: 0.7 mm, 1.8 mm, and 2.5 mm x 2. There are actually three: all 2.5 mm.

bb-during

Bottom bracket shell (68 mm) – crankset removed

I removed the crankset when upgrading from Deore to Deore XT, supplied with a Hollowtech II BB (I've used the old Hollowtech II BB on another bike to replace the square taper it came with). The only tools required are Allen key, a torque wrench (preferably), a special spanner for the external bearings – Shimano refers to them as 'adapters' for some reason – and a small plastic ring with teeth on to turn the preload cap. In less than two minutes the crankset is off and you can clean inside the BB shell with a rag (the browny colour is copper grease I put on after).

Chain line and Q-factor

Chain line: (i) the direction the chain runs from a chain ring to a sprocket and (ii) the distance of the chain from the bike's centerline. For maximum efficiency and minimum wear it should be parallel to the centerline. With a derailleur geared bike, of course, this won't always happen – so as parallel as possible by gear selection and also by setup. The distance from centre depends on various factors: number of chain rings, thickness of seat tube where the front mech is mounted, and the type of crankset and BB.

Q-factor, also known as tread factor, is the distance between the outside of the cranks at the pedals. It measures 180 mm on my Ridgeback's Deore chainset – on the wide side and would be less with a road crankset. There's nothing to be done about it with a Hollowtech II BB because the spindle that goes through is part of the right crank and the left crank sits in a pre-determined position on the other end of the spindle. So the Q-factor is fixed. To move the chain line inboard or to centre the middle chain ring with the middle sprocket, the only scope seems to be placement of the three spacers.

bb-after

After: two spacers on the left, one on the right (the black rings either side of the BB)

Mrs Taylor's Scott Sportster Solution also has a Hollowtech II BB and is fitted with two spacers on the right. Like the Ridgebacks the chain line is too far outboard so the two spacers should be on the left! It was my gear ratio analysis that led up to this conclusion. It's only a small modification but it gives a better placed big chain ring and less time wearing out the smaller ones. And the pedals are centralised.


Added the morning after... the chain line distance from bike centreline can be a question of preference and type of cycling as well as the setup one is faced with – Q-factor etc. An MTB might benefit from the middle chain ring further outboard to allow the smaller chain rings to engage more sprockets, and vice versa with a road bike ridden in flat terrain where you'd want to maximise the use of the bigger chain rings. Either way, it seems worth checking the setup (mine are all 27-speed; I've no experience of 30-speed or double chain ring bikes).

How to remove a Hollowtech II crankset

  • Unscrew the two left crank arm fixing bolts using a 5 mm Allen key (alternately in stages)
  • Unscrew the preload cap using the special TL-FC16 plastic ring
  • Remove the left crank arm after lifting the little black stopper plate
  • Lift the chain off the chainwheel and rest it on the BB shell (protect with rag)
  • Slide out the right crank arm, chainwheel and spindle (all one unit)
  • Unscrew/remove the Hollowtech bearings and spacers (anticlockwise on the left, clockwise on the right) using the special spanner; the cable guide screw may need unscrewing to allow the plastic inner cover to slide out freely

Refitting the crankset is more or less the same sequence in reverse but the use of a torque wrench is desirable to achieve 12-14 N-m on the left crank arm fixing bolts. The preload cap is tightened first but not too much or the bearings will be over-compressed and the cranks won't turn freely. If in any doubt read Shimano's technical service instructions but it's all pretty straightforward and much easier IMO than with a square taper bottom bracket.

8 comments on “Hollowtech II: chain line and Q-factor”

  1. Hilary wrote:

    Patrick wrote

    In less than two minutes the crankset is off and you can clean inside the BB shell with a rag

    Sounds excellent. Last time I tried to get my bottom bracket out it took a friend 2 hours to make a tool to remove the dustcap from the cranks and a further hour to discover he still couldn't remove the cranks! Then 2 hours on the train to Roberts! Since realising my cranks have self extracting bolts (of which the dustcaps are an integral part) it should be a bit easier next time! :)
    I don't know much about Q factors I'm afraid but I can use all the sprockets on all the chainrings altho I always avoid the extreme combinations.

  2. Chris wrote:

    Patrick wrote: In less than two minutes the crankset is off and you can clean inside the BB shell with a rag

    And yet ironically, with the bearings outside the bottom bracket shell (if that's still the right term for that part of the frame) it doesn't matter so much if there is crud inside the frame there as the sealed bearings are on the outside!

    I've replaced my external bearings (Tiagra – on a Sora chainset – to Ultegra), but calling that star-shaped fitting on the nearside crank a "cap" – I thought "dust cap" – isn't helpful. I reckoned that if that's all the thing is it wouldn't matter if I left it on and tried to remove the nearside crank by just undoing the two allen key bolts that clamp the crank around the spindle that slots through from the drive side. I thought I'd been sold all the tools I needed. Er, it didn't work, and it meant another trek to a (different) bike shop to get the little fiddly tool. Grrr.

    I couldn't resist a Deore chainset and Tiagra front mech during an online sale going for silly money so, in time, I'll no doubt be playing with my spacers to get an acceptable chainline. (The chainline for a Deore chainset is 50mm, but my current Sora is 45mm.)

  3. Patrick wrote:

    Chris wrote: ... the bottom bracket shell ... it doesn't matter so much if there is crud inside the frame there ...

    Probably more relevant with a steel framed bike to prevent internal rusting. It's surprising how much dirt accumulates inside the BB shell. Water can also trickle in from the top of the seat tube. It does seem worth cleaning it out and putting some copper grease in when the bottom bracket is removed.

  4. Chris wrote:

    Oh, yes. As far as water ingress goes I was thinking of the bearings and my own aluminium frame 😳

    I agree that it's much easier to replace the bearings with this sort of set up compared to cups with loose bearings – or even those in a ball race. Just means yet more tools...

  5. Joanne wrote:

    Patrick

    i have an odd problem, which i should have been able to resolve via a google. but cant. Firstly some numbers

    shell = 68 mm
    chainline = 50 mm ( mtb triple)

    The problem is the tread isnt even, Shimano say ( on the leaflet and on various websites) that the correct set up is 2 ( 2.5mm) spacers on the drive side, and one on the
    non drive side. which is fine BUT when i measure the pedal against the frame chainstay as a rough reference its hugely out on the NDS with the NDS spacer removed its still over 2.5 mm out. Im supprised im the only one with this issue but im fining it hard to come up with anyone voicing it. and yes i can feel it when riding.

  6. Patrick wrote:

    I'm surprised you can feel that the NDS pedal is 2.5mm further outboard than the drive side (if that is what you mean). IMO the relationship between the chainset and cassette is more important than a couple of millimetres one way or the other – to keep the chain straight for as much of the time as possible.

  7. Martin wrote:

    Hi, Just came across this site, great reading through all the posts, and particularly this one as I’ve been installing a few bottom brackets recently, so noted with interest the comments on playing around with the spacers either side of the external bearing shells.

    Shimano advises the Ext. shells/bearings are non-replacable, but the bearing races can actually be pulled out, and when I recently attempted this with my BB, I noticed they only had grease seals on the external facing side, relying on the back face of the cup to protect the inner unsealed side (which in my case, it didn’t!), along with the protective plastic connecting tube.

    I haven’t measured its length, but would have thought that the tube would only be correctly sealed onto the shell cups when 2 RH spacers and 1 LH spacer are used on a 68mm BB, or 1 RH spacer on a 73mm BB? – If the spacers were changed around to adjust the chain line as suggested, could this maybe cause the shells to either compress the tube, maybe splitting it, or causing it to only be joined at one end, leaving space for muck to enter? Its also fairly critical to protect the crankshaft, as any wear on it would cause the whole crank to be replaced.

    In my case, the LH bearing was trashed, and as I like trying to repair 'non-repairable' items, and don’t mind the time it takes, I’ve since purchased and refitted some replacement sealed bearings (6805-2RS, sealed both sides!), into the cups, for around £1.50 each, so will see how these perform over the next few years. There’s a few guides on the web on how to do this, for those who are interested.

  8. Patrick wrote:

    Thanks for the comment. As long as the same number of spacers is used, I don't think there's a problem. It just shifts everything over a millimetre or so.

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