Cycling UK Forum

looking to change to a compact chainset 50/34 from 59/32 Sora set up, currently have what I believe is known as square taper mounting for the cranks with internal B/B bearings, frame mounted front changing mech (not lugged).

I note that now some chainsets have a fixed axle to the right crank and external bearings.

What are the advantage of the external bearings and fixed axle?

Would this set up affect the distance the chain wheels are from the frame therefore requiring different front changing mechanism?

Would my Orbea have standard (English) bottom bracket thread?

What if any tools, other than a standard crank puller and B/B tool are required? to accomplish the change to the fixed axle.

Any likely problems to be encountered or tips would be appreciated.

Would it really be wiser to stick with the existing format?

Novice mechanic on a modest budget.

Warsash Blue wrote:What are the advantage of the external bearings and fixed axle?

there is a benefit to the manufacturers, not the bicyclist -it's a lack of compatibility with spare parts for people trying to mend bikes in the future. they'll be stuck with getting new bearings for a given crank from a given crank manufacturer.

Warsash Blue wrote:Would it really be wiser to stick with the existing format?

i would have thought so, yes. here's a start for your reading

http://www.sheldonbrown.com/gloss_bo-z.html#bottom

http://www.sheldonbrown.com/gloss_n-o.html#octalink

good luck

I've just stuck an external bottom bracket on my old galaxy after rebuilding.
It is noticably stiffer, but in the real world does that make much difference? Jurys out on that one. My reasoning was that I wanted to complete the conversion to 9 speed and most new chainsets are this flavour now. One of the big advantages of this system is that it moves you're bearings out to there most effiecint place meaning the whole set up is incredibly stiff and strong but also really light.

I expect that your BB shell will have standard threads but somebody else will hopefully confirm this.

One thing that you will come across is that technically shimano recomend that the edges of your shell are faced (That is there perfectly parralel, something your LBS needs to do) Now you'll find as many people saying that a load of rubbish as will say it's the right thing to do. Luckily I've just had the frame resprayed so it made sense to get them faced while I was at it.

Tools wise you'll need a new set of specealist tools. One to fit the BB and another for the crank cap. Park make an all in one tool, however you can't use this with a tourqe wrench. Ice tools make two seperate tools which you can. The park tools website gives you advice on fitting as well as other sites.

The distance of the rings from the BB shell is the same as normal so no need o change your mech. However if your old chainset wasn't a compact then you might find that the cage on the mech is profiled for a large chainring, and when you change to a compact set up it may not work as sweetly. Again someone else may clarify/correct me on that!
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I'd have a look for a tapered axle chainset were it me. They are now cheaper and require no special tools or Torque wrench apart from the BB tool and crank puller. A lot less faffing around too.

I would avoid the external bearing systems. The price you pay with them is very vulnerable bearings that wear quickly. I would personally prefer a more tradtional 110mm bcd chainset such as the Sugino XD. Smallest chainwheel here is 34t. If you want anything smaller, you are into Specialites TA territory.
Willem

I can't really see any reason to change to the new style with external bearings, I would get a Stronglight chainset from Spa Cycles if I was you:

http://www.spacycles.co.uk/products.php ... 2b0s109p14

I use the Impact triple and it is a good quality chainset at a good price.

A couple of years ago I fitted an ISIS chainset - FSA Gossamer (anything but "gossamer" by the way, it's quite heavy! - but it was cheap). I'd always assumed that the flex which resulted in the chainring of my old Campag record rubbing the front mech was flex in the frame - not so - technically there must still be some flex but in practice it's not discernible at all.

I don't know anything at all about external bearings or one-piece RHcrank-and-axle setups so I can't comment on it, but the ISIS system seems a pretty good thing so far. It works the same as square taper as far as fitting/removal is concerned, you can even use the same remover with a spacer to fit the larger axle (a coin the right size?), or get the new remover which is the same except has a bigger centre ram. The cranks I got came with self-extract bolts anyway. The system feels a lot more solid than the old square taper. not that I've got anything against the 5 other chainsets I use...

PS I don't quite understand what the "gossamer" label covers cos there seem to be lots of different ones at different prices under the same name - including an external bearing BB... but the one I got was the one in the link below and takes a 34T ring. I'm afraid I don;'t know whether ISIS is a particularly FSA thing or if other brands use it too - but I'm pretty happy with this one.

http://www.dotbike.com/ProductsP936.aspx?TRACK%3dDFR

there is a benefit to the manufacturers, not the bicyclist -it's a lack of compatibility with spare parts for people trying to mend bikes in the future. they'll be stuck with getting new bearings for a given crank from a given crank manufacturer.

Years ago they had the bright idea that having inboard bearings on rear wheel axles was not really that good so they moved them out to the end of the axle and the free hub was born. At the time there was no doubt a lot of gnashing of teeth, but now it's the norm and the best of it? No more broken rear axles because from an engineering point of view it's the best solution.

It was only a matter of time before someone cottoned on to the fact that the same applies to BB axles. Placing them outboard puts them in the place they should have been all along. This means that the chainset can be made stiffer stronger and lighter.

If we moaned about compatibility problems all the time there would never be any progress. The price of new external BBs is reasonable unless you decided to go for the super duper all singing all dancing ones.

would avoid the external bearing systems. The price you pay with them is very vulnerable bearings that wear quickly.

I really don't subscribe to this view at all, my wheel bearings are on the outside as well and there well protected by rubber seals as are these bearings. That said I will watch mine with intrest and will happily eat a fair dose of humble pie if I'm wrong, but I personally don't see it and at 15 quid for a new one this won't break the bank if they do.

I swapped the GF's bike from square taper BB to external BB recently. It's Campag, rather than Shimano, but the technique is mostly the same.

Fitting the bearing cups is a piece of cake but needs a specialist tool. I'd recommend one you can fit to a torque wrench as it's worth getting the torque right. It's far less than you'd think. Then it's dead easy to fit the cranks. Just follow the instructions. I think for the Shimano ones you need the right size allen key and a tool for the caps.

Once you've done that you'll need to reset the front mech. Follow the instructions on the Park Tool website and it's straightforward.

chrisw wrote:

. . would avoid the external bearing systems. The price you pay with them is very vulnerable bearings that wear quickly.

I really don't subscribe to this view at all, my wheel bearings are on the outside as well and there well protected by rubber seals as are these bearings. That said I will watch mine with intrest and will happily eat a fair dose of humble pie if I'm wrong, but I personally don't see it and at 15 quid for a new one this won't break the bank if they do.

You really should have a look at the posts in the various forums complaining about the durability of some outboard bearings. FSA Gossamer outboard bearings wearing out at 2000 miles for example.
I would also hesitate before accepting the usual advertising spiel about the increased lightness, stiffness etc. of these over the traditional type of BB. I cannot recall meeting anyone who has complained that their BB axle is not stiff enough or even of the weight of the thing. I'm all for advances in technology, but often these may not be in the interests of the consumer as some who have bought integrated headsets have found to their cost.

Well I wouldn't call it advertising speil because I've got a new external BB chainset and theres no two ways about it, it definately is a lot lighter than the old set up and certainly feels a hell of a lot stiffer, especialy going uphill (living in the Lakes we have some big ones of those!).

As I posted earlier though, your right in the fact that in the real world does this really make much difference to me? I doubt it very much and certainly this fact alone wouldn't persuade me to buy them.

I have looked at various posts which partly was why I was having a grumble. Like I said I'm sceptical about some of the low mileages claimed and will certainly be watching mine with intrest. I'm more than happy to eat a fair dose of humble pie if i'm wrong!

chrisw wrote:it definately is a lot lighter than the old set up

Like I said I'm sceptical about some of the low mileages claimed

you're clearly convinced then chris in a way us cynics won't be. tell, next time that oval chainrings make an appearance, will you be getting some? the metric pitch chain? aluminium spokes?


but seriously - i've two questions for you.
1. how much lighter than the old set up is it? definitely a lot sounds like a saving worth having. what are we talking here, 1kg, 2kg?
2. do you have a theory about why people would lie about their own experiences, i can't see what they could possibly gain from doing so?

sadly, i do clearly see what manufacturers stand to gain from making parts with a shorter lifespan

I have them on all my bikes and they work fine.
They are ideal on MTB's the bearings are readily available and (not that any of mine have needed changing so far, compared to two square taperred sealed units that only lasted about 6 month each off road) and are easy to change.
Some inovation is pure rubbish ( L shaped cranks Ian Cammish) others are pure common sense. This sits firmly in the latter.

Apologies I hope I've not annoyed anyone that wasn't my intention.

I wasn't trying to call anyone a liar, I'm just naturally curious and wonder about all the variables that contribute to early failure. Wether there is something endemically wrong with the design (certainly putting them outside the shell into the path of the spray is on the face of things not the best idea in the world) or wether theres other factors involved, like not having the ends of the shell faced, or not running mudgaurds.

I will be the first to put my hand up if bearings fail after a few thuosand miles and apologising for being a doubting thomas.

As for the lightness, It was just quite noticable thats all. I've never wheighed them or the bike so who knows how much lighter it is and frankly I'm not that bothered. Just suprised at how noticable it was thats all.

While the manufacturers specify that the BB shell should be faced there is some discussion about this at the moment. The outboard bearings do rely on the BB face to be perfectly flat as otherwise the bearings could suffer from excess wear but some would argue that this may be acceptable in that they are cheap. The price of a facing tool is out of reach of most home mechanics so this means a LBS job. It's worth checking that all paint is removed from the BB face' preferably with a non-metallic tool, before fitting the bearings.

Personally I tend to look twice at any innovation which takes the job out of the province of the home mechanic.