Quick bottom bracket question

Jamey

My BB is square taper and the Specialized website says its measurements are 68m x 103mm.

Looking on Wiggle and Evans websites I cannot find a single square taper BB with those measurements... However, there are plenty of square taper BBs that measure 68mm x 113mm.

Is this a typo on Specialized's website, do you think? Or have I just got a BB that's going to prove difficult to replace when the time comes?

Jamey

Hmmm... BikePedia seems to think it's 113mm:
http://www.bikepedia.com/QuickBike/Bike ... &Type=bike

Jamey

Ok, my brain is officially beginning to melt now. Here's why...

I don't actually need a new bottom bracket or chainset but with my newfound interest in maintaining my bike I decided to look around at prices for things, to see what sort of damage I'm in for when things need replacing.

To begin with I thought I had a rare size of BB (hence the opening post) but then I realised it was a mistake on Specialized's website. However, while looking around I noticed that the splined type of bracket (Octalink or otherwise) was much easier to buy than the square taper type, which seems to be on the way out.

I also started looking at chainsets and then again I noticed that the square taper variety seems to be a lot harder to find. So I began to wonder if I should change to splines when my current BB dies.

Then I noticed that as well as splines, there's also a lot of external-bearing brackets around and this is basically where my brain started to fail me - as I was trying to work out what chainsets work with what BBs, and which ones will fit onto my frame.

Can someone school me please? Using the simplest words (and least jargon) possible?

I've currently got a 68mm x 113mm square taper BB in a Tricross Sport frame. The chainset is a triple.

When it comes time to change the BB, what should I go for? If I simply replace things it looks like I might have trouble finding a square taper triple chainset. There don't seem to be too many around.

I know you can just replace chainrings but there's a distinct possibility I may have damaged a crank arm so may need/want (depending on whether I end up riding around with mismatched cranks on one side) to replace the whole thing at some point.

And also, I'd just like to know what's best for the future tbh.

nicklouse

ok skooling starts.
Square taper and Splined cranksets need to be used with the correct length axles no fast rule here. please not there are 2 octalink spline patterns, one ISIS, one Holzfeller, and powerspline splined interfaces. and they are not cross compatible.

External bb set ups require the bb shell to be faced. there is some cross compatibility on the bearings but not on all. (tend to fit both 68 and 73mm shells).

So really all i can say is ask before you buy or order.

salsarider79

As Nick says, you need the right sized axle for square taper.
If you go longer or shorter then your cranks will sit further out or in and mess up your gears (not mentioning the extra stress on your chain).
Both Isis/Holzfeller/powerspline and square taper are similar in so far as the cranks bolt onto the BB axle (i.e. http://www.chainreactioncycles.com/Models.aspx?ModelID=1002). External BB's are different. The bearings sit in cups which screw into the frame (http://www.chainreactioncycles.com/Models.aspx?ModelID=7638 The black piece goes inside the frame.) The axle is then built onto one of the crank arms. These are much stiffer and a better option if you can afford it.
Crank lengths generally go from 165mm up to 180mm in 2.5mm increases.

I'd look at something like this http://www.chainreactioncycles.com/Models.aspx?ModelID=28075. As your bike isn't that old, you may be able to get a small discount with your LBS....

Jamey

Ok so my current axle length is 113mm, but I was looking at Octalink BBs last night and it said you need to use 118mm axles, I think it was because of oversize chainsets or something.

So would it be ok for me to go to 118mm or would I still need to stick to 113mm?

nicklouse

Jamey
Sorry not relevant or as simple.

what crankset model and year?

is is not simple.

Jamey

Oh, I can't remember what I was looking at now.

Never mind, I guess I'll just ask here when the time comes.

Or just replace like-for-like where possible.

nicklouse

Jamey

here is a look into the minefield that can be BB's

http://www.sheldonbrown.com/bbsize.html

scroll through it :shock:

ride_whenever

There is also the tune sixpack interface, but don't worry too much about it, as it is only used by tune, and the cranks cost £200 as does the BB!!!!!!!

The best thing to do would be replace the whole lot (BB, cranks, chainrings, chain and cassette) in one fell swoop once the BB dies, and not worry about it til then!

Big Red S

I've not had a read through for a while, but this was pretty good when I was last active on Wikipedia (though I suppose I would say that)...

http://en.wikipedia.org/wiki/Bottom_bracket

Jamey

ride_whenever wrote:

The best thing to do would be replace the whole lot (BB, cranks, chainrings, chain and cassette) in one fell swoop once the BB dies, and not worry about it til then!

I can understand doing the chainset at the same time as the BB but why do you need to do the chain and cassette as well?

And wouldn't that mean doing the derailers too?

Big Red S

During use, the chain stretches. As it does, the rivets become further apart.

During pedalling, the chain then wears into the teeth on the sprockets it runs along, because they're closer together than the rivets. There is more wear on the cassette because the sprockets are smaller (and therefore each tooth is subjected to higher force) than the chainrings.

It is generally advisable to replace the chain and the cassette together. A new chain on old sprockets will have rivets that are too close together, so they'll not sit in the teeth properly.

You can often get away with a new chain on a nearly-new cassette, but you have to be quite early. If the wear isn't too bad on the chain and cassette you can often get away with new chainrings without changing them, but it's rare that you notice the need for new BB/cranks/rings without also needing new chain and cassette.

You don't need to change the derailleurs unless you change the amount of gears you have (in which case you need new shifters), the shifters, or use markedly different sized cogs.

Jamey

I've got a chain checker tool and replace chains when they get to 0.75 on the wear scale.

By doing this, I can get away with about three or four chains per cassette and I would expect to have to go through a few cassettes before the chainrings needed doing.

So given that I'll occasionally have brand new chains and cassettes with old chainrings and that will work fine, I'm still not clear why it would cause problems the other way round?

At this stage, I'm just trying to understand basic compatibility issues for the future. Chain slipping is something I already know a little about and I'm not fussed about it for the theoretical purposes of understanding which BBs I can and can't buy.

Jamey

Ok, new question...

If you needed to buy a new triple chainset (preferably black) and bottom bracket (preferably cartridge type rather than external bearings) today, what would you buy?

And don't just say things, you have to find it in stock online somewhere

biondino

Here you go.

Jamey

I guess I walked into that one really... My fault for not setting a reasonable price limit

ride_whenever

walton street cycles have some tune cranks and a bb in stock, about £400 for the lot (no rings included)

or I'm sure poshbikes will have the clavicula external setup available for a paltry £650

I would just go for external bearings, so much simpler, 105 or the superstar components cranks.

nicklouse

Oh and add the cost of a quick bb shell facing.

Jamey

Ok, let's say under £80 for the pair (BB and chainset).

Big Red S

Hollowtech II Deore?

Jamey

Doesn't Hollowtech mean using external bearing BBs, though?

All the Hollowtech cranks I've seen have been missing anywhere for a crank bolt to go, so I assumed they all had the axle built in.

Underscore

Jamey wrote:

Doesn't Hollowtech mean using external bearing BBs, though?

All the Hollowtech cranks I've seen have been missing anywhere for a crank bolt to go, so I assumed they all had the axle built in.

Yes, that's true but I've just replace the crankset on my commuter with HT2 Deore and i) it's available in 48/36/26 which I find ideal for a commuter bike, and ii) the crankset was £43 delivered from Merlin plus £15 for the facing of the frame, leaving you plenty of your £80 budget to get the tools to fit it.

Having said that, I had some creaking from it yesterday morning. However, I noticed that my headset was slightly loose also. Both are fine today so I assume that it is due to yesterday morning being a lot colder here than today. Would I be right in thinking that the creaky crank is likely to be too little preload of the bearings (as the headset is)? I did only preload the crank bearings just enough to stop any sideways play (as I've heard that preloading too much can cause early bearing failure).

Cheers,

_

Big Red S

Jamey wrote:

Doesn't Hollowtech mean using external bearing BBs, though?

<pedant>
No.
Hollowtech is a means Shimano have been using to make hollow crankarms for many years.
Hollowtech II is this added to the idea of external BB bearings and an axle bonded to the right crankarm.

Jamey

Oh, I see.

I guess it's looking more and more like external bearings are the future, from what I can see then. Pretty much everyone has forgotten square tapers and even splines seem to be on the way out.

One thing I can't find anywhere... With external bearing systems, where the spindle is part of the right crank, how does the left crank attach to the right one?

And do you need to tighten them as much as I just did with my square tapers?

Underscore

Jamey wrote:

One thing I can't find anywhere... With external bearing systems, where the spindle is part of the right crank, how does the left crank attach to the right one?

Basically in the same way as the stem attaches to your steerer tube: You use the end cap to preload the bearings slightly and, then, tighten two bolts to clamp the crank onto the axle.

_

nicklouse

or you have one bolt to do the same job.

Jamey

I see.

How come it doesn't work the end cap loose over time, then?

nicklouse

some do....

Jamey

Right, I think I'm starting to get this...

So if I took my Tricross to the shop and got them to face the BB shell then I could buy this bottom bracket and this chainset and install them in my frame, provided I got the 68mm version of the BB, is that correct?

And according to Park Tools webby, I need to have some spacers between the BB cups and the frame. It says I need two spacers on the drive side and one spacer on the left, if I'm reading it correctly (my front mech is a band-on Tiagra).

Is this correct?

What length cranks would I need? I'm 6'4'' tall so should I just buy the longest?

And for the BB tool, I assume I'd need one of these:
http://www.parktool.com/products/detail ... em=BBT%2D9

nicklouse

in a word yes. presuming that the bb shell is 68mm wide.

the spacer info comes with the bb cups.

But as bb is separate you could get some from http://www.enduroforkseals.com/id180.html

or hope 8)