ISIS, External, Octalink BB's ?

[jimihendrix]

After a run of bad luck with crank tapers on my Zaskar going to go for a different system on my current project, ain't got a clue though, only ever used square taper BB's.

After a bit of research going to avoid Octalink as there does'nt seem to be a lot out there (not as much as ISIS), that leaves ISIS or External (or is there another i've missed ?) .

Questions

Are ISIS BB axles measured the same as square taper, e.g if the bike used a 113 square axle will it use a 113 ISIS axle ?

What about External BB's ? if i bought these cranks -

http://cgi.ebay.co.uk/DMR-EX-type-Chain ... 33605c97a6

- how can i be sure the axle will be the right length for chain line and chainstay clearance ?

Also what are the pros and cons of ISIS/External ?

 

[cyfa2809]

i run isis but every system has its haters. isis seems fine for me. i think your cranks need an external bb. normally externals are aimed at hardcore riding
as are your cranks i believe
the axle is attached to one side of your cranks, and uses one bolt only

its a newer system, ex type
comes under lots of guises currently, x-type, ex type, hollow tech i think

 

[KeepItSteel]

both systems have worked great for me in the past.
not sure about external being for hardcore riding, most high end road bikes are external these days.

Ive found external to feel genuinly stiffer than anything else, and they tend to come in at a lighter weight too.
However, it can take a few more minutes to get the preload right when tensioning up the bearings.

ISIS for me is the most foolproof and neatest looking, with more stifness over square taper.

I think the measurements/chainlines tend to be quoted on the product, so shouldnt be too tricky to work out which size to buy.
Some external systems use integrated washers to help acheive correct chainline.

I'd have no qualms going for either set up.
Given the option, id possibly plump for external, being lighter and stiffest. You can also bling up the external bearings with some fancy hope/king jobbies...

 

[jimihendrix]

Ah, cheers guys , cranks are for this DH8 so big and burly is the order of the day

May keep an eye on those DMR ones

 

[cyfa2809]

:shock: :shock: :shock:

oh i thought youd already bought the dmr ones :roll:

 

[Scrat]

RaceFace Northshores with ISIS for that one matey.

or Truvativ do a bastard child "Howitzer" spelling?
basically a ISIS spline with external bearing cups.

In the era of the club roost though, all the cool kids were running steel cranks a la DMR Azonic etc

 

[pigman]

ISIS for me is the most foolproof and neatest looking, with more stifness over square taper..

right, I'll say first that Ive only ever used sq taper, so happy to stand corrected.
How can a sq taper chainset not feel as stiff? Its a steel axle, cant see anyone flexing one??

Ive heard isis and octalink suffer premature bearing failure cos of the small bearings.

I certainly wouldnt buy into isis or octalink - now obsolete systems with very limited spares.

 

[perry]

How can a sq taper chainset not feel as stiff? Its a steel axle, cant see anyone flexing one??

Martin Ogden http://lp1.pinkbike.com/photo/4590/pbpic4590530.jpg can't use square taper because he can snap them . I can make them flex and I'm half the size of the guy

They flex because they are narrow . A 10mm rod will bend a hell of a lot easier than if that same amount of material was made into a tube . it's how external cranks work , make the axle a larger diameter and it increases stiffness while making them no heavier . Trouble is we're still using a very old shell size so by increasing the axle diameter the bearings need to be much smaller , smaller is weaker and wears quicker ( the larger the bearing the less affected by dirt it becomes ) not to mention loads placed on them .

BMX briefly used a mtb sized shell and by putting a 19mm or 22mm axle in the bearings just gave up because they were tiny , they now use a larger ( but not as large as the older " american " ) size with a press fit bearing .

The mtb market can't just say " hey lets all just use a different shell size " so the bearing gets moved outside of the shell in a cup that protrudes . This also has the benefit of making the distance between bearings wider and the further apart they are the stiffer they feel ( to a point of course )

So a larger diameter but no heavier axle and wider spaced bearings makes the stiffness increase massively . It is one of those things that when you don't have to build a bike to a retro spec is a massive step forward and I recommend it whole heartedly .

Chainline is pretty much a non issue . The frame is 135mm rear spacing and the shell either 68mm or 72mm . I'm guessing the shell is 68mm so will need two of the spacers on the drive side and one on the non , this will place the middle ring in the center of the cassette , even if not the spacers can be shuffled around as long as enough of the cup is in the frame . The only thing to bear in mind is the need to maintain the width from the outer faces of the bearings , the two piece design needs a certain width otherwise the whole crankset can shift laterally . But it's not something your going to need to worry about , when its in your hands it's obvious how the whole thing works and is pretty foolproof .