basic questions

[paulsrje]

I have finally bitten the bullet and purchased a frame to build up.It has amazed me how little i know about putting a bike together!
Any way a couple of questions,sorry if they seem like a beginners!
Frame is a Trek 8700 and it needs a bottom bracket-it measure 68 across so where can I find what type i need.
I also need forks i bought a pair that had 175mm steerer-this just pokes out of the top of the frame so looks like i need a longer steerer or is there another way round this?
Finally headsets how do the work is there a specific type for the frame?
Thanks
Paul

 

[We_are_Stevo]

Blimey! You need to do some reading!

Bottom bracket size is dependant on two things; BB shell width (68mm in your case) and the crankset (the bits with rings on one end and pedals on the other!) and the best guide is this one...

http://sheldonbrown.com/bbsize.html

If your fork in threadless (ie. smooth for the whole length rather than having a thread round the top) then you can either buy one of these...

http://www.wiggle.co.uk/bbb-bhp-2021-st ... m_Extender

...to make it as long as you need, or buy another cheap'ish fork.

Steerers and headsets come in two main sizes; 1 1/8" and 1 1/4" to fit the size head tube of any given frame. You can find headset dimensions on the Sheldon Brown site too...

http://sheldonbrown.com/cribsheet-headsets.html

...so measure the inside diameter of your frames headtube to find the correct 'frame cup outside diameter' (or someone who has one of these frames may take pity on you and save you the trouble??)

Headsets are the bits that hold the bearings that your fork steerer turns in; pictures here...

http://sheldonbrown.com/gloss_ha-i.html#headset

...a steel or alloy cup goes in either end of the headtube; a 'crown race' slides over the steerer and sits on top of the fork crown for the lower bearing to act on; the top bearing slips over the steerer above the head tube and then some other bits fit over that depending whether you have threaded or Ahead steerer...

...that's about as basic as you get but Google is your friend, and Sheldon Brown your Fairy Godfather

 

[FMJ]

Many (most) here will advise against using one of those steerer tube extenders in a threadless set-up (myself included). They are made for using a threadless stem in a threaded headset set-up, where the threaded top race and lockring take care of the bearing preload and clamping pressure. In a threadless system, the preload/clamping pressure on the bearings is maintained by clamping the stem to the steerer. With one of those extenders, the preload/retention is supported by the quill in the extender. They can and will twist/work loose under strain, sometimes with catastrophic results. Bottom line, they're your teeth, but it's really just a skint, bodge work-around to the proper solution. Figure out what length steerer you need and put an ad in the wanted section for your particular fork's steerer.

 

[sylus]

what age is the 8700..if it's early it could be a 1 inch ..later could be a 1 1/8

any pics would help

 

[We_are_Stevo]

Many (most) here will advise against using one of those steerer tube extenders in a threadless set-up (myself included). They are made for using a threadless stem in a threaded headset set-up, where the threaded top race and lockring take care of the bearing preload and clamping pressure. In a threadless system, the preload/clamping pressure on the bearings is maintained by clamping the stem to the steerer. With one of those extenders, the preload/retention is supported by the quill in the extender. They can and will twist/work loose under strain, sometimes with catastrophic results. Bottom line, they're your teeth, but it's really just a skint, bodge work-around to the proper solution.

Sorry, but what a load of tosh!

 

[Koupe]

Many (most) here will advise against using one of those steerer tube extenders in a threadless set-up (myself included). They are made for using a threadless stem in a threaded headset set-up, where the threaded top race and lockring take care of the bearing preload and clamping pressure. In a threadless system, the preload/clamping pressure on the bearings is maintained by clamping the stem to the steerer. With one of those extenders, the preload/retention is supported by the quill in the extender. They can and will twist/work loose under strain, sometimes with catastrophic results. Bottom line, they're your teeth, but it's really just a skint, bodge work-around to the proper solution.

Sorry, but what a load of tosh!

Not wishing to start/continue an argument, but FMJ's argument makes total sense to me, too. The quill was only ever intended to provide enough friction to steer and to prevent upward force on the bars lifting the stem out of the steerer i.e. not a great deal. If it was strong enough to maintain pre-load pressure on the headset bearings, why did manufacturers ever waste time and effort cutting threads into steerer tubes in the first place?

I stand to be corrected by We_are_Stevo's superior engineering experience, though

 

[We_are_Stevo]

S*d all to do with 'engineering experience...'

Far more respected members on here than I have used the steerer extender for years without any issues whatsoever; how many 'stuck quill stem' threads do we see on here? Now all of a sudden the extender is apparently dangerous because it's going to come loose?

I suspect the biggest clue to the antipathy towards their application is in the use of the word 'bodge' in the objection above, and the 'sniffy' attitude towards anything that even hints at such?

Much like the complete lack of response to the OP's admission of requiring some very 'basic' help other than my own...

 

[paulsrje]

Thanks

Hey guys thanks for the replies looks like Sheldon is going to be my new best friend,.
the steerer extender looks like for the money a way of keeping the build moving whilst i look for another set of forks that are the right size...
off to MTB sales now!

 

[FMJ]

how many 'stuck quill stem' threads do we see on here?

A hell of a lot less than quill stems I have seen come loose. In crashes or otherwise.

I suspect the biggest clue to the antipathy towards their application is in the use of the word 'bodge' in the objection above, and the 'sniffy' attitude towards anything that even hints at such?

So ignoring how an assembly was designed to work and using something for other than it's intended use in a bodge fix is solid engineering? Riiiiight.

Much like the complete lack of response to the OP's admission of requiring some very 'basic' help other than my own...

The OP was given good advice. Do it right and get the proper length steerer/crown for his fork, but that was glossed over. Usual Red Mist response when someone dares to question your "advice".

S*d all to do with 'engineering experience...'

Now that I think about it, the guys that empty the bins I put out on Monday mornings call themselves engineers, too.

 

[oldave]

Many (most) here will advise against using one of those steerer tube extenders in a threadless set-up (myself included). They are made for using a threadless stem in a threaded headset set-up, where the threaded top race and lockring take care of the bearing preload and clamping pressure. In a threadless system, the preload/clamping pressure on the bearings is maintained by clamping the stem to the steerer. With one of those extenders, the preload/retention is supported by the quill in the extender. They can and will twist/work loose under strain, sometimes with catastrophic results. Bottom line, they're your teeth, but it's really just a skint, bodge work-around to the proper solution.

Sorry, but what a load of tosh!

Just so! Might as well condemn all, traditional, quill systems.