Stupid Newbie Question ?

Flak Monkey said:

I'm happy with the diameter sizing on both items but have come up against a brick wall with regard
to the lengths. There are several different sizes off bottom bracket width fittings & front fork
steering tube lengths, now I would have thought that these would be determined by the width of the
bottom bracket housing & the length of the steering tube housing on the particular frame, or am I
completely off track ?

Yes, you're right, but there's just a bit more. The width of the bottom bracket *is* determined by
the dimensions of the shell in the frame, this is likely to be 68 or 73mm. However, you also need
to ensure you use the right length BB axle. This is to get the correct chainline between front and
rear rings. It's important for the efficiency and longevity of your drivetrain that the chain runs
as straight as possible to the rear sprockets.This is what people are talking about when they
refer to chainline. The BB axle will need to match the chainset you intend to use so that this
spacing is correct.

If it's a modern chainset you're using then it will likely have a recommended BB axle length
included with it's spec. (Shimano have this kind of info available at their website).The shop really
should be able to help you with this but if they can't then post here with some more details of what
you'll be using and perhaps someone here can guide you.

Quoted message said:

the front fork steerers come in 220mm & 240mm lengths both statements still leave me totally
confused as there are no corresponding measurements in the frame description.

Because most modern mtb's (and most roadbikes it seems) now use the threadless type headset
arrangement the handlebar height isn't easily extended once the fork steerer is cut to size.
Basically, unless you want to start buying bolt on adapters and gizmos, then the length of the
fork steerer will determine the maximum height of your handlebars. Install a longer steerer, you
have more adjustment available, a shorter steerer will allow less. The extra length on the
steerer is taken up by spacers which sit either above or below the stem depending on the height
adjustment you want.

More info and pics on headset/stem adjustment here:

parktool.comhowfix headthreadless.shtmlOpen ↗

If you buy a fork with extra length in the steerer you can always cut it down yourself later (or
have your LBS do it for you).

I've assumed that your new MTB frame and fork *does* have this threadless type set up, if not,
ignore what I've just said 🙂
--

"Bob"

'The people have spoken, the [censored]'

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Thank's Guys,

That's made things a lot clearer, at least as far as the steerer tubes goes, I shall get the longer
one as I can always cut it down, although on my last MTB I was always leaning far too heavily on the
bars so I'll most likeley get spacers. I will have a look on the Shimano site as suggested and,
hopefully, be able to determine the axle size for the BB.

Thanks again...

Cheers

Flak Monkey