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Question on bottom bracket size

Craig321Craig321 Posts: 169
edited April 2010 in MTB workshop & tech
Hi

I've been getting parts together to build my first own bike for the past few days now, and am almost there.

I have the frame dimensions (Dirty Jo Semi Creme):
Seat post 27.2
Seat clamp 31.8
BB shell 68mm
Headset 11/8

The seat post I have chosen is 27.2, seat clamp is 31.8, and the headset is 11/8". All good.

However, I'm not 100% sure on the stem length and the bottom bracket size.

The bottom bracket sizes are listed as:
68mm x 110mm
68mm x 113mm
68mm x 122.5mm

How do I know whether I should be going for 110, 113 or 122.5?

Stem length is a bit more straight forward - I assume I'd just go into a shop, find a bike that feels comfortable and find out what stem length it has? Or is there an easier way of determining which one I should go for?

May have posted this in the wrong section, sorry if I have!

Thanks
Craig.

Posts

  • peter413peter413 Posts: 5,120
    The second number is the chainline. I think the standard is 113mm but there are exceptions, not sure if your bike is.

    Shroter stems make handling quicker and jumps easier but longer stems are better for climbing.
  • andrewjosephandrewjoseph Posts: 2,165
    Craig321 wrote:
    Hi


    I have the frame dimensions (Dirty Jo Semi Creme):
    Seat post 27.2
    Seat clamp 31.8


    Craig.

    Craig, there is a large discrepancy between seat clamp and seat post. Are you planning on using shims to pad out the difference between seat tube inner diameter and actual seat post size?

    For example, i have a seat tube inner diameter of 31.6mm and an outer diameter ~35mm. I'm using a seat post of 31.6mm

    my wife's bike has narrow tubes, 27.2 inner seat tube and 32mm external diameter.
    --
    Burls Ti Tourer for Tarmac, Saracen aluminium full suss for trails
  • nicklousenicklouse Posts: 50,675 Lives Here
    peter413 wrote:
    The second number is the chainline. I think the standard is 113mm but there are exceptions, not sure if your bike is.

    .

    sorry wrong. please get your facts right.

    andrewjoseph
    it all depends on many things.

    what he has listed is very common.
    Craig321 wrote:
    Hi


    However, I'm not 100% sure on the stem length and the bottom bracket size.

    The bottom bracket sizes are listed as:
    68mm x 110mm
    68mm x 113mm
    68mm x 122.5mm

    How do I know whether I should be going for 110, 113 or 122.5?


    Craig.

    stem length is personal.

    axle length is crank relevant, but it is and also irrelevant depending on what crank system you go for.

    so what cranks are you getting?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Craig321Craig321 Posts: 169
    @andrewjoseph
    Not 100% sure what you mean? I would have thought going for e.g. the 31.8mm version of this:
    http://www.ukbikestore.co.uk/product/55 ... black.html
    and the 27.2mm version of this:
    http://www.merlincycles.co.uk/?fn=produ ... egoryId=55 then it'd be fine?

    Craig.
  • Craig321Craig321 Posts: 169
    nicklouse wrote:
    peter413 wrote:
    The second number is the chainline. I think the standard is 113mm but there are exceptions, not sure if your bike is.

    .

    sorry wrong. please get your facts right.

    andrewjoseph
    it all depends on many things.

    what he has listed is very common.
    Craig321 wrote:
    Hi


    However, I'm not 100% sure on the stem length and the bottom bracket size.

    The bottom bracket sizes are listed as:
    68mm x 110mm
    68mm x 113mm
    68mm x 122.5mm

    How do I know whether I should be going for 110, 113 or 122.5?


    Craig.

    stem length is personal.

    axle length is crank relevant, but it is and also irrelevant depending on what crank system you go for.

    so what cranks are you getting?

    http://www.jejamescycles.co.uk/shimano- ... d6441.html
  • nicklousenicklouse Posts: 50,675 Lives Here
    ok so, now do you know what chain line you want? 47,5 or 50mm

    all the info is Here

    but i would get these at 49,99 and the BB is included.
    http://www.chainreactioncycles.com/Mode ... elID=40496
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • nicklousenicklouse Posts: 50,675 Lives Here
    Craig321 wrote:
    @andrewjoseph
    Not 100% sure what you mean? I would have thought going for e.g. the 31.8mm version of this:
    http://www.ukbikestore.co.uk/product/55 ... black.html
    and the 27.2mm version of this:
    http://www.merlincycles.co.uk/?fn=produ ... egoryId=55 then it'd be fine?

    Craig.

    ignore as you are using the numbers provided by the seller/supplier.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • peter413peter413 Posts: 5,120
    nicklouse wrote:
    peter413 wrote:
    The second number is the chainline. I think the standard is 113mm but there are exceptions, not sure if your bike is.

    .

    sorry wrong. please get your facts right.

    Whoops :oops: It is the spindle/axel length isn't it. Sorry, really tired and facts are getting mixed up.

    Probably got it wrong again haven't I. I do know what it is, just my mind is so fuddled :?
  • Craig321Craig321 Posts: 169
    From what I can tell from the PDF above I'm limited to 68mm x 110mm or 68mm x 113mm.

    I know the chainline depends on if I go for the 68x110 or the 68x113, but I am unsure which is actually compatible?

    Also, on the chainset, what's the significance of 170mm/175mm?

    Thanks
    Craig.
  • stu8975stu8975 Posts: 1,334
    Craig321 wrote:
    From what I can tell from the PDF above I'm limited to 68mm x 110mm or 68mm x 113mm.

    I know the chainline depends on if I go for the 68x110 or the 68x113, but I am unsure which is actually compatible?

    Also, on the chainset, what's the significance of 170mm/175mm?

    Thanks
    Craig.
    As Nick says, ignore that chainset/bb and get the Deore HT2, it's a much better chainset. The 170mm/175mm refers to the crank arm length..175mm is the most commonly used size.
  • Craig321Craig321 Posts: 169
    stu8975 wrote:
    Craig321 wrote:
    From what I can tell from the PDF above I'm limited to 68mm x 110mm or 68mm x 113mm.

    I know the chainline depends on if I go for the 68x110 or the 68x113, but I am unsure which is actually compatible?

    Also, on the chainset, what's the significance of 170mm/175mm?

    Thanks
    Craig.
    As Nick says, ignore that chainset/bb and get the Deore HT2, it's a much better chainset. The 170mm/175mm refers to the crank arm length..175mm is the most commonly used size.

    I could go for the set that's guaranteed to be compatible with no further research required, but that doesn't really teach me anything about building a bike.

    Still unsure which BB I should be going for, the 68x110 or the 68x113 :?
  • supersonicsupersonic Posts: 82,708 Lives Here
    113mm to be safe.

    But yeah - get the Deore, much better.
  • Craig321Craig321 Posts: 169
    supersonic wrote:
    113mm to be safe.

    But yeah - get the Deore, much better.

    I'll definitely check the Deore out, am open to any changes at the moment :)

    I assume a slightly longer BB doesn't really matter then? Would it be best if I found out the BB width from the manu?
  • nicklousenicklouse Posts: 50,675 Lives Here
    no check the chain line recommended buy the maker.

    you know the BB size but you need to know the chain line required so you can get the correct axle for those old cranks.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Craig321Craig321 Posts: 169
    Thanks, will find out :)

    So, from what I can tell from the PDF above, I'd get the 110mm if the recommended chain line was 47.5mm and the 113mm if it was 50mm?
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