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rebuilding front wheel: new hub with larger flange dia

naveed.ausafnaveed.ausaf Posts: 17
edited June 2015 in MTB workshop & tech
HI All,

I need to replace the front hub on my MTB that has 26 inch wheels. I have ordered a new Shimano Deore XT front hub which has the same number of holes (32), over-locknut-dimension (100 mm) and number of rotor bolts (six) as my existing hub.

However, as measured by a vernier guage, the new hub has slightly larger flange diameter (70.XX vs 68.XX). Also, the distance from one hole to the opposite hole is also slightly greater.

Does this mean that I would have to order a new set of spokes or will the current spokes be ok? Would I need to trim the ends of the spokes (at the rim end)?

Many Thanks,

Naveed

Posts

  • RockmonkeySCRockmonkeySC Posts: 15,247
    You will need new spokes. Unfortunately different hubs have different flange dimensions, there is no standard.
    This website can be useful for getting the right spoke length
    http://www.prowheelbuilder.com/spokelengthcalculator
  • bikaholicbikaholic Posts: 350
    I don't want to unnecessarily raise your hopes, OP, but there may be a slim chance that you may be able to reuse the spokes.

    The fact that you gave incomplete details about your new hub indicates that the following may be above your head but I offer up the little bit of knowledge just in case...

    Measure the new hub, the rim ERD (or search for the manufacturers specs) and plug the numbers into the spoke length calculator to see what it spits out. Incidentally, I use my own excel spreadsheet and, sometimes, the DTSwiss spoke calculator (which may output one or two quirky results).

    Compare the calculated spoke lengths to the spokes from your wheel.

    Note that when unlacing a wheel, remember to keep the disc-side spokes separate from the non disc-side spokes as they may be of different lengths.

    If your spokes are longer than that calculated then you can try and change the lacing pattern to take up the slack.

    The standard lacing pattern on mtb disc wheels (using j-bend spokes) is 3-cross (intersections) on both sides - increasing the number of crosses increases the spoke length required so plug 4-cross (which is doable) into the calculator to see what you get...

    Utilising the snowflake lacing pattern also takes up slack. Doing the double twist snowflake (using plain gauge 2mm spokes) requires a spoke that is about 9mm longer than calculated, a single twist is about 4mm.

    Of course, you can combine these two lacing patterns as well.

    There are other exotic lacing patterns that mix up usage of the spokes unlaced from each side but they depend on certain length differences.
  • The RookieThe Rookie Posts: 27,747
    Snowflake is a bad idea on disc wheels, if the spokes aren't within 2mm of right, you'll need new spokes. You can't cut them as you won't have enough thread and the spokes will bottom out on the threads inside the nipple.
  • cooldadcooldad Posts: 32,904
    The Rookie wrote:
    Snowflake is a very very very very very bad idea.
    FTFY
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • bikaholicbikaholic Posts: 350
    The Rookie wrote:
    Snowflake is a bad idea on disc wheels, if the spokes aren't within 2mm of right, you'll need new spokes. You can't cut them as you won't have enough thread and the spokes will bottom out on the threads inside the nipple.

    Hold on, didn't you just build your first wheel a couple of months ago and suddenly you're a pro on the subject?

    If you are an internet kudos junkie (as obvious by your huge post count), then here's a tip: you don't get negative kudos for abstaining from a forum topic, especially where it is not in your area of expertise.
  • cooldadcooldad Posts: 32,904
    Just because someone hasn't built a bridge doesn't mean they don't know that building one out of jelly and custard is a bad idea.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • bikaholicbikaholic Posts: 350
    cooldad wrote:
    Just because someone hasn't built a bridge doesn't mean they don't know that building one out of jelly and custard is a bad idea.

    Buildings made out of jelly and custard have their uses and their place. I will put forward that idea when it is appropriate, for instance, when someone needs inspiration on The Great British Bake Off.
  • The RookieThe Rookie Posts: 27,747
    An engineer will tell you what is a good and bad thing to do, a technician does it, I'm an engineer and now have the ability to build wheels, but I don't need to have done the build to tell you that hub braking with snowflake spoke patterns is a bad idea, doesn't really improve rim brake wheels either but at least, apart from weight, it's not a bad thing.
  • bob6397bob6397 Posts: 218
    Just look at snowflake wheels - in what way does that pattern look in any way to be even close to the structural integrity of more modern patterns?

    You will almost definitely need new spokes - unless you can cut them and re-thread them and have the tools to do so...
    Boardman HT Team - Hardtail
    Rose Pro-SL 2000 - Roadie
  • RockmonkeySCRockmonkeySC Posts: 15,247
    cooldad wrote:
    The Rookie wrote:
    Snowflake is a very very very very very ****ing stupid idea.
    FTFY

    There's a reason why snowflake spoke patterns died with the advent of disc brakes. Any idiot can see they have absolutely no strength to resist torque.
  • The RookieThe Rookie Posts: 27,747
    Exactly, in the same way you can radial lace a rim brake front wheel but not a disc braked wheel, snowflake is 'OK' with rim brakes, but not hub brakes, not really a good idea for the rear in either circumstance at all.
  • RightarmbadRightarmbad Posts: 216
    Nobody has mentioned the flange spacing.
    If the new hub has slightly different diameter, it may very well be offset by a different flange spacing.

    Also the actual drilling diameter has not been stated, only that it is slightly different whereas the totally useless overall diameter has been stated.

    4 cross is not possible on a 26" 32 spoke low flange hub wheel so that is not an option, but there are other ways.
    Nipple washers can be used to use old longer spokes and there is more then likely 1mm of thread left in a standard build anyways.
    If brass nipples are used, it is quite possible to roll extra threads as you go should it be necessary to scrape a bit more tension.
    More than likely if you run through a spoke calculator as suggested above, you will find that your old spokes will be close enough in length.
  • RockmonkeySCRockmonkeySC Posts: 15,247
    Nobody has mentioned the flange spacing.
    If the new hub has slightly different diameter, it may very well be offset by a different flange spacing.

    Also the actual drilling diameter has not been stated, only that it is slightly different whereas the totally useless overall diameter has been stated.

    4 cross is not possible on a 26" 32 spoke low flange hub wheel so that is not an option, but there are other ways.
    Nipple washers can be used to use old longer spokes and there is more then likely 1mm of thread left in a standard build anyways.
    If brass nipples are used, it is quite possible to roll extra threads as you go should it be necessary to scrape a bit more tension.
    More than likely if you run through a spoke calculator as suggested above, you will find that your old spokes will be close enough in length.

    I hope you don't build wheels too often. I certainly wouldn't let you build mine.
  • OuijaOuija Posts: 1,386
    HI All,

    I need to replace the front hub on my MTB that has 26 inch wheels. I have ordered a new Shimano Deore XT front hub which has the same number of holes (32), over-locknut-dimension (100 mm) and number of rotor bolts (six) as my existing hub.

    However, as measured by a vernier guage, the new hub has slightly larger flange diameter (70.XX vs 68.XX). Also, the distance from one hole to the opposite hole is also slightly greater.

    Does this mean that I would have to order a new set of spokes or will the current spokes be ok? Would I need to trim the ends of the spokes (at the rim end)?

    Many Thanks,

    Naveed

    Depends what your old hub is? If you know that you can find the dimensions, along with the Deore XT, and type the measurements into a spoke length calculator (use any rim with the same number of spokes and lacing) and then see what the average difference in length is between the two. If it's 2mm or less you might be able to get away with using the original spokes (kind of depends how far up the nipple they currently are sitting).

    Can always try it with the original spokes anyway, just to see if it works. You might find the nipple can't get far enough up the spoke or that the end of the spoke pokes out into the innertube area. If that's the case buy new spokes. All you've wasted is time trying to find out (and it'll give you some practice lacing and building wheels)
  • RightarmbadRightarmbad Posts: 216
    Care to elaborate Mr monkey?
    Which part or parts of my post are incorrect.

    Your post is simply unqualified bashing.
    Feel free to discuss any part of my suggestions.
  • step83step83 Posts: 3,866
    I used this wheel calculator came out fine me.

    If its the current Deore XT M765 it should have a left flange of 44mm and right of 38mm. any info on the old hub? Make and model would be useful.
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