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  1. #1
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    Wheel Build Safety Concerns...

    Hello!

    Forgive me if this has already been covered. I tried searching and found similar results but I wasn't able to find a thread that completely settled my concerns.


    I have a set of road bike 700x23c wheels and I would like to swap out the hubs for ones that can accept 6-bolt disc rotors.

    Question:
    Is it unwise to repurpose rims designed for use with cantilever brakes and use them on a disc brake setup? Is 28 spokes too few spokes for the front wheel of a disc brake setup? Should I choose larger diameter spokes when re-lacing wheels intended for use with disc brakes? I'm concerned about having some kind of wheel related failure and want to know if this is a bad idea.

    Details:
    The plan is to save only the rim (which is designed for standard cantilever brakes), then lace new spokes and hubs. The rear wheels are 32 spoke and the front are 28 spoke. I will have supervision and specialized equipment during the build through a local DIY bike service co-op.

    Background:
    This wheel build is part of a larger project: a disc brake retrofit on my road bike. Its part of an engineering project, otherwise I would just find a more practical and cost-effective way to do a disc swap. I use the bike exclusively for urban commuting around San Francisco (40 miles per week). Lots of hills, pot holes, and bad roads. The bike never gets jumped from curbs, never goes off road, and never sees rain.


    Any guidance or direction would be greatly appreciated! thank you!

  2. #2
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    Sine nobody step over this already, I never done such a thing but I don't see why It should not work. I would try to use just straight gauge heavy duty spokes with 3x pattern. There are plenty of CX wheels in 28 spokes, thats why dont see why it should fail, worse case scenario the wheel will get untrue quite easy but doubt (because never seen it or even happen to me) you will get like a tragic explosion of spokes in one second you know.

    The only thing i would do is to use like 28's or 32's tires to softer the ride since you are going to commute in bad roads with this. Heck i would just go with regulars 23s anyways

    W/o trying is hard to know, and sometimes when you are naive enough things work out just fine.

    Good luck keep us posted.

  3. #3
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    Haha! Well thanks for the input ultraman6970! Thats a good point about cyclocross wheels using 28 spokes. Browsing various CX wheel designs I had seen a few different 28 spoke setups, but I wasn't sure if that meant it was safe for use with road rims. I suppose you're right, the realist worst case scenario is it goes out of true faster than normal.

    Quote Originally Posted by ultraman6970 View Post
    Sine nobody step over this already, I never done such a thing but I don't see why It should not work. I would try to use just straight gauge heavy duty spokes with 3x pattern. There are plenty of CX wheels in 28 spokes, thats why dont see why it should fail, worse case scenario the wheel will get untrue quite easy but doubt (because never seen it or even happen to me) you will get like a tragic explosion of spokes in one second you know.

    The only thing i would do is to use like 28's or 32's tires to softer the ride since you are going to commute in bad roads with this. Heck i would just go with regulars 23s anyways

    W/o trying is hard to know, and sometimes when you are naive enough things work out just fine.

    Good luck keep us posted.

  4. #4
    Senior Member TugaDude's Avatar
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    I don't think it is a particularly good idea. If building wheels that you will use for awhile, just get the ones that suit your needs and budget. Lots of hoops out there on sale, good deals to be had. Or look on your local CL and find 29er disc-only wheelsets. I found an unused pair, Unused takeoffs for $40.00 and they are very nice.

    You can do whatever you like, but to me, if you are spending the time, don't settle. Good luck!

  5. #5
    Senior Member TugaDude's Avatar
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    Forgot, the 29er wheels will take a variety of tires. Schwalbe makes some nice road tires that fit 29er rims.

  6. #6
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    IMO re-hubbing a wheel rarely makes sense, unless there's a hub failure on a fairly new wheel in otherwise good shape. First of all you have the issue of spoke length differences which may mean only the rim is salvageable. But even if the spokes are right consider the costs and waste involved in this method, vs. starting fresh and having a spare wheel, or one you can sell used to recoup some of the cost of the new one.

    However, if you decide to go ahead, and use the old rim, there's no reason the unused brake track will be any kind of hindrance. As for wherher 28 spokes is enough fo a disc wheel, the existence of 28h disc hubs answers that question. Of course if you weigh 240#s you might want to think long and hard about a lightweight hub brake wheel.
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  7. #7
    Constant tinkerer FastJake's Avatar
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    It will be fine. It doesn't matter one bit whether you use a disc rim or a rim brake rim with disc brakes. The bonus of using a rim brake compatible rim is that you can convert back once you realize rim brakes are superior

    Regarding the 28 spokes, you put a lot more load riding on the wheels than you do using the disc brakes. You don't have to use more spokes, or heavier spokes, or anything like that. The only thing you cannot do with disc wheels is build them full radial, just like you can't build a rear wheel full radial.

    Quote Originally Posted by TugaDude View Post
    Forgot, the 29er wheels will take a variety of tires. Schwalbe makes some nice road tires that fit 29er rims.
    News flash. "29er" and 700c are both a 622mm bead diameter. So they're cross compatible, assuming the widths are not too far off.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  8. #8
    Senior Member TugaDude's Avatar
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    Why is that a news flash? I know they are both 622. My point was to make sure the OP didn't think he was limited to MTB tires. A lot of folks don't know that. I have friends that should have known better but didn't. Just pointing it out to the OP.
    Last edited by TugaDude; 03-08-14 at 04:27 PM. Reason: Grammar

  9. #9
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    That's also a good point. The more I'm price out this wheel build the closer I get to the cost of good quality disc takeoffs. Right now I'm estimating about $100-150 to build these wheels. I've found a few people selling take-offs on the local CL with tubes and tires. Pretty difficult to justify the hassle of building these things. Thanks for pointing that out TugaDude!


    Quote Originally Posted by TugaDude View Post
    I don't think it is a particularly good idea. If building wheels that you will use for awhile, just get the ones that suit your needs and budget. Lots of hoops out there on sale, good deals to be had. Or look on your local CL and find 29er disc-only wheelsets. I found an unused pair, Unused takeoffs for $40.00 and they are very nice.

    You can do whatever you like, but to me, if you are spending the time, don't settle. Good luck!
    So that brings me to another question. I read the Sheldon Brown thread on wheel sizes but I'm still a bit confused about the size convention and naming schemes of ISO 622 wheels. Are 29er rims as compared to the 700x23c road rims on my bike? Are there any differences between cyclocross wheels and 29er wheels?

    Quote Originally Posted by TugaDude View Post
    Forgot, the 29er wheels will take a variety of tires. Schwalbe makes some nice road tires that fit 29er rims.

  10. #10
    Senior Member Bill Kapaun's Avatar
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    A 29'r rim will be wider than a "road" rim, since they are designed for "fat" mountain bike tires.
    The rear hub is spaced for 135mm instead of 130mm road spacing.

  11. #11
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    Oh wow! While I was replying to TugaDude a bunch of other people chimed in.

    To FBinNY, thank you. The more people give input on this, the more it seems its just not worth the time or effort. My wheels are 3 years old and have had a pretty hard life.

    TugaDude, thanks for pointing that out about 29er tires. You're right, I didn't know that. As I mentioned in my last post, I'm still a little confused about the differences between cyclocross wheels and 29er wheels. Am I right in assuming there isn't a difference?

  12. #12
    Senior Member TugaDude's Avatar
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    There is much confusion. What I was referring to in the post above is that when I bought my first 29er, several friends honestly thought the diameter was bigger than a 700c rim. When I told them that my vintage 27" rims were in fact larger (630 versus 622) than 29er rims they thought I was nuts.

    As you know, marketing hype is such that 29er is much sexier than saying "rim accepts huge tires".

    I have a dirt jumper with micro knobby tires on it. The rims are conventional 26" mtb, but the tires make them look much larger. I believe they are 2.25", but look massive.

    The latest thing is to call something a "cross" whatever, bike, tire, frame, rim. Just like adding "touring" in front of an old beater is supposed to help sell it I guess.

    Getting off-topic, but how many products use the word titanium in their marketing. Golf balls even. Way overused and overhyped.

  13. #13
    Senior Member TugaDude's Avatar
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    Gonna post this and hope the other members don't make me give up my C&V card! This is way fun to ride...and even can take gears maybe someday.

    image.jpg

  14. #14
    bike whisperer Kimmo's Avatar
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    Disc fronts use as little as 24h, AFAIK. I think this is regarded as the minimum.

    I don't see any issue with the wheels (aside from some extra metal in unworn brake tracks), but the frameset is the thing - am I correct that you intend to braze or weld disc mounts onto your frameset?

    If so, bad idea, unless you have a very well thought out plan to also add reinforcements.

    Hang on a sec...

    Quote Originally Posted by alexxander.fost View Post
    The bike ... never sees rain.
    That would make the discs pretty pointless. I consider them more trouble than they're worth, except for the wet braking performance.

  15. #15
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    Its a complex plan that has a lot of variables. As I mentioned in the first post, this is for an engineering project for my undergrad otherwise I probably wouldn't bother. But I do appreciate the heads up. I know this is not a project for the weak.

    If you or anyone else is curious, here's what I'm planning: Over the next few months I'm going to be developing a CAD model of the bike frame and evaluating its stress responses to various types of brake mounting methods. Some of the mounting ideas I'm toying with involve:
    - welding in a plate
    - cutting out the existing plate and replacing it with a different design
    - drilling and welding in threaded aluminum zerts
    - developing a clamp-on system
    - welding on simple tabs to the seat stay tube and reinforcing that tube

    As for he CAD testing, that requires I know how much torque the brakes are capable of generating, which is going to require a bunch of testing. I'm probably going to develop a bench testing system for the BB7 Road calipers and rotors and relate the pull distance to torque applied.

    Lots of work to do!

    And regarding using discs in the rain, I hear ya. Quite a few people have mentioned something like that to me since I've started preparing for this project. But that's not why disc brakes are valuable to me. They're valuable to me because the friction compound isn't prone to hardening like rubberized brake shoes are. The hills here in SF are considerable. About once every two weeks the heat generated from braking vulcanizes the brake shoes on my bike. This is a common problem here and all the local bike shops say the solution is to just hit it with some sand paper to remove the hardened layer. I'm tired of that.

    Quote Originally Posted by Kimmo View Post
    Disc fronts use as little as 24h, AFAIK. I think this is regarded as the minimum.

    I don't see any issue with the wheels (aside from some extra metal in unworn brake tracks), but the frameset is the thing - am I correct that you intend to braze or weld disc mounts onto your frameset?

    If so, bad idea, unless you have a very well thought out plan to also add reinforcements.

    Hang on a sec...



    That would make the discs pretty pointless. I consider them more trouble than they're worth, except for the wet braking performance.

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    Quote Originally Posted by alexxander.fost View Post
    I'm still a little confused about the differences between cyclocross wheels and 29er wheels. Am I right in assuming there isn't a difference?
    Kinda-sorta. A 29er wheel will have (at least) 135 mm rear spacing, or one of the MTB-specific axle configurations.( 142/142+ etc)
    A 29er wheel MAY be built with a hookless rim, possible a bit wider too.
    A CX wheel CAN be either 130 or 135 mm, regardless if it's disc or rim brake.
    135 + disc would be more common, but both exist.

    And CX and 29er both use 622 mm bead seat diameter and will be able to use the same tires after a fashion.
    Last edited by dabac; 03-09-14 at 08:59 AM.

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    Wow! So it sounds like there is very little standardization between similarly named wheels. That would explain why I keep finding differing width rear hubs for CX wheels on craigslist and ebay. That would also explain why I keep seeing odd hub widths on the 29er wheels like 110mm front. Interesting. Well, I would prefer not to squeeze in a 135mm hub into my frame if I don't have to, so it sounds like CX would be a better wheel type to look for.

    Thanks for the clarification dabac! The differences between the two have been bothering me for a while now.

    Quote Originally Posted by dabac View Post
    Kinda-sorta. A 29er wheel will have (at least) 135 mm rear spacing, or one of the MTB-specific axle configurations.( 142/142+ etc)
    A 29er wheel MAY be built with a hookless rim, possible a bit wider too.
    A CX wheel CAN be either 130 or 135 mm, regardless if it's disc or rim brake.
    135 + disc would be more common, but both exist.

    And CX and 29er both use 622 mm bead seat diameter and will be able to use the same tires after a fashion.

  18. #18
    coprolite fietsbob's Avatar
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    I have rebiilt a wheel hub and spoke switch, to go from a regular hub to a Schmidt Dyno-hub,

    rim was a MTB type anyhow , Mavic EX721CD. it was not my first wheel build.



    there have been a custom 110 front, there the fork has to be made to suit.

    the dish for the disc gets to be less, or none. so wheel is asymmetrical by 10mm.




    CX bikes, to run discs have to be 135 in the back because that is what the hubs are.

    you may want to shop for another bike around the disc brake wheel desire ..

    N+1 , leave the rim brake bike as is . or n-1 sell it.


    Computer software writers can get paid better than most , just buy a new bike .
    Last edited by fietsbob; 03-09-14 at 03:17 PM.

  19. #19
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    Since it is an "engineering project" and you (think you) have a need for discs, I'd say go for it. Hang the expense. You seem to have a good handle on the fact that caliper mounts will be somewhat of a challenge, so you're not going in blind.

    The only issue I'd be concerned with is the frame material. If it's steel- no problem. You can easily weld mounts, and reset the dropout spacing if you are forced to go with 135 spaced hubs. Of course some engineering is required for the mounts to reduce frame stresses.

    If it's an alloy frame it's still doable but would require more care and thought. Welding may or may not be appropriate, depending on the alloy. OTOH, careful placement and design of the mounts may not mess with the heat treat to the point of becoming a failure mode. Or, design the mounts in such a way that welding isn't necessary. As far as spacing- alloy doesn't like to be "set" much for rear spacing, but I, and others have done it successfully. It's only 5mm if you are stuck with 135 spaced hubs. Or you can change the hub spacing by thoughtful elimination and changing of parts. Depends on the hub though.

    As for the 110 front hubs- generally these are thru axle hubs. These can be changed to 100mm spacing if required, and there are conversion kits to convert these to 9mm axles. It will require some slight machining, but no biggie. One should check the clearance of the disc in the fork however. Depends on the fork type whether there's room for a disc. Then there's the caliper mount. This is where one must be cautious and design the mount so as not to compromise the fork's integrity.

    (Even though I prefer rim brakes) sounds like a worthwhile project. Don't give up.

  20. #20
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    Hey reddog3,

    Thanks for the input and support! I agree wholeheartedly with your observations about the welding to alloy. I'm a bit concerned about changing the crystalline structure of the surrounding material during a weld. And I'm not really in a position to control that other than hire a welding specialist. As for the frame material, its made from 6061-T6 aluminum so there's no lucky breaks with this project. The more I think about this, the more I think a gusset with an integrated mounting tab at the drop out is probably the least risky option. But I wont know until I get the CAD model going.

    Regarding the front fork, I'm going to just buy a CX carbon fork from Nashbar or something. With the braking bias, the asymmetrical center of gravity of the bike, and the rather delicate nature of the front fork, its just not worth the risk. And its especially hard to justify building a front fork when new budget carbon fiber disc brake ready forks can be had for less than $200.

    As for the hub spacing information, that is VERY helpful! Thanks for pitching that to me. I didnt know the 110mm hubs could be converted. I'll have to take a closer look at those hub widths again on CL. And yeah, I think you're right about the rear spacing. 5mm is so negligible. I've seen a few articles discussing the impacts of throwing in wider wheels with regards to the chainline and it seems that you loose the front derailleur low gear / rear derailleur high gear -which we all know we shouldn't be doing anyway for safety reasons

    Anyway, thanks again for all the advice and input!

    Quote Originally Posted by reddog3 View Post
    Since it is an "engineering project" and you (think you) have a need for discs, I'd say go for it. Hang the expense. You seem to have a good handle on the fact that caliper mounts will be somewhat of a challenge, so you're not going in blind.

    The only issue I'd be concerned with is the frame material. If it's steel- no problem. You can easily weld mounts, and reset the dropout spacing if you are forced to go with 135 spaced hubs. Of course some engineering is required for the mounts to reduce frame stresses.

    If it's an alloy frame it's still doable but would require more care and thought. Welding may or may not be appropriate, depending on the alloy. OTOH, careful placement and design of the mounts may not mess with the heat treat to the point of becoming a failure mode. Or, design the mounts in such a way that welding isn't necessary. As far as spacing- alloy doesn't like to be "set" much for rear spacing, but I, and others have done it successfully. It's only 5mm if you are stuck with 135 spaced hubs. Or you can change the hub spacing by thoughtful elimination and changing of parts. Depends on the hub though.

    As for the 110 front hubs- generally these are thru axle hubs. These can be changed to 100mm spacing if required, and there are conversion kits to convert these to 9mm axles. It will require some slight machining, but no biggie. One should check the clearance of the disc in the fork however. Depends on the fork type whether there's room for a disc. Then there's the caliper mount. This is where one must be cautious and design the mount so as not to compromise the fork's integrity.

    (Even though I prefer rim brakes) sounds like a worthwhile project. Don't give up.

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