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  1. #1
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    Is a dave scott ironman expert a good candidate for a 650b conversion?

    I have an old 56cm dave scott ironman expert, I think 1987 or 1988, which I have just recently started riding again after about ten years off any bike. I use it mostly as a daily commuter. My commute is about 7 miles over pretty good roads, but traffic is heavy. There is a trail/path that if I could use, would bypass the worst of the traffic. It's not an extremely rough trail, but after trying it once with my 700c 25 tires, I realized that it's just too rough to do 5 miles twice a day on that trail with my current setup. I'd rather brave the traffic. I also want to be able to put on fenders to be able to ride in poor weather as well, but the dave scott just doesn't have clearance for fenders, at least not with the 25mm ties and the 105 brakes.

    So I have been considering a 700c to 650b conversion, to be able to put slightly bigger tires on, and to be able to get clearance for fenders. I'm not looking to put on anything super fat, just something with a little more volume. Probably not bigger than 32-35. From what I've read, it seems like Japanese road bikes from the 80s are generally good candidates for this conversion, but I haven't been able to find a success story with anyone using a dave scott model in particular.

    Does anyone know of a successful 650b conversion using a centurion dave scott? Is this a good candidate for this conversion?

    Right now the bike has shimano 105 brakes. Will any long reach brake work? Any recommendations?

    I'm assuming that the current 165 cranks would be too long after the conversion. Is that correct?

    I plan to get the frame powdercoated sometime this summer because the paint is pretty chipped in places and starting to rust. Would it be worth it to get a local shop to add braze-ons for racks and fenders before I send it to the powdercoater, since I'm planning to do the powdercoating anyway, or is that just investing too much in this frame, and would I be better off just getting a new bike?

  2. #2
    Senior Member IthaDan's Avatar
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    What size tire would you run with 650b? Depending on the width, you might not be all that much smaller in overall circumference and would run into the same clearance issues you're currently experiencing with 700c. This also depends on the shape of the stays and the fork- if the taper is gradual, you might get away with it because the wheels will be smaller in diameter.

    And 165mm cranks are NEVER too long.

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  3. #3
    Motorcycle RoadRacer cehowardGS's Avatar
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    IMO, I wouldn't subject the Ironman Expert to bad roads. IMO again, the Expert is pure road machine. I would get something else for riding on the not smooth trail, and leave the Expert in road condition.
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  4. #4
    Constant tinkerer FastJake's Avatar
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    I've read Sheldon's stuff on 650b conversions, and it's one of the things I just don't get. For the riding you describe, I think you could do much better to get a '90s Trek MultiTrack (or similar) and doing a drop bar conversion if that's what you're looking for. I've seen some sweet looking drop bar MultiTracks.

    Quote Originally Posted by cehowardGS View Post
    IMO, I wouldn't subject the Ironman Expert to bad roads. IMO again, the Expert is pure road machine. I would get something else for riding on the not smooth trail, and leave the Expert in road condition.
    Agreed.
    Why "derailer" is the correct way to spell the gear-change mechanism: sheldonbrown.com/derailer.html

  5. #5
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    Basically, you have the wrong bike for the riding you want to do. The 650B conversion will likely continue to give you clearance problems and the brake mis-match will be very difficult to overcome. I agree with the recommendations to find a decent Hybrid or Cyclocross bike which will take the wider tires and suitable brakes with no problems.

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    Quote Originally Posted by HillRider View Post
    Basically, you have the wrong bike for the riding you want to do. The 650B conversion will likely continue to give you clearance problems and the brake mis-match will be very difficult to overcome. I agree with the recommendations to find a decent Hybrid or Cyclocross bike which will take the wider tires and suitable brakes with no problems.
    Or get yourself a rigid mountain bike and add Michelin City Tires or similar and some fenders.

  7. #7
    Senior Member Iowegian's Avatar
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    There's a difference between what's possible and what makes sense. In this case, I agree with the above that you should get a new bike. The expense and compromises required to make this bike into a good commuter don't make sense. A hybrid or cross bike will fit your needs perfectly for a lot less trouble. If you want to go with something new, there are lots of good all purpose commuter bikes being built these days by companies such as Surly, etc.

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    There are a few online resources that explain what to measure on your frame to determine if 650b will fit. Rivendell has an article that also covers the brake issue. If the clearances work, I don't see why you couldn't make a nice commuter. Add some braze ons and get it a color you like. It might not be the cheapest way but the frame is probably nice enough to warrant making it useful.

  9. #9
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    Quote Originally Posted by shelbyfv View Post
    There are a few online resources that explain what to measure on your frame to determine if 650b will fit. Rivendell has an article that also covers the brake issue. If the clearances work, I don't see why you couldn't make a nice commuter. Add some braze ons and get it a color you like. It might not be the cheapest way but the frame is probably nice enough to warrant making it useful.
    There's a difference between what's possible and what makes sense.
    Read the second quote.

  10. #10
    Senior Member surreal's Avatar
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    OP:

    Here's what you'll need to measure to see if your DSIM is gonna work with 650B/584 wheels (I'm guessing it will):
    -measure the space between the chainstays at exactly 320mm from the axle. This is where the tire is most plump on a 584 wheelset. You'll need about 42mm (or more) to run nominally 584x38mm tires. Measure the distance between the forkblades at 320mm from the center of the axle. Again, at least 42mm if you wanna run 38s. Less if you're gonna run 33s; at least 48mm if you plan to run hetres. Remember, most of these tires are a few mm less wide than the advertised sizes.

    If the frame passes this test, measure the distance between the brake-bolt hole and the pads where they contact your 700c rim. Take that measurement both front and rear; the measurement is not likely to be the same. whatever that measurement is, in mm, add 16mm to it. (So, if it's currently at 45f/40r, the new measurements will be 61f/56r.) Depending on these measurements, you'll need either mid-reach (typically 47-57mm reach) calipers or long-reach (typically 55-73mm) calipers. Tektro offers a few brake sets in either size.

    While you're at it, make sure that the frame takes modern, recessed-nut brakes. Finding standard nut brakes is hard these days, and using the MacGuyver methods makes fender installation problematic. While we're at it, does your DSIM have eyelets for full fenders? I'm thinking it doesn't, but it probably takes recessed brake-nuts. I could be wrong; it's been quite a few years since i had a good look at a DSIM frame. I see you'd asked about the idea of brazing on some fender eyelets, so I'm guessing it doesnt have em...

    For the record, going from a 700(622)x 25c wheel to a 650(584)x38b will only drop the BB height about 6mm. So, the 165mm cranks will likely be fine. Standover will only go down that same 6mm, as well.

    Some ppl will be offended if you convert this bike, as they recall a time when it was a super-HAWT road bike. Those days are long gone now, and it sounds like the original finish on this particular example is thrashed, so collector value is very low. That being said, i think I'd be tempted to go forward with this plan. Buying a used hybrid or cross bike in decent condition probably won't save you alot of coin, b/c even with the cost of a new 650b wheelset, new 650b tires, and longer-reach calipers, you'll likely spend as much to bring whatever cheap hybrid/cross bike up to snuff (possibly including new tires, wheelset, etc...) You gotta decide for yourself, ultimately, but I don't think that frameset would have trouble surviving commutes over a MUP....especially with fatter rubber installed.

    There is a difference between what's possible and what makes sense, but there's also a difference between doing what you'd really like to do and following the advice of bike-curmudgeons who typically frown upon any unorthodox bicycle practices. You'll certainly learn more from doing the conversion.

    hth,
    rob

    ps- I have a late 80s 4130 Fuji Tivoli that originally had 105 7speed on it;loved the bike, but hated that even 23mm tires would rub the smallest sks fenders on the 700c wheels. I've converted it to 650a wheels/tires so i could run 38mm tires and fenders...been very happy that i did it. It still a very roadish and lightweight ride, but with more capable tires. A hybrid would not ride the same at all

  11. #11
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    Thanks to everyone for all the advice and info. Very helpful. Sounds like the majority opinion is to not do it, and I'm thinking I'll probably decide not to and just only ride in fair weather until I can afford a new bike.

    But I'm still thinking about it. The one reason I'm still tempted to go forward is that I don't really want a hybrid; I want a road bike with slightly more capability. Other than my commute, which is all road, but with a path option, most of my weekend riding is along the Erie Canal towpath, which is a gravel/crushed stone path smooth enough around here that a lot of people ride there with straight road racing rigs, so I definitely want whatever I ride to have a heavy road bias, and I don't need a heavy duty cyclocross rig. Also, I don't want a heavy touring bike because I don't plan to do any touring at all, and all I would us a rack for would be to carry a few files and clothes from the office. Certainly not more than 10 pounds. My messenger bag is more than big enough, but as it gets hotter, I'd like the option to get it off my back.

    Surreal, I'm intrigued by the idea of 650a rather than 650b. If I decided do follow your lead, would the clearances I need be the same?

    The original finish on the ironman (the pink and yellow "miami vice" color scheme) is indeed pretty thrashed, at least along the seat stays and the chain stays. The main triangle and the fork isn't too bad, other than a few chips and rub marks, but I'd rather just strip it down and get a nice even powdercoat than mess with putting fingernail polish or primer on the bad parts. Like you said, the collector value is basically killed by the paint damage on the seat stays.

  12. #12
    Senior Member surreal's Avatar
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    jkimballcook:
    650a is a 590 vs the 584 of 650b. 6mm of differenc ein overall diameter translates to 3mm difference to find brake reach/tire clearance. So, measure at 323mm to find tire clearance, and add 13mm to current brake reach to find what brakes you'd need. So, the clearances would basically be the same.

    Benefits of the 650a vs 650b would be mostly money savings. 650b offers more choices in tire size (virtually all 590 tires are 37 or 38mm, or 1 3/8", and made with commuting in mind....you can find 650b tires in sizes ranging from 33mm to 55mm, with cheap commuter treads, supple road treads, fast road treads, semi-knobbies, full on mtb treads, etc) and much nicer tires available (hetres or pari-motos vs the best 650a tires being schwalbe delta cruisers or panaracer col de la vie.) I mostly went 650a to buck the new convention; i secretly despise the current trend of fake-french cycling, so i opted instead for fake-brit. If you love the performance side of your DSIM, i'd go with 650b velocity synergy (with o/c rear!) and some grand bois hetres, if they'll fit. I was content to save money, so i went with 650a sun-ringle cr18 rims with schwalbe delta cruisers...

  13. #13
    Wookie Jesus inspires me. Puget Pounder's Avatar
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    I suspect you can get 650B x 32s in an expert, but measure first for sure.

    There is nothing inherently better about 650B vs 26", but The thing about 650B conversions that you can't get from simply putting drop bars on MTBs/hybrids is the geometry. You can create a whole new beast with those bikes that have tight clearances and geometry. I dipped my feet in the 650B water a few months ago since I got the wheelset and tires for suuuper cheap. The RB-2 is a "pure road machine" as well, but I had a lot of fun riding this off-road.



    This bike is no longer around. I sold this with 700C parts and am now building up a rodriguez as a 650B tight geometry, all-road bike.

    One thing I really want is a disc bike so I can readily swap between 700C and 650B wheels without changing brakes.

    Most people want to change to 650B for the wrong reasons, but I think you have a legitimate one. Since you plan on a repaint, think about adding on some things like rack/fender braze-ons. Just know that this is going to be a pretty expensive undertaking, so make sure you REALLY love that frame. Alternatively, Sport-Touring Treks make great conversions.

    Or you can just get a CX bike...
    Last edited by Puget Pounder; 05-03-12 at 05:29 PM.

  14. #14
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    old thread I know, but curious if a dave scott conversion occurred. I am looking at a dave scott centurion to buy, and am thinking about 650b. I might just use pclamps for fenders if necessary and leave it be, but.... As for a rack, you could always put a decailleur thing on the handlebars and use a handlebar bag instead of rear rack. Such a bike might not handle well with extra weight on the back anyway.
    I realize there may some headscratching as to why one would want to do this, but trust me, if you have a limited budget, getting the modern equilivant of a tange 1 bike or similar would cost a fortune. Even with the cost of repainting and adding braze ons a conversion costs less. Using an old loved road bike or second hand vintage is the only option really. If you are short like me, it can be hell trying to find a high end bike small enough, and a 650b conversion is the way to go. Modern 650B framesets are still limited to boutique, custom and expensive. Conversions cost much less, but you would have to settle for 650b x 32 or 38 instead of glorious 42 hetres. If you read bike blogs etc, you read about people who have endless resources buy the latest fast 650b trail capable road bikes with hetres blah blah. It can get frustrating, you want to try it within your budget.
    I would not go 650a, I have a 650a wheeled bike and the tires options are limited to comfort, city riding, touring and recreational. The only goodie is the panaracer 650ax38 col de la vie which is even too wide for road conversions.
    From experience hybrids are horrible. They are not designed for riding long distances, or riding fast, racy etc. They are designed to be recreational, meaning mostly sitting in garages except for occasional short ride.

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