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  1. #1
    Senior Curmudgeon
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    Various mechanical questions

    Could I please get a mechanic / frame builder to check post #188 in thread:

    http://www.bikeforums.net/showthread...999#post818999

    I've posted chain stretch, crank breakage, and aluminum frame durability questions in that message (perhaps I should have put it in this forum?) that I'd really like to have some professional opinions on.

    Thanks in advance for your patience with this newbie!

  2. #2
    Senior Member sydney's Avatar
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    Quote Originally Posted by FarHorizon
    Could I please get a mechanic / frame builder to check post #188 in thread:

    http://www.bikeforums.net/showthread...999#post818999

    I've posted chain stretch, crank breakage, and aluminum frame durability questions in that message (perhaps I should have put it in this forum?) that I'd really like to have some professional opinions on.

    Thanks in advance for your patience with this newbie!
    So, why don't ya just post it here?

  3. #3
    Senior Member mtbikerinpa's Avatar
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    If the bike was enineered propperly the frame will be fine. As far as chain strech, how is that a concern?
    Aviation Mechanic, Bike racer, Fitness Equipment Restorer

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  4. #4
    Senior Curmudgeon
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    COMMENT: The Townie offers one advantage that other "cruiser" style bikes don't. I'm 6'2" tall, and on my current exercise bike/cruiser (A Dyno-Glide), the stock seat post can't be extended adequately to provide proper seat height. Since the original seat post immediately bent at full extension, I've replaced it with an industrial, stainless-steel pipe (with a brass shim to make it fit the seat tube). Even this is beginning to bend! With the Townie, the gusseted seat tube extension above the upper frame tube allows proper seat height with their stock seat-post! The few added inches of braced, seat tube extension make the difference. This is NOT a trivial issue for taller & heavier riders, who are poorly served by conventional cruisers. Unfortunately, good double-diamond frames with coaster brake hubs (like the old Schwinn Racer) are no longer available. This means that the ONLY currently-available frame with a coaster hub that will fit larger riders is the Townie (to the best of my knowledge..) If I'm mistaken, please let me know!

    QUESTION ONE: The design of the Townie requires an exceptionally long distance between the bottom bracket and the rear hub (significantly longer than double-diamond or cruiser frames). Is chain stretch a major issue for the Townie? I ask this question because I'm frequently having to adjust the chain tension on my Dyno-Glide as I pump during exercise. About once a month, the chain gets stretched to the point where I either readjust the tension or it begins jumping gears.

    QUESTION TWO: I've also broken the crank once on my Dyno-Glide (just twisted that puppy right in two in the middle of the bottom bracket!). I see that the Townie has a cotterless crank in aluminum. Since the steel ashtaubla crank on the Dyno-Glide didn't stand up to my stresses, will the aluminum crankset on the Townie be adequately robust? I'd like to hear from heaver riders who have purchased and used Townies for some period of time.

    QUESTION THREE: I've never owned an aluminum frame before. The steel frame on my current Dyno-Glide cruiser flexes noticably when I get down on it. Is there any reliabiliby problem with aluminum frames in general (or the Townie's in particular) that I should consider prior to purchase? Since everybody's probably wondering by now just how monsterous I am (broken cranks, stretched chains...), I'm currently at 260#. In spite of this weight, I have muscular legs and walk, run, and/or ride daily. I used to ride double-diamond frame 10-speeds, but now stick with coaster brake hubs for reliability. Again, I'd be interested in hearing heavier riders' experiences with the Townie.

    Thanks in advance for being gentle and helpful with me on this, my first post at BikeForums.

  5. #5
    Senior Member mtbikerinpa's Avatar
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    Why do you insist that the Townie is the only coaster brake frame? The frame itself is nothing unique to accomodate it. Bolt for bolt, the frame needed to accomodate a coaster brake is no different from a disc braked single-speeder. Those I can guarantee to be strong and of appropriate size for your power.
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  6. #6
    Senior Member Retro Grouch's Avatar
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    What you perceived to be chain stretch on your old bike was probably caused by the rear axle being pulled forward. You might continue to have that issue. If you want to check, a new chain will have two pins exactly 12 inches apart. That distance will increase as the chain wears. When it gets to 12 1/16", it's time to replace the chain.

    In general, I'm gonna say that a three piece aluminum crankset will be stronger than a 1 piece Ashtaubla crank. Unfortunately, cranks aren't all created equal and some are much more robust than others. With your history of breaking parts, stay away from Dotek.

    Frames made from any material can flex and/or break. Less than 1% actually do fail. That's what your bike warranty is for. "Lifetimg warrranty" means the lifetime of the company that's offering the warranty. If they go out of business, your warranty has no value.

  7. #7
    Senior Curmudgeon
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    EXCELLENT INFORMATION! Thank you so much.

    You are exactly correct about the rear axle sliding forward in the stays rather than the chain itself stretching. Despite significant torque on the rear axle bolts, the axle slips about once per month or so. I don't dare apply additional tightening because I don't want to strip threads.

    As to frame flex, you're also right. Despite the fact that my steel Dyno-Glide frame flexes, it has never cracked or failed. Aluminum frames are probably going to be OK too.

    As to the gentleman who thought I said that the Electra Townie was the only coaster brake frame, I don't contend that at all. What I do say is that all currently-manufactured coaster brake frames are either made in "curved-top-tube" cruiser style or in "top-tube tilted downward toward the seat tube" comfort-bike/mountain bike style. The problem with both of these styles, for very tall and very heavy riders, is that this frame geometry causes SHORT SEAT-TUBE LENGTH. The problem with short seat-tubes, as I've mentioned, is that the seatpost must then extend excessively from the top of the seat-tube to accommodate the rider's height. With excessive seatpost extension comes the likelihood of seatpost failure if the rider is also heavy.

    The advantage of the Electra Townie (look at the photos of their men's model for clarification) is that their seat-tube extends almost three inches above the curved top-tube. Additionally, the extension is gusseted with a fillet that attaches the seat-tube extension to the top-tube. This additional seat-tube extension and strengthening allows the seatpost to extend less above the seat-tube support. With less extension, the maximum bending moment is less where the seatpost meets the seat-tube. This means that the seatpost is less likely to bend or crack under the weight of tall, heavy riders.

    Finally, on the topic of crank failure, you're probably right again. The actual axle of cotterless cranks is steel, and usually of somewhat larger cross-section than the crossbar of one-pc. cranks. Provided the aluminum cranks are adequately pinned to the crank-axle, they should be adequately robust.

    Thanks again for the good information and prompt reply.

  8. #8
    Senior Member mtbikerinpa's Avatar
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    I am just recalling the bike I made for my dad a while back. An older Schwinn mountain bike, 21" frame. It had zero flex issues and my dad is 6'4 and was 235. In earlier times he would snap pedals off spindles. There are several large cromo frames out there, not the least of which is the Zion EBB. The dropouts are vertical notch(like standard mtb) and the tension is made by an eccentric BB shell that a standard crank unit can mount into. Thus it eliminates any of the axle sliding issues.
    As far as cranks go, hve you looked into the newer Shimano units such as the Hollowtech II 2-peice design?
    Considering all the stuff I just listed is freeride dirt jump rated, a normal person even of great force should be able to work it.
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  9. #9
    Senior Curmudgeon
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    Thanks for the suggestions - I'll look into them all.

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