Aluminum or Steel? Which do you prefer?

Discussion in 'Motorized Bicycle General Discussion' started by Cafe Racer, Aug 10, 2010.

  1. Cafe Racer

    Cafe Racer New Member

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    I have an aluminum framed bike right now and this was going to be my first build. But before I begine I was wondering what you floks feel is best.

    Pros / Cons.....?

    Aluminum has its advantages in many areas. Weight savings. Rigidity. But it costs more too.
    Steel? Less expensive. Stronger?

    Whatcha think? Throw it all out there?

    Thanks!

    Miguel
     
  2. professor

    professor New Member

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    What is the point of using aluminum when you have an ENGINE?
     
  3. Cafe Racer

    Cafe Racer New Member

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    I dont understand your comment. Are you stating that an aluminum frame is not strong enough? Or that the weight savings of aluminum are of no consequence since there is a motor.

    If the question refers to weight then there is a reason to choose aluminum. If I can cut weight by 5lbs that would be fantastic. The bike will need to be carried upstairs. Into the subway stations. Into office buildings or lofts. So weight is an issue and I would like to use lightweight components anywhere that is financially feasible.

    Miguel
     
  4. GearNut

    GearNut Active Member

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    Steel for sure. Chromoly for double sure.
    Aluminum frames are more prone to cracking.
    I am not a fan of cracked frames.
    Any of the wally world frames can crack though.
    Caveat Emptor!
     
  5. KCvale

    KCvale Well-Known Member

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    To me it all depends on your front tube.
    If the stock motor mounts fit around it you are golden, if not then with steel you can just use channel locks and squeeze it in and not loose any strength.

    With aluminum it is another story.
    If you can crimp it to fit the mount you just put a huge failure point in your frame.
    If it is that thin even drilling it for a single bolt mount is a failure point too.

    If it is good thick aluminum no problem, you can drill it.
    I had to do that on my current ride, but it is a heavy duty ALUXX-Grade Aluminum frame.

    Hope that helps.
     
  6. Chalo

    Chalo New Member

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    If you plan on welding anything at all to your frame in the course of your conversion, use steel. Aluminum is dramatically weakened by welding, and it takes a special (expensive) heat treatment process to bring the strength back. So if you want to weld on motor or tank mounts, racks, braze-on fittings, etc., use a steel frame.

    I have never installed a frame-mounted engine, though I have fixed some bad installs at my bike shop. From reading kit installation instructions and the postings on this forum, it appears to be a lot simpler to mount an engine on a frame with small diameter tubes than one with large tubes. Steel frames can be of small or large diameter, but aluminum frames are all large diameter.

    Something like a mid-1980s MTB will offer the best combination of characteristics for an uncomplicated conversion-- rugged construction, smallish diameter tubing, level top tube (for ample space inside the frame), stable handling qualities, good clearance for drive sprockets and fat tires, strong brakes, and a relatively long wheelbase. In this category, look for bikes that are high-quality but less collectible like Miyata, Ross, or Univega, because mid-'80s Specialized, Mongoose, Ritchey, Gary Fisher and other sought-after bikes can be very expensive.

    Chalo
     
  7. BarelyAWake

    BarelyAWake New Member

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    I'm sorry man, but I feel I gotta point out that ya really shouldn't "squeeze" or crimp any tubing you're depending on for structural integrity regardless of it's material - for exactly the same reasons stated for aluminum.

    While it's true that aluminum is even less forgiving - the thin wall tubing used for our bikes really shouldn't be compromised by distortion. It's chancy at best and while sure, you can get away with it somewhat, it's an unnecessary work-around with the potential for catastrophic consequences - there's now a plethora of oversize mount options that don't entail damaging the frame.
     
  8. professor

    professor New Member

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    Cafe, sorry about the misleading post.
    My preference is steel. I think if you do a real vibration -free deal and don't drill any holes alum will be OK.
     
  9. taddthewadd

    taddthewadd New Member

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    Cafe Racer, Chromoly steel frames are the best. The steel is stronger and dampens vibration better. The tubes are smaller diameter which helps with mounting the engine kit. Here is another thought about aluminum frames. In most cases they aren't lighter than a steel frame or at least any substantial amount. Now let me back this up. If you buy a cheap Walmart or Target aluminum bike the aluminum is a heavier poor quality aluminum. Usually thicker walled too. You won't see any weight savings going aluminum until you get into higher quality bikes. I bought a Specialized Stumpjumper for 1500.00 (not for a mb project) and the frame is maybe 1.5 pounds lighter than my GT chomoly frame on my mb. The Walmart bikes that are aluminum are a marketing ploy that tricks the consumer into thinking it is a better bike because it is aluminum.

    All that being said, you aren't going to loose 5 pounds on your bike unless you spend more then two thousand dollars on a high end bike. So I would recommend the chromoly since you can find them on craigslist really cheap and they work much better for a mb application.
     
  10. Cafe Racer

    Cafe Racer New Member

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    Thank you all for the excellant information and insight. What have I learned???

    Frame for frame the weight savings would not be much unless I were to spend alot of $$$ for a small drop in lbs.

    Chromoly/Steel frames tend to be stronger and easier to aquire at a lower price point.

    Mounting a motor to either frame should not be a problem due to the availability of various motor mount kits. But a steel frame may offer better vibration isolation then an aluminum frame.

    And the older steel frames may offer a better motor mounting position because of the top bar configuration and other aspects of the eariler mountain bike frame designs.

    I currently have my 1999 DBR Racing Mountain bike. Was thinking of doing the conversion on this bike first then try another on a steel frame. But after receiving all of this information i may just locate a quality vintage mountain bike.

    Thanks folks,

    Miguel
     
  11. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    And then again, there is aluminum.....my current frames of choice. And for various reasons that I won't go into....steel (chromoly) is better right?

    Anyhow, my current rides, both 2-stroke and 4-stroke are built on really cheap Chinese frames and they're awesome! Before I put engines on them, they were the lightest, most easy to ride cruiser's I have ever owned. They handle like a dream with or without the engines, but when you put an engine on them (with the kit and all), they just become HEAVY....period.

    Still aluminum is my choice for frame and component material and titanium is my second choice....different feel and more costly. Butted chromoly is my third choice, but hey....who really cares!

    Ummm, I guess I dolaffdance1


    And Honda too:http://powersports.honda.com/2011/crf450r.aspx

    If motorcycles use aluminum for frames.....guess what?
     
    #11 scotto-, Aug 11, 2010
    Last edited: Aug 11, 2010
  12. Cafe Racer

    Cafe Racer New Member

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    Good points. But the difference between motorcycles and bicycles are that motorcycles have frames designed to work with motors. Bicycles on the other hand we not designed that way.

    I believe that if the motor is properly installed on a quality frame thre shouldnt be any issues of stress cracks or metal fatigue.

    Miguel
     
  13. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    INTO office buildings? I will assume you intend to use an electric motor, in which case any savings on weight will absolutely be a benefit. If you can't be talked out of aluminum, splurge on a really good frame. Some members of the forum ride aluminum, have had good luck with it, and can advise you from here.
    If you are talking gas, office building administration may be less than happy with having a fire hazzard in their building.
     
  14. KCvale

    KCvale Well-Known Member

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    In my option is it depends on the thickness of the tube material and how far you have you have to squeeze it.

    Take this old Moon Dog I started motorizing today.
    The back tube was perfect size, but the front tube as just a 1/4" too wide to let the front studs by.

    On something like a Cranbrook you can just squeeze it with channel locks, but not this heavy steel Moon Dog, I had to break out the heavy duty C-clamp

    [​IMG]

    That clamp is as old as I am, it was my dads, and that black on it is roofing 'hot tar' from decades ago when I did roofing

    All it took was a couple of turns at the fattest spot to tweak it in at a little spot for the studs.

    [​IMG]

    As you can see I didn't squeeze it all the way in for the rounded mounting brackets to fit over too, just enough for the studs to squeeze by.

    This had the added benefit of just enough room on the bottom bracket to leave the shifter cable where it was, and with studs snug against the frame, that right stud will counteract the motor torque well too.

    In short that motor is mounted in solid and I just can't see that compromising the frame integrity in any way, and certainly better than a single stud through a drilled hole in the middle.
    That way provides no lateral support at all.
     
  15. BarelyAWake

    BarelyAWake New Member

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    I see whatcha doing now & I agree that specific application is prolly acceptable... but I dunno if I'd recommend it to others as it's a lil dicey unless they really understand what the consequences may be.

    Squishing tubing is a chancy game, it'd not take much to fracture or even dent & compromise it's integrity, particularly with the bikes most commonly motorized & folks unfamiliar w/the ways of metalworking...

    I see now you accounted for some of the things that worried me, like galling (ya used a C clamp w/uniform, slow pressure) and fastener side load (tubing expands, breaks engine case where studs are) by adding an extra rear mount in the front as a standoff.

    It's far from ideal what with pressure points instead of a nice solid contact & while it's completely acceptable to do things like that w/yer own bike as you'd be familiar w/it... I'm not so sure I'd be comfy recommending it instead of an oversized mount or selling it as a finished product...
     
  16. Cafe Racer

    Cafe Racer New Member

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    Do you have a picture of the final install? I am curious as to how the motor sits. I am dealing with an oversized tube installation.

    Thanks,

    Miguel
     
  17. KCvale

    KCvale Well-Known Member

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    It is far from final but here is how the motor sits mounted with the chains on.

    [​IMG]

    [​IMG]

    It needs more work obviously, but the motor is pretty level and there is just enough for the air cleaner to fit on too, and as you can see by the front tube, there isn't much if any frame strength compromise.
    Certainly less than a drilled hole and singe shaft with lateral force on the hole.

    "I'd be comfy recommending it instead of an oversized mount"

    Well, I think what we nice would a different version of the second front bottom U block I used.
    If the first one could bolt to it with standard studs, and it was larger with it's own studs that were wider and fit the tube that would be ideal.
     

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