Why not mount engines in rear instead of squeezing them into the frame?

Discussion in 'General Questions' started by boyntonstu, Jan 11, 2015.

  1. boyntonstu

    boyntonstu Member

    After speaking to several motorized bike builders, I notice that there seems to always cutting away of the engine to make room for the air intake etc.

    Wouldn't it be nice to have all of that room?

    I suggested a rear mounted kit to fit all bikes from 20" all the way to 29".

    Take a look at these videos and see how you would do it on your 26" bike.

    Last edited by a moderator: Dec 15, 2015

  2. troyg

    troyg Member

    GEBE, friction drives, axle-mounts are all rear-mount, and all old hat.I prefer rear/rack mounted to frame mounted, frame mounts look like motorcycles, not bikes, and with rear mount I can put a 1 gal. gas tank in the frame and ride without fill ups. I don't watch vids, is it drastically different?
  3. boyntonstu

    boyntonstu Member


    Exactly my opinion.

    Does the center of gravity shift result in any negative ride characteristics?

    (I suggest that you watch the 3 short vids and give us your opinion.)

    Photos of you mount?
  4. KCvale

    KCvale Motorized Bicycle Vendor

    Of course a high center of gravity results in negative ride characteristics.
    Ever pedal your bicycle with someone on the handlebars or a 50 pound package on a back rack?
    That's why they have painner bags and baskets to lower to fixed loads center of gravity.

    Most of bicycle steering is done by leaning, when your center of your gravity has weight that does not lean with you will feel it.
  5. troyg

    troyg Member

    It's all personal opinion when it comes to "looks".No negative gravity shift, except when it's on the kickstand, even then minimal.Think of the avarage human rump (these days) how far does each side hang off the saddle, a friction or GEBE is only inches more than that, you can't really tell.If you're into jumping, frame mount is really the only safe option, but I just commute.No pics, I just take an old RV antifreeze bottle, hit it with a hotgun, shape it to the diamond bottom and you have long distance riding, if it leaks it's at calf level.I don't watch vids, the pics explain it, it's a rack mount china girl.Pretty neat, I personally don't use (never bought never would) chinese engines, tanaka, RS, or Mitsu are the only things I trust.
    PS:KC what rack drive system weighs 50lbs?? A gearbox and 49cc would only come to 35lbs, a FD with engine is around 20lbs, a GEBE about 15lbs, you know like a few books on the back rack, no where near 50lbs.
  6. wheelbender6

    wheelbender6 Well-Known Member

    I think most builders that mount the engine in the frame do it because they like the way it looks.
    Every mounting position has advantages if you select the right engine for that mounting location.
    There are many paths to enlightenment.
  7. KCvale

    KCvale Motorized Bicycle Vendor

    I mid mount because that's the best place for an engine other than maybe an electric hub, that's about as low a center of gravity and sturdy mount as you get and they stand up with your kick-stand just like a mid mount gas.

    Bottom line is if it can pass the Good Mount test.
    Form a side..
    Hold the top bar of your bike with one hand...
    Hold the top of your engine with other hand...
    And try to push and pull your motor AS HARD AS YOU CAN...
    If it moves AT ALL it will fail eventually, usually sooner than later unless you tighten it every trip.

    Don't get me wrong here, small 4-strokes on a back rack can work very well if it's a good rack, it's is just the last option I would choose for motorizing a bike is all.
  8. troyg

    troyg Member

    Not to be contrary, but that's bad advise.That would surely bend something out of alignment.A "Friction" holds fine, the only forces on it are up and down, not side to side, locktight on the mounting nuts (fingernail polish works great) an I've never had a problem.A GEBE, they are $600 plus for a reason, they are delicate, highly refined motor assist at it's finest.I personally have just had to change a belt at 3000 miles, nothing has ever come loose, or broken, simplest maintenance of any vehicle I've ever driven. Just saying.
  9. SunkyWorks

    SunkyWorks Member

    Attached Files:

    Last edited: Jan 13, 2015
  10. boyntonstu

    boyntonstu Member

    That looks heavy, but it seems to work fine.

    Tandem, HMMM!

    Take a tandem, remove the back seat components, mount your engine low down in the new space.
  11. HeadSmess

    HeadSmess Well-Known Member

    theres one thing about rack mounts i find personally frustrating that noones has mentioned.

    parking them. pushing them round. the general awkwardness of a bicycle is increased tenfold as the weight tries to topple it over.

    holding the handlebars doesnt help...

    try opening a gate on a cold morning while holding the bike upright between your legs... a bicycle will do its utmost to annoy you at such times :jester:

    anyway, nah...last rack mount i made for someone, a wee little puff of a girl... she did exactly that...dropped it opening a gate. the thing just keeps going over, and invariably the front wheel lifts off the ground as one vainly struggles with the handlebars to keep it up...

    all of a sudden the whole lot pivots through the headset, and the engine gets slammed to the ground, and in this case, broke off one of the starter studs...all good, except it took a great chunk of crankcase with it!

    that was the final straw for me and racks...

    a trike is completely different and you can stick anything on there within reason...

    but motorbikes have engines in the frame for a reason... though honda once found that getting the cog too LOW can be as bad as too high :jester:

    i helped a friend put one on the front of a bike years ago... it was a great drive system, but heavy on the steering...
  12. boyntonstu

    boyntonstu Member

    Have you experienced a Chinese engine rack mounted on a 20" bike?

    2 up on a scooter raises the cg quite a bit, yet going away from a traffic light seemed OK to me when I rode back seat.

    How unstable is 2 up compared to rack mount?
  13. butre

    butre Well-Known Member

    if putting it on a rack was the best way to do it I think Harley would have started doing it 100 years ago
  14. troyg

    troyg Member

    A bicycle, is not a harley. Also, bikes are for riding, I rarely judge a bike by how easy I can park/carry/stow it, just thinking of the comment about the girl with the rackmount, that sound like it would happen to her with a basket on the bike.For the "frame mount" people, have any of you tried, or seen a GEBE?Just curious.As I said before, for stunting/jumping it pretty much has to be frame mount, otherwise, GEBE is the tops (IMO) sorry.
  15. Purple Haze

    Purple Haze Active Member

    One point to make; rack mount is ok IF you never carry anything on the bike. I prefer the in-frame mount because I do carry things like groceries, 12 packs of beverages, etc. Plus, it just looks right. I hate the look of a bike with a lawncare engine on it.
  16. boyntonstu

    boyntonstu Member

    Here is an very low 2 stroke mount:

    Low mount 2 stroke.jpg
  17. jamesburr36

    jamesburr36 Member

    If rack mount works for the rider/owner I say go for it. Be creative and do things others don't even think up. We all have our preferences. I saw a small pick up last week with a v* mounted on the bed and nothing under the hood. Would I ever do that? Hell no for safety reasons but that configuration works for the owner of the truck I suppose.
  18. troyg

    troyg Member

    Rack mount allows for storage ( I carry an extra 50lbs in grocries on mine, before trailer), you can carry plenty extra, you just have to be creative with your panniers.What rack mount allows me that evens out the weight, is a full gallon of fuel in the bottom of the diamond, 90 miles of rough riding without even thinking about gas.It is all opinion, they both have theier places, but I could get nitpicky, weigh difference/simplicity/lack of wear and tear compared to most frame mounts.I approached my bike with the aircraft build idea, the vehicle has to meet a certain weight to fly (ride like a bike).With enough HP you can make a brick fly, but it still flys like a brick.On a side note does anyone remember the RC flying pig in the 70's?
  19. butre

    butre Well-Known Member

    the first harleys were bicycles with engines in the frame
    Timbone likes this.
  20. troyg

    troyg Member

    Yes, and how much did the engine weigh?Was there even an option because of size/weight?? As far as I can tell your agument is " all birds are birds, a swallow is the same as an albatros".Using antiquated utilities is not a well thought out comparison.
    Anything that makes you splay your legs is going to take from the natural way you move, as in you can't pedal efficiently, a motorcycle is not a bike.Is it that harley put the engine in the best place, or is it like all motorcycles, the engines are heavy enough that they MUST be placed under the mass of the rider so body english will still have the same effect?If you had a pocket sized engine that could be placed anywhere, would you still place it in the frame?I'd start considering other options (aero) as weight shift would be negligible
    Here's a good example of "a bike is not a harley".You can still mount extra, gas/panniers.It's a different/better setup, unless you've tried it, there's no explaining it
    Last edited: Jan 15, 2015