Rack Mount Stability

Discussion in 'Rack Mounted Engines' started by 5-7HEAVEN, Sep 9, 2011.

  1. 5-7HEAVEN

    5-7HEAVEN Active Member

    I just bought a used MB that had sat idle/neglected for three years. It has a Mitsubishi TLE43 engine, Staton chain drive and NuVinci hub. The bike is a 2000 Trek 6700 SLR w/ ROCKSHOX fork and 18" aluminum frame.

    Is it just me, or do rack-mounted drivetrains seem EXTREMELY light at the front? I have a center-mounted Tanaka engine w/shift kit. It seems MUCH better balanced than my new MB. I DID have a STATON friction drive setup on my cruiser. It was somewhat balanced at the front(but heavy!), because it had a SECOND friction drive on the front wheel. The extra front weight kept the cruiser's front solidly on the ground.

    How do you members w/rack-mounted drivetrains handle your bike's light front end? This bike weighs about the same as my center-mounted MB, but weight bias is way off!:ack2:

  2. darwin

    darwin Well-Known Member

    Total wt for a fd is 16lbs you dont even notice it. I've carried more weight in groceries in a basket then that. Thats with a honda 50, i'm sure the sooby i have weighs even less.
  3. Happy Valley

    Happy Valley Active Member

    Yep, what he said^
    No issues whatsoever on that with either TLE43 or EHO35.
  4. Mike St

    Mike St Member

    My new rs 35/cvt bike is so well balanced, it's like I'm riding a bicycle, no sensation at all that there is a motor on the bike.
  5. 5-7HEAVEN

    5-7HEAVEN Active Member

    Maybe it's the NuVinci's extra weight.The front end seems VERY light, especially climbing the stairs w/the bike.:ack2:

    I'm also building a Staton twin-engined 29" bike. That'll add more weight to the rear end. Unsure if I'll be using another NuVinci hub on this one.

    Maybe I'll add weight to the front ends.:idea:
  6. jander6442

    jander6442 New Member

    Just throw some tools in a bag on the front to even out the weight... maybe a beverage holder.
  7. 5-7HEAVEN

    5-7HEAVEN Active Member

    I'll be adding a handlebar tool kit, for sure.

    Right now, the front/rear weight bias is not 50/50, of course.:detective:

    Using a scale, 50lbs of 62lbs is on the rear.

    That's 81%/19% rear/front bias.

    In comparison, my Diamondback bike w/center-mount engine, shift kit and 8-speed cassette has 37lbs of 69.2lbs on the rear.

    That's 53%/47% rear/front bias.


    A three-quart fuel tank and my 15lb backpack(with tools) up front will help.

    My 13lb. Fuggetaboutit chain wrapped up front would make it 50-something%/40-something% front-rear bias.

    This bike might need to add over 30lbs. up front. The backpack and fuel tank are necessary items I carry on the center-frame bike. They need to be on this Staton/NV bike too.

    In my opinion, without changing the front/rear weight bias, this bike is a death trap.:detective:
    Last edited: Sep 20, 2011
  8. loquin

    loquin Active Member

    What's the ratio when you're sitting on the bike, leaning forward in riding position?

    There should be plenty of weight on the front wheel then...
    Last edited: Sep 21, 2011
  9. 5-7HEAVEN

    5-7HEAVEN Active Member

    Hi Lou,

    My concern is that sometimes I'll lean back on my seat unintentionally, especially after cresting a hill, or a long cruise. The front end is extremely light. A motorcycle racer friend once told that one of the most important features on a motorcycle is how the front end behaves. I rode the bike when I first got it. It felt okay, but I never pulled back on the reins.

    No wonder my friend Rick could easily pull his front wheel off the ground. He had a Honda 35, Staton drive and NuVinci hub. He then replaced the Honda with a CY460 engine. Rick is in the Middle East right now. I should try to contact him.
  10. Virginian

    Virginian Member

    I have a rear mount GEBE system with a Tanaka 32cc engine. I find not problems at all with balance. It feels and rides just like a regular pedal bike, except it's much faster.
  11. 5-7HEAVEN

    5-7HEAVEN Active Member

    Thanks for your responses.

    I'll add the heavy chain to the front and see how the bike rides.:detective:
  12. lowracer

    lowracer Member

    I've done quite a bit of rack mounting & had a bike that had the engine up front then out back & flip flopped back & forth a few times (for test purposes...yeah right).
    I now run my 2 more powerful MB's with front engine racks & the difference in handling is huge compared to rear rack. The rear engine has its advantages (noise behind, oil spit behind) but for handling the front drive works much better. Sitting on a bicycle, the heaviest component is where your rearend is...rearward. Add the engine back there & handling gets squirrely. Lowering the handlebars helps but still.
    Putting the engine/rack weight out front balances things out & gives the bike a nice 'motorcycle' feel at speed & rails corners like a pro...
    I'm surprised more folks dont build front rack front engine machines...
  13. 5-7HEAVEN

    5-7HEAVEN Active Member

    Thanks for advice from an experienced front-engined rider, lowracer.

    When I ran twin-Mits engines, the front end was left-biased at walking speed. This was prolly due to Staton's long aluminum channel w/engine hanging out from the left. If the channel was a few inches shorter and the engine more centered, it would've made for a better feel at jogging speed.

    However, I agree with what you said. The front end feel was solid at speeds faster than 5mph.
  14. lowracer

    lowracer Member

    After a few front drive engines & installs the sweet spot seems to be getting the engine as centered as possible & fairly close to the tire & as close to the headtube as possible (without interfering with the fork brace or v-brakes).
    Engine too far forward, up, or over, & the bike handling gets squirrely. I almost did a jackshaft front drive v-belt setup in the hopes of centering the engine perfectly, but scrapped that project since my MB building philosophy is K.I.S.S & the jackshaft would have broke my 'practice what you preach' theme...LOL
    I am truly looking forward to seeing your project completed. I still have ideas floating in my head of doing twin pocketbike stage 2 engines on one bike (front & rear rack). I already have the 2nd engine on another bike. Perhaps do a friction rear drive with a one way roller & keep the front v-belt drive just the way it is now. I know it would be scary powerful anywhere from a dead stop up to 55. It is already impressive w/one engine...
  15. 5-7HEAVEN

    5-7HEAVEN Active Member

    LOL, with racers and hotrodders(me included), we become accustomed to the scary powerful and yearn for more power. What I intend to build is a machine that can scoot out of harm's way with the extra torque. Methinks that with a 22t/44t engine/chainring and 36t chainring with 11t-34t cassette, it'll work well. If the chains keep breaking, then I'll bolt on the NV hub. Unsure if I'll be using the 22t/44t engine drive, and the 36t or the 18t NuVinci rear sprocket to connect to the bicycle chainring.

    I'm getting ahead of myself. :ack2:

    What fun it is, to run different gear ratios for front and rear. I used a 1.25" roller on the front and 18.75" Staton gear drive on the rear. Using identical engines and starting off with the front engine only, when you slack the throttle at midrange and jump on the rear engine's throttle, it sounds EXACTLY like a gear shift!:tt1: Then later, I ran two 1.5" Staton friction drives.

    If the BMP chain/pulley drives were in existence, I would've definitely tried them, front and rear.:idea:
  16. Tinker1980

    Tinker1980 New Member

    I ran a HF 2.5 hp engine on a rack mount for a long time, the entire engine was to the right of the back wheel... I only ever noticed an imbalance when I was rolling the bike out of the garage.

    Of course, in my commute at the time, there was a lot of "Go" and very little "Stop". Adjusted the throttle so that when the lever was against the handlebar, it was going 30 MPH.

    I've got a 32 cc tanaka GEBE on the way, I'll probably not even notice it's there.
  17. lowracer

    lowracer Member

    I recently took the 7 lb pocket bike engine off the front rack & built a lightweight aluminum rear rack. Having the engine on the rear, pushing the seat forward & flipping the riser handlebars upside down to get more weight onto the front wheel still has ill handling effects compared to front engine drive. However, the benefits include less handlebar vibration, noise to ears, & no oil spit onto my legs.
    I dont get the vibrating handlebars on my full suspension rig with the engine mounted out front due to it being mounted to a DH MTB triple clamp fork. The suspension fork dampens the vibes & keeps it out of the handlebars.
  18. 5-7HEAVEN

    5-7HEAVEN Active Member

    I'm just gonna run the bike as is, after installing new chains.

    The bike has a mild 2.2hp Mitsubishi engine w/stock muffler, so things won't get crazy.