poor handling at top speed

Discussion in 'Motorized Bicycle General Discussion' started by taddthewadd, May 9, 2010.

  1. taddthewadd

    taddthewadd New Member

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    I have a very sturdy mountain bike with a 66cc engine on it. I built it from the frame up. I am using a 38T sprocket. When I cruise at about 75% throttle it is fine and I think this around 20-25 mph but when I go any faster the bike gets squerly. The front tire wants to shutter and the whole bike feels like it is wiggling.

    My question is this normal or do you think something is wrong?

    I spent 5 months building this bike very maticuolously using high end parts. It is a steel GT tripple triangle frame and I have built custom wheels for it with heavy duty hubs spokes and double walled rims.The tires are high end specialized kevlar tires. I am running avid v-brakes front and rear. It has a heavy duty sealed headset holding a nice suspension fork. The stem and handle bars are aluminum with the bars that taper to a larger diameter where the bar attach to the stem. The bottom bracket is a sealed cartage type with shimano cranks. I was able to set it up with no tensioner on the engine chain. I am running a stock engine that I port matched to the intake and exhaust. I am also running an air filter and expansion chamber from SBP. The engine runs well and smooth. I mounted the engine very solidly to the fram with no rubber just right up against the metal and I made sure the front and rear mounts are lined up with the frame tubes to the right angle so they are flush.

    This thing is like a solid tank.

    The only thing I can think of is the concept of a gyro. I used to play with this toy designed to excercise your hand and wrist. It has a neon ball in a clear plastic case and you get the ball spining real fast and you can twist it around in a circular motion to keep the ball spinning for a long time and it was called a gyro. On the bike since the wheels are spinning so fast maybe if it starts to shudder the gyro affect makes it get thrown off and it gets worse and worse until you slow down or you try to correct it with the strength in your arms.

    I hear of guys going 30+ mph on here and some up to 40mph all of the time but no one mentions this problem. Just wondering if its my bike or a common problem here

    Thanks for your help guys!
     
  2. Cabinfever1977

    Cabinfever1977 New Member

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    "The front tire wants to shutter and the whole bike feels like it is wiggling"

    You will want to check your wheels, one of them may be slighty bent,if it is you can true it so it will be straighter. I know cause this happened to me before. Also check your brakes and make sure a brake shoe is not rubbing a wheel causeing a wheel to be pushed over.
     
  3. corgi1

    corgi1 New Member

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    Out of balance?
     
  4. BarelyAWake

    BarelyAWake New Member

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    I agree :)

    From your description it does sound like the dreaded "tank slapper" - the "wiggling" bit in particular. Caused by out of true and/or balance wheels I've not yet had a problem with it on my bicycles, but remember it ...fondly... from my motorcycles. With the limited speed/weight of an MB I dunno if it'd be the same - but on a motorcycle the symptoms are pretty constant, if the wobbling starts at say 80mph, it'll always start at 80 - it'll get worse if you go faster - but won't stop till you drop down to 60mph or so, depends on variables - but it's always a lot less than the starting point.

    The only other thing I can think of is tracking, your front and rear wheel's alignment with each other and the bike...
     
  5. taddthewadd

    taddthewadd New Member

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    Cabinfever, I just had the wheels trued at the bike shop and the brakes are setup perfectly with no pads touching the rims. Those where good ideas and I should have mentioned that.

    Corgi, if you also mean the wheels then yes they are balanced, if you mean the engine, there is very little vibration. I think I got lucky with this engine.

    Barelyawake, I believe what you have described is exactly my problem. It is common for mountain bikes to dish the rear wheel off center to make room for the cassette of gears on the right side. When the bike shop trued my wheels I also asked them to center my rear wheel. I know it is center because when installed the gap between the tire and both chain stays is equal and the gap inbetween the front tire and the forks is the same. So since the front and rear wheels seem to be center that leads me to believe the tracking is ok.

    The only thing I can think of is I am using tubes filled with slime. I thought at speed the slime would disperse and even out keeping the tire balanced. Well maybe not. I here of others using slime and no one mentions this problem. Who knows maybe they just think this is normal so they don't say anything.

    Do you think the slime is the problem or could it be something else. And Barelyawake I think I read something about you balancing wheels by wrapping solder around the spokes. How do you get the solder to stay on the outer part of the spoke and not slide down towards the hub? I know this would be pointless until I remove the slime tubes.
     
    #5 taddthewadd, May 10, 2010
    Last edited: May 10, 2010
  6. BarelyAWake

    BarelyAWake New Member

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    I would bet it's the slime tubes, my wheels aren't balanced on my rides & I've no problems - but I'm not runnin' the goop. I imagine it's prolly variable, if ya goop the tubes and ride immediately for a while mebbe it spreads it out more uniformly than if ya goop 'em and let it sit?

    I dunno... I thought about the slime stuff... but then was horrified by the mental imagery of a blow-out and the resultant mess, so I put it back on the shelf heh. I've really not had a problem with flats ever since I got good tubes & tires *shrug*

    I'd run w/o goo and see before I got into "balancing" bicycle wheels, motorcycle rims use clip on weights and/or stick-ons BTW
     
  7. BarelyAWake

    BarelyAWake New Member

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  8. taddthewadd

    taddthewadd New Member

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    I noticed that too when I started researching slime. Thanks though.

    I will let you know if replacing the tubes with non slime tubes works or not.
     
  9. civlized

    civlized New Member

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    I agree. Slime can be a nightmare for balance at higher speeds. Though, I have seen some that was made for motorcycles! I guess I would put it in the tire if I had a flat, just to get me home but that's about it.
     
  10. Cabinfever1977

    Cabinfever1977 New Member

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    Must be the slime.
     
  11. mapbike

    mapbike Active Member

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    I run Extra thick "Flat Proof" Bell tubes that have sealant in them and my bike will top out @ 38MPH and has NO wiggle or wobble and no wheel balancing has been done on mine.
    So this is a ????

    I say just to cover all points I would go with non slimed tubes and see if it makes a difference, it does sound like a out of balance problem of some sort.
    Hope you get it figured out soon, good luck.
     
  12. taddthewadd

    taddthewadd New Member

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    Thanks mapbike, I have been riding motorcycles for a long time including dirt bikes to cruisers to sportbikes and have never felt this. I do remember hearing the term tank slapper as said by barely awake at some point before.

    When this happens it is a bit scary. When it starts to happen I have to hold the handle bars really firm and or back off the throttle. I will update you guys and if you think of anything else please let me know.

    Thanks
     
  13. 2door

    2door Moderator
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    Taddlewadd,
    After you have the correct weight, (wraps of solder), added to the spoke, put a dab of silicone adhesive on it to keep it from moving. It doesn't take much and if you crimp the lead to the spoke you might not need anything to keep it from moving. Additionally the centrifugal force as the wheel spins will keep it out where it will do the most good.
    To add to this; I've done some experimenting since that old thread that Barley posted a link to was entered. I've found a significant difference in ride after balancing my cruiser wheels and, the 'Slime' most certainly effects the balance until after it has distributed evenly throughout the tire. Cold temperatures increase the effects. Like everything else, the warmer, the better.
    Tom
     
  14. corgi1

    corgi1 New Member

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    and there is no play in the suspention fork slides.....
     
  15. Goat Herder

    Goat Herder Gutter Rider

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    I don't use the paper thin preslimed tubes. I use thick heavy duty thorn proof tubes with lots of slime in them. A little More than the directions state to use like to think I have a little side wall protection. I have used this stuff with thick tubes for over 20 years. Never have I ever had a problem with tires being out of balance at high speed, If I had a jumbolia reflector on the wheel I had always took those off. My thought was they would loosen the spokes where they were mounted to. To this day I will brag that they balance a wheel.

    Whats more is the paper thin preslimed tubes in my experience come with a minuscule amount of slime in them.[Not going to balance a tire] Also a paper thin tube is a racers deal for cutting corners on weight in my opinion. A pin hole in a paper thin tube is very unforgiving for any stop leak. Uber speeds on a Motored Bicycle I go with a thick tube! I found slime works really well with a thick Heavy Duty tube...

    Some folks live where there is very little road hazards , Sickers cacti etc. Not where I live!
     
    #15 Goat Herder, May 11, 2010
    Last edited: May 11, 2010
  16. Goat Herder

    Goat Herder Gutter Rider

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  17. taddthewadd

    taddthewadd New Member

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    The fork is brand new and seems to be ok. I will look at it a little closer.
     
  18. mapbike

    mapbike Active Member

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  19. Junster

    Junster New Member

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    Slime is heavy. If you have really good kevlar tires please try a decent set of normal bike shop tubes. Not Walmart, not super hvy duty either. They make the tire get way hotter at speed on the road and they are heavy. You only need hvy tubes for trail riding thorns or to make up for cheap tires. I run servas drifter S tires with standard tubes. They have 5 layers of flat protection and inverse tread. Use good rim strips. I have zero flat problems. You want to keep the spinning weight at a bare minimum if you want to go fast. I have no balancing weights and standard weight spokes on good rims and hubs. If you have good quality wheels they are too light and well made to need balancing. At over 20mph about 30% of your HP is being used spinning the spokes thru the air. Fat spokes equals slower speed. Look at a Olympics Bike, that's why they have 3 wide thin spokes. If your not jumping rocks good quality spokes in the standard size are fine if you have a shift kit or one of Jim's Hub Adapters so your not torquing the spokes themselves. I use a $25 3/32 drive chain with riveted pins for the shift kit. Standard shimano hub/cluster. If you look at a Walmart bike rear hub closely you will see the bearing on the cluster side is set nearly in the middle of the hub. Shimano hubs run the bearing close to the outside. It's spreads out the support on the axel. Whether you like shimano or not they are a much stronger hub for a reasonable price. Dishing the wheel for a cluster has nothing to do with it as long as the spokes are tight and right. My bike will run with mods including shift kit,CNS carb,tuned pipe,slant head,opti-2 oil/75 to 1, at 42mph in a calm wind on a dead flat 4 lane road. That's clocked by 2 different cars not by a bike speedo. I ride a steel GT triple triangle frame just like yours. Broke a costco bike frame last year. I have no suspension at either end not because I wouldn't like it. Adding a suspension fork to a bike that didn't come with one, esp if it's a long travel fork is dangerous. Bikes with no suspension have less fork angle than a frame built for a suspension front end. As the suspension colapses the angle gets less and less. I promise it's the slime unless your new fork is a suspension fork and the frame isn't made for one. It sounds like you have done everything else right. It will cost you less than 20 bucks to prove I'm right or wrong. I weigh 220lbs. I have over 2500 miles on my bike including the rebuild.

    newtank.JPG

    I'm not trying to ruffle any feathers. I'm just saying what works for me. I do Zero offroad.
     
    #19 Junster, May 11, 2010
    Last edited: May 11, 2010
  20. Goat Herder

    Goat Herder Gutter Rider

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    Why are tubes thick for ATV's and car tires? My goodness they should be overheating! Slime is worth its weight in gold it balances a tire and helps prevent flats! That weight disperses. At slow speed can't ever be felt at high speed can't ever be felt. My bike 80 pounds me 240 , cargo up to 40 pounds. I got 15,000 miles on the motored bike thing. 60,000 plus miles pedaling.

    I try to run 26x2.7 tires on all my bikes there as smooth as you can get one , and yeah that's a lot of slime. Oh yeah I don't cut corners in weight on my pedaling bikes they all get the same recipe. Need pictures? My pedal bikes are full sus down hill bikes retrofitted to touring gears 52 tooth front sprocket always rain or shine.... I use 135mm bottom bracket , Tripple Trap Pedals , and Tripple Crowned 700mm travel plus forks. 6 foot 11 inches I am.... I do zero off road myself.


    My testing and tried true deal was avoiding road bikes and any thin tires I don't like the bumps in the road beating me up or the handling. 26x1.75 tires down are two rough for me and I they don't hold traction to my liking. A tire that will sponge a little will hold a road. Down hill world cup tires steal bead for my rides! I do enjoy the exercise!

    So point being I run heavy tubes, great big honking tires with zero balancing issues.

    The only tank slapping I do is gettyup!laff
     
    #20 Goat Herder, May 11, 2010
    Last edited: May 11, 2010

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