loud noise over 35 mph...

Discussion in 'General Questions' started by spencercan, Aug 27, 2014.

  1. spencercan

    spencercan New Member

    i bought a 2012 Giant (brand, not size lol) mountain bike last year and married her to one of these standard "80"cc 2 stroke engine kits. it sat in the garage for about a year making me angry, until i was told that it wasnt working correctly because i had 34 spokes and i needed 36. thats a huge detail that was conveniently left off of the instructions for the kit, but it did the trick.
    it runs great now, still in break in period, running through my last little bit of 24:1 mix. i have several questions, but first i am concerned that whenever i get at or above 35 mph, it sounds like its about to break. it sounds as if the back tire is rubbing on something. it doesnt sound like an engine noise to me, and it only happens above 35 mph (which is about its top speed on slight downhill). anybody know whats going on here and/or how to fix it? it has me scared to test its limits, which makes me mad.
    also wondering if i need special tires or brakes for higher speeds? do i need to use any certain octane level gas? id really like to start modifying and making it faster, but not if its going to kill me!
     

  2. shinjinian

    shinjinian Member

    You don't need special tires or brakes but some cheap bikes have brakes that won't work well at high speeds. As for your issue if something was rubbing you should notice it at any speed, even low ones. Pictures of the bike would help.
     
  3. Fabian

    Fabian Well-Known Member

    You shouldn't even be going anywhere near 35 MPH on a motorised bicycle - that's simply suicidal.


    You shouldn't even consider riding a motorised bicycle unless it has front and rear disk brakes, with at least an 8 inch front disk rotor, because stopping the bike is far more important than making it "go".


    Although it won't make any more power, use the highest octane (non ethanol) pump grade fuel you can get your hands on, then jet the carburettor to suit the fuel.


    You don't need the bike to go faster. You should be riding the bike slower if wishing to stay out of the hospital emergency ward.


    You can only ride as fast as your guardian angel can fly, and motorised bicycle guardian angels can't fly faster than 25 MPH.


    You will be really mad that a hospital emergency ward visit was necessary to test the limits, because you "will" end up in the hospital emergency ward.
     
  4. shinjinian

    shinjinian Member

    I think Fabian's being a little dramatic. Though he does have a point, there's no need to go over 35, the bearings on bikes wheels aren't made to withstand sustained high speeds and going fast if you have crappy budget brakes is dangerous. My recommendation is to try to cruise around 25mph and not go any faster, disc brakes aren't an absolute need on a motorized bike but they're something you should have if you're going to be traveling on one at high speeds.
     
  5. KCvale

    KCvale Motorized Bicycle Vendor

    Ya, and that's an understatement...

    "You shouldn't even be going anywhere near 35 MPH on a motorised bicycle - that's simply suicidal."

    Come on Fabian, thousands of use routinely ride 35MPH or more every day and there have been what, 3 documented cases of some idiot killing himself on an MB because he rode faster than his bike could stop?

    "You shouldn't even consider riding a motorised bicycle unless it has front and rear disk brakes, with at least an 8 inch front disk rotor, because stopping the bike is far more important than making it 'go'."

    Ohhh come one, Really?
    Nothing is safe without DUAL discs and it's needs to be 8" on front?
    Tell that to millions of people with a direct drive to a rear sprocket where a disc would need to be that are sill alive.

    This topic is about a new Giant build and Giant makes some darn fine bikes that will take 35MPH without bating an eye for thousands of miles.

    Show us some pics of your drive-train and maybe we can see what is giving the noise at high speed but these guys are right about brakes, don't skimp and test how fast you can stop in an emergency situation before you have one is my advice.
     
  6. grinningremlin

    grinningremlin Active Member

    Fabian loves overstating things, "flamboyant" I believe is the word.People have, and still do bomb hills at 50mph+ on touring bikes fully loaded.I personally have done over 60mph down Little Mountain in SBDO CA with a racing 10 speed and calipers.I don't care what brakes you have at that speed, you need MUCH time to THINK about the stop.Brakes are only as good as the users forethought.
     
  7. butre

    butre Well-Known Member

    Fabian is being incredibly over dramatic. wear appropriate safety gear at all times and you'll be fine.
     
  8. spencercan

    spencercan New Member

    ill post some pictures in few...
    lots of stuff to respond to here.
    brakes - no disk brakes right now, im just using regular v brakes. keep in mind this is a new build and a work in progress. i want rear disk brakes especially badly, as my front brakes work very well at all speeds so far. it seems to me that mounting the rear would be difficult due to the sprocket and cassette. ive never installed disk brakes, so im not sure what i would be getting myself into, but front looks a lot more feasible (but im not lacking front brake power right now...i have too much if anything). any thoughts?

    now, about this hospital stuff...why do we have all of this stuff to modify our engines and forums to help us go faster if the engines already go a speed that is too fast to be considered safe? i must say, i was half expecting someone to ask about the quality of the replacement rim i used, but not to be told that i had a death wish. by the way, i do wear safety gear and i try to ride responsibly in places where cars are not driving. and im not sure if it matters, but as the above poster stated, this is a $600 giant mountain bike frame; its not exactly a cannondale, but its not a $100 huffy or schwinn either. i figured it would provide me with a little more durability.
    i cruise at anywhere between 22 and 28; and its fine. i definitely do not try to cruise faster than the bike feels safe. i see all this racing stuff. i want my bike to go fast like the racing ones do, but...i do t wanna die! pics coming..
     
  9. spencercan

    spencercan New Member

    hmm cant really see too much in these photos, but here they are.
     

    Attached Files:

  10. Fabian

    Fabian Well-Known Member

    Please don't post pics of your untimely death. I have a weak stomach for that sort of thing.
    Racing stuff is for racing and should not be used on the road.

    Much better to boost the useable torque range of your engine than push man and machine beyond sensible limits.
     
  11. butre

    butre Well-Known Member

    my bike is well into the 40 mph club and doesn't feel particularly sketchy up there. so long as your wheels are true, your tire pressure isn't too low, and your frame is of reasonable quality there's no reason your bike can't be a speed demon and still reasonably safe.

    not that I regularly do 40+, but it's there if I need it. sort of like how your car does 120 but you haven't taken it past 80 but once or twice
     
  12. Fabian

    Fabian Well-Known Member

    Because some people are born with a penchant for putting their life on the line, and sometimes over it.
    Fortunately the human mind has enough intelligence to value the concept of self preservation, even though a small percentage of people have abdicated themselves from it.
     
  13. jhammondcpa

    jhammondcpa Active Member

    There was an article in a mid-west newspaper that reported a great bike that could reach the speeds being discussed here. Shortly after that the Secretary of State wrote that person featured in the article to let them know at those speeds the bike was considered a motor cycle, not a motorized bike which meant is should be inspected and tagged and that the driver should immediately get a new drivers license with a motorcycle designation. I am sure you can make your machines safe at the speeds discussed, but the states have the ultimate word in this argument.
     
  14. Fabian

    Fabian Well-Known Member

    Where i live, the state lists a motorised bicycle as a motorbike if engine power is greater than 0.27 horsepower and if engine power allows it to travel faster than 12.54 MPH.

    These figures are absurdly low, and don't take into account riders who might be on the heavier side, nor does it take into account riders who tow a loaded bicycle trailer, or riders who live in a location with very steep hills.
    Unfortunately the police don't give a damn about your situation or your reasons for breaching the regulations, and will happily nail your arse to the wall, if they know what they are looking at, which in my location (legislation) is a heck of a lot of nails through your arse.
     
    Last edited: Aug 28, 2014
  15. Slogger

    Slogger Member

    I go slo

    Hi ya'll, I'm new here.
    I am putting a 49cc on an Onyx 29" WWorld bike. They're actually getting scarce. I bought it from Dax, and told him I don't really care to go fast. I intend to use it under 20mph around here. It's illegal but the cops in this town put up with a lot if you're not trying to act like a racer/motorcyclist.

    I started riding motorcycles in 1971 and sold my Roadstar a few weeks ago.
    I've crashed a few times over the years but never got hospitalized (knock on wood), but the worst case of road rash and bruises I ever got was when I was a kid and crashed all tangled up in a 20" bike. Weak brakes, short wheelbase, high CG, no suspension, bicycles are spooky above 30, for me.

    I ordered a 48" sprocket to fix the tall overall gearing the 29" rims would have had, and to help it pull my heavy butt up the railroad overpass between me and my convenient store. I'm just going to be a bicyclist that pedals very little. I bought a bell bike helmet (cops love that) even though I rode m/c's bare headed all those years.
    Drug dazed, texting drivers are the threat, the helmet seems like a good idea on a bicycle that moves a little quicker than they expect.
    I just wish I could figure out a way to quiet down the engine. Engine noise draws the cop's eye. I called the desk sergeant, he told me to go by bicycle rules and keep off the sidewalks and there shouldn't be a problem.
    We'll see.
     
  16. piecepatrol99

    piecepatrol99 Member

    Spencercan

    I once rode my 20" 10 speed at 72mph. A friend and I tried to ride from the Bronx to Bear Mtn State Park. Hit a nice long down hill about 5 miles north of the George Washington bridge on Rt 9W north.
    I reference that ride because the day before, I toer my bike down to clean and grease the bearings. Crank, head and axels. The preload on the bearings is critical!
    I now have a 26" beach criuser that I've swapped the rear wheel for one with a 7 speed hub. That combined with my 49cc 2 stroke and a jackshaft kit maxes me out @28mph on flat ground. If I find a nice downhill, when I hit 32mph I hear and feel the same vibration you spoke of.
    My rear axcel was too tight.
    $469 to have the wheel built and they just about crushed the bearings =-O :O
    I've since cleaned the bearing cups, replaced the bearings and properly snugged the axcel (not crushed the bearings).
    No more vibration @54mph ;-)

    You'll want to at the least, pull the wheel you're getting the vibration from and check that your axcel is properly torqued.
    Too loose and you can feel it wiggle in the hub. Too tight and the friction on the bearings (no matter how much or what type of grease you use) can make a wheel feel like its going to explode at speed.

    I hope this helps...
     
    spencercan likes this.
  17. piecepatrol99

    piecepatrol99 Member

    Spencercan

    I once rode my 20" 10 speed at 72mph. A friend and I tried to ride from the Bronx to Bear Mtn State Park. Hit a nice long down hill about 5 miles north of the George Washington bridge on Rt 9W north.
    I reference that ride because the day before, I toer my bike down to clean and grease the bearings. Crank, head and axels. The preload on the bearings is critical!
    I now have a 26" beach criuser that I've swapped the rear wheel for one with a 7 speed hub. That combined with my 49cc 2 stroke and a jackshaft kit maxes me out @28mph on flat ground. If I find a nice downhill, when I hit 32mph I hear and feel the same vibration you spoke of.
    My rear axcel was too tight.
    $469 to have the wheel built and they just about crushed the bearings =-O :O
    I've since cleaned the bearing cups, replaced the bearings and properly snugged the axcel (not crushed the bearings).
    No more vibration @54mph ;-)

    You'll want to at the least, pull the wheel you're getting the vibration from and check that your axcel is properly torqued.
    Too loose and you can feel it wiggle in the hub. Too tight and the friction on the bearings (no matter how much or what type of grease you use) can make a wheel feel like its going to explode at speed.

    I hope this helps...

    P.S.

    After getting some sleep I thought of a few more safety tips: some are pretty basic but a refresher course never hurts ;-)

    I'm on my second motorized bicycle and I've noticed some differences between the two buils...
    1: I'm never building on another inexpensive 'Aluminum' frame or a frame design that requires an over sized spindle. Aluminum has more flex than steel and the oversized spindle created a monkey wrench effect. The torque output of the motor actually twisted the bttombracket housing every time I hit the gas.
    I had to sacrifice/reduce my chain ring sizes from 48/44 to 36/24 so the chain from the jackshaft output would clear the clutch cover.I still top out at about 26mph and my hill climbing ability has almost tripled.
    2: Please wear a helmet. Many of the people near me that have motorized their bicycles complain about being stopped by the police. I never have. The one difference between me and them is I wear a helmet.

    I know this a little off topic but ultimately the topic is safety.
    Know your equipment and its limitations. Make sure every thing is properly adjusted. We are trusting our lives to bearings and brakes that are abut the size of your pinky.
     

    Attached Files:

    Last edited: Aug 29, 2014
  18. Rockjaw

    Rockjaw Member

    It's always a beautiful day in the neighborhood,..I ride a lite bike with a 66cc engine..i do 25-38 mph all the time.
    My mom may have dated a Mr. Rogers but she didn't marry one.
     
  19. KCvale

    KCvale Motorized Bicycle Vendor

    Beautifully put ;-}

    I am no stranger to Mr. Rogers Neighborhood and it's kinda fun when youngsters scratch their head about our old time references ;-}

    For the short running around I do I like 35-38MPH, but what I like more is getting up to 25MPH in the blink of an eye so I don't get rear-ended in traffic, after that it is all about being seen buy people in front of you liable to cut you off.

    A daylight front strobe is my first defense, but great brakes make the difference between a scary panic stop and the hospital.
     
    Rockjaw likes this.
  20. spencercan

    spencercan New Member

    thanks for your post piecepatrol...i will be sure to take the rear wheel off and check everything out. im sure that must be the problem. if it is...is it dangerous to leave it as is for now? in other words...is it just a harmless noise or is it the symptom of an impending disaster?
    i dont like wearing a helmet, but i do use one because i have a rear view mirror attached to it (hate having to turn around).
    theoretically id like to put disk brakes on the rear and since the v brakes work so well in the front, leave them as is. usually i see the opposite though...why? is it difficult or expensive to put disk brakes on the rear as opposed to the front? my front brakes already make me stop abruptly enough to seemingly send me flying over the handlebars. i cant see needing more stopping power than that.
    this is definitely off topic, but id also like to change gas tanks, as the stock one just looks so silly on my bike. i saw some cylindrical looking stainless ones that mount in the rear that looked cool. any ideas? any recommendations on where to buy performance parts online (or in store)?
     
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