I wanna go faster! Help me do it =)

Discussion in 'Motorized Bicycle General Discussion' started by JohnLL, Aug 4, 2010.

  1. JohnLL

    JohnLL New Member

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    Ok, I haven't been here in a while, but I came and asked some questions before building my first motorized bicycle using the Grubee Skyhawk 66cc angle fire engine kit. And it worked out great! I've put over 2500 miles on it using it as a daily commuter and for shuffling around town. Now I have a few questions before attempting to enhance my build on my next bike.

    First, I used the basic setup, on a single speed Kona Unit mountain bike with 2.125 inch tires, and was able to hold a steady speed of about 35 mph, topping out around 38. This was a blast for a while, but now I want to go faster xct2

    My main questions are about my options to get more speed out of my next build. If I were to simply use a smaller 36 tooth sprocket on the rear wheel as aposed to the standard one, how much faster should that get me?

    My father also said that I could make the front sprocket in the engine a bit larger, not only helping my top end speed but helping to keep my chain better in place, has anyone done this?

    Also, I've been considering moving to a multispeed bicycle and finding a jackshaft kit. I'm not too familliar with how they work, but I may try moving up to one of those also. If anyone is using one and can give me feedback I would appreciate it.
     
  2. Mind_Reader7

    Mind_Reader7 New Member

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    I went down to a 32 tooth sprocket and noticed a difference. I made a custom exhaust, and noticed a HUGE difference. At lease 30% more speed all around. I cut the pipe from the stock exhaust, welded it to a straight through chinese exhaust, and now it flys/soudns awesome.
     
  3. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    It's unlikely you'll get any more than 1-2 mph extra out of it by gearing up. These engines just don't have enough power to add gear to go faster. The 32 will result in a lower RPM cruise and top speed.

    A pipe will increase power a bit, but you'll need to have a major hp increase to raise the top speed very much, and these engines also don't rev much past 7500 rpm unless you get an extremely rare one.

    Try a Morini if you have the $$$.
     
  4. karryhunt

    karryhunt New Member

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    I don't want to sound like a doubting Thomas but I have one question......

    1. By what means have you used to veify the accuracy of your speed?

    2. My Trek Cruiser Classic is set up with the same engine you have with a 10/42 tooth sprocket properly installed without tensioner, perfect chain alignment with Jim's hub adapter, properly mixed Opti 2 oil, 45 lbs in each tire and I challange anyone that tells me they can cruise at 35 MPH for an extended period of time without the bike putting you to sleep or falling apart.

    3. I know there must be someone out there that will challange this but I would like to hear from them and see some proof on the speed accuracy.

    4. Any takers?
     
    #4 karryhunt, Aug 4, 2010
    Last edited: Aug 4, 2010
  5. ferball

    ferball New Member

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    You may want to invest in a motorcycle if you are looking for speed...Don't get me wrong tinkering on these things is fun, but if all your looking for is "bolt ons" for speed a cheap late 70's early 80's honda or yamaha might be cheaper in the long run.

    That being said I want to hear the results of changing the drive sprocket, that sounds like an interesting idea. If you realy want some speed look into ram jets and pulse jets, I have been trying to figure out how to fabricate and mount one, you could be the first jet biker......
     
  6. 2door

    2door Moderator
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    Like the man said...go buy a motorcycle. These are, always have been and always will be MOTORIZED BICYCLES. They are not designed or meant to keep up with traffic. If your 35 mph claim is accurate consider yourself lucky and if you're not satisfied, go see the Harley or Honda dealer. I'm sure you'll find something there that will satisfy your need for speed.
    Tom
     
  7. ferball

    ferball New Member

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    I still think a small pulse jet mounted to the rear rack would be something to see...oh wait it has been done..
    Jet Bike
     
  8. Mind_Reader7

    Mind_Reader7 New Member

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    *puts on coolface* I break the 50kmh speed limit.
    .shft.
    ^^ litereally what happens when I take off.
     
  9. BarelyAWake

    BarelyAWake New Member

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    Although I gotta say that extended trips @ 35mph isn't an unreasonable expectation (provided the engine/bike is built for it ofc) - I think you're gonna be hard pressed to get anyone to cough up anything in the way of proof, there seems to be quite a number of folks more than willing to throw numbers around - but precious few of 'em seem to have anything to back it up with lol





    To answer the poor guy's original question though (sorry about that, you stumbled on a touchy subject heh) there's a lot of really good info here: High Performance Bicycle Engine Tips - but I'd recommend a true expansion chamber exhaust & port matching the intake and exhaust manifolds as the most pronounced gain for the money/effort.

    Honestly - it's not that we're "against" speed or getting the most performance outa yer ride, it's jus' being the internet we get all sortsa outlandish claims by those whom may not have anythin' other to show than duct tape & wishful thinking ;)

    So generally we settle on a compromise - we yap about performance mods alla time, but unless peeps have some sort of real substantiation, we pretty much skip talkin' bout the numbers :)
     
  10. JohnLL

    JohnLL New Member

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    All these people doubting my speed has me worried about getting another engine. My father is a Pinellas County police officer, and according to his radar my bike will go 43mph top speed. If that is that unusual for having done virtually nothing to the bike, we drilled out the exaust cap by 5/8" and he fussed with something else...but its all stock, than I'm worried my next engine won't perform equally.

    Maybe it was how I worded it. When I said I cruise at 35, I'm talking about going for .75-1 mile. If I'm going any further than that I usually hold around 30. That still doesn't change the fact that my bike tops out at 43. I also have a Bell digital speedometer on it and that also reads between 42-44 top speed with a +/- .5 mph reading.

    I am not using a cruiser, I'm using a single speed aluminum frame bike, but still using 2.125" tires. I also use super tubes which I have from downhill racing before I moved to Florida, which hold more like 65 psi, maybe that makes some difference, but I doubt it. If my speeds really sound that far fetched perhaps I will buy an engine to give to my father and keep my bike as is.

    EDIT: Also, to the poster above me. If I need to ride one handed and record my speedometer I can do that lol. I'm not looking to make my bike go 60. The road I ride on has a speed limit of 35. Which would be fine if most people didn't go 45. If I could get my cruising speed from 35 to 40 that would be a big help with the number of cars passing me WAY to close I have to watch out for.
    Also another question now. I noticed they have a boost kit now saying it can give a 4-6 mph speed increase, has anyone used these?

     
    #10 JohnLL, Aug 5, 2010
    Last edited: Aug 5, 2010
  11. robbdaman

    robbdaman New Member

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    Hit the gym and lose 50 lbs and you're sure to go faster. =)
     
  12. camlifter

    camlifter Active Member

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    i have a mongoose with 28" wheels and a 66cc grubbe 44 tooth, took it out with a hand held gps, it runs up to 37mph prety ez, if you then tuck in and keep it pegged it will slowly reach up to 40mph but it's wound tight as a cheap watch by then, it will cruise in the mid 30mph range ez. so i don't doubt your clam. 43 mph means you got a really good one. don't expect other kits to be able to do it. the top speed is all about how many rpm the engine can pull with a certain size sprocket, drop to too small a sprocket and the motor can't reach the same rpm as it used to. a 40 tooth is probably the best all around sprocket. speeds over 40 are asking for trouble, even speeds of 25 need better brakes.
     
  13. BarelyAWake

    BarelyAWake New Member

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    I suppose I could dredge up the controversy regarding the accuracy of both radar guns and bicycle speedometers - but I'll skip to the chase, that with our scale & relative speed the margin for error (usually only 5mph or so) makes all the difference between an average bike and what may appear to be an exceptional one... but given that both the speedometer & gun agree than it may well be accurate.

    It is unusual but not unheard of to get the speeds you say, so you may wish to keep that motor lol High pressure tires alone do actually make a significant difference, but weight (aluminum frame) would only really effect acceleration.

    As for speed validation... other than pretty much the speeds you've quoted, it starts getting really hard to believe - sure it's not impossible, the land speed record for an Altered Gasoline 50cc engine is around 70mph, but there's no way in heck these Chinese engines are gonna reach that, it's unlikely they'll hold half that if they're stock out of the box.

    But we get outlandish speed claims all the time lol - and it's not always dishonesty, people will happily report downhill speeds (which obv doesn't count heh), forget to switch from KPH to MPH, or not even know how to correctly calibrate it to begin with... then there are those that'll *cough* "round up"... just a lil, ya know - to impress and all :p

    Problem is not only can't we really tell who's honest or not - but it messes up people's expatations, just as you worried about getting another engine so is the new guy concerned and disapointed when his shiny new engine "only" does 30mph... when in fact that's perfectly normal for a well tuned, broken in stock kit.

    So we ask for substantiation for any claims beyond these "average" speeds, mostly in the interest of getting good info out to the members. You don't need to risk life... or at least limb to get video proof if you don't wish to try to impress others with your maximum speeds *shrug*


    As for the boost bottles, heh... well we've had some reports that they improve idle, we've had just a few swear they have a "huge" effect - but most seem to agree they pretty much just look cool :D
     
  14. Techbiker

    Techbiker New Member

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    My 2 stroke after some tuning can hit 30 mph but nothing more. I'm pretty sure that I just got an average engine though. An "exceptional" engine can probably get to the high 30's. Regardless, you can go with a tuned pipe and a shift kit for maximum versatility from your engine. I wouldn't go much smaller on the sprocket if you are not getting a shift kit because it makes it difficult to get up to speed quickly. With a shift kit, you'll be able to get every last ounce of power out of your engine. You might be able to raise your "crusing speed" up 3-4 mph from 35 but I doubt that you will be able to cruise at 40 without properly balancing your engine internally. The vibrations usually just get too severe. Good luck though!
     
  15. wezwheels

    wezwheels New Member

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    sir, if your pulling a top speed at 40+ your one lucky cat! this is unheard of in the motorized bike world. i`ve seen the better of 38+ on a cool non humid morning. but pulling a 40+ and holding it is like being married twenty years and getting some every week. it just don`t happen. these other guys are right. your one in a million and i`m still waiting for the weekly. hahahahha!!!
     
  16. ferball

    ferball New Member

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    I was once clocked at about 30 by a friend driving by. I do not dismiss out of hand 30+ claims as I know given the right conditions I can almost hit it on a stock kit with no mods and I weigh about 320. I question anybodies sanity that wants to hit it. I usually only ride at 3/4 throttle because my bike gets scary at high speeds and my base bike is a mid level mountain bike that was made for hard riding and abuse, so if you are on $100 cruiser from walmart you are just asking for a large hospital bill.

    That all being said I am often reminded of an old Isuzu commericial when speed claims start flying...Joey Isuzu is extolling the virtues of a new Isuzu..."It can 200MPH....down hill in a hurricane, with a good tail wind...."
     
  17. sradabaugh

    sradabaugh New Member

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    New 2010 48cc grubee with the CNS Carb and it does 27mph. I think a little tuning and it will hit 30 mph but I think as someone mentioned a few posts earlier.... thats the norm for unmodified.
     
  18. muddybike

    muddybike New Member

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    Wow can we get bigger text next time , and all caps too pls !
     
  19. BarelyAWake

    BarelyAWake New Member

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    o_O

    So you made it better by quoting it... how?


    lol - while it's true I'm inclined to agree such font abuse may well be excessive - we don't worry about it too much here, if we did - rest assured we'd have edited it by now ;)
     
  20. Alson

    Alson New Member

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    My bike goes 36 mph top end, it went that fast without an expansion chamber, but now I have one. I noticed the gain when I ported my exhust and intake. I have a 66cc SkyHawk slant head.wee.
     

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