gas mileage comparison

Discussion in '4-Stroke Engines' started by Vishnu Tensleep, Sep 1, 2008.

  1. I just mounted a Hua Sheng / Hoot system on a mountain bike. After 30 miles of short break-in rides, I took it on a 22.6 mile ride today, in part to get an accurate measure of gas mileage. I live in Seattle, and although I took a fairly flat route for this city, I included some hills, including a couple of about 9% grade.

    I estimated the gas used by measuring the depth in the tank before and after, and doing a fairly careful measurement of the surface area (needed due to teardrop tank). By my measurements I used 0.27 gallons of gas, which comes out to right around 85 mpg. While this is more than is advertised by the scooter companies, it's a lot less than the 150+ mpg often touted by a few folks on this forum. I'm interested to hear what folks are getting, and if anyone has any ideas about why my mileage might be significantly lower than others get.

    For the record, I weigh about 205, and the bike is a standard old Trek with no suspension. I had about 50 psi in new high-quality 2" road tires. I'm running a 50 tooth rear gear, and the engine seems to settle into a nice cruise at about 20-21 mph. It won't go faster than 23 on the flats (yes I know I'm not supposed to floor it, but I couldn't resist this AM with nobody around...) The 50 tooth gives me nice speed up grades in Seattle - with some pedaling I go about 16 up the 9% hill by my house. Would I get better mileage if I used a smaller rear gear? I wouldn't think so, but maybe others have found this.

    Also, towards the end of the ride, there was some occasional power fade, but nothing alarming, and the bike finished strong up the hill to my house.

    Any info would be greatly appreciated.

    My gas mileage

  2. am I revving the engine too high during break-in

    Another question - is the "20 mph break-in" rule too fast for this engine? As noted above, the bike tops out at about 23 mph on the flat with a 50 tooth sprocket. It doesn't seem to be revving excessively high to me at 20, but maybe I don't know squat. Certainly, it just purrs at 15 mph.
  3. arceeguy

    arceeguy Active Member

    My guess is that you will probably see 100+ mpg at 15mph. If you were cruising at 20, and it tops out at 23, the engine was not operating at its most efficient rpm and revving too high for maximum efficiency. If you "gear up" you'll be able to cruise at a higher speed with better fuel economy, but you may not be able to pull some hills without pedaling.
  4. thanks

    Thanks for the tip. I don't mind pedaling, and the bike bores up the hills. Sounds like I should try a signifcantly smaller sprocket. At the same rpm, if I want to go 30 mph, I'd need a 50*20/30 tooth or 33.33 tooth sprocket. Alternatively, I'd go 20 mph at 2/3 of the rpm.
  5. Be Careful

    Just a little bit of input. I live in Florida where it is dead flat. Had a 56 tooth and went to a 44 tooth for the same reasons. Now I am putting on a 50 tooth because it is really hard on the clutch to get up to the speed it is happy at. Also, with a little bit of headwind, you slow to a crawl.
  6. Irish John

    Irish John Guest

    I can do a 55 km trip for just less than 3/4 litre. At that consumption I get 207 miles per gallon but it is actually more than that. That is running hard at near top speed whioth a HS\Grubee on a 48T sprocket. When I used the 56T sprocket fuel consumption rocketed and top speed was way down and engine vibrations, wear & tear way up. To get good consumption you have to have a really good line of chain and a true sprocket with no wobble. The engine must be tuned right with the air\fuel mix. If you run a sprocket that is too small so the motor struggles on hills badly you will use more fuel and get really sooty plugs which eat more fuel. A 50T is probably perfect for the HS and a 48T perfect for the Honda cos the power is more on the Honda. I know that seattle is seriously hilly and the home of the famous 'Skid Row' where they slid logs down to the ships so you might need a bigger sprocket. On really seriously hilly country the 50cc 4-stroke frame mounts can't cope no matter what sprocket you have. There are some hills I have to avoid and my bikes are nicely set up to freewheel really fast down hills. If the bike can't freewheel really fast downhill it won't do well uphill. On a Honda\48T I get similar fuel consumption and much higher average speeds. The Honda drives like a car.
  7. Happy Valley

    Happy Valley Active Member

    Wouldn't it be most accurate to get an average over several tanks from a measured gas can and well broken in engine?
  8. Irish John

    Irish John Guest

    That is precisely what I have done. I fill the tank up to the brim and I know how many litres that takes and how many miles since the last fill therefore I can tell you that I usually get somewhere between 60 and 88kms to a litre. The 60 figure is when I've been running the engine stationery quite a lot and the 88 figure is when I've been running along the road all the time. I frequently let the motor warm up for 5 minutes before I take off in the morning. The fuel consumption is very good and the cost of fuel doesn't really affect me. The 4-stroke is a fraction of the cost to run compared to the HTs because I don't get breakages. The HS has done 4000 kms and the Honda only 300 but I much prefer the Honda and it is money well spent.
  9. John - why is this? Seems to me that the freewheeling feature wouldn't have any relation to gas consumption when it's not engaged (going up a hill). What am I missing?

    On a related note re freewheeling, I realized soon into riding the Hoot gearbox that because it doesn't freewheel, the engine does most of my braking when coming to stops. I only rely solely on my bike brakes under about 5-7 mph, which seems like a safety feature. That said, on long downhill grades the engine doesn't get a chance to "rest." I suppose this might this affect the gas mileage, since I'm maintaining speed by having the engine revved well above idle, even if the engine is also acting as a brake.
  10. Irish John

    Irish John Guest

    Firstly if your bike won't freewheel really fast then there is something stopping it and producing drag. Maybe the chain is too tight, the wheel isn't balanced or the cones are too tight on the bearings or the brakes are engaging. This makes it harder for the engine to pull the bike along.
    The Hoot, without a freewheel, will use more fuel because you can't coast down hills. I often freewheel for over 2 kilometers at a time and that is often my fastest speed because the engine is just ticking over.
    A well set up bike will use less fuel, accellerate better and pull better uphill.
    Engine breaking has its advatages but I find brake pads are cheaper than fuel.
    There are hills where my bike will freewheel at over 80 km\hr if I was foolish enough to let it. If you hit a dog at over 50 km\hr the chances of being killed are pretty high. At 30 km\hr your chances of survival are increased many times.
  11. freewheeling etc.

    Perhaps I misunderstood what was meant by freewheeling. From a dead stop and with the engine idling (i.e., the clutch is not engaged) my bike will coast nicely down slight grades. The gears in the gearbox are being turned by the chain, but there's no connection to the engine. However, decelerating from cruising speed, the clutch doesn't disengage until I drop to about 5 mph. I could stop at the top of a hill, let the clutch disengage, and then coast down it, but I think I'd want to turn the engine off so as to not accidentally rev the engine and abruptly engage the clutch. My concern is that it would be easy to damage the clutch, gearbox, or perhaps even the engine. Is this an unnecessary concern?
  12. ZnsaneRyder

    ZnsaneRyder Member

    With a 196cc 6.5HP engine............
    Getting around 100MPG when cruising at moderate speed (25-30mph) with a good belt and just 1/3-1/2 throttle.

    With a worn slipping belt and running full throttle and hard riding and playing around I still get over 60MPG.

    I check my exact trip mileage with mapquest and calculate my MPG. I even got 91MPG one day but I rode a flat tire with the tube removed for over 8 miles to get to the store where I could replace the tube. Now I have a flat-free foam tube for my back tire.

    Being the engine is larger and doesn't work as hard as a small engine I feel helps the MPG.
  13. Irish John

    Irish John Guest

    Can't talk for the Hoot but the Grubee will coast just as well with the engager in and the throttle closed as it will with the engager out.
    You can pull the engager in when you are going along at speed and the revs can match the speed but if you pull it in stationary with high revs you'll snap the key in the final sprocket shaft. You only do this once and then you learn not to do it again.
  14. Irish John

    Irish John Guest

    Isn't this a 2-stroke motor? or is the Lifan a 4-stroke
  15. I can't really talk about the free wheeling thing because I use the staton chain drive with a centrifugal clutch and a freewheel my gearbox never inteferes if I want to freewheel.

    I get (if my odometer is correct) about 175 mpg using a 22 tooth on the gearbox and a 16 tooth on the wheel with staton's 18.75:1 gearbox. I upgraded to the 22 tooth for more speed and in the process I took a hit in my fuel economy as I was getting 190 mpg with the 19 tooth gearbox sprocket. It is important to note that my area is completely flat (coastal plain of virginia and nc).
  16. Danny3xd

    Danny3xd Member

    Just finished first gallon of gas on a Honda GX50 and came to almost exactly 100 MPG. I have been told that other 4 stroke engines get between 185 and 200+ MPG and am really curious.
  17. bamabikeguy

    bamabikeguy Active Member

    MPG always improves over time, but I'd guess nearly 75% of the 4 strokes MBers are using are under 40cc, in that 1.6-1.8 horsepower range, which accounts for a lot of the difference.
  18. Danny, I use the gxh50 2.5 horspower 49cc. If you look at my post from last year I posted about 175 mpg. I have since returned to a 19 tooth on my gear box. I've noticed a significant difference in fuel economy based on my average speed. If I venture too high out of the rpm sweet spot I can loose 25 mpg or more. I estimate the sweet spot to be somewhere around 4-5000 rpms by looking at the power and torque curves. Anything beyond this and the power still goes up but the torque goes down (the engine is starting to fight itself to go faster). I try to keep it at around 5500 rpm...its a nice compromise of fuel economy for speed (approx 27 MPH). BTW, my bike is really loaded. I welded my own rack using an old bed frame and I carry a bag on the front of my bike. With the battery the bag weighs at least 25-30 pounds. Even with this I get excellent mileage (admitedly I have no hills to climb). I have recently made some changes (added an idler sprocket and extra large gas tank from an old commercial lawnboy) which will likely have little to no effect on mileage, but I still like to watch it since this will likely be my first clue there is an engine problem. Of course, with gas prices going BACK up :icon_cry: I will be doing all I can to maximize my mileage

    Your fuel economy will depend on a lot of factors like engine rpm, hills, weight, sprocket ratios, prevailing winds, tire inflation, tire tread, general aerodynamics, type of oil used, quality of gas (no don't use hi octane...the extra octane is only useful for high compression engines), chain/friction/belt drive, gearbox or no, quality of all components, etc...if you're geared for power you'll lose fuel economy. If you're geared for speed you'll gain fuel economy (within limits of course). I'm curious, what's your speed at 5500 rpm's?
    Last edited: May 28, 2009
  19. Danny3xd

    Danny3xd Member

    Very cool. Thanks Bama and TV. More I learn about and ride the GX, the more I like it.
    Last edited: May 28, 2009
  20. HoughMade

    HoughMade Guest

    I will never approach 175mpg. If I was cruising around at 20 mph or lower, maybe...or if I weighed less than 220 lbs....but I don't see either happening any time soon.