gas mileage comparison

Local time
2:12 AM
Joined
Jul 15, 2008
Messages
35
Location
Seattle
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
 
Local time
2:12 AM
Joined
Jul 15, 2008
Messages
35
Location
Seattle
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.
 

arceeguy

Active Member
Local time
4:12 AM
Joined
May 20, 2008
Messages
1,102
Location
Central New Jersey, USA
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.
 
Local time
2:12 AM
Joined
Jul 15, 2008
Messages
35
Location
Seattle
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.
 

waxsurfer15

Member
Local time
2:12 AM
Joined
Apr 10, 2008
Messages
46
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.
 
I

Irish John

Guest
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.

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.
 

Happy Valley

Active Member
Local time
4:12 AM
Joined
Jul 13, 2008
Messages
1,720
Location
WMass
Wouldn't it be most accurate to get an average over several tanks from a measured gas can and well broken in engine?
 
I

Irish John

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

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.
 
Local time
2:12 AM
Joined
Jul 15, 2008
Messages
35
Location
Seattle
If the bike can't freewheel really fast downhill it won't do well uphill.

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.
 
I

Irish John

Guest
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.

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.
 
Top