Motorized Axle Mount Mountain Bike

[MotorizedBikeRider]

This is a motorized axle mount bike I just finished:

Huffy Rangeline 27.5" 21 speed, disc brakes
33cc 2 stroke (I live in Oregon, legal size limit is 35cc)
40 teeth large sproket
10 teeth small sprocket
Tear drop gas tank
Speedometer

I removed the rear disc brake, and mounted the large sprocket using the disc brake mount holes. I put on a caliper brake, but braking performance is less than stellar, so I am making a bracket (I am a machinist) for a v-brake set up, which should perform better. Wheel rim is anodized and probably I need to remove it to improve stopping power, but, am waiting the v-brake parts to determine if this is needed.

My focus was not speed, I wanted this to be slower, maybe top speed of 20-25 at most, but I easily go 32mph. Cruises real nice at 20mph, I live out in the country about 5 miles from town, I've been driving into town each day, no problems at all. The motor is very LOUD, sometimes I turn motor off while driving downtown and pedal, but not always.

Climbs hills great, no need to pedal when starting off, but sometimes I pedal anyway.

.

motorizedbikerider

 

[Greg58]

Looks good, welcome to the forum. I’ve never done one but have seen the kits available from time to time.

 

[Sidewinder Jerry]

You didn't say how much your reduction gearbox is. I live in the mountains of Tennessee. I have a 4-stroke 33cc shifter bike and can drop the reduction range as low as 66.79\1. I also weigh 235 lbs and my bike weighs around 100 lbs. Always pedal on taking off. This will save your clutch. Mine has held up for 12 years.

Is this your first motorized bicycle? I don't know how much you know about cycling but your bike is a 3x7 drive. 21-speed is a marketing phrase. You have 21 shifting combinations but you don't have 21 different ratios, many are redundant. A 3x7 is shifted like this:

1(1-4), 2(2-5), 3(4-7)

This gives you 12 sequential non-redundant ratios. Take-off gears are 1(1) for starts going uphill. All other take-offs use 2(2). If a gear is too easy or too hard to comfortably maintain a cadence (crank rpm) of 70-90 it means you're in the wrong gear.

My main purpose for sharing about using bicycle gears is for when the day comes you do have to pedal home. It eventually happens to us all lol.

 

[MotorizedBikeRider]

Hi Sidewinder Jerry,

My gearbox is 5:1 reduction.

The two sprockets 40/10 should be 4:1 for a total of 9:1 reduction, right? I was considering putting a bigger wheel sprocket, like 44 or 48, but, this setup seems good to me for now. I think the bigger 27.5 wheels gear it up some compared to a 26" wheel.

I only weight 160lbs. The hills I climb when I'm pedaling my other bikes seem a bit tough, but this motorized bike I only give it a little more gas to maintain speed. It's only a 33cc motor, but seems to have a lot of power, but, very loud. I chose a 2 stroke, but might buy a 4 stroke and mount it for comparison of power. I understand a 4 stroke 35cc should be about 90 decibels, about 20 times quieter.

For break in of the motor I was driving it easier, and also the carb is set rich, and high idle is set rich to limit engine speed. I just today, leaned the idle mixture a bit and the speed increased from 28mph top speed to 32mph top speed on flat road. I can make it go faster by changing high rev mixture but I don't want to go faster, cruising at 20mph to 24mph the engine is just purring, kind of a sweet spot.

Yes, this is my first build.

I ride my road bike, (no motor), perhaps 10-12 miles a day, 4 or 5 days a week. I do not ride fast, maybe 12mph or so average. I am not super heavy into cycling, I just ride because of health benefits, and also I enjoy it. Now sometimes I ride this motorized bike, sometimes I ride one of my other bikes.

Sometimes I drive it in motorized, then, pedal around town for exercise, then start the motor and ride home. Nice to be able to do either, so I can pedal on sidewalks and bike paths, but also use the motor on the streets.

I have not weighed the bike yet. I don't think it's 100 pounds, though, more like 60 or 70. But yes, I need to weigh it.

Pedaling home is no big deal. Pushing it home is never fun. Carrying it home is worst!


motorizedbikerider

 

[Greg58]

The multi speed bike makes it much easier to pedal when I need to, I built single speed bikes until 2019 when I used spare parts to put together a 24" tire mountain. My latest bike is a Electra townie that is very easy to pedal, your speed is really good, both of my 48cc in frame engines do about the same speed.

 

[Sidewinder Jerry]

Your reduction is 20\1not 9\1. The reduction range on my shifter bike is 66.79\1 to 16.25\1. Your total weight is probably 210 lbs at the most. The Honda 35 has 1.2 hp at 7000 rpm and a Robin Subaru had 1.6 hp at 7000 rpm. So though quieter, you will be giving up some power. Both of these engines are on the pricey side. I use a rear rack mount on my bike.

With your setup to do 32 mph, it means your engine is turning at least 7823 rpm. You may want to get a tachometer/hour counter. Especially if you do get a 4 stroke. The hour counter is good for maintaining a maintenance schedule. The tach is good to prevent over-revving and engine strain.

 

[MotorizedBikeRider]

How are you computing reduction rate?

motorizedbikerider

 

[MotorizedBikeRider]

The multi speed bike makes it much easier to pedal when I need to, I built single speed bikes until 2019 when I used spare parts to put together a 24" tire mountain. My latest bike is a Electra townie that is very easy to pedal, your speed is really good, both of my 48cc in frame engines do about the same speed.

What is 'Electra Towne"?

I was considering multi-speed to be moot. Will be nice for pedaling, though.

I am surprised at the power of this engine, and my top speed I attain. I don't really want to travel at over 30mph on this bike, although it does so very nicely. I was curious how fast it will go so I opened it up. I can go faster if I adjust the high rpm fuel adjustment. What I like about the 2-stroke is I can adjust the carb for the performance I want, what I don't like is that is is very loud, and also fuel economy is not as good as I thought it would be. But also fuel economy might be related to running motor rich. I could do a number of things to increase horsepower but no intentions to do so. I will be buying a 4-stroke so I can get a good comparison of power and noise. It does not take very much to take the motor off/on.

motorizedbikerider

 

[Sidewinder Jerry]

To calculate the total reduction you multiply instead of adding. 5\1 × (40/10)\1=20\1

Here's my speed formula:

(RPM × Wheel Diameter × π)÷(1056 × Total Reduction)=MPH.

The Honda 50 engines are really good without giving up too much power (49cc, 2hp). The Robin Subaru 35 is probably the best 4-stroke in that size; both are a bit expensive.

The 142f engines (49cc) have 1.6 hp at 6800 rpm and the 144f (53cc) have 2 hp at 6800 rpm; these engines are very affordable.

You should adjust your carburetor to peak performance; this will improve your fuel consumption. If you have 3 adjustment screws a tachometer will help with getting the best settings:

First, adjust the high screw till you get a max rpm at full throttle; then leave the setting there

Next, adjust the low screw to max rpm at no throttle; then turn back towards the rich side to where the rpm just starts to drop and leave the setting there.

Last, adjust the idle screw to the recommended setting.

Either remove the engine drive chain or have the rear wheel lifted off the ground when doing this. You may also have to set your idle screw a bit high at the beginning of this.

 

[MotorizedBikeRider]

To calculate the total reduction you multiply instead of adding. 5\1 × (40/10)\1=20\1

Here's my speed formula:

(RPM × Wheel Diameter × π)÷(1056 × Total Reduction)=MPH.

The Honda 50 engines are really good without giving up too much power (49cc, 2hp). The Robin Subaru 35 is probably the best 4-stroke in that size; both are a bit expensive.

The 142f engines (49cc) have 1.6 hp at 6800 rpm and the 144f (53cc) have 2 hp at 6800 rpm; these engines are very affordable.

You should adjust your carburetor to peak performance; this will improve your fuel consumption. If you have 3 adjustment screws a tachometer will help with getting the best settings:

First, adjust the high screw till you get a max rpm at full throttle; then leave the setting there

Next, adjust the low screw to max rpm at no throttle; then turn back towards the rich side to where the rpm just starts to drop and leave the setting there.

Last, adjust the idle screw to the recommended setting.

Either remove the engine drive chain or have the rear wheel lifted off the ground when doing this. You may also have to set your idle screw a bit high at the beginning of this.

Thank you for the useful information!

MotorizedBikeRider

 

[Greg58]

Here’s the townie, a neighbor up the road gave it to me. I made the rear mount to move the engine forward to use the pipe.

 

[MotorizedBikeRider]

MotorizedBikeRider

 

[MotorizedBikeRider]

Here’s the townie, a neighbor up the road gave it to me. I made the rear mount to move the engine forward to use the pipe. View attachment 111383

Very nice motorized bike.

In Oregon, I cannot letally mount a motor over 35cc on a bicycle, so it limits what I can do. I see a few motorized bikes around town (Cottage Grove), I know they are all 49cc or bigger. One guy has a trailer he pulls behind his rig. I want to mount a 35cc 4 stroke in a bike frame. The Bike Berry kit looks good, but their motors are too big. I may need to make my own engine mount to fit the smaller engine. If I get pulled over, I don't want to lie to the officer about engine size.

MotorizedBikeRider

 

[Greg58]

That bike has a 48cc engine which is legal here in Georgia, I have a couple of the larger engines but I don’t leave our road with them. Right now I have a back up engine of each size and three running bikes. Warning: this hobby is like eating potato chips, you can’t stop at one.

 

[Sidewinder Jerry]

Very nice motorized bike.

In Oregon, I cannot letally mount a motor over 35cc on a bicycle, so it limits what I can do. I see a few motorized bikes around town (Cottage Grove), I know they are all 49cc or bigger. One guy has a trailer he pulls behind his rig. I want to mount a 35cc 4 stroke in a bike frame. The Bike Berry kit looks good, but their motors are too big. I may need to make my own engine mount to fit the smaller engine. If I get pulled over, I don't want to lie to the officer about engine size.

MotorizedBikeRider

My 33cc bike with a triple chainring shift kit

 

[albertjohnnson]

A motorized axle mount mountain bike is a type of mountain bike that is equipped with an electric motor for added power and control. This type of bike has a motor mounted directly to the hub of the rear wheel, and is powered by either a battery or a fuel-powered engine. The motorized axle-mount mountain bike is designed to provide extra support when riding through rocky and difficult terrain. It provides greater control and power when climbing and descending hills, and it helps to reduce the risk of fatigue or injury while riding. Motorized axle mount mountain bikes are becoming increasingly popular among mountain bikers, as they offer an easier and more enjoyable riding experience.