Golden Eagle Bike Engine

250 mpg bicycle assist motor

I live in Phoenix, Arizona which has a vast network of grossly under-utilized bicycle trails and paths. My daily work commute is 50 miles, which, by car, is environmentally obscene (and not at all uncommon) and further costs about $7/day just in fuel alone.

I tried bicycling the old fashioned way for a couple weeks, but 25 miles urban each way in a Phoenix summer is suicide no matter how good your physical condition. I began looking for an assist-motor for my bike. Most “whizzer” type bicycle engines are a hassle. Electrics don’t have the range for a 50 mile daily commute. Two-stroke motors are a pain and become expensive due to the necessity of pre-mixing oil and fuel. Friction-drive bicycle motors wear out tires rapidly and behave badly on rough surfaces & water.

I eventually found a 4-stroke motor and belt drive kit from Golden Eagle Bike Engines that weighs very little, operates quietly, and gets me to work and back for about 45 cents a day in fuel. This engine comes as a 25cc Subaru-Robin 4-stroke kit for $549 including shipping. It was delivered 4 days after I ordered, and it took me just under 1/2 hour to install on my $200 department store mountain bike.

This is the smallest and lowest powered kit Golden Eagle sells, and requires me to pedal a little when accelerating from a stop or climbing steep hills. Doing this is very natural and it feels just like riding a bike the old fashioned way. Top speed with 26×1.95 dirt tires is about 25mph on flat pavement, or 23mph on flat dirt. Wind, inclines, sand, and other factors significantly impact the top speed, but it will even typically maintain 18mph under most typical adverse conditions. I know from prior experience with the same bicycle that I can sprint it up to 24mph without the engine, so having the engine on is equivalent to being able to sprint all the time. Up very steep inclines I pedal with the engine at partial throttle and maintain 12mph where previously I would go 3 or 4mph without the engine. I have ridden in moderate rain with no ill effect other than getting myself very wet. The drive is unaffected.

Getting to work across Phoenix now takes me about 10 minutes longer than it typically took me by car (yes, traffic is THAT bad) but the ride is far less frustrating or stressful because I’m not stuck behind someone, I’m hauling ass. There are some fun shortcuts and interesting parts of the city to see, as well. One tank of ordinary pump gas gets me 22 to 25 miles, urban riding. The tank on this model is just about 11 ounces, so that equates to somewhere approaching 250 miles per gallon!

About the engine: it has an automatic centrifugal clutch that just kinda applies power all the time (when you are pushing the throttle) so you otherwise ride the bike like normal. But it’s more like as if you’re always riding downhill — so you don’t need the lower gears. My mountain bike has relatively low top gears and with this motor I leave it in the topmost gear almost 100% of the time — and just pedal 4 to 6 strokes when accelerating from a stop while applying moderate throttle. I also give the pedals a few kicks when re-gaining speed after slowing down. The motor drive is fully independent of the pedal-chain drive. There is only one “gear” for the motor, it does not have any type of transmission or torque converter, just an automatic clutch. When you let off the throttle, the motor disengages and keeps idling but does not apply force to the bike until you press the throttle again.

The first time I ever started it, it started first pull. Since then, in normal operation it starts first-pull almost all the time and never more than third pull. I routinely shut it off when riding across areas where motors are not legal, and then just reach back and give it a yank while riding to get powered again, without slowing down.

It has a muffler, albeit a small one. It makes about as much noise as a modern low-noise weed wacker. In other words, it’s not silent by any means but makes much less noise than an average dirt bike or go-ped. However it is not quite as quiet as a proper scooter like a Honda Helix, and there is an unfortunate rasp to it. I ride it through my urban neighborhood at 6AM and feel confident I am not waking people from their slumber any more than a typical car might.

The drive belt makes very little noise, just a very quiet “whirr” that you can’t hear over the engine. When pedaling without engine power, you hear the “whirr” a little. If you take the time to disconnect the belt entirely (takes seconds) it has no effect at all on standard pedaling and makes no sound at all.

I feel this model is superior to other bicycle engines because: the belt drive is quieter and significantly lighter than gear or chain type drives; the name-brand engine, Subaru-Robin, which is well respected in professional applications like compressors, yard tools, etc, is presumably superior to other, questionable brands; the belt drive does not wear tires or slip around or beat up the engine bearings like friction-drive kits do; the 4-stroke engine allows you to fill up anywhere on regular gas.

This thing is not without its faults. I found that:

1. It does put more wear on the bike because you can maintain much higher continuous speeds over varied terrain than the bike was made for. Brakes, for example, need to be replaced more frequently. Bearings that you would just ignore before require tightening periodically.

2. You do have to change your urban riding style, due to those speeds. A diagonal curb-hop is very easy at 6 mph, but impossible at 15mph. Sliding onto a sidewalk to avoid aggressive car traffic is not as simple a maneuver as it is with an unpowered bike, and is more likely to draw unhappy responses from pedestrians.

3. The added weight (11-13 pounds) is not even noticeable when riding on flat ground – but has a dramatic effect when you are trying to jump things like berms, curbs, etc. This leads you to slamming your wheel into those… which leads to becoming quite adept at truing rims in your spare time.

4. I am especially cautious around law enforcement because the state law specifically allowing these engines doesn’t go into effect here until next month.

5. On very rough terrain the belt tensioner can slip from “engage” position to “disengage” position, which can put undue wear on the belt. This is rare, but has happened twice.

I highly recommend a good quality bike with very good brakes at both ends. A department store bike is fine, if it’s one of the best ones on the floor. I have seen people using motors with poor quality “cruiser” bikes that only have rear hub brakes, and that strikes me as a TERRIBLE idea with a 25mph top speed (mind I have the smallest motor available).

Finally, $659 is a steep price, but the ease of filling up your tank for $0.25 cents on regular pump gas and not having to mix expensive smelly 2-stroke oil, and the quiet and easy ride make it worthwhile. If my daily commute were less than 10 miles each direction I would not even consider owning this and would just pedal the old fashioned way. Since I have to go more than double that, it becomes practical due to increased fuel saving and the increased difficulty in riding that distance routinely. For me, it pays for itself financially in 84 trips to work and back.

-- Apanthropy 08/28/06

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