Am I sane?



I currently have a suitable bicycle, as well as a) machine-tools; b) experience with engines, motorcycles, and related things; and c) some real questions, some of which might sound weird.

1) I am currently thinking of going rack-mount friction drive using a four-stroke motor. I've heard how these setups tend to devour tires and slip in inclement weather, and I just might have a partial solution. It involves two rollers pivoting such that both rollers contact the tire at 'ninety degrees', with the rollers being roughly 1.6 inches outside diameter and coated with grit of some kind. (aluminum oxide, silicon carbide, others.) The central shaft drives both rollers using #25 chain, and in turn is driven from the engine clutch using the same type of chain. (I'm working on the drawings still)

Question: do I need to have my head examined?

2) While I do not mind the smoke, smell, and noise of two-stroke motors, I strongly suspect discretion is advisable in my case - hence the use of a four-stroke. I'm leaning toward the Honda GX35, though I've read about the Subaru Robin eoh35.

Question1: is the Subaru Robin a 'better' (term used loosely) engine?

Question 2: I've heard my share of weed-cutters, backpack blowers, Go-Peds, motorized skateboards (long years ago) and related engines. I've not yet heard either of the two engines mentioned previously. Are they significantly quieter, or is the chief difference the tonal quality of the engine noise compared to say, uh, a Zenoah or Tanaka? I'm prepared to assemble a large-volume muffler if needed - and should I do so, I can just hear the comments:

"What is that thing there?" (points to muffler)
"The muffler. Why?"
"I've never seen an engine that small with a muffler that big..."

3) My goal is to manage groceries and related shopping on a semi-regular basis, and longer trips (possibly hundreds of miles) now and then. Currently, I need to lose a great deal of weight (enough that I'm embarrassed to say how much), I've had surgery on both knees (they complain if I ride any real distance), and I wish to avoid undesireable attention (chiefly from constables). Also, I will commonly be towing a trailer (one of which I already have; I hope to make another.)

Question: I'm planning on gearing the thing such that normal 'cruising' speed is in the ten to twelve miles an hour range. (i.e. 5,000 rpm or so; both engines have their torque peaks in that region.) I've seen signs locally describing distances and 'nominal' times for bicycles, and that speed range seems to fit. (It's also nearly double what I can pedal for any distance).

Am I crazy? I know these setups are capable of higher speeds, but I do not feel comfortable traveling at twenty-plus on a bicycle. (Besides, I'm not a teenager any more - top of ten gears, a slight downgrade, chain singing, and clocked at 50+)

Thanks in advance for your consideration


If you just want to putt and you keep your gear ratio that low you will have great power. Great hill climber. I don't know if I would go with the friction drive. I would say the friction drive would be the worst performance.(tire wear,wet slippage and to much unnecessary presser on the rear tire for starts). Chain or belt would be better.


We are on the internet need to hold back.

If you are 300#++ and going to pull a trailer full of shopping, go for the Staton set-up. David Staton only charges $55 for a 48 x 12g stainless spoked rear wheel, as long as it is bought with the kit. Mr. Staton likes the R/S 35 over the 35cc Honda, he has a short article as to why over at his site but I could not find it. The Tanaka 33 is a bit more powerful and quieter that the Robin 35 but does requior mixed gas. When using the R/S35, the Staton set-up does not have the fuel tank issues at fill-up that the GEBE system does with some bicycles.
David will help you select gearing for 20mph and that can always be changed at a later date anywho.

Portland = damp & rain so a friction drive is probably not a good idea.


:cool:the 35cc ROBIN engine is very tame, and has more than enough power for your needs. in fact, ya might get by with the smaller 25cc ROBIN.
i had the 35cc friction drive. a pedestrian standing right next to me stated that my engine was very quiet at idle. that's without a muffler.
unsure if friction drive will work for your environment. gear chain drive might be overkill under 20mph and low HP. GEBE setup and 25cc ROBIN would probably work best for you.


Robin-Subaru VS Honda

I own a Robin-Subaru and Honda powered bicycles. (I should say my partner and I own them.) Here's what we know:

In terms of MPG and power-- no difference that we notice. No, we've never drag raced the two of them nor have we put them through time trials. We've ridden then daily and switched from time to time and can't tell much difference. My partner weights about 150 lbs and I weigh 208 so a drag race wouldn't prove much anyway.

In terms of money-- same cost for both engines.

But here's where things differ: The Robin-Subaru is built in Japan and has a steel cylinder liner. The Honda is built in Indonesia and has aluminum cylinders with no liners. My guess is both engines will remain about the same until time for a rebuild. The Robin-Subaru you rebuild, the Honda you throw in the recycling can or scrap metal pile.

As for comparisons to 2 cycle engines I can be of no help. The only 2 cycle engine I own is a 45 year old Homelite Chain Saw that belonged to my grandpa, my daddy and now me. Motor runs great but the chain and bar are shot again. (You would not believe how many chains a saw can wear out in 45 years.)

In the good news department: I mated a Honda to a CVT transmission today in the machine shop. Now we've got to build a frame and see if we can break it.

You mentioned the friction drive and the dual rollers. I'm not saying my idea is better but give this some thought: They make tires that are slicks in the center and knobby on the sides. (Sort of an on-road-off-road tire.) What if a roller was designed so that it had gear teeth on both ends that would engage the knobby portion of the tire? Mass production would probably require castings but one-offs could be machined.

Also, on friction drives: I like the idea of grit covered rollers but what if you used one hour glass shaped roller that sort of wrapped the tire instead of two rollers? Just a thought.


"Question 2: I've heard my share of weed-cutters, backpack blowers, Go-Peds, motorized skateboards (long years ago) and related engines. I've not yet heard either of the two engines mentioned previously. Are they significantly quieter, or is the chief difference the tonal quality of the engine noise compared to say, uh, a Zenoah or Tanaka? I'm prepared to assemble a large-volume muffler if needed - and should I do so, I can just hear the comments:"

I think if you use a decible meter the 4 strokes and 2 strokes will register about the same but the tone of the 4 stroke is a lot easier on grumpy old men like me. Those "bees in the can" make my head hurt.


Dimension Edge

I have a DE set up with the wooden rollers and the carborundum wheel. While the area I live in is, uh not wet I don't know if I can give you great advice. However I have been surprised how well the wood rollers grip the tire. I am going to upgrade to a Maxxis Hookworm tire on the rear. This should give plenty of grip to the roller. Just looking at the roller, if you chucked it up in and took some sandpaper to it to make the roller fit the tire where it is gripping it on part of the sides as well as the top of the tire, there should better grip. The wooden roller does not seem to wear the tire like the rock does. And DE claims they have a roller that will work in wet conditions. DE has been in business a long time and while I bought my kit off ebay, it is of great quality and except for two plastic do-hickeys that have been removed, the thing works well.


Comments from a GEBE newbie

I did a lot of research before I went with the GEBE/kit. It's not perfect, but I'm still convinced I made the right decision. If you went with the GEBE/kit and got their Velocity rim with the 12g spokes, I'd be very suprised if you broke any spokes, especially if you tied the spokes and kept the wheel trued.

I have the R/S 35 cc and recommend it. The only disadvantages I know of for this motor is that the R/S engineers assumed you would have no problem tipping the motor nearly 90 degrees to fill the gas tank or to empty the motor oil. It just didn't occur to them that it would be bolted to something awkward, like a bicycle.

I suspect that both of these inconveniences can be overcome by:

1. Using a Liquavac. ( I bought one for $30 at Lowes. It is a hand pump vacuum designed for vacuuming oil out of small engines.

2. Installing an auxilliary fuel tank. This not only solves the problem of having to tilt your bike at an absurd angle to fill the R/S "u" shaped gas tank, but also extends the range of your bike.

Please note that I am currently still field testing both of the above items, so I'm not able to recommend them yet.

About the engine power and gearing issue, keep in mind that, just because you have a bike that can go 30mph, doesn't mean you have to! I rarely go that fast, but it's very nice to know you have that power in reserve when:
- You are on a street with no bike lane and you want to ride in a car lane to avoid the "door zone".
- You need some reserve power to scoot out of someone's way, or when you are crossing a freeway access ramp.
- You are going up a *very* steep hill or towing a heavy trailer.

Also keep in mind that, the more you ride, the more skilled and comfortable you will be riding at higher speeds. There are plenty of bicyclists who will occassionally reach 30 mph, without a motor.



GEBE R/S35 owner

I have the R/S35 GEBE belt drive setup and would highly recommend it. I haven't had ony other engine or drive system so I can't comment on that. The only problems I have had are the same ones Sam mentioned in previous post...gas tank...oil change. Also the mounting of the engine....which is discussed in my setting up R/S35 thread and a lot of others, which you should take the time to read if you haven't already. I do not travel over 10-20 mile roundtrips, so I get by carrying a MSR fuel bottle...$12-15 at sporting goods store.. (33OZ) in my sidebag to get me to a gas station if I run out. I love puling up to the pump and putting in 25 cents worth of gas while the guy next to me is putting in $40.00 worth!! Also no mixing oil with the just 'filler up!! I solved the oil change problem by using a old anti-freeze tester I had laying around to suck the old oil out...and a old turkey baster I had which I had used to suck old power steering fluid out of my vehicle ( that stuff goes bad too ) to refill the R/S35. The engine is very quiet at idle..which I set very low, but at acceleration gets fairly loud but is not as irritating as a two stroke weed whacker engine sounds. I am also thinking of getting a small trailer for store trips where I cant get everything in my bag. Welcome aboard Prism!


The original post might have been "too long", so I did not include the following:
1) I had planned on making the 'rack' such that removal (with the proper tools) would be a five-minute affair.
2) I had hoped to eventually fit disk brakes.
3) I really want to lose weight, but have had no luck as of yet. (Yes, I do walk as much as I can, and I try to be careful as to what and how much I eat.)