Fat man needs advice

[Deleted member 12676]

click on my signature link if you want more suggestions than you'll know what to do with

 

[JunkyardDog]

I am on the heavy side myself. I went to a friction drive because I was almost killed by one of those Chinese chain tensioners getting pulled into the rear wheel. I have a Honda GX35 4 stroke. I do have to pedal to get it started, but once up to speed it will pull me along nicely at around 20 mph on flat ground. I'm in AZ, and the MB speed limit here is 20 mph. It needs a little help on steep hills. A smaller roller would help there, and I may change to one. I don't really need to go over 10 mph, which is about the speed of a pedal bike around here.

However, I may be doing another Chinese engine build in the not to distant future, as a couple of products have come out since my crash that solve the two main problems with the Chinese kits. An engine mounted chain tensioner, and a clamshell rear sprocket mount. Yes they are expensive by the standards of this forum, they would add almost $60 to the build. But I expect the total to be close to $800 by the time it's all done, including the cost of a high quality used bike from Craigslist. Older name brand steel framed mountain bikes with small diameter frame tubes work well, and already have good front brakes. I convert them to very low geared single speeds.

 

[Tibilt]

I been doing some reading and YouTube viewing. Plus through life experience I know two cycle engines just have especially more bottom end torque. There RPM's are way higher like 8000 to 12000 in comparison.

Stanton has a .93 friction roller where they seem to run one to one and a half inches most other sources. I know the size don't seem like much, but an old trick is to take 3 teeth away from the front sprocket instead of adding twice that many on the back sprocket.

I weigh 360 lbs. I'm getting the Stanton kit with the .93 roller and a Tenaka or Zenoah @ 40 cc two stroke motor. See we need a mule rather than a stallion in terms of roller size. At full throttle a 4 stroke is turning 133 revolution per second where a two stroke is turning 200 revolutions per second. That an two cycle low end torque is the solution. Oh course some of that gets lost in slippage on the tire, but more is transferred to the rubber on the road.

You might try seeing if the .93 roller will fit before replacing the motor. Call Stanton, he WILL call you back.

I'm in save up stage. This is pricer,but like you I need to use my bike for exercise, but need to get my ya ya's out too.

I will report back my results on this idear/therom.

Somewhere there is a kid with a Tanaka 2 cycle friction drive on YouTube that is having noooo trouble at all with power/speed.

Tibilt

 

[Tibilt]

Oh, play with more and less roller pressure on the tire. The Bikeberry friction drive video says there is a sweet spot.

All the best!

 

[Deleted member 12676]

If you look at horsepower graphs of 2 strokes (with expansion chambers) and 4 strokes you will see that 4 strokes have more low RPM power (as a percentage of their peak power).
Maybe without the expansion chamber the 2 strokes would be even. I don't know but I doubt they would.
But since the law requires the same engine size limit for 2 strokes and 4 strokes then the 2 strokes have the advantage in power because they have twice as many power strokes for the same RPM.

 

[JunkyardDog]

The more I think about it, the more i think you need a 4 stroke shifter bike. While My GX35 friction drive works fine in the desert, it would not be suitable for mountains, and we do have mountains here. I was unable to climb those mountains with a 125cc CVT type scooter, because it did not have a low enough gear range to pull me up the mountains. It lugged the engine badly. But a 125cc manual transmission motorcycle had no trouble climbing anything I could find. Yes it was slow, but the manual transmission kept the engine rpms up and it just kept going. Gears are everything. With the right gearing, a 50cc motor will climb almost anything. Shifter bikes are not cheap, but you could have someone build it or buy it from someone. Being close to your weight myself, I have never been able to climb much of anything with a small engine without a super low gear ratio. A low enough gear ratio for climbing is going to be too low for flat roads. That's why pretty much all motor vehicles have several gears, either manual or automatic. Same thing applies to pedal bicycles. Internal combustion engines simply do not have the ability to operate over the wide range of speed and load conditions you need.