I Want To Reach And Maintain 40MPH...I Am So Close

Using "The Dragon Lady", a dual-engined girlie cruiser to commute 12-mile roundtrip to work. Mostly flat ground with two medium hills I can easily handle.

Bike and fully loaded rider weigh 300 lbs.Aerodynamics is challenged by full front basket and rider with raincoat always on. Raincoat needs to be worn.

Twin 2.2hp Mitsubishi engines on friction drive. Front has 1.375" roller; engine screams at 10,500rpm @ 38mph. Stock exhaust, flame arrestor removed.

Rear engine has 1.5" roller; engine buzzing at 9600rpm with ADA S1 expansion pipe.

Redline/peak hp rpm is probably 8900rpm.

Extreme rpm at WOT(wide-open-throttle) at intervals only on a 2-mile stretch of highway. Riding in commuter traffic. Claiming the curb lane.

I can keep up with traffic. I just want to be able to maintain 40mph for a safety margin.

When not buzzing at insane rpms, engines and I are cheerfully humming along between 20-25mph. That's at 6900rpm-front engine and 6300rpm-rear engine.

Engines have never protested but I'm pushing my luck. I need to change something so I don't kill them or wear them out prematurely.

The simplest and zero-cost solution is to switch the rollers front to rear. Rear engine location is the quietest and the screaming engine can suck on the expansion pipe as a pacifier.

Next option is to buy a second expansion pipe for the screaming front engine. However, exhaust must be rerouted; if not the fumes blow constantly in my face.

Another choice is to buy another 1.5" roller to drop engine rpm. Cost of roller and, drum and spacer w/shipping is $120. Local machinist charges $80 to loosen the drum.

Staton charges $12 for a pair of bearings. I bought TEN on ebay for $30, including shipping.

How about carburetors, tuning or air filters?

Maybe offset timing keys to shift power to higher rpms.

I realize the powerband would shift and I'd lose HP and TQ at the low end ...

but I have TWO engines so power loss is not an issue.

An EXPENSIVE and labor-intensive option is buying a 4.25hp GP 460 engine..or two. Clutch issues can be solved with 3000 rpm springs. However, I'm doing research on them to see if they're dependable and reliable.

Any ideas, fellas?

I am SO close to 40 mph. That's as fast as I wish to go.
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Honey, it's just a bicycle. and i REALLY need it to excercise, and to ride it to work.(hehe)

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mabman said:

Try a motorcycle. It's not like you are looking to pedal anyway.

Click to expand...

You're not observant. Research my threads. I pedal too. I just like to ride faster than 25mph with just a coaster brake.

Then there's that insurance/registration thing.

I have a motorcycle.

It's called a Whizzer, and it's slower than my bicycle.

Mechanickid, that's one of my options.

If I switch the 1.375" roller to 1.50", the engine will thank me.

Yeah, a roller change, less cargo, relocating front basket to rear, 91 octane and more tire pressure should push my bike to 40mph.

Thanks for props, Hawaii Ed.

Before I biked to work, I ordered another ADA S1 expansion chamber, silencer and 1 meter of rubber exhaust tubing from here:

fd320

and here: fd108

When I ran an expansion pipe on the front engine before, engine smoke blew in my face. This time I'll reroute the exhaust with the flexible tubing.

Then I felt sorry for my screaming front engine. So I ordered the 1.5" roller from Staton.

The roller change from 1.375" to 1.5" will produce a higher gear ratio and decrease low and midrange acceleration. Then extra hp boost from the pipe should compensate for the large roller's negative effects.

Maybe I'll install the pipe this weekend, play with that then install the roller next weekend.

Pipes are so much easier to install, takes less than an hour.

A roller change is labor-intensive, takes a real commitment. The old 1.375" roller SHOULD slip thru the 1.375" bearing support holes in the friction drive housing. So the roller, spacer, clutch drum and bearings can be removed as a unit. The new 1.5" roller assembly won't pass thru the housing, so must be installed piece by piece.

THENNN, when removing the 1.5" roller assembly, EVERYTHING must be removed from the roller before it will fall outa the housing. The clutch drum is a MAJOR pain to remove without special tools, especially if you intend to re-use the drum and bearings.

I envy Dimension Edge engine kits for their ability to swap friction roller in less than a minute...and for their "gravity clutch".

I'll consider myself lucky if I swap friction rollers in a day...after I pay $117 for the new clutch drum, spacer, spindle and bearings.

If I need to get gouged by the local machinist, that's another $80.

I Need To Slow Down.

Originally Posted by Mountainman
good point HY

and I have fallen short a few times myself here
wasn't the right THING to do or say

at times it all boils down to what we do or what we do not do
what we say or what we do not say

I have pushed the -- ride that THING a little far at times

some of the high speeds mentioned for MBs are a little crazy
most do not have the skills to be riding at those speeds

we wish to share in this thread -- The Safe Top Speed
not the speed attained by a few daredevil's

ride that thing

Guilty as charged.

I need to slow down. My quest for 40mph is probably too dangerous for me.

Dropping maximum speed down to 30-35mph on the highway.

I might buy a moped/motorscooter to ride above that speed in traffic.