Need help with gears on chainsaw bike

[Mrgoodcat]

This is my first time building a chainsaw bike and im having trouble figuring out the best way to hook up the chain from my 42cc poulan pro to my aggressor gt 7 speed with 14t-34 t with the least amount of frame modifications possible and the best gear ratio. Any advice???

 

[Sidewinder Jerry]

Are you wanting to do a left side single drive ratio? Or are you trying to run through the bicycle gears like we shift kit builders do?

 

[Mrgoodcat]

I want to use my gears i figure it will b the most efficient im still at the beginning stage and don't want to screw up a $$1000 bike and don't want to waste my time on a **** one either but I get confused when it comes to the gear ratios

 

[Mrgoodcat]

Its a tight fit and no room for any kind of shock absorbers on the motor but I think I have that on down now I need to figure out the best way to mount the drive chain and still utilize my gears

 

[Sidewinder Jerry]

If you paid a $1000 for that bike. Somebody stole a high dollar wheel off the back and replaced it with a 7 speed 34-14 freewheel (34,24,22,20,18,16,14). The higher end bikes use 8 speed and up cassettes instead of freewheels. It kinda of looks like a Kent frame and a blue spray paint job.

On my bike I use a custom built 7 speed freewheel (34,28,24,21,18,15,13). I also have a Staton Inc triple chainring shift kit. The chainrings are 28,36,44. I use a 4 stroke Robin Subaru 35 engine [33cc 1.6 hp]. The engine is ran through a Staton Inc 18.75:1 reduction gearbox. The RGB uses a 15:44 drive. The reduction range is 66.79:1 to 16.25:1.

It gets shifted like this:

Steep hill climbing and heavy load pulling
1(1-3)

Around town general use
2(3-5)

Open road use
3(5-7)

The only time chainrings will be shifted is when either using cogs (3) or (5). All shifting is done with the left hand. I also use a techometer to shift by.

I'm a large person and live in the mountains. The bike I built didn't come cheap.

Now you could get a Sick Bike Parts shift kit and I can even teach you how to build a 4 speed 34-16 freewheel or you could also use a 3 or 5 speed internal geared hub.

 

[Sidewinder Jerry]

Is this your bike? Though this bike has an 8 speed cassette. However, perhaps an older model used a 7 speed 34-14 freewheel.

 

[Mrgoodcat]

Wow thats awesome man but I'm not really looking to go all out on this i just need to no wat the best way to mount the chain for reliability and simplicity i don't really have the capability to make parts or even understand pretty much anything u just saìd im just getting into this .. And lol the bike is a 2019 aggressor gt

 

[Mrgoodcat]

Thats the way I got it brother like I said I'm new to all this

 

[Mrgoodcat]

Lol thats the one.. seen me coming lol

 

[Sidewinder Jerry]

So are you wanting to do a left side single ratio drive?

As for how to shift a 3x7 drive system on a bicycle it's done like this:
1(1-4), 2(2-5), 3(4-7) for 12 non redundant sequential gear ratios. Starting gears are 1(1) for stops going uphill. All other stops use 2(2).

A 3x8 is shifted like this:
1(1-5), 2(3-6), 3(5-8) for 13 non redundant sequential gear ratios. Starting gears are 1(1) for stops going uphill and 2(3) for all other stops.

If a gear is to easy or to hard to comfortably maintain a cadence (crank rpm) of 70-90 it means you're in the wrong gear. For pedal only purposes I always advise getting a bicycle computer with a cadence meter on it.

Never cross chain (big big or little little)
Never use both shifters at the same time
Never stand while shifting
Never shift while pedaling backwards

 

[Mrgoodcat]

No I was thinking about sticking to the right and maybe trying something like a jack shaft i want to still be able to use my peddles and gears. And thanx no one has ever explained how it works to me I just switch to whatever gear feels easiest at the time

 

[Sidewinder Jerry]

Are you wanting something like whats on my bike?

 

[Mrgoodcat]

If I knew wat the **** that was LOL this is wat im working with i want to keep the rear gears and utilize the pedals so I can still use it as a regular bike. SIMPLE BUT EFFICIENT. Thats what I'm looking to achieve

 

[Mrgoodcat]

Ya now that i took closer look at it thats exactly wat im aiming for exept i am mounting the engine in the middle hope its guna work out like i kinda have planned... maybe

 

[Mrgoodcat]

So what would my optimal gear ratio be to keep top speed and still have climbing ability what gear would I put on the motor And the rear 7

 

[Mrgoodcat]

And without changing The ones I have in the back what would I use on the motor rate now I have 14 16 18 20 22 24 and 34T

 

[Sidewinder Jerry]

Ok first you need a reduction for the engine. Chances are it turns more than 8000 rpms. So the rear wheel can't turn that fast. You'd also need a shift kit. I use a Staton Inc triple chainring shift kit.

Here's a video of Fabian building a triple chainring shift kit using a Sick Bike Parts shift kit.

 

[Mrgoodcat]

Kewl man , so until i get one built how can i hook it up right now that would gimi top speed

 

[Sidewinder Jerry]

You can't run through your gears without a shift kit or the pedals will spin every time you use your engine. Much too dangerous. You can run a left side jack shaft. Then to the left side of the rear wheel. You'll need a better centrifugal clutch. Use a 9t sprocket on the clutch and run to a 36t sprocket on the jack shaft. Then put a 9t sprocket on the jack shaft and run it to a 36t sprocket on the left side of the rear wheel. This'll give you a 16:1 reduction.

 

[Mrgoodcat]

Ok thanx and do u know what that would give me for top speed? I'm aiming high, looking for something around 70km/h with maybe 5-6000rpm range on the motor is this possible? I'm getting conflicting information about this i want to Use a jackshaft to the gears on my rear tire with these specs 6t-44t motor to jack input and 32t-14t output to rear tire and it gives me a ratio of 3.208 with a top speed of 44.643mph BUT.... then I get this ..... y would it be so far off with the same gears??????