Sick bike parts 4stroke kit and Nexus 8 IGH gear ratio

[UtiliD]

So I'm wrapping up a build and need to figure out where to make adjustments for optimal gear ratio

26" wheels

Huasheng 49cc 4 stroke tapered shaft with
4g belt drive tranny 20t - 100t pulleys(5 to 1) to final 9t sprocket

9t sprocket to 17t SICK Bike parts left side jack shaft sprocket

Other side of Jackshaft 9t to 48t sprocket on outer side of front freewheel

Inside sprocket on front freewheel 30t sprocket to sprocket on Shimano nexus 8 hub (I've tried 18-22t)

I've only been able to use gears 4-8 and that's not going to fly.

Goal: be able to use all 8 gears and have a top speed of atleast 40-45

What do I need to change?

Will do a full build thread once it's worked out.

 

[5-7HEAVEN]

Sorry I didn't get back earlier. The entire issue was I wouldn't just sit down and do the calculations.
On the nexus 8 assuming an 18t sprocket installed to the actual hub and not factoring anything else in...
The hub doesn't hit 1 1 gearing until 5th gear so the nexus 8 and an 8 speed derailleur set-up are differect balls of even different waxes. I already knew this in terms of ride(I'm a IGH junkie & taught myself how to service them and for the most part repair them-if worth repairing). I didn't grasp how different the gearing was with regard's to shift kitted motorized bicycles but, I do now. It really becomes apparent in IGH's with 7 or more gears.

Takeaway---- use the 80t pulley on the Grubee 4g tranny(and possibly... swap out the 9t sprocket the 4g tranny came with to a 10t or 11t out put sprocket to make up for several granny gears in 7-speed or higher Internal geared hub..... Now this is not what I did on this build but, for those thinking of doing a similar build, its worth a thought. I emphasize this for optimal gearing but also left crank clearance ( yes I did have the widest bottom bracket spindle Sick bike parts offers & I will elaborate more about this in the build thread)

The 30t chaining attached to the front freewheel that shares it's chain line with the nexus 8 hub needed a 36t. I also put a 18t cog on the hub its self. It has more than enough on top and bottom. Haven't hooked up a speedometer yet but, I hit a roadside radar while riding slightly uphill and no where near WOT at 34mph.

Coming soon... will have a build thread on this and another build thread on a Nirve cruiser I put a 3 speed Nexus and a Sick bike parts shift kit on(plus a bunch of other custom work). The Nirve will hopefully be finished tomorrow.(issue with petcock from vintage lawn mower tank I restored).

Truly appreciate everyone's input.

Jay

I respect your experience with motorized bikes with IGH.

Is there a certain method of shifting, especially with engine power?

 

[UtiliD]

I respect your experience with motorized bikes with IGH.

Is there a certain method of shifting, especially with engine power?

It really pretty simple. It's important to have good shift cables(inner & outer) and to make sure the shift cable is set up correctly(the method on setting up shift cables are different for each hub. From there you just let off the gas before up or down shifting. You get a feel for when the centrifugal clutch has disengaged the clutch bell, as soon as it has you can shift.

 

[5-7HEAVEN]

Thanks!

 

[Sidewinder Jerry]

I've often wondered how a Kilduff auto shifter might perform on a motorized 3 or 5 speed IGH.

 

[UtiliD]

I've often wondered how a Kilduff auto shifter might perform on a motorized 3 or 5 speed IGH.

I was following a thread for an autoshifter build awhile back. In this particular thread the guy abandoned the project. I can't remember why.

If I were to have an auto shifter, I would want to be able to swith back and forth from auto shifting to manual shifting. But I'm sure that's opening a can of worms that I'd never get around to.

 

[UtiliD]

I finally got my 10t sprocket from grubee for the 4g transmission. I also found a 11t 5/8th" bore sprocket for the right side of the jackshaft from Staton. Should have it put together by tomorrow. Then I'll be interested to see where this bad boy tops out at.

 

[Sidewinder Jerry]

I was following a thread for an autoshifter build awhile back. In this particular thread the guy abandoned the project. I can't remember why.

If I were to have an auto shifter, I would want to be able to swith back and forth from auto shifting to manual shifting. But I'm sure that's opening a can of worms that I'd never get around to.

I had a bike that shifted 7 gears automatically and rode it for around 11 years. However, I wasn't able to switch between manual and automitic. The closest I was able to do to that was the rear 7 sprockets shifted automatically while I was able to manually shift the front 3 chainrings.

 

[yuckfoo]

With 30t chained to 18t, your final drive is 30.22:1.

WAY way too low!


Pulleys equals 5:1.
Change to 9/9 or 17/17, equals 1:1
Change the 48t/9t to 36t/9t equals 4:1.

5 x 1 x 4 = 20:1.

Use 36t chainring and 22t rear sprocket.
22/36 = .611
20 x .611 = 12.22:1 in 8th gear.

Unsure what final drive should be for your engine.

Just rode it again & figured out that I just wasn't giving enough throttle in the lower gears 1 - 3. They all work they just red line immediately and top speed in 8th gear is in the mid to high 20s. Pointless for a shift kitted bike in my opinion. I'm absolutely sure now the 36t sprocket will put me right where I want to be.

Maybe it's not the sprockets and chain rings? Maybe it's the engine. Is it tuned? Perhaps run the bike on the gear that most closely approximates the gear on a one speed bike and tune the engine based on that? I don't know much about these things. I'm in the middle of my first build. A Mongoose Dolomite with a sickbikeparts shift kit.

Also, I've heard another guy say that he purposely does not use all 8 gears. In stead he uses 2, 4, 6, 8 or 3, 5, 8 I can't remember exactly. The point being that it's unlikely that you really need to progress through all 8 gears.

 

[5-7HEAVEN]

Yes, I used only 4 gears on an 8-speed shift kit/cassette.

1-3-5-7, with 8th gear for overdrive.

Moreover, sometimes I skipped a gear while driving the 4-speed on my '57 Chevy, or my 5-speed Toyota.

I imagine some car guys skip a gear on their 6-speed high-performance vehicles.

 

[Sidewinder Jerry]

Here's a tread I did about a 4 speed freewheel. It gives you the larger jumps between the ratios while reducing the amount of cross chaining.

Thread '4 Speed Freewheel' https://motoredbikes.com/threads/4-speed-freewheel.58615/