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.

 

[Sidewinder Jerry]

Bottom line is you don't know how an IGH gear ratios work. It is your bad information that is going to mess up someone's IGH

 

[5-7HEAVEN]

Bottom line is with your trig background, you forgot high school math and physics.

Where it really counts.

 

[Sidewinder Jerry]

UtiliD, please don't try to take off in 8th gear. Just switch the 30t chainring to a 36t chainring. It should give you're looking for; you'd have a top speed around 33 mph. Since the IGH can be shifted without the pedals having to move, I recommend always taking off in 1st gear but at least at the minimum use 3rd gear for take offs

 

[5-7HEAVEN]

To the OP:

Im installing a 212cc engine in my bike, and replacing my 7-speed freewheel with a Sturmey-Archer 8-speed.

The engine has a 23t pulley clutch.
It is directly belted to a 120t pulley on the left-side of the bottom bracket(BB).

Then power runs thru the BB.
A 27t chainring connects to the 25t sprocket on the hub.

The 8-speed hub ranges from 1:1 to 3.25:1.

First gear is 15.7:1 and final drive is 4.83:1.

I have 2.25 x 19" moped tires-
The OD is 23.5", so gearing is slightly more.

Im still working on my project bike.

I double-checked my calculations online.

If my hub explodes, it'll be because of my 212 engine's awesome power.....

not my miscalculations.

I

 

[Sidewinder Jerry]

To understand this better let's simply it.
If you used a 28t chainring to drive a 28t rear sprocket on the IGH, you'd have a 1:1 input ratio. Therefore 1 full turn of the crank would make the rear wheel on the Nexus turn slightly more than a half turn in 1st gear. One full turn of the crank would make the Nexus turn the rear wheel slightly more than 1 3/5 of a turn in 8th gear.

Shimano Nexus 8 speed
(1)52.7% to (8)161.5%

Strumey Archer 8 speed
(1)100% to (8)325%

Using a 28t chainring and a 28t rear sprocket for a 1:1 input on the SA in 1st gear would produce 1 full turn of the rear wheel with 1 full turn of the crank. In 8th gear 1 full turn of the crank would produce 3 1/4 turns of the rear wheel.

Sturmey-Archer | X-RF8

For more than 100 years, Sturmey-Archer has been a pioneer in the design of internal gear hubs, hub brakes and dynamo lighting. Sturmey-Archer makes cycling easier and safer.

www.sturmey-archer.com

On both hubs 1st gear is the low gear and 8th is the high gear.

 

[Chainlube]

Would either of you guys mind if I let the seat of my pants decide?

 

[UtiliD]

To the OP:

Im installing a 212cc engine in my bike, and replacing my 7-speed freewheel with a Sturmey-Archer 8-speed.

The engine has a 23t pulley clutch.
It is directly belted to a 120t pulley on the left-side of the bottom bracket(BB).

Then power runs thru the BB.
A 27t chainring connects to the 25t sprocket on the hub.

The 8-speed hub ranges from 1:1 to 3.25:1.

First gear is 15.7:1 and final drive is 4.83:1.

I have 2.25 x 19" moped tires-
The OD is 23.5", so gearing is slightly more.

Im still working on my project bike.

I double-checked my calculations online.

If my hub explodes, it'll be because of my 212 engine's awesome power.....

not my miscalculations.

I

To understand this better let's simply it.
If you used a 28t chainring to drive a 28t rear sprocket on the IGH, you'd have a 1:1 input ratio. Therefore 1 full turn of the crank would make the rear wheel on the Nexus turn slightly more than a half turn in 1st gear. One full turn of the crank would make the Nexus turn the rear wheel slightly more than 1 3/5 of a turn in 8th gear.

Shimano Nexus 8 speed
(1)52.7% to (8)161.5%

Strumey Archer 8 speed
(1)100% to (8)325%

Using a 28t chainring and a 28t rear sprocket for a 1:1 input on the SA in 1st gear would produce 1 full turn of the rear wheel with 1 full turn of the crank. In 8th gear 1 full turn of the crank would produce 3 1/4 turns of the rear wheel.

Sturmey-Archer | X-RF8

For more than 100 years, Sturmey-Archer has been a pioneer in the design of internal gear hubs, hub brakes and dynamo lighting. Sturmey-Archer makes cycling easier and safer.

www.sturmey-archer.com

On both hubs 1st gear is the low gear and 8th is the high gear.

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

 

[Sidewinder Jerry]

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

Possibilities could be things like you were going down hill before going up the slight hill. The only way to know for sure what you're doing is to get a tachometer and speedometer. The speed of roughly 34 mph is at 6800 rpm in 8th gear using the 36:18; not necessarily at full throttle. If in 8th gear you can easily go over 6800 rpm at full throttle on level ground then you need to consider a lower reduction for 8th gear. You may want to consider a 38t chainring or a 17t rear cog. You should be able to get both a tachometer/hour counter and bicycle computer for less than $30 on eBay. Before you do any other changes get those 2 things first.

 

[5-7HEAVEN]

I’m glad you’re on your way to the 40mph +.

 

[Sidewinder Jerry]

If you keep the 36:18 and change one of the 9t sprockets to an 11t you'll mathematically hit 41 mph in 8th gear at 6800 rpm. Switching one of the 9t's to a 10t sprocket would be around 37 mph. Still realistically consider yourself very fortunate at 230 lbs total weight to hit 37 mph on level ground with only 1.6 hp.