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]

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.

 

[UtiliD]

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.

By its self the nexus 8 has a 307% range gears 1-8 are as follows
1st .53
2nd .64
3rd .75
4th .85
5th 1.0
6th 1.22
7th 1.42
8th 1.61
(Not sure if you took that into account)

That being said are you saying I should change my 30t to a 36t?
This is a sick bike parts kit so I'm limited as to what I can change I've had a hard time finding sprockets with a 5/8" bore for either a 415 or 410 chain.

Sick bike parts offers 3 different sizes for the 410 sprocket on the right side of the jackshaft(9t is what I have they also sell a 10t and an 11t) $16each

The 30t sprocket(chainring) that bolts to the front freewheel and runs the chain from there to my nexus hub seems to be the cheapest part to change. 36t sprocket is $8.

FOR My Hub I have everything from 17t to 23t I don't think 16t fits the nexus 8.

 

[5-7HEAVEN]

Sorry, I mistook your 30t for a 36t.

What speed do you expect to cruise in final drive?

What rpm would you like to be in the gear above final drive?

Recalculating.....

 

[UtiliD]

Sorry, I mistook your 30t for a 36t.

What speed do you expect to cruise in final drive?

What rpm would you like to be in the gear above final drive?

Recalculating.....

It's a huasheng 49cc 4 stroke I think max is 7500 so...
6000 or 6500

 

[UtiliD]

The kit came with a 30t I was thinking I needed a 36t are you thinking I need bigger?

 

[Sidewinder Jerry]

5×17÷9×48÷9×18÷30=30.22:1 going into the hub. Therefore 8th gear would be 18.71:1.

6800 rpm ÷ 18.71×26×⚻÷1056=28.1 mph

The cheapest remedy is to put the 22t sprocket back on the rear IGH and replace the 17t sprocket on the left jackshaft side with a 9t sprocket. This'll give you around an 11.7:1 reduction in 8th gear. Just be fully aware a reduction that low on an 8 speed IGH is probably going to damage it.

 

[UtiliD]

5×17÷9×48÷9×18÷30=30.22:1 going into the hub. Therefore 8th gear would be 18.71:1.

6800 rpm ÷ 18.71×26×⚻÷1056=28.1 mph

The cheapest remedy is to put the 22t sprocket back on the rear IGH and replace the 17t sprocket on the left jackshaft side with a 9t sprocket. This'll give you around an 11.7:1 reduction in 8th gear. Just be fully aware a reduction that low on an 8 speed IGH is probably going to damage it.

Wouldn't that gear it lower?

Im pretty sure I figured it all out. Because the 1st 4 gears of the igh are below a 1-1 ratio It's geared to low. I ordered a 36t chainring to replace the 30t chainring on the front freewheel. I have 17, 18, 19, 20, 21, 22, 23 I can use on the Hub it's self to tweak it from there.
I'm suprised I couldn't find a single thread where someone worked out the gear ratio on one of these nexus 8s with a shift kit or did a detailed build thread with a SBP shift kit and a nexus 8. I've had quite a few nexus 7s and 8s and never had one fail. I've ridden them on electric bikes well over 1000 watts. As long as I let off the throttle between shifts, check for shift cable alignment(which I do every time I get on the bike) and top off the grease on the bearings occasionally between full service overhaul intervals I know it will hold up. The nexus 8 hubs that have problems on MBS are the coaster brake and roller brake hubs because of all the heat those brakes generate(and hubs that arent maintained). Just having the shift cable off alignment can mess things up because the hub is trying to run between gears when parts aren't locked in place where they're supposed to be.

 

[Sidewinder Jerry]

When you can't move in a gear it means that you don't have enough reduction; it doesn't mean you have too much reduction. You are then under engine strain. Signs of this mean you have to use a lot of pedal assist. Over revving occurs from having too much reduction. If a gear is going beyond max hp rpm at full throttle it means you need to shift to a higher gear. If you can't reach minimum max torque rpm at full throttle it means the gear is too high and you need to shift to a lower gear.

I built a motorized bike that shifted 7 gears automatically and rode it for 11 years. I'm retiring that bike and am currently building a triple chainring shifter. Which will be shifted like this 1(1-3), 2(3-5), 3(5-7) for 9 non redundant gear ratio.

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So trust me if your bike isn't moving in the gears 1-4 something is very wrong.

I do know of one person who used an 8 speed IGH that was a regular on the late KC Vale forum "KC Kruiser's". However he only rode at speeds of 20 mph.

The thing about electric motors is they have consistent torque regardless of what rpm they're at. Combustion engines have varing torque depending on the rpm. So this can create a jolting effect to the drive system. This is why most IGH builders limit their builds to predominantly 3 speed hubs and sometimes maybe 5 speed hubs.

I'm not trying to discourage you; I was told the auto shifter would never work but rode it for 11 years. Maybe you'll discover ways and things that have been overlooked or never even thought of.

 

[UtiliD]

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.