Grubee 4G 1A freewheel hub reliability

[Otto Neumann]

(RPM × Wheel Diameter × π)
÷ (1056 × Total Reduction)
= MPH

Those two engines max hp rpm is 6800.

If you aren't very good at figuring up Total Reduction, use this formula. Teeth pulleys and sprocket can be interchangeable

(RPM × Wheel Diameter × π × Drive Sprocket(s)T)
÷ (1056 × Driven Sprocket(s)T)
= MPH

Assuming a total RPM of 5k, as my preference is rolling to a gentle pace:
(5000 x 26 x 3,14 x 28) / (1056 x144)
11429600 / 152064 = 75 mph

*Wheeeze* Oh wow, that's quite fast for a 53cc, something feels off

After fiddling around a little, I came across an unnoticed issue, I believe you saved my bacon:
I double checked my math document, apparently I had calculated my ratios with a 144T pulley, planned to be machined, instead of the 122T that I currently have assembled on the bike; everything was off.

I recalculated everything, and I placed, as comparison, the equivalent 415 chain sprocket pairing.

- HTD-5M belt to 415 chain -

15T-122T = 8,13:1 (10T- 81T)
20T-122T = 6:1 (10T-60T)
24T-122T = 5:1 (10T-50T)
25T-122T = 4,88:1 (10T-48T)
27T-122T = 4,52:1 (10T-45T)
28T-122T = 4:36:1 (10T-43T)
30T-122T = 4:1 (10T-40T)
32T-122T = 3,8:1 (10T-38T)

I have a 28T drive pulley, so it's gonna behave like when I was running a 43T sprocket, which NGL was a good compromise between torque and speed; oh well, at least the mistake didn't turned my bike any worse

 

[Sidewinder Jerry]

Assuming a total RPM of 5k, as my preference is rolling to a gentle pace:
(5000 x 26 x 3,14 x 28) / (1056 x144)
11429600 / 152064 = 75 mph

*Wheeeze* Oh wow, that's quite fast for a 53cc, something feels off

After fiddling around a little, I came across an unnoticed issue, I believe you saved my bacon:
I double checked my math document, apparently I had calculated my ratios with a 144T pulley, planned to be machined, instead of the 122T that I currently have assembled on the bike; everything was off.

I recalculated everything, and I placed, as comparison, the equivalent 415 chain sprocket pairing.

- HTD-5M belt to 415 chain -

15T-122T = 8,13:1 (10T- 81T)
20T-122T = 6:1 (10T-60T)
24T-122T = 5:1 (10T-50T)
25T-122T = 4,88:1 (10T-48T)
27T-122T = 4,52:1 (10T-45T)
28T-122T = 4:36:1 (10T-43T)
30T-122T = 4:1 (10T-40T)
32T-122T = 3,8:1 (10T-38T)

I have a 28T drive pulley, so it's gonna behave like when I was running a 43T sprocket, which NGL was a good compromise between torque and speed; oh well, at least the mistake didn't turned my bike any worse

To the best of my memory a GruBee 4G transmission comes with the choice of a:

{20t} < {80t,90t,100t} pulleys. You then have to put a drive sprocket on the transmission's output shaft and a sprocket on the rear wheel. Unless you're talking about using belt pulleys instead of roller chain sprockets.

If that's the case then you're looking at a speed around 20 mph; if a 100t is being used inside of the transmission. .

(6,800×26×π×28×20)
÷(1,056×144×100)
=20.4547299457

 

[Otto Neumann]

To the best of my memory a GruBee 4G transmission comes with the choice of a 20t|{80t,90t,100t} pulleys. You then have to put a drive sprocket on the transmission's output shaft and a sprocket on the rear wheel. Unless you're talking about using belt pulleys instead of roller chain sprockets.

If that's the case then you're looking at a speed around 20 mph; if a 100t is being used inside of the transmission. .

(6,800×26×π×28×20)
÷(1,056×144×100)
=20.4547299457

Oh yes; everything is belt driven, from the transmission to the rear wheel connection.

That pic features the old engine and transmission, they will be gone soon; the ratio between the old and new transmission hasn't changed overall:

Transmission has a 20T pulley on the clutch bell; a 100T pulley on the reduction side; a 28T pulley on the output shaft, and a modified 122T pulley on the rear wheel.

 

[Sidewinder Jerry]

Oh yes; everything is belt driven, from the transmission to the rear wheel connection.
View attachment 228251
That pic features the old engine and transmission, they will be gone soon; the ratio between the old and new transmission hasn't changed overall:

Transmission has a 20T pulley on the clutch bell; a 100T pulley on the reduction side; a 28T pulley on the output shaft, and a modified 122T pulley on the rear wheel.

With the 122t pulley you're looking at a top level ground speed of 24 mph.

 

[Otto Neumann]

With the 122t pulley you're looking at a top level ground speed of 24 mph.

Good enough for me, thanks for the math:
The pulley sizes I have in the tab up above are actually premade ones you can find on Ebay or Aliexpress, but at worse, the ratio can be finely adjusted with custom made ones.

I got tired of the clicking noise from the chain drive, so I experimented on a belt drive; before the straight shaft clutch failed me, it felt much easier to pedal and much less snappy when the clutch engaged.

 

[Sidewinder Jerry]

Good enough for me, thanks for the math:
The pulley sizes I have in the tab up above are actually premade ones you can find on Ebay or Aliexpress, but at worse, the ratio can be finely adjusted with custom made ones.

I got tired of the clicking noise from the chain drive, so I experimented on a belt drive; before the straight shaft clutch failed me, it felt much easier to pedal and much less snappy when the clutch engaged.

With those engines max torque is at 4500 rpm, max hp is at 6800 rpm, idle is 2800 rpm, max rpm 7500, and clutch engagement should be around 4000 rpm. I strongly suggest getting a tachometer/hour counter.

The tach is useful with tuning the carburetor and throttle control/pedal assist. The hour counter is useful for maintaining a routine maintenance schedule. I change my oil every 25 hours and check the valve lashes. I clean the air filter every 10 hours. My engine is 15 years old with more than 5000 hours of use on it. All I've ever replaced is spark plugs and I did replace the non-adjustable diaphragm carburetor with a adjustable one.

 

[Otto Neumann]

With those engines max torque is at 4500 rpm, max hp is at 6800 rpm, idle is 2800 rpm, max rpm 7500, and clutch engagement should be around 4000 rpm. I strongly suggest getting a tachometer/hour counter.

The tach is useful with tuning the carburetor and throttle control/pedal assist. The hour counter is useful for maintaining a routine maintenance schedule. I change my oil every 25 hours and check the valve lashes. I clean the air filter every 10 hours. My engine is 15 years old with more than 5000 hours of use on it. All I've ever replaced is spark plugs and I did replace the non-adjustable diaphragm carburetor with a adjustable one.

I have a tac/hour meter on its way to me, I want the new engine to be broken in and maintained following the rules of art, with Valvoline 5W-40.

I have tried, on the straight shaft, to slap on a Dell'Orto PHBG 15 AS; but I couldn't fully tune it before the engine's clutch kicked the bucket; it sure was a good upgrade tho; if I see the new 144F performs well with its stock diaphragm carburetor, I will leave it:

PHBGs are a staple in matter of tuning, especially for 2 strokers, but requires lots of fiddling, especially with the needle, and there are about 19 to 20 different ones, I don't think I'd get the bicycle tuned anywhere before this year's thanksgiving xD

 

[Sidewinder Jerry]

I placed my tachometer right below my speedometer. I use my tachometer to shift my gears with.

 

[Otto Neumann]

I kind of wanted to work on a shifter bike in the beginning, but then, I preferred to keep it simple; at the time of starting this build, I had not a TIG welding machine yet, for DIY a jackshaft; by now, I'm far too close to the end for a change of plans

 

[Sidewinder Jerry]

I kind of wanted to work on a shifter bike in the beginning, but then, I preferred to keep it simple; at the time of starting this build, I had not a TIG welding machine yet, for DIY a jackshaft; by now, I'm far too close to the end for a change of plans

Unless you're a large person, have a low powered engine, and have steep hills you don't need gears. I'm 250 lbs, have a 1.6 hp 4 stroke engine, and live in the mountains so yes I need gears lol