CVT Honda GXH50 & Comet torque converter?

hlombard

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Mar 27, 2008
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I'm planning to install a Honda GXH50 on a Delta trike (2 x 26" wheels at the rear).

1. Will the Comet TAV2 Torque converter fit on the Honda ? I'll need a bushing to go from 5/8" to 3/4" shaft, but is there space to mount the TAV?

2. Can someone confirm my speed calculations?

- Tav have reduction ratios of 2.7:1 at slow end and 0.9:1 at fast end.
- Tav has 12 tooth sprocket and I have 48 tooth for axle
- TAV kicks in at 2,200 rpm
- Honda has max rpm of 7,000

What is my minimum and max speed whith 26" wheels?

I tried this but get crazy numbers.
 


H

HoughMade

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You will get crazy numbers because you would need to gear this down more.

A jackshaft that reduced it another 3:1 would result in an approximate top speed of 50 mph at 7000rpm, assuming no wind resistance or friction losses- in reality, a top speed in the 40s.
 

loquin

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Jan 11, 2008
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The gearing suggests 15.7 MPH at the low end... 150 MPH at the high end. Obviously, you'll run out of oomph from the engine LONG before you get anywhere close to that. As Houghmade suggests, add more reduction. Really, 4:1 or 5:1 additional reduction wouldn't hurt. Especially with a trike. At high speeds, rolling a trike in the event of an emergency maneuver becomes a real possibility. At 5:1, you could take off from a standstill, and have outstanding acceleration up the top end of about 30 MPH. 4:1 would give you good acceleration and a top end near 40 MPH.
 
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reclaimer

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I have read (over in wild in the streets) the tav2 is only good up to a 20" wheel. I however have zero experince with them. hope to find out different.
 

loquin

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I have read (over in wild in the streets) the tav2 is only good up to a 20" wheel...
If it's hooked up directly, that would be true. But, we're talking about adding a jackshaft between the output sprocket of the CVT and the rear sprocket, to further step down the rear wheel RPM.
 
R

reclaimer

Guest
I always assumed reducing the rear wheel rpms to a suitable level would make it horribly slow. Top speed in the 40s isn't slow.

Is the goal to get the jack shaft to turn near the same rpms a correct sized wheel would?(edit, or the rear wheel maybe)

Good luck with your project, an please keep us posted on how it comes out.
 
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HoughMade

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An engine has to operate in a certain rpm range to make enough power. In the case of the Honda GXH50, that would be between 3500 and 7000 rpm. Due to wind resistence and friction, you cannot simply reduce the gear ratios and reap higher and higher top speeds. The goal of a jack shaft is to reduce or multiply the gear ratio at whatever rate is needed to keep the engine in the optimum rpm range at the speed you want.
 
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loquin

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Jan 11, 2008
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2,214
reclaimer said:
I always assumed reducing the rear wheel rpms to a suitable level would make it horribly slow. ... Is the goal to get the jack shaft to turn near the same rpms a correct sized wheel would?
Suitable wheel RPM for a small wheel (pocket bike or scooter) is MUCH higher than suitable RPM for a 26 inch diameter tire. Think if it this way. When a 10 inch diameter tire makes one complete rotation, the wheel moves forward 31.4 inches (by the circumference.) When a 26 inch tire makes one complete revolution, it will move forward by it's circumference, which is 81.6 inches! Both tires have made one revolution, but, the 26 inch tire has gone 2.6 times further... This means that a 10 inch (outer) diameter tire must spin 2.6 times faster than a 26 inch tire, just to travel at the same speed.

for a 26 inch wheel to be traveling at 40 mph, it needs to be spinning at approximately 517 RPM. If an engine is running at 7000 RPM, then, between the engine and the wheel, you need to reduce the RPM by a factor of about 13.5.

Since the Comet CVT actually INCREASES the output RPM at the high end, (by apx. 11 percent,) the output shaft is actually turning at about 7780 RPM at the high end.

So, to get the final wheel RPM, the total reduction between the Comet and the wheel, you need a total additional reduction of a bit over 15 (15.04)

Adding a jackshaft with an input sprocket with 48 teeth, (assuming an 11 tooth sprocket on the Comet,) an output sprocket with 14 teeth, and a 48 tooth sprocket on the wheel would result in a 14.96 additional reduction. That 14.96 reduction, coupled with the .9 reduction of the comet at high rpms, results in a total reduction, engine to rear wheel of about 13.46, which, at 7000 RPM, would put your speed at a bit over 40 MPH.

Let me reiterate, though. On a bike, 40+ MPH is fast, but manageable. On a three-wheel bike, it verges on the dangerous. You can lean into a turn on a bicycle. You can't lean a trike into a turn. It is much more susceptible to flipping when you turn, especially an emergency turn.
 
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reclaimer

Guest
Wow I figured a 26" would go a bit faster than a 20", didn't realize it was such a dramatic difference.

Thank you for explaining that so well. I think I'm starting to get it.

What is it that causes damage to a centrifugal clutch when going up wheel size? Is it that the gearing changes so much it cant make enough low end power to engage the clutch proper?(previously I had thought it was the added mass of the wheel, learning is fun)

I was playing with that spreadsheet last night(found it in another of your posts) pretty neat and I'm sure it will be of great value to me. Once I get my head wrapped around it anyway.
 
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