Torque Converter vs Clutch

[Jin Da Bull]

Ok so I recently obtained a frame, some tires and a Briggs 5.5hp engine. All used but I figured it would be a good starting point for the project I have in mind.

With that said, I'm looking to replace the back tires with this:


It's 24x12x12. I know. It's very large for a kart. It will be a single on the back. The question I have is about torque conversion. I'm learning about gear ratios and wanted to get advice about what would work best. I think a clutch alone would "burn out" so if anyone has experience working with larger tires and can point me in the right direction with gear ratios and torque conversion please let me know. I was looking into the 30 series converter thinking this might be the best set up.

Any advice is appreciated.

 

[Denny]

Wow, 24 is a mighty tall tire. If it was me building this I would use #40 sprockets and chain with a 10 tooth primary and 60 tooth secondary. Tav II is out! I would use a 30 series primary with the 7” secondary. It will give you a lower gear for starting off.

 

[madprofessor]

10:60 ??? That tire is over 6' around circumference. I won't open my yap again on guessing proper ratios, but I'll be watching this space for a larger axle sprocket.

 

[Jin Da Bull]

Wow, 24 is a mighty tall tire. If it was me building this I would use #40 sprockets and chain with a 10 tooth primary and 60 tooth secondary. Tav II is out! I would use a 30 series primary with the 7” secondary. It will give you a lower gear for starting off.

So what you're saying is with the ratio of 10:60 in a converter I'll start off with higher torque/ lower speed then hit good speed as I go? Is it a negligible difference?

 

[madprofessor]

The average spec I've seen on common TC's is that at a standing start the pulleys are resting at a 3:1 ratio (regardless of a gear ratio or anything else outside of the TC). As speed builds and load decreases the pulleys start closing/opening (driver/driven) until final ratio of (1:1.1). So you've basically described it correctly. The difference is enormous, mainly in low end torque. Changes your performance from a "pull" off the line to a "jump' off the line.

 

[Jin Da Bull]

Well, its good thing that the only line I'll be pulling from is the occasional stop sign, lol.

So I'm clear here, the recommendation is a 30 series CV with a 10T on it and a 60T on the axle with a #40 chain?

 

[madprofessor]

I trust Denny's judgement on the CVT series and on the #40 driveline. Reserving judgement on that gear ratio based on my own experience. Running 16" tall tires on current build, and just changed 5:1 (12:60) ratio to 6:1 (12:72), same ratio Denny recommended for you. Still unhappy, need more like 7:1. When it had 12" tall tires, 5:1 ratio was just right.
Clarification: With 10:60 (6:1 being the common way to say it) we're talking about the GEAR ratios of the driveline, completely outside of the CVT. The small sprocket would be mounted on the output shaft of the CVT, with the chain going from there to the big axle sprocket.
The 3:1 standing start I referred to is only on the inside of the CVT, with its 2 variable pulley ratios and belt, instead of gears and chain.

 

[Denny]

Notice I recommended the larger secondary (driven) clutch. You will not be able to use a back plate with it. You will have to use a jack shaft for it. I don’t think the larger driven is made by the Chinese yet. You will have to search the web for one as I don’t remember who carried them. After rolling it around in my head you may be better off going with a 40 series cvt and just lower the gear ratio a bit. I would also not go less than a 8 hp engine.

 

[Jin Da Bull]

Ok, first the gears.
Considering what madprofessor said and his experience it seems like it would be better to run a 12:72 vs a 10:60 considering my tire size. It still sounds like that will give it a pull start but maybe not as bad as a 10:60?

Now on the CVT.
So what you're saying Denny is the stock driven pulley on the 30 series kit should be upgraded to a 7" but won't fit on the stock plate so ill have to jackshaft it. Is the 7" pulley necessary or is that more of a "it will run better with" deal?

 

[Denny]

Ok, I’m pretty sure madprof is thinking #35chain and I’m talking 40. If I’m not mistaken, they are the same ratio. 6:1. I do have dyslexia and can’t grasp the concept of math. I actually changed my recommendation to a 40 series cvt instead of the difficult to find 30 series stuff. I base my advise off of past experiences building stuff, owning or repairing.
Some people say
I’m a savant, some say I am an idiot I think I am both. As far as I am concerned if people take my advise, ok. If they don’t I’m ok with that too. (I have Starrett mikes and I can read them.).

 

[Bansil]

Here is more info to ponder, cyclekart have been running 6.5 engine with tav30 and 72 sprockets for 20+ years, they are about 250# with a 22-1/2" tire.
They run about 40mph.....so who has fresh

 

[Jin Da Bull]

Well overall it seems like it's going to come down to the engine since some of examples you guys have given revolves around at least a 6.5hp.

The 30 Series CVT is rated up to 8hp. I've also read its rated up to both 3100 and 3600 rpm.

My briggs is a 5hp with up to 3600 rpm.

I've also read the 40 series CVT is for over 8hp. Then again other vendors says its fine for a 5hp. (Then we wonder why people make bad choices.)

Thats is where it gets so confusing for novices like me to make an informed choice. So the advice you guys have given is great. It has provided clarity and I feel that ill definitely go 12:72 on the gears and a 30CVT. I'll allow a bit of space on the frame to eventually upgrade to something like a predator 6.5hp or better.

 

[madprofessor]

Back up to your previous post #9 (see upper right corner of each post). You refer to a 12:72 vs a 10:60 ratios. Your not picturing correctly what the ratio says, as those 2 ratios are identical in the final analysis, ratio of 6:1.
Whether you say 6:1 or say 1:6, it's the same statement. Think of it as (for 6:1) the small sprocket mounted either on the engine or on CVT output if used, and the large sprocket mounted on the rear axle. The small sprocket has to revolve 6 times to revolve the large sprocket 1 time, regardless of whether it's 12:72, or 10:60, or 73:438 ratio, they're all 6:1 (or 1:6). Simple math, lowest common denominator for simplification.
My original setup used a 12-tooth sprocket on the CVT output, and a 60-tooth on the axle, a 12:60 ratio (or a 1:5 or a 5:1 ratio).
I changed the axle sprocket (ONLY) from 60 to 72-tooth, so my ratio went from a 5:1 ratio to a 6:1 ratio. I now have better acceleration, but on the top end would have less top speed. And I still want more acceleration. Maybe a 7:1 ratio.

 

[Jin Da Bull]

Back up to your previous post #9 (see upper right corner of each post). You refer to a 12:72 vs a 10:60 ratios. Your not picturing correctly what the ratio says, as those 2 ratios are identical in the final analysis, ratio of 6:1.
Whether you say 6:1 or say 1:6, it's the same statement. Think of it as (for 6:1) the small sprocket mounted either on the engine or on CVT output if used, and the large sprocket mounted on the rear axle. The small sprocket has to revolve 6 times to revolve the large sprocket 1 time, regardless of whether it's 12:72, or 10:60, or 73:438 ratio, they're all 6:1 (or 1:6). Simple math, lowest common denominator for simplification.
My original setup used a 12-tooth sprocket on the CVT output, and a 60-tooth on the axle, a 12:60 ratio (or a 1:5 or a 5:1 ratio).
I changed the axle sprocket (ONLY) from 60 to 72-tooth, so my ratio went from a 5:1 ratio to a 6:1 ratio. I now have better acceleration, but on the top end would have less top speed. And I still want more acceleration. Maybe a 7:1 ratio.

Well damn. There's the math. That makes so much sense now. I feel kinda silly for not realizing that sooner.

So in your case, you had a 12t and a 60t (5:1).
You upgraded the 60t to a 72t thus making it 6:1 which improved your take off but reduced your top end speed. Then going 7:1 would further increase your take off at the sacrifice of more top end speed.

It's all about the balance I want to achieve between take off and top end speed.

The lower ratio (5:1 for example) will give me higher top speed but a slow take off and 7:1 would do the opposite.

Thank you very, very much. It has finally clicked.

 

[madprofessor]

Remember that my new 6:1 gear ratio, possibly going soon to 7:1, is for my 16" tall tires. 16" x 3.14 = 50.24" around the outside (travel distance) for every revolution of my axle.
Your 24" tall tires means 24" x 3.14 = 75.36" of travel distance for every revolution of your axle, about 150% of my travel distance.
You're going to need a ratio that reflects that higher load of distance per revolution. Ratios too small like to burn up clutches.

 

[Bansil]

This is my issue also, most of the Karts like mine, run on flat terrain with 6:1, I may have To go to 7:1 for our mnts/hills.
Then when you put the reverse box ratio into it....things change again

I think bmi or azusa have a gear calculator for free

 

[madprofessor]

Reverse box ratio??? Didn't know about that, never had one, want to do one in future. Is that a common thing for all reverse boxes, and what is that ratio? Pure mechanical, internal gears driven, not changeable? Same ratio forward as in reverse?

 

[Bansil]

This is from ad

Shaft Size: 5/8" with 3/16" Keyway

Suitable for # 35 chain 12T or #40/41/420 Chain 10T

10T Sprocket OR 12T Sprocket (Both included)

Includes All Mounting Hardware

Forward Ratio: 1:1:3

Reverse Ratio: 1:2:6

Good for 11/13 hp or so, hell the 2 I bought prec-covid, with shipping was less than 1 now !!!!​

 

[Jin Da Bull]

I checked out that BMI calculator. This is what I got:


Now I know there are other factors to consider such as kart weight, driver weight, etc but 36 mph?

Considering EVERYTHING I think I am going to try this CTV (unless I find the same one cheaper elsewhere):

Amazon.com: 212CC Torque Converter 6.5 HP 3/4" Go Kart Mini Bike Comet Clutch 10T 40/41 and 12T 35 Chain Predator Driver Pulley Replacement Set - 30 Series: Automotive

Buy 212CC Torque Converter 6.5 HP 3/4" Go Kart Mini Bike Comet Clutch 10T 40/41 and 12T 35 Chain Predator Driver Pulley Replacement Set - 30 Series: Transmissions & Parts - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Then I'll use the 12T it comes with and slap a 72T on the axle with a #35 chain.

Taking that tire size, everyone's advice and some math I feel like this will be at the very least a good starting point and I can tweak it from there. It doesn't need to be perfect it just needs to run solid. It's about having fun.

 

[madprofessor]

Cheaper elsewhere? Look down the page at the other ones, there's one $6 cheaper right there.
With your tire height there's plenty of ground clearance for any size sprocket you care to use. Paying for a new one anyway, might as well go ahead and jump on getting one with as many teeth as you can.