Need some clarification on Gear Ratios

[Brandon1023]

I somewhat understand what a gear ratio is.. the teeth on the axle divided by the teeth on the clutch equals the ratio. Now I'm confused as to why people are so concerned. For example. I have a 60 axle and 11 sprocket. 5.45:1. Right? I go 28 mph @ 3600 and I can still get up hills with momentum. What if I had say.. 40 teeth on my axle and 11 on the sprocket? Is this more torque? I always thought for example in a car's transmisson 1st gear is the smallest in dia. So this is why the car revs much quicker as opposed to 6th gear. Whe you're crusing down the highway at 90 mph @ 3k rpm, is the gear really big or really small? I'm confused.

Another thing is.. what is this "roasting clutch" ? I know the clutch can wear and stuff, but what does tire diameter have to do with the clutch? Does a bigger gear and bigger tires give less torque which causes the clutch to be unable to turn the tires?

Finally, what is a jackshaft, and why do I need one on my go kart in order to have a Comet 40? Also, how hard are they to install?

I'm curious b/c 1. I want to learn about it and 2. I want to put a torque converter and axle to make my kart off road-friendly, but I want torque and bigger tires so its not so bumpy. If someone can clear up my confusion, ill greatly appreciate it.

 

[r_chez_08]

I somewhat understand what a gear ratio is.. the teeth on the axle divided by the teeth on the clutch equals the ratio. Now I'm confused as to why people are so concerned. For example. I have a 60 axle and 11 sprocket. 5.45:1. Right? I go 28 mph @ 3600 and I can still get up hills with momentum. What if I had say.. 40 teeth on my axle and 11 on the sprocket? Is this more torque?Nope, more speed, less torque. I doubt it would work, depending on your engine and terrain. I always thought for example in a car's transmisson 1st gear is the smallest in dia. So this is why the car revs much quicker as opposed to 6th gear. Whe you're crusing down the highway at 90 mph @ 3k rpm, is the gear really big or really small? I'm confused.It would be like a kart with a small rear sprocket or large clutch. 1st gear would be like a kart with a small clutch sprocket or big axle sprocket- more torque.

Another thing is.. what is this "roasting clutch" ? I know the clutch can wear and stuff, but what does tire diameter have to do with the clutch? Does a bigger gear and bigger tires give less torque which causes the clutch to be unable to turn the tires?
Pretty much. If you have a larger tyre, one rotation equates to a further distance covered, so more speed. It also takes more to get a bigger tyre going because it is heavier and acts almost like a heavy flywheel.

Finally, what is a jackshaft, and why do I need one on my go kart in order to have a Comet 40? Also, how hard are they to install?A jackshaft is a shaft of usually 3/4" or 5/8" (for karting). It can be used to gear down lower, change side of sprocket and for mounting torque converters. Search the forum for jackshafts and you will find many setups. You need a jackshaft of some kind for a comet 40 series. If you have a drill and maybe a welder you can mount a jackshaft. You don't even need a drill if you buy a kit. Just depends how mechanically inclined you are.

I'm curious b/c 1. I want to learn about it and 2. I want to put a torque converter and axle to make my kart off road-friendly, but I want torque and bigger tires so its not so bumpy. If someone can clear up my confusion, ill greatly appreciate it. Yeah a torque converter will give you more torque. In low ratio you can times your gear ratio by 2.43 (IIRC) so it is like having a car in first gear or a 2.43x larger axle sprocket. What engine do you have? and what tyre size do you plan on?

Replies in red

 

[Brandon1023]

Thank you r_chez. That makes more sense. Right now, ihave a 420cc Predator on the way here. I'm gonna go through with the whole conversion slowly at a time. I'd like to be able to go up maybe 30 degree slopes and get my @$$ out of loose dirt when needed while still being able to go faster than 28. I know everyone on here has great ideas so if someone can tell me what the best set up would be, ill be interested. Once I get home from school, ill upload some pictures for you all.

15 x 6.00-6 turf saver tires,
Approx 13 HP Predator,
Current ratio is 5.45
Bigger tires would be a plus
Frame is big enough to work with and I'm good enough to do some minor welds. If not, my neighbor welds. Money isn't too much of an issue and ill just save I need a decent amount.
I'm not removing the gov. Because I spent $350 on the new engine after the rod blew and the whole block shattered lol.

 

[Doc Sprocket]

30* is quite an incline. I do believe you're going to want to gear a bit lower for the kind of oomph you expect. I'll need some time to think on that.

Good answers by Rchez! I'll add a few points.

*Re: clutch "roasting"- literally- If the ratio is too tall, the clutch cannot hook up and is forced to slip much more than it can tolerate. Too much slippage between friction surfaces= heat. Too much heat builds, and the clutch friction material burns. Altered by excessive heat, the friction material will no longer do it's job. In addition, the excessive heat can alter the temper of the springs, rendering them useless, too. It will ALSO burn off the lubricant from the bushing, and burn that, too.

Also bear in mind that your engine will have less leverage on bigger tires. If you increase tire size, your theoretical top speed (with ratios unchanged) will increase- but the reality of it is that you will lose torque.

You WILL be able to get away with a higher ratio using a CVT than you would with a clutch. Plan your purchases well to avoid regearing again.

Real-world experience- I was running an 11hp GX340 at 4200RPM with a comet 40 and 17.5" (measured) tires at 4.8:1. Actual onboard speedo measured 46MPH, verified with several long GPS readings. I was still quite overgeared for the circumstances. While top speed was respectable, torque was too weak...

 

[Brandon1023]

Ok that makes much more sense. So, how does a torque converter work with ratios? When you're sitting still at idle, what happens when you hit the gas? It starts at a low ratio and flips through various speeds? I'm confused since its only a belt and 2 pulleys.

 

[anderkart]

This video shows how they work:

http://www.youtube.com/watch?v=pptnRGTH_XA

 

[Brandon1023]

Ugh I gotta get one of those. Does it come with that back plate, to mount the driven on?

 

[anderkart]

Yep