Gear ratios?

[BirdFanatic]

Ok i know the gear ratios for normal karts should be above 5 with a cheap clutch and about 4.5 with a $$$ clutch .Do the same rules apply to my shifter kart that has a transmission ? .What ratio is good what ratio is bad ?

 

[landuse]

Ok i know the gear ratios for normal karts should be above 5 with a cheap clutch and about 4.5 with a $$$ clutch .Do the same rules apply to my shifter kart that has a transmission ? .What ratio is good what ratio is bad ?

This is a highly incorrect blanket statement to be making. There are so many variable that come into play. I have never heard of 5:1 being a standard either. 6:1 is the number that always gets brought up. Tyre size plays such a huge role

 

[Russ2251]

Ratios are probably the single most misunderstood aspect of our hobby.
A lot of this is due to some really bad information.

As landuse pointed out,

Tyre size plays such a huge role

.

For a ~10"-12" tire, a ~5 or 6 to 1 ratio is just fine.
Increase the tire size to 22 inches in diameter with a 5/1 ratio utilizing a centrifugal clutch and kart will not want to move.
Said clutch will burn-up in just a few minutes of use.

 

[BirdFanatic]

This is a highly incorrect blanket statement to be making. There are so many variable that come into play. I have never heard of 5:1 being a standard either. 6:1 is the number that always gets brought up. Tyre size plays such a huge role

Its a general statement Anything from 4.5 and up is good (just as long as its not super high ) .Honda cr85 (considered a 125 after i found that it has a stroker crank )

 

[JoeKR]

You'd be better off to calculate the final ratio for top speed. The one on this site works fine. A 3 to 1 @ 7000rpm w/a 12" tire yields 83mph. YMPHMV.

A single speed ratio is a compromise between top speed and being able to start moving. A transmission eliminates the need for that compromise.

 

[firemanjim]

You'd be better off to calculate the final ratio for top speed. The one on this site works fine. A 3 to 1 @ 7000rpm w/a 12" tire yields 83mph. YMPHMV.

A single speed ratio is a compromise between top speed and being able to start moving. A transmission eliminates the need for that compromise.

He still needs to know what the internal gear ratios of the engine itself, to figure out the top speed.
http://www.gearingcommander.com/
You can use that speed calculator, for dirt bike engines....

 

[firemanjim]

Its a general statement Anything from 4.5 and up is good (just as long as its not super high ) )

I CANT run 4.5:1 with 15" tires on a cc..... Without damaging the cc.....
6:1....
6:1.....
6:1....... Is a good starting point, for a standard yard kart with 15" or smaller tires....(12-13" preferably/ideally )

 

[BirdFanatic]

I CANT run 4.5:1 with 15" tires on a cc..... Without damaging the cc.....
6:1....
6:1.....
6:1....... Is a good starting point, for a standard yard kart with 15" or smaller tires....(12-13" preferably/ideally )

True ig your right about the tire thing there .I have seen people go all the way down to .8 and lower on the shifter karts i have 11 inch tires i just bought a 23 tooth axle sprocket and i have 18 on the engine output shaft.Im not sure about the lower or higher gears on a kart like this because with a cc as you said they burn up because they slip get hot .But what about a transmission ?

 

[firemanjim]

True ig your right about the tire thing there .I have seen people go all the way down to .8 and lower on the shifter karts i have 11 inch tires i just bought a 23 tooth axle sprocket and i have 18 on the engine output shaft.Im not sure about the lower or higher gears on a kart like this because with a cc as you said they burn up because they slip get hot .But what about a transmission ?

Yes, they slip a little too, but are in a constant oil bath, holding down the heat. They are designed to eventually wear away. Then you buy new friction plates, and are back in business..... Those were designed to be rebuildable..... A cc wasn't.....

 

[BirdFanatic]

Yes, they slip a little too, but are in a constant oil bath, holding down the heat. They are designed to eventually wear away. Then you buy new friction plates, and are back in business..... Those were designed to be rebuildable..... A cc wasn't.....

wonder what my top speed will be with a 1.2 11 inch tires 80-100 pound frame and a 185 pond me lol i guess it also matters what the tranny is .

 

[JoeKR]

He still needs to know what the internal gear ratios of the engine itself, to figure out the top speed.
http://www.gearingcommander.com/
You can use that speed calculator, for dirt bike engines....

Unless it's an overdrive, I'll take a wild stab and say 1 to 1.
It would be handy to know the ratio of all the gears, it's just less important.

Using my 3 to 1 ratio let's say first is 3.3 to 1. That gives me a darn near 10 to 1 first. Just about anything will move with that, and be gentle on any clutch. I just threw a number out there and it would work, that's the beauty of a transmission.

Also keep in mind speed uses stuff like logarithms and exponentials, a final of .5 to 1 is not going to get you to 200 mph. But that kind of math hurts my brain. IOWs, figure the max speed you and your engine are comfortable with and gear accordingly.

 

[firemanjim]

Unless it's an overdrive, I'll take a wild stab and say 1 to 1.
It would be handy to know the ratio of all the gears, it's just less important.

Using my 3 to 1 ratio let's say first is 3.3 to 1. That gives me a darn near 10 to 1 first. Just about anything will move with that, and be gentle on any clutch. I just threw a number out there and it would work, that's the beauty of a transmission.

Also keep in mind speed uses stuff like logarithms and exponentials, a final of .5 to 1 is not going to get you to 200 mph. But that kind of math hurts my brain. IOWs, figure the max speed you and your engine are comfortable with and gear accordingly.

Yeah, I guess I kinda over thought that one....
3spd 4spd and 5spd WOULD still typically have a 1:1 final, huh.... ? It's the 6spd that gives you the overdrive.
Ok, .....
Bird, slow your a## down!

 

[OzFab]

What ratio is good what ratio is bad ?

Honda cr85 (considered a 125 after i found that it has a stroker crank )

Here's a simple "rule of thumb":
On what vehicle did the engine originate?
What was the size (overall height) of the rear wheel?
What was the size of the drive sprocket (measurement, not tooth count?)

Once you provide that information, we can better help you determine what would be the ideal sprocket size to match the smaller 11" tyres by matching the ratio between the original tyre & sprocket...