Need help deciding on sprocket sizes

[raposak]

As the title says, I need some input as to the size of the sprockets on my cbr600 powered kart. I have to replace all sprockets so i'm starting fresh. I'm going to run #50 chain. It will go from the engine, to a sprocket on a jackshaft and than another sprocket on the jackshaft to the rear axle. By the time i'm done it will weigh in at about 500 lbs with rider. I'm also looking at 27" rear tires. This is a full suspension cart to be used offroad and should be able to handle hill climbs with ease.

Any help would be appreciated.

 

[used2jeep]

I read on the site somewhere (lately):
on road - 5 to 7 :1
off road - 10 to 12 : 1
for final ratios.

I know it isn't exactly answering your question but with the calculator on the site here then you should be able to figure out easily what 2 jackshaft sprockets you will need.

HTH

 

[raposak]

Ok, how does this sound?
12 Engine
16 Jackshaft input
13 Jackshaft output
70 axle
I believe this give me 7.18

 

[DaiSan76]

According to google, the final drive sprockets for the average cbr 600 are 15/43, which gives you a 2.8 final drive ratio. You are probably going to be allot heavier with your cart, but the tires will be smaller. I would think that 7.18:1 would be kind of high considering you have a 6 speed gearbox, but you should have truckloads of torque.

 

[raposak]

Would this be better for my situation?
12 Engine
16 Jackshaft input
12 Jackshaft output
54 axle
I believe this give me 6.0:1

 

[used2jeep]

Try this for a tool: http://www.fasttrackraceway.com/calc/index.php (just use the 4 left hand boxes). Don't forget that you can switch the 4 sprockets on the jack shaft for many many options/combinations.

Good luck!

 

[landuse]

I wish I could help out, but I get stumped with ratios when working with motorbike engines. Because they have gears themselves, I am clueless when it comes to the calculations.

Maybe PM people like toystory or Anderkart. They are good with this stuff

 

[raposak]

Well I got this from this site so now I have to figure 2.8 into the equation which is the final drive ratio of the motor. hmmmmmm now i'm really confused lol.

Also, if you are using a motorcycle engine, there is also a primary ratio (the ratio between the crankshaft and the clutch shaft) that has to be figured in. On my RM 250 motor, it's 3:1, so you must multiply the final drive ratio x the primary ratio to get the overall gear ratio. For example, right now my final drive ( front and rear sprockets) is 13/23 which works out to about 1.7:1, then I have to multiply that by 3, and 1.7 x 3 = 5.1, so that is my overall gear ratio.

 

[raposak]

Ok, I think I actually figured it out. Here are my numbers, tell me what you think.
13 Engine
13 JS in
12 JS out
28 Axle
This equals 2.33
2.33 x 2.8 = 6.524 final ratio. How does this sound for an offroad cart that will see hills.

 

[island]

I wish I could help out, but I get stumped with ratios when working with motorbike engines. Because they have gears themselves, I am clueless when it comes to the calculations.

Maybe PM people like toystory or Anderkart. They are good with this stuff

X2, But does it need a jackshaft?

 

[christeeezy]

I've done a lot of researching about gearing for motorbike engines, so don't write me off as a noob just because of my post count

Since you said you're looking to run 27" tires, that's pretty close to what the bike was originally turning, so you don't have to make a drastic change in your gearing.

Regardless of what your ratios may be inside of the transmission, you can go off of what the stock final drive was: 15/43 (2.866:1)

Obviously the CBR would reach speeds of over 100mph, and I'm assuming you do not want to run that fast. Win win, because if you gear it down a bit, you'll receive more torque.

You want to find a ratio where you will have a bunch of torque, but one that will not make you redline too quickly on each gear.

I'd say something like a 50% lower ratio would do the trick:

4.3:1 ratio. That would be:

15 tooth engine output
30 tooth jackshaft input
15 tooth jackshaft output
32 tooth axle


I'll edit this post after I test the numbers in a gearing calc.

-Steezy

 

[anderkart]

I used these 2002 CBR 600 F4i specifications: http://jesture.com/misc/f4igearingform.php

I entered that info into this speed calculator: http://www.rbracing-rsr.com/gearspeed.html

___________________

At 14,500rpm redline

with 27" tall rear tires

16-tooth counter sprocket
70-tooth axle sprocket

Jackshaft-in: 20-tooth
Jackshaft-out: 15-tooth

The results were:
1st gear: 34mph
2nd: 47mph
3rd: 62mph
4th: 72mph
5th: 83mph
6th: 92mph

These are estimated top speeds, but if your engine will redline in each gear they should get you in the ballpark.

_________________________________________

If you wanna recalculate some different ratios/top speeds, (or double check my results) a couple things I found kinda tricky using the rbracing speed calculator were:

Don't use a coma when entering your redline rpm. (just enter 14500)

For your front primary, type in 20 teeth. For the rear primary, enter 40 teeth. (because your specs claim a 2 to 1 primary reduction)

For tire growth, I just entered 1

 

[raposak]

Speed is good, but I also need stump pulling torque. I want to be able lug the engine up a hill without feathering the clutch.

 

[anderkart]

I recalculated with all the other gear counts remaining the same, and only replacing your 20-tooth Jackshaft-in for a 25-tooth instead. It showed 27mph in 1st. gear / 74mph in 6th.

Or with substituting a 30-tooth J/S-in, it showed a 23mph top speed in 1st, and a 62mph in 6th...

 

[raposak]

According to your numbers, my ratio would be 7.29 but does not include the engine reduction of 2.8 which would give me a final ration of 20.412 which is WAY too high. Now i'm totally confused lol

 

[anderkart]

I'm pretty sure that speed calculator I used already factored in your engines primary and final-reduction, so you wouldnt multiply by 2.8 to get your ratio.

 

[raposak]

I put your numbers into this calculator which doesn't account for the engine and got those numbers.
http://www.fasttrackraceway.com/calc/index.php

 

[anderkart]

You dont multiply by 2.8 after using that sites calculator. If you got 7.29, that's your ratio.

The 2.8 'engine' reduction your trying to factor in here is your Final Reduction. This is simply the result of the CBR600 motorcycle originally having a 16-t countersprocket and a 46-t rear wheel sprocket. (its not from some extra set of gears in your transmission)

In my gearing suggestions we completely changing that 2.8 final reduction with the jackshaft gearing and a larger rear sprocket.

If you use this calculator: http://jesture.com/misc/f4igearingform.php?showbike=1 You'll see the final reduction for your stock motorcycle was originally 2.875. But If you enter any different countersprocket (or rear sprocket) tooth count into the pink "new gearing" boxes (and then click on Refresh all calculated values) you'll get a different final reduction #.

Does that make more sense now?

 

[raposak]

Yes, thanks for taking the time to drill it through my thick head.

 

[r97]

one more suggestion; Make the jack shaft's primary (input, or whatever you want to call it) ratio 1:1, or better yet just eliminate it if you can. Many people using mini buggies have had problems with snapped secondary chains when using a jack shaft.