Let's Talk Gear Ratios

[Mike Bean]

If anyone has any input on specific gear ratios (sprocket and clutch setups) for specific engine sizes like 6.5, 5.0 etc. with an average rider weight of 160 lbs can you post them here?

I am not an expert on drive setups and can only go off of what I have actually tested and used. But I am sure someone on here has a basic formula we could all benefit from and use to get out barstool racers going.

Thanks in advance to all that contribute!

Mike Bean
:blob_red:

[nsanesider]

Hear is a list of Gear Ratio's..Hope this helps...

9 10 11 12 13 14 15 16 17 18 19 20 (Clutch Gears)
53 5.89 5.30 4.82 4.42 4.08 3.79 3.53 3.31 3.12 2.94 2.79 2.65
54 6.00 5.40 4.91 4.50 4.15 3.86 3.60 3.38 3.18 3.00 2.84 2.70
55 6.11 5.50 5.00 4.58 4.23 3.93 3.67 3.44 3.24 3.06 2.89 2.75
56 6.22 5.60 5.09 4.67 4.31 4.00 3.73 3.50 3.29 3.11 2.95 2.80
57 6.33 5.70 5.18 4.75 4.38 4.07 3.80 3.56 3.35 3.17 3.00 2.85
58 6.44 5.80 5.27 4.83 4.46 4.14 3.87 3.63 3.41 3.22 3.05 2.90
59 6.56 5.90 5.36 4.92 4.54 4.21 3.93 3.69 3.47 3.28 3.11 2.95
60 6.67 6.00 5.45 5.00 4.62 4.29 4.00 3.75 3.53 3.33 3.16 3.00
61 6.78 6.10 5.55 5.08 4.69 4.36 4.07 3.81 3.59 3.39 3.21 3.05
62 6.89 6.20 5.64 5.17 4.77 4.43 4.13 3.88 3.65 3.44 3.26 3.10
63 7.00 6.30 5.73 5.25 4.85 4.50 4.20 3.94 3.71 3.50 3.32 3.15
64 7.11 6.40 5.82 5.33 4.92 4.57 4.27 4.00 3.76 3.56 3.37 3.20
65 7.22 6.50 5.91 5.42 5.00 4.64 4.33 4.06 3.82 3.61 3.42 3.25
66 7.33 6.60 6.00 5.50 5.08 4.71 4.40 4.13 3.88 3.67 3.47 3.30
67 7.44 6.70 6.09 5.58 5.15 4.79 4.47 4.19 3.94 3.72 3.53 3.35
68 7.56 6.80 6.18 5.67 5.23 4.86 4.53 4.25 4.00 3.78 3.58 3.40
69 7.67 6.90 6.27 5.75 5.31 4.93 4.60 4.31 4.06 3.83 3.63 3.45
70 7.78 7.00 6.36 5.83 5.38 5.00 4.67 4.38 4.12 3.89 3.68 3.50
71 7.89 7.10 6.45 5.92 5.46 5.07 4.73 4.44 4.18 3.94 3.74 3.55
72 8.00 7.20 6.55 6.00 5.54 5.14 4.80 4.50 4.24 4.00 3.79 3.60
73 8.11 7.30 6.64 6.08 5.62 5.21 4.87 4.56 4.29 4.06 3.84 3.65
74 8.22 7.40 6.73 6.17 5.69 5.29 4.93 4.63 4.35 4.11 3.89 3.70
75 8.33 7.50 6.82 6.25 5.77 5.36 5.00 4.69 4.41 4.17 3.95 3.75
76 8.44 7.60 6.91 6.33 5.85 5.43 5.07 4.75 4.47 4.22 4.00 3.80
77 8.56 7.70 7.00 6.42 5.92 5.50 5.13 4.81 4.53 4.28 4.05 3.85
78 8.67 7.80 7.09 6.50 6.00 5.57 5.20 4.88 4.59 4.33 4.11 3.90
79 8.78 7.90 7.18 6.58 6.08 5.64 5.27 4.94 4.65 4.39 4.16 3.95
80 8.89 8.00 7.27 6.67 6.15 5.71 5.33 5.00 4.71 4.44 4.21 4.00
81 9.00 8.10 7.36 6.75 6.23 5.79 5.40 5.06 4.76 4.50 4.26 4.05
82 9.11 8.20 7.45 6.83 6.31 5.86 5.47 5.13 4.82 4.56 4.32 4.10
83 9.22 8.30 7.55 6.92 6.38 5.93 5.53 5.19 4.88 4.61 4.37 4.15
84 9.33 8.40 7.64 7.00 6.46 6.00 5.60 5.25 4.94 4.67 4.42 4.20
85 9.44 8.50 7.73 7.08 6.54 6.07 5.67 5.31 5.00 4.72 4.47 4.25
86 9.56 8.60 7.82 7.17 6.62 6.14 5.73 5.38 5.06 4.78 4.53 4.30
87 9.67 8.70 7.91 7.25 6.69 6.21 5.80 5.44 5.12 4.83 4.58 4.35
88 9.78 8.80 8.00 7.33 6.77 6.29 5.87 5.50 5.18 4.89 4.63 4.40
89 9.89 8.90 8.09 7.42 6.85 6.36 5.93 5.56 5.24 4.94 4.68 4.45
90 10.00 9.00 8.18 7.50 6.92 6.43 6.00 5.63 5.29 5.00 4.74 4.50

Here is the llink to that information....http://www.mrhkarting.com/techtip2.htm

[Mike Bean]

Thanks for the post. Now let me ask you.. In all that information, I am supposed to take the top sprocket count and the match it with the left column for my rear sprocket and then follow to my actual gear ratio?

Mike

[nsanesider]

That's Correct....Now if your running a 1" axle it may be a little different.Not sure.Ill see if I can find one for the 1" axle ratio as well.. The Link should make it a little clearer....http://www.mrhkarting.com/techtip2.htm

[Mike Bean]

Here is another way to determine your gear ratio.

If you have a 40 tooth rear sprocket and a 11 tooth clutch sprocket you will divide 11 into 40 (40/11) and you get your drive ratio. In this example 3.64.

Now my question is, what would be a good gear ratio for lets say 6.5 HP and 160 LB rider weight. -vs- 5.0 HP and 160 LB rider weight.

I am sure there is a ball park figure table we could figure out to help builders determine what they need.

ex. I weight 215 lbs, I use a 6.5HP engine with a 40 tooth rear sprocket and I believer a 10 tooth drive on my tork-a-verter that works great. I also used a 54 tooth on the rear which had lots of tourqe and also worked great.

Now tork-a-verters are a whole new area which I don't think we need to dig to deep into. I think if you can determine a clutch and sprocket ratio then a tork-a-verter will just add to the top end. The main concern is having enough gear ratio to get the stool moving at an acceptable rate with various engine HP.

Mike Bean
:hot:

[bombadierx5]

Mike, I use this little freebie program made for karts. It works well with bar stools. You can download it here http://www.gregorybraun.com/ look for kart data 2000. It has a lot of kart setup calculations that will give ratio, mph and corner weight calculations.

[Canadiankid]

If you know engine rpm (my 5 hp honda is 3900) and can measure tire circumference or remember that diameter x 3.14 is circumference then http://www.gokartracing.org/Calculate.htm will help you find top speed and let you play with gear ratios.

[mike gilliam]

Im new to all this , but we do race karts on dirt we run a 8 hp animal dynod at 12.8 turning 6500 rpms we run a 12 tooth clutch with a 60 tooth bottom gear which translates to a 5.00 gear ratio on a 1/8 th mi track we turn laps at just over 10 sec thats right at 50 or so mph kart and driver weigh 318 lbs. Im putting the sister race moter on my BSR and am going to really gear it up to about a 68 tooth on the back and it will fly

[voodoo_stepchild]

Im new to all this , but we do race karts on dirt we run a 8 hp animal dynod at 12.8 turning 6500 rpms

The animal is not 8 hp its a listed 6.5 206CC. Its simply the motorsports version of the intek 6.5
Voodoo