GEAR CALCULATOR
APPLY YOUR DETAILS IN THE FIELDS BELOW TO VIEW THE MPH.
1:1 ratio
1/2 o.d.
Full o.d.
Clutch Ratio |
Number of Drive Sprocket Teeth |
Track Pitch |
Constant |
1 to 1 |
8 | 2.86 | 46.1 |
1 to 1 |
9 | 2.52 | 46.6 |
1 to 1 |
10 | 2.52 | 46.6 |
1 to 1 |
11 | 2.52 | 38.1 |
1 to 1 |
12 | 2.52 | 34.9 |
.83 to 1 |
8 | 2.86 | 38.4 |
.83 to 1 |
9 | 2.52 | 38.6 |
.83 to 1 |
10 | 2.52 | 34.7 |
.83 to 1 |
11 | 2.52 | 31.7 |
.83 to 1 |
12 | 2.52 | 29.1 |
1:1 CLUTCH RATIO VS. OVERDRIVE
The gear calculator gives you the mph for 1:1 clutch ratio. Remember that this is where the belt climbs to about 7/8 of an
inch from the rim of the primary. The only way the belt will or should go to the top of the primary “rim” is when you are
able to do the highest mph attainable with your current drive ratio.
Example 21:45 @ 8150 rpms with 46.1 constant will offer up 82.5 mph.
@ 82.5 mph the belt will go up the primary clutch as high as approximately 7/8 from the rim. To get the belt to go up to
the rim of the primary then the sled will have to go about 93mph (full shift overdrive)
Calculate Full shift overdrive (O.D. or o.d.)
For XP chassis you take the 1:1 mph and divide by .89. So then (82.5mph / .88) = 92.69mph
For MXZ/REV chassis you take the 1:1 mph and divide by .83. So then (82.5mph / .83) = 99.39 mph
When using the calculator, always good to calculate the mph for both shift ratios. 1:1 mph and the overdrive mph.
1:1 = 82.5
O.D. = 93
Click on (Engine overrevving on road (summit))
CALCULATE A MILE PER HOUR – A “HOW TO”
Bottom gear / Top gear = Gear Ratio
Example 43/27 = 1.59 ratio – Note that gears are generally discussed with mentioning the top gear first like “Twenty
seven, fourty three”
Gears are displayed in text as 27:43 with a ” : ” to separate the values.
More examples, 44 / 24 = 1.83 ratio and then written and spoken as 24:44
Example Top Speed Calculation; 2008 mxzx 600RS
Engine rpms – 8400
Top gear 23
Bottom gear 49
Gear ratio (49 / 23) = 2.13
Clutch ratio – 1:1
Track pitch – 2.86″
Constant # – 46.1
Formula then is (8400 / 2.13) / 46.1 = 85.5mph
HOW TO CALCULATE A DRIVE SPROCKET CONSTANT
Here is example of skidoo 2.86 pitch track with 7 tooth. You can replace the numbers with your own details.
The formula is also in Aaen clutch tuning manual.
When you scroll down the page, you will eventually see a chart with all the constants.
(2.86 pitch x 7 tooth driver) / 12 = X
(60 / 5280) = Y
(x)*(y) = Z
1/z = Constant
Therefore – (X = 1.67)*(Y = 0.01137) = 0.0189
1/0.0189 = 52.6651 (52.66)
Constant = 52.66
The formula is in any BRP race manual (drive section) and you just have to use the last part of the formula to figure out
“Z” and then just go 1/Z = constant.