ATV Tire Sizing

For most 4WD ATV’s, Tire Sizing is not a problem because there is a direct 1:1 front-to-back ratio drive train.

However, on my Polaris 300 4×4 the front wheels turn faster than the rear. This means the front wheels need to be a smaller diameter than the rear wheels in order for the front Hilliard hubs to engage properly. You also must remember that the tire diameter stamped on the tire itself may not reflect the true diameter of the wheel. The differential in true diameter to stamped diameter seems to be manufacturer dependent. This can be a useful benefit once you do your calculations.

In an effort to calculate the correct diameter of wheel that I would need for my machine I developed an application that would do the calculations for me. I have made this available in a web application below. For an alternative approach see table at bottom of page.

The calculations in the above web app are as follows:

• Pi = 3.14159265359
• Wheel Diameter * Pi = Circumference
• Circumference * Revolutions = Distance Traveled

Once you have the distance traveled by each wheel diameter you can then determine the drive ratio needed to have each wheel travel the same distance.

Once the ratios are determined you can then calculate either the rear wheel diameter needed based on a designated front wheel size. You can also determine the front wheel size needed for a designated rear wheel size.

Alternatively, you could change the one sprocket on the Center Tightener Assembly and the Rear Sprocket to make the front and rear wheels rotate at the same speed. This would allow you to use the same diameter tire on the front and back. I have not tried this myself but it does look like it would work.

The table below is used to compare the part numbers between a 300 4×4 and a 400L 4×4. The 400 L 4×4 uses the same diameter tires on the front and back. The theory is that the 300 4×4 can be converted to use the same size tires on the front and back by using the one 400L 4×4 sprocket of the Center Tightener Assembly and changing the Rear Sprocket to match the same teeth of the 400L 4×4. Being that the shaft of the Center Tightener Assembly is the same between the two models there should be no problem using the sprocket from the 400L 4×4 on the 300 4×4. Tire clearance would still need to be taken into consideration. Also, changing a 40T rear sprocket to a 34T rear sprocket might be too large of a change for 300 4×4 to handle without a clutch kit or reduction in tire size.