Calculated Driver Diameter vs. Actual Diameter Issues

[PowerJoe]

Not sure if the was the best place to post this....

If you measure the diameter of a 9 tooth 2.52 pitch driver (Arctic Cat for example) it is actually 6.94". If you calculate what the diameter is, it comes out to 7.22" Now if you take a 2.52 pitch track and lay it on the floor and then place the driver inside the track and roll the driver inside the track you will see that the teeth of the driver do not stay centered in the lugs as you roll the driver. You can actually see that the diameter is too small and the timing or pitch between the driver and track are not exactly the same.

On Whal brothers website they sell drivers and list the diameters. They are all about an 1/8" undersized versus the calculated diameter. It seems like they are doing this intentionally for some reason. Wouldn't you want the diameter/pitch of the driver to exactly match the track for best performance?

I have heard of racers building up the diameter of the drivers but I don't know if they are doing it to solve this problem or for some other reason.

 

[LoudHandle]

The track Pitch is actually measured at the cords that are inside the rubber belting that makes the track. So while the driver will not measure the actual pitch, most are far too undersized for my liking. Cats seem to be the worst. The Polaris drivers I've measured are fairly close and all the lugs touch when wrapped around the driver as they should be. If they do not all touch each other, you are slipping, which is wasted motion, creates frictional heat, and accelerates the wear on both parts.

That said most aftermarket offerings are equally "loose" and therefore I got some drivers custom CNC'd to my spec's to rectify the lousy tolerance choices of some of the factory offerings as well as the aftermarket offerings.

Your best bet is Indy Specialties Roller drivers, if he has tooled up to make the 3" pitch drivers yet. I have not looked at his offerings lately, but his 2.52" and 2.86" pitches are the bomb!

 

[PowerJoe]

Great! This is the info I was looking for. I need to check with the driver and track in the sled and with proper tension. I wasn't aware of the Indy Specialties drivers and that concepts looks good.

I am actually building vintage race sleds where horse power is limited so we are looking to gain efficiency everywhere else. We are not running extrovert drivers. I will look at starting with Polaris drivers as I can turn them down if they are too big in diameter where as I think the cat drivers are too small to start with like you mentioned.

 

[joshkoltes]

With the torque of the motor driving the extros everything fits. When your rolling it in the track on the ground your not applying pressure on the window edges so they just look a bit off. At least that's what I figured when I did the same thing