Mountaineerfan 44 Report post Posted April 9, 2023 I just purchased the Rostra universal cruise control for my 69 vert. I’m planning on using the magnetic VSS on the driveshaft. I’m supposed to set the dip switches for the ppm of my car. I cannot find a chart in the instructions for my car or any car. Has anyone here installed this and have a setting I should use? I have a 302 with C4 automatic and 3.00 gears. Thanks! Quote Share this post Link to post Share on other sites
69RavenConv 286 Report post Posted April 10, 2023 Let me take a shot... Measure your tire diameter in inches: D Calculate tire circumference: C = (pi * D) = (3.1415 * D) There's 63,360 inches in a mile. (12 in/ft * 5280 ft/mi) So tire-rotations-per-mile = 63360/C Finally, your 3.00 differential spins 3 times per tire rotation, so the driveshaft speed is (3*Tire-rotations-per-mile) Example, tire is 24" in diameter... D= 24 C = (3.1415 * 24) = 75.6336" Tire-rotations-per-mile = (63360 / 75.6336) = 837.72 Driveshaft-rotations-per-mile = (3 * 837.72) = 2513.19 [edit] Maybe easier just to measure your tire circumference instead of doing it the long way? 1 Mountaineerfan reacted to this Quote Share this post Link to post Share on other sites
det0326 179 Report post Posted April 10, 2023 1 hour ago, 69RavenConv said: Driveshaft-rotations-per-mile = (3 * 837.72) = 2513.19 Man until one starts calculating what goes on in a drive train, its a wonder they stay together as well as they do. Quote Share this post Link to post Share on other sites
Mountaineerfan 44 Report post Posted April 10, 2023 Thank you! So 2315 is what mine came up to, so I'll stick with the 2000ppm setting, as it's the closest. 1 69RavenConv reacted to this Quote Share this post Link to post Share on other sites
