Constant Ratio Chart


Rear Tire Circumference in Inches



33 33.5 34 34.5 35 35.5 36 36.5 37 37.5 38 38.5 39 39.5 40
53 .623 .632 .642 .651 .660 .670 .679 .689 .698 .708 .717 .726 .736 .745 .755
54 .611 .620 .630 .639 .648 .657 .667 .676 .685 .694 .704 .713 .722 .731 .741
55 .600 .609 .618 .627 .636 .645 .655 .664 .673 .682 .691 .700 .709 .718 .727
56 .589 .598 .607 .616 .625 .634 .643 .652 .661 .670 .679 .688 .696 .705 .714
57 .579 .588 .596 .605 .614 .623 .632 .640 .649 .658 .667 .675 .684 .693 .702
58 .569 .578 .586 .595 .603 .612 .621 .629 .638 .647 .655 .664 .672 .681 .690
59 .559 .568 .576 .585 .593 .602 .610 .619 .627 .636 .644 .653 .661 .669 .678
60 .550 .558 .567 .575 .583 .592 .600 .608 .617 .625 .633 .642 .650 .658 .667
61 .541 .549 .557 .566 .574 .582 .590 .598 .607 .615 .623 .631 .639 .648 .656
62 .532 .540 .548 .556 .565 .573 .581 .589 .597 .605 .613 .621 .629 .637 .645
63 .524 .532 .540 .548 .556 .563 .571 .579 .587 .595 .603 .611 .619 .627 .635
64 .516 .523 .531 .539 .547 .555 .563 .570 .578 .586 .594 .602 .609 .617 .625
65 .508 .515 .523 .531 .538 .546 .554 .562 .569 .577 .585 .592 .600 .608 .615
66 .500 .508 .515 .523 .530 .538 .545 .553 .561 .568 .576 .583 .591 .598 .606
67 .493 .500 .507 .515 .522 .530 .537 .545 .552 .560 .567 .575 .582 .590 .597
68 .485 .493 .500 .507 .515 .522 .529 .537 .544 .551 .559 .566 .574 .581 .588
69 .478 .486 .493 .500 .507 .514 .522 .529 .536 .543 .551 .558 .565 .572 .580
70 .471 .479 .486 .493 .500 .507 .514 .521 .529 .536 .543 .550 .557 .564 .571
71 .465 .472 .479 .486 .493 .500 .507 .514 .521 .528 .535 .542 .549 .556 .563
72 .458 .465 .472 .479 .486 .493 .500 .507 .514 .521 .528 .535 .542 .549 .556
73 .452 .459 .466 .473 .479 .486 .493 .500 .507 .514 .521 .527 .534 .541 .548
74 .446 .453 .459 .466 .473 .480 .486 .493 .500 .507 .514 .520 .527 .534 .541
75 .440 .447 .453 .460 .467 .473 .480 .487 .493 .500 .507 .513 .520 .527 .533
76 .434 .441 .447 .454 .461 .467 .474 .480 .487 .493 .500 .507 .513 .520 .526
77 .429 .435 .442 .448 .455 .461 .468 .474 .481 .487 .494 .500 .506 .513 .519
78 .423 .429 .436 .442 .449 .455 .462 .468 .474 .481 .487 .494 .500 .506 .513
79 .418 .424 .430 .437 .443 .449 .456 .462 .468 .475 .481 .487 .494 .500 .506
80 .413 .419 .425 .431 .438 .444 .450 .456 .463 .469 .475 .481 .488 .494 .500
81 .407 .414 .420 .426 .432 .438 .444 .451 .457 .463 .469 .475 .481 .488 .494
82 .402 .409 .415 .421 .427 .433 .439 .445 .451 .457 .463 .470 .476 .482 .488
83 .398 .404 .410 .416 .422 .428 .434 .440 .446 .452 .458 .464 .470 .476 .482
84 .393 .399 .405 .411 .417 .423 .429 .435 .440 .446 .452 .458 .464 .470 .476
85 .388 .394 .400 .406 .412 .418 .424 .429 .435 .441 .447 .453 .459 .465 .471
86 .384 .390 .395 .401 .407 .413 .419 .424 .430 .436 .442 .448 .453 .459 .465
87 .379 .385 .391 .397 .402 .408 .414 .420 .425 .431 .437 .443 .448 .454 .460
88 .375 .381 .386 .392 .398 .403 .409 .415 .420 .426 .432 .438 .443 .449 .455
89 .371 .376 .382 .388 .393 .399 .404 .410 .416 .421 .427 .433 .438 .444 .449
90 .367 .372 .378 .383 .389 .394 .400 .406 .411 .417 .422 .428 .433 .439 .44

How To Use: Use largest tire on rear axle. Example: if your old rear tire circumference is 34.5" and your old gear is 65, then your constant gear factor number is .531. If your new tire measures 36.5" in circumference, then scan the 36.5" column to find the constant gear factor number closet to .531. In this case the closet number is .529, which corresponds to a 69 tooth gear. Therefore, you would need to use a 69 tooth rear gear to maintain the same gear ratio.