Hello guys,

Please help understand gear ratio, transmission and final drives, I've done some calculation let me know if they are correct.

I have a 2 speed transmission on my MT2.

If I understand correctly our final gear is 2.92, correct??
I've just upgraded the stock tires to a larger diameter tire, it's 6/8" taller than stock...well maybe less my stock tires are worn out.

With the stock tires the 2 speed tranny had no problem shifting into 2nd gear, and it was setup the way I wanted. Now with the larger diameter tires it just doesn't change to 2nd gear.
I think it's due to the larger diameter of the new tire, could that be correct???

The stock tire took 13" to complete one rotation,
the new tire takes 15" to complete the rotation.

These were my calculations:

current setup with stock tires:
1st gear13/47 ratio of 3.61*2.92(final gear)= (final drive ratio) 10.54.........stock tire 13"/10.54(final drive ratio)= 1.23" (travel of the car for each rev of the pinion)
2nd gear-16/44 ratio of 2.75*2.92(final gear)= (final drive ratio) 8.03..........stock tire 13"/8.03(final drive ratio)= 1.61" (travel of the car for each rev of the pinion)

With new tires:
1st gear13/47 ratio of 3.61*2.92(final gear)= (final drive ratio) 10.54........new tire 15"/10.54(final drive ratio)= 1.42" (travel of the car for each rev of the pinion)
2nd gear-16/44 ratio of 2.75*2.92(final gear)= (final drive ratio) 8.03.........new tire 15"/8.03(final drive ratio)= 1.86" (travel of the car for each rev of the pinion)

The size of the tire does make a little difference, is it possible that's the reason the tranny is not switching to 2nd gear???? If I'm doing this right.....

If I was to change gearing to:

1st gear11/47 ratio of 4.27*2.92(final gear)= (final drive ratio) 12.46.....new tire 15"/12.46(final drive ratio)= 1.20(travel of car with each rev of pinion)
2nd gear-14/44 ratio of 3.14* 2.92(final gear)= (final drive ratio) 9.16......new tire 15"/9.16(final drive ratio)= 1.63(travel of car with each rev pinion)

Based on the above if indeed any of it is correct I would need to change my pinion gear to a 11/14 to match the setup that I currently have, and maybe that will fix the problem with the second gear not changing

What do you guys think????