Lou, you can calculate the gear ratios...
Factory gearing is 14T front sprocket and 36T rear: 36/14=2.57 (any number bigger is geared lower and any number smaller is geared higher)
If you drop a tooth on the front: 36/13=2.77 (dropping teeth on the front lowers gear ratio)
If you raise a tooth on the back: 37/14=2.64 (adding teeth on the back lowers gear ratio)
If you add a tooth on the front: 36/15=2.4 (adding teeth on the front raises the gear ratio)
If you drop a tooth on the rear: 35/14=2.5 (dropping teeth on the rar raises the gear ratio)
It is commonly accepted that one tooth change on the front sprocket equals three on the rear sprocket...let's test it out:
If you drop a tooth on the front: 36/13=2.77
If you add 3 teeth to the rear: 39/14=2.79
Hmm, now, how did changing your tires affect everything? Taller tires raise your gear ratio and shorter tires lower it...
Here is a sample calculator for your tire changes...
Find new gear ratio with new tire size calc
Your old tires were 18" tall, your new tires are 20" tall, your factory gear ratio is 2.57...according to the calculator you will need a gear ratio of 2.86 to have the same ratio with your new tires as the bike had stock...which would be a 13T front and a 37T rear...37/13=2.85.
Does this make sense?
I wanted to add this to the thread:
I do not know how many of you have seen this but it is a very nice calculator built by 86atc250r from .org...Gabe is his name. Also, FYI, read the notes on the bottom of the calc...you can change tire height to roll out instead, etc.
He has the LTR in their now...