Sorry about that.
Yes you can go lower in the rear but only one tooth to a 41t. This is the only sprocket they offer under 42 teeth. With a 17t front and 41 tooth rear it should give you a ratio of 2.41 which will put you between the ratio's of 18t front/43 rear of 2.39 and 18t/44rear ratio of 2.44.
My replacement front sprocket does not have the rubber isolators on it and I am not using them. I have had no adverse reactions yet.
Fryguy
