New Gearing help

[Twofeathers]

I was curious what a reasonable cruising RPM should be. My 82 400 twin (13,00 kms) runs at about 5,000 rpm at 100 Km/hr but I would like to travel at 120 km/hr, currently 6000 rpm. My daily commute takes about an hour on average, traveling a distance of 65 kms each way. I have 16/43 sprockets giving me a 2.69 ratio and I was thinking about increasing the drive sprocket to drop the RPM. If I am doing the math right, with a 17 @ 120 km/hr = 5643 rpm, an 18 @ 120 km/hr = 5330. A 19 @ 120 km/hr = 5040 rpm. The formula I used was new sprocket/old sprocket x old sprocket rpm = new sprocket rpm.

Thanks

[trippivot]

good math.

changing 1 tooth in the front is approximately equal to changing 3 in the rear.

the unfortunate thing is you might not like the way your bike behaves in stop and go traffic.

[Nessism]

Try up one tooth on the front and see how you like it. The front sprocket is fairly cheap, hopefully your chain is long enough. If you go much taller than this the bike will be very sluggish in town, when crusing away from stop lights. And don't worry about the engine spinning high rpm's, it's designed for it.

[Twofeathers]

17 and 18 Sprocket

I think that I will get acouple of the sprockets. As they are very easy to chang and realtivley inexpensive. My concern was with the 5500 to 6000 rpm at 120 that I was concerned about. I also found this pdf at jtsprokets that illustrates the final ratio based on your sprockets if you really hate math.

http://www.jtsprockets.com/fileadmin/files/jtgearratio.pdf

Thanks Ed.