Join Date: Mar 2007
Location: Fort Sask , Alberta, Canada
Best way to figure it out is to use a tire size calculator. Keeping same width and going to a 130/70-17 will decrease the diameter about 1" or lower the bike 1/2". That's the simple way. but motorcycle tires are not sold like car tires. Seldom (never) can you find a tire where you can maintain width and just change the aspect ratio. You would have to find a manufacturer that makes that specific tire size in a dual sport tire. IRC doesn't.
Just looking at the IRC tire you are considering, in 17" size you have a choice of a 5.1x17 (which is equivalent to stock) or a 4.6x17 which is a narrower width. I suspect that the aspect ratio for the 4.6 would be 90 so effectively the outside diameter is the same as the stock sizing.
Best bet is to stick to stock tire sizing.
My Kaw Barn - 2004 KLR, 2006 Concours (sold), 1997 Bayou 400.
"It's a friggen motorcycle, it's not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you shit your pants every now and then. "
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Last edited by klr4evr; 02-16-2019 at 11:51 AM.