I bought a new set of Shinko 230's from Bike Bandit to install on the Rescue Bike.....riding on 12 year old tires just didn't seem like a good idea even though there is plenty of tread on them.
The tires were ordered on Friday, and delivered on Tuesday...the 130/90-15 rear tire was $ 66.31, the 100/90-19 front tire was $ 56.42....total cost was $ 122.73. The tires were built in November 2015 - so they are nice and fresh!
Now for the surprise....the 130/90-15 tire is not a downgrade in width from the 140/80-15 IRC. I measured the width of the 140/80 IRC before I took it off, and it was 132mm wide......and the 130/90 Shinko measured 136mm wide when mounted. I suppose that this can be explained by looking at the following chart. The 140/80 tire uses a wider 3.50" rim as the standard size....and it can be mounted on rims between 2.75" - 3.50" wide - so the Savage rim pulls the sidewalls in 3/4" narrower than what is "standard" for the tire. The 130/90 tire is acceptable on rims from 2.50" - 3.50" - so the Savage rim is right in the middle of the range for that size tire.
So I believe the 130/90-15 tire is definitely a good replacement tire for the standard 140/80 rear tire. It is just a bit taller and will change the gearing by only 1%, and there will likely be no noticeable change in the handling (except for the improvements that a new tire allows). The even taller and wider 140/90 tire will increase the gearing by 4% and the extra weight and inertia does slow the bike handling and acceleration down a bit.....and for some folks that is a beneficial change as they like the extra stability and reduced engine rpm when cruising.