Just a note to share my tire education. I have found out that 16 x 2.5 tire means three different things.
I did a google search and then making a purchase of tires and tubes listed as 16 x 2.5. When I received them I found them to have a 16" ID rather than a 16" OD.
In looking at tire sizing I found three different ways of sizing.
Tires are measured by:
A. Overall diameter, normally given in inches, but can be in mm. approximate diameters, so 16" could be 15 7/8" actual dimension.
B. Section width in inches or mm. Width of the widest part of the tire.
C. Normal rim diameter, normally given in inches but can be given in mm. Measure of the diameter of the bead width, or overall rim width. Different manufacturers reference differently.
D. Section height. Often given as a percentage of the section width.
So we have the sizing we see on automotive tires such as,
250/70-16
Which is (B)250/(D)70-(C)16 or the section width is 250mm, the section height is 70% of the width or 175mm and the rim diameter is 16".
Most motorcycle tires are listed in the same way as automotive tires. Example: 130/70x12 which is 130mm wide by 91mm high for a 12" rim.
Now bicycle tires are different. They most often are just measured by overall diameter and width. Example: 26x1 1/2, which is overall diameter 26" with overall width 1 1/2".
A x B x C 16 x 6.5 x 8
B/D-C 410/3.50-10
A x B 20 x 2.125
Now isn't that all so very clear? Yea, right!
And to make it even simpler, every manufacturer can have their own specific sizing. They can be a few mm difference and a tire with the same size markings can be too loose or too tight for the rim you are trying to fit.
I see three real options here to properly fit your tire. One buy the exact same tire your bike came with. Accept no substitutes. Which may mean you end up buying low quality fast wearing tires all the time. On my bicycles I like using high quality, high pressure tires, so fitting can be an issue.
2. Always take in your old tire or rim into the store for proper sizing. Once you find a store that carries your size stick with them.
3. Get on the phone and talk to the people who sell the tires and know their brands. Have the actual dimensions of your rim and tire (if you have one). They should know their stock, if they don't go to some one else.
What I have found for the GM HBS 16 x 2.5 is that this is a common size for mobility scooters. And there seems to be a limited supply of them. In fact I am having to go to Canadian stores to buy them.
I would think that some stores that sell GM equipment would have at least a supply for these....just a hint you GM dealers....People buying GM equipment want and need a store that can be our go to store for all things GM. Even if you just advertise the parts needed and set up a drop ship relationship with a supplier (a nice arrangement as you don't have to purchase inventory and make a sellers commission on each part sold through you...)