GB500 CONSTANT Rear wheel-side Wall Inner Tube Tears

I've become a proud owner of a 1989 Honda GB500 and am very much looking forward to cruising around some desert scenery outside of Phoenix.  

My dad was the previous owner of the bike and informed me that any longer rides that he did (over 150 miles), the bike kept taking side wall inner tube tears on the rear wheel. He thought that it was getting a pinch, but the rim appears to be in perfect condition on the inside. He has put at least two new tubes in and two different tires, but still had issues.

Does anyone have any suggestions on what the problem could be?

Thanks for any input!!

Crappy tubes was my first thought. The other one is that either the tire or the tube has enough movement to rub.

I was thinking movement too. It's odd though that it constantly happens on longer rides even after new tubes and tires were put on. Completely understandable if it were crappy tubes, but I'm sure that ONLY really good quality tubes and tires were installed on the bike considering how well he took care of this motorcycle.

I don't know if other GB500 owners have this issue...

28,000 miles on my GB with no tube issues ever. Actually, we owned a Kawasaki/Suzuki/BMW/Ducati dealership for 15+ years and I’ve never heard of that problem with spoke rims/tubes. 

I would disassemble everything, carefully inspect the inside of the tire, check over the rim for rust/corrosion and look at the tube to see what it currently looks like. Note and mark the orientation of the tire on the rim and see if something coorelates to damage on the tube. 

Upon reassembly, get the BEST tube you can buy.

Other than that, I’ve got nothing. 

I will preface my post by saying that my GB500 experience is limited to admiring them and once owning a used GB500 gas tank, but I have tons of bicycle inner tube, and a decent amount of moto inner tube experience. I haven’t come across your particular circumstances, but would suspect movement/chafing.

I’d start by disassembling and replacing the rim strip and tube...cheap insurance, and all rubber components deteriorate with time. Inspect everything (including the rim and tire carcass all around) with a fine tooth comb as mentioned above. During reassembly I would dust the inside of the tire and/or the outside of the tube with talc to minimize the chance of chafing. This is a common approach to troublesome bicycle tubes. I would make certain is isn’t under inflated, or maybe even shoot a few psi high. Put matchmarks on the rim and tire sidewall with a grease pencil or chalk that will allow you to see if the tire is slipping on the rim. Pack a spare tube and some tools and/or a phone and AAA card and go for a long ride. (The lengths we go to for troubleshooting!) 

At work we assemble lots of tubed tires, moto and vintage car. We've developed a process that seems to work and gets no pinches.

Hopefully you've checked the inside of the tire and rim for anything sharp.

Put a little air in the tube so it holds it's shape a bit and give it a good dusting of talc, put some talc inside the tire too.

Put the tube in the tire and the tire on the rim as you normally would, pull the stem through the wheel and put a nut on loosely.

With the valve core out, air up the tube to seat the tire on the rim, once it's full and seated, run the stem nut down finger tight.

Let all the air out and then air the tube up again. Repeat this process a few times to allow the tube to move around and settle into it's happy place in the tire.

Put the valve core in and air it up a final time, tighten the stem nut carefully.

Never had a pinch flat since I started using this process, only punctures and bad valve cores.