Tires! Tires! Tires!

Y'ok, it's time to replace the tires on my '75 GT380. The book says
front 3 x 19
rear 3.5 x 18

Currently on the bike, a pair quickly approching dry rot critical mass:
front: Dunlop Gold Seal 100/90-19 57H
rear: Dunlop K627 110/90-18 61H

I can't find these two tires anywhere, I guess that means they are no longer produced? Any suggestions? I'm mainly looking for a vintage ribbed front tire, and a back tire that has a vintage tread pattern. So far, the few choices include IRC GS-11 All Weather Front 3.25x19, IRC Rear GS-11 AW (All Weather) 3.50Sx18



maybe a Continental Conti Twins RB2 Front Tire or Avon Speedmaster...or Bridgestone Accolade?


with an Avon SM MkII Rear TT?



Choices are pretty limited
Vintage pros, weigh in here, what do you think? What are you running and on which bike?

I have a not-so-new bike and I well remember ribbed front tires when I was a kid. For pure safety and ride-ability, I would stay away from ribbed tires no matter what the "proper" tire would be for the bike. I put right sized modern tires on my airhead, while many other owners spend lots of time trying to find the "right" period look for their tires. I don't see the tread while I'm riding.

Thanks, Manfred. I put a lot of miles on motorcycles with these type of tires in the 70s, so I'm okay with them now.

I'm wondering what you other 60s and 70s riders are using... I am leaning towards the IRCs, mostly to have the same brand fore and aft. One thing that puzzles me--the tire conversion between inches and metric. Why is one tire listed as 3.25 x 19 and another as 3.5 x 19, yet they both show as 100/90-19 metric?

The rear tire is even worse, it is listed as 3.5 x 18 and 4 x 18, yet both show as 110/90-18...

Avon AM Roadrunners or Dunlop 501 GTs.