GS550t Rear Tire correct size?

[CafeRookie]

Hey,

I'm buying my first set of tires for my 1981 GS550T.

Stock:
Front: 3.75-19
Rear: 4.25-17

I can't figure out the rear tire conversion. I've called two tire shops and they have a hard time figuring it out too. There are only a couple of conversion charts that list 4.25 as a rear tire option. The charts list the 4.25 as 110/90, but I can't find any tires 110/90-17 tires.

Can/should I just go up a size and get 120/90-17? Any suggestions? I would like to buy something similar to Shinko 005 Advanced tires.

Any thoughts?

Thanks,

Mike

[phydeauxmutt]

Using 25.4 mm per inch, the literal conversions are 82.5 for the front and 108 for the rear. Of course, those sizes are non-existant, so go with a 90 on the front, and you can safely go to a 120 for the rear.