What tires beyond stock size will fit?

[Guest]

I have seen several threads on tires sizes but none so far have answered the question of limitations on sizing up tires.
My 1980 gs450s currently has a 3.5x18 rear and 3.0x18 front.
Converting to metric sizes that's a 90/100 18 and 76/100 18. (Inch to millimeter conversion and 100% ratio width to height)

Obviously new tires of that size will fit, but what can be safely sized up for modern tires?

As an example, this gs450s clearly has bigger than stock (width and height) tires:
http://imgur.com/a/qyPP8 -For all pictures
http://www.dotheton.com/forum/index.php?topic=51126.15 -came from this build thread

Another example - my car rear tire is a 285 but I can go up to a 305 that will still fit on the wheel and will not rub the fender.
What are the options/limitations for a gs on mag wheels?

[mmattockx]

You can usually go up one size without serious problems. If you want to be more comfortable than that check with the tire manufacturers. They usually publish rim width limitations for their tires and you can see what they think is acceptable. That said, you seldom will improve the handling by upsizing beyond the original sizes and often the handling gets worse. My 1100E wears a 130 rear tire stock. I tried a 140 BT-45 and found that it did nothing for the bike and left significant chicken strips of unused rubber because the tire is pinched out of round to fit onto the skinny rim. The next set of tires I am going back to the 130 and sticking with it.


Mark

[gs450s]

Good point Mark. My main concern was getting a modern tire that fit which all seem bigger. The next thing that came to mind is how much bigger is possible.

In case anyone is curios and hasn't seen it in my other thread, looks like the tires from the link I posted as an example are shinko 712 front and rear.
Best guess for sizes is 100/90 18 front and 110/90 18 rear.

Based on the look and what Mark mentioned I don't think I would risk going any larger.

Out of curiosity though, if anyone has gone further, let us know.

[Big Rich]

Have a look at IRC tires (their moped / light weight tires especially).

http://www.irc-tire.com/en/mc/

I'm on my phone so it's a real pita to search their site, but I saw they do make some 18" tires.

[Gorminrider]

I have a T and an E- The E's 18" rims are narrower than the T's rear.... E's 1.85x18 versus a T's 2.15x17.
.... so, while I have yet to do it , I speculate that I can simply swap wheels....and mean to try it someday soon... perhaps, if you want a fatter tire for the rear, the easiest way to do it might be to get the 17" rim from a T and put it on the E. It's definitely wider.

(Or maybe even from an L that has a 16" rim ...)