Afternoon all,

Tyres not really my thing so I am struggling with advice received. Need to replace the front tyre on my 1985 K100RT outfit. No shortage of suggestions but I'm struggling to reconcile them with the actuality.

I know what I'm looking for in terms of profile, usage and looks and have been pointed at (inter alia) the Metzeler K block and the Avon Speedmaster (using a rear tyre mounted against the indicated rotation) etc.

Open to all suggestions, but none of these tyres are available for my 'book' designation of 100/90 V 18 Tubeless. I infer from reading here that adherence to these designations seems to be discretionary.

If I were to seek out different width and aspect spec tyres - how much discretion do I have?

Would appreciate feedback from anyone actually running an 'off-spec' tyre. Thanks and kind regards, Stu

A common 'upgrade' in tyre size is a 110/80-18 on the standard Y spoke front wheel. The factory sticker under the seat of my 10/86 K100RS, as well as actual use, shows this to be a valid and legal size option for the width of the factory rim. There are also plenty of tyre choices using this size. Out in back a 140/80-17 can be used on the standard wheel. There's a myriad of posts in the forum on this subject:

https://www.google.com/search?ei=zVHnW-j5BYPK8APG_ZTYCw&q=tire+choice+site%3Awww.k100-forum.com&oq=tire+choice+site%3Awww.k100-forum.com&gs_l=psy-ab.3...10152.10463..10729...0.0..0.86.172.2......0....1..gws-wiz.......0i71.s0puLGf3eyE

Thanks Two Wheels,
Sorry for starting a redundant thread, obviously I need to get smarter with my searches. You've put me on the right track now though so I'll get out of your hair.
Cheers, Stu

Two pages to help you.
(1) Article on all K-bike and R-bike wheel sizes available: http://www.largiader.com/parts/wheels.html
(2) Thread on Honda forum talking about Tire sizes versus Rim sizes: https://www.hondatwins.net/forums/52-tires-wheels-brakes/26962-wheel-rim-tire-sizing-important-considerations.html

Put these two sources of information together to answer your query. The charts offer minimum and maximum tire sizes that will physically fit on a rim, and the wheel discussion will give you an idea of the various rims available for K-bikes. Remember that very fat rear tires will hit the swingarm, so do your research before you invest.

Thanks Robert, very helpful.
Cheers, Stu