Tire size?? Whats Good??

Hi my 1977 KZ650 has 100/90 19 H CS Marquis tire on front and a 120/90 18 H CS Marquis Rear tire. I plan on changing them out due to weather checking pretty bad. The stock oem tires are different sizes then whats on the bike. Should I just us the same size thats on the bike or get oem size tires? 3.25-19 front and 4.0-18 rear. The local shop said 3.25-19 is a 110/80 19 and the rear was a 110/90 18???

This has been talked about quite a bit. For years I ran the 100/90-19 up front, 120/90-18 in the rear. This is a good combo, but too wide in the rear. Don't run a 110/90-18 in the rear, it looks stupid to put it bluntly. No tires are the "same" as a 3.25-19 and a 4.00-18 so if you want those sizes they are still available and by far work and look the best if you want original. If you want the hopped up look with a little wider tire use the 100/90-19 and 120/90-18.

Inch-size tires are getting increasingly hard to find. The Dunlop fitment guide indicates just what the local guys told you. You may check with other tire manufacturer websites, but I'll bet the results will be about the same.

These are Bridgestone Spitfires on Lesters, 100/90-19 front and 110/90-18 rear.

Replaced a rear 110/130-18 that looked slightly too wide for the rim width.

Next time will most likely use 110/120-18 on rear.

Good Luck!

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On my '77 KZ650C1, I recently replaced my Michelin Macadam tires with Pirelli Sport Demons. The Macadams had about 6,700 miles on them and they were the source of a high speed (90+ mph) wobble despite being properly mounted and balanced and having much tread left. Below 90 mph the wobble was not noticeable, but even though I only hit 90+ occasionally the thought of the wobble waiting there for me was unnerving. I replaced my bike's wheel bearings, steering stem bearings, and swingarm bushings in trying to eliminate the wobble; I already had new top quality shocks. I'm glad I replaced these items, and doing so reduced the severity of the wobble somewhat, but these items obviously were not the source of the problem as it persisted. After replacing the Michelins with the Pirellis the wobble is eliminated. I have taken the bike up to an indicated 120mph and it is completely stable. As a bonus, the Pirellis have better traction, particularly in braking, than the Macadams. I used a 100/90 V 19 on the front and 120/90 V 18 on the rear using new Metzeler tubes as recommended by Pirelli. These are the same tire sizes as the Macadams I replaced. I have only put about 500 miles on the new tires, so I cannot give a long term opinion, but so far I really like them. I have not yet driven in the rain so I reserve judgment there. These tires have a modern asymmetrical tread pattern similar in appearance to some radial tires. The link shows the tread pattern. I bought mine at Ron Ayers. Ed

Sport Demon

One thing to remember is to grow the tires equally. If you go taller on the back, go taller on the front to match. Width as well. Wide back tire and skinny front doesn't do too well.

mzandmz wrote:

Hi my 1977 KZ650 has 100/90 19 H CS Marquis tire on front and a 120/90 18 H CS Marquis Rear tire. I plan on changing them out due to weather checking pretty bad. The stock oem tires are different sizes then whats on the bike. Should I just us the same size thats on the bike or get oem size tires? 3.25-19 front and 4.0-18 rear. The local shop said 3.25-19 is a 110/80 19 and the rear was a 110/90 18???

Those are the closest metric equivalents, but they are not exactly the same. I run the 110-90 rear on mine and it is a bit smaller than the stock 4.00-18. The 120-90 is a little bigger than a 4.00-18.