Rear Tire Question.....

I have a Avon Roadrider front tire, going to put a Avon RR on the back. My question is will a 130/80 fit on the back without clearance issues? There is a Challenger 120/90 on the back now from the previous owner and it looks ridiculously tall. Bike is a 76 KZ900 A4.

I don't know if it will fit the Kz900, but I have a few bikes and one has a 130/80 and the other has 120/90 rear. They both end up at the same height, but the 130 is wider. The 80 or 90 is a ratio, so if you use a lower ratio on a wider tire, you end up near the same height. The 130 might get better grip in a straight line, but the 120 has way better control on curves.

Thanks for the input, something to consider, here in South Florida there are no twistys, just straight roads for miles. My main concern is clearance, and of course fitting on the stock hoop...

I used 130/90-18 tires on the rear of my KZ650 for quite a few years. I had to replace the stock plastic chain guard with a narrower chrome one because the 130 tire rubbed the stock unit. I found that because the 130 tire had to be squeezed onto the stock rim the tire's profile was somewhat distorted. This resulted in no more tread touching the ground than there was when using a 120 tire. The 130 tire was a bit of a challenge to mount on the stock rim, but with practice (and sore knuckles) I could do it. The 130/90-18 tire worked ok, but not any better than a 120/90-18 tire which is what I eventually switched back to using.

Unfortunately, if you want to switch tires to reduce the bike's height you will be disappointed. The total height of the 120/90-18 tire is 26.50". The total height of the 130/80-18 tire is 26.19". The total difference between the diameters of the two sizes is only .31". Since the height of the bike is only affected by the distance from the center of the axle to the bottom of the tire the .31" must be divided by 2 to find the difference in the bike's height. That distance is a mere .155" which is just a shade over 1/8". That's not enough to make any difference one way or the other. Here's the link to the tire size calculator I used to come up with those numbers. Ed

www.rbracing-rsr.com/tirediamcalc.html

Fantastic information! Loving the information in this forum! Thank you. 120/90 it is for Avon....

I'm using a 130/90-18 on my Z1 and a 110/90-19 on the front. I like the solid feel they give the bike. The 120 on the rear went away faster and the 100 on the front made the bike's front end feel light at over 100. If Shinko offered a 80 series I would have bought them but the 18 and 19" sizes are only in 90.
Steve

Avon's site gives all of the measurements for their RR tires. Just pick the 18" rim size from the drop down menu: www.avontyres.com/en-us/tyre-details/59/.../?cartype=motorcycle I just put a 4.00 - 18 on my rear 200 km ago. So far so good.

Good Fortune!

:lol: :lol: :lol:

Alternately

A 130 is too wide for the stock 2.15" wide rear wheel. The tire profile is distorted and pinched in at the sides. By most tire manufacturers accounts a 120 is borderline too but Kawasaki chose that size so what the heck?

Nessism wrote: ... a 120 is borderline too but Kawasaki chose that size so what the heck?

I thought the stock rear tire for most of the KZ models was a 4.00-18. A 4" wide tire would nominally be 102mm. The reproduction Dunlop k70 gives 4.17" width, or 106mm. I've also seen other sources say that a 4.00 is equivalent to a 110 tire.

www.dunlopmotorcycletires.com/tire-line/k70/

On the other hand, the Bridgestone BT45 and the Avon roadrider both come in 4.00-18, and are listed as 119 and 116mm width. So it's hard to find a source for what those vintage tires were.

In any case, I agree with you completely. The two 130 tires I've had rub slots in the chain cover, and look pretty distorted on a 2.15" rim. My bikes now all have 120 on them, with no issues.