Need new tires, don't know where to start

Hi all,

I have a 1980 KZ550-A1. This is my first bike. For the most part I know nothing about bikes and this question proves it.

The Clymer's manual states I need these tires:
front 3.25 H - 19 4 PR
rear 3.75 H - 18 4 PR

the first number is the section width, the letter is speed rating, the next number is rim diameter, the last number is casing strength.

But websites do not use this system. Frustrating!
Websites do not list my bike model. Frustrating!
I have no idea about what tire brands, patterns to choose. Frustrating!

Anyone have any suggestions on how I should start to shop for new tires?

Goto the top of the forum and hold your cursor over "Kz Information" Select filebase and open the "non model specific folder". Scroll down and you should see a file tited "Tire Conversion" or something like that. That file should help you.

Later, Doug

The H is the speed rating. Really doesn't effect us, as most tire ratings are H=130mph, or V=149mph. I doubt many KZs will be doing 130 very often so either will do. The 4PR is the load rating. This really doesn't matter either on a motorcycle. Look at the conversion chart Doug referred to, but comparable sizing between the systems is not exact. A 3.25-19 front tire is still available pretty widely, a 3.75-18 rear is not. For the rear you can go 4.00-18 or a 110/90-18. I just got Avon Roadrider tires in 3.25-19 and 4.00-18 through Dennis Kirk and they look great.
Other options are a 90/90-19 front that will get you the same width, but a lower profile, a 100/90-19 that will get you a wider tire with about the same height as original.
If it was me, I'd stay with the 3.25-19 up front and go 4.00-18 in the rear. These are 100% aspect tires instead of 90%. I don't think low profile looks right myself.

Thanks for the thoughts.

What is the aspect ratio? I'm sure it has something to do with the exposed profile but numbers like 90% or 100% mean nothing to me.

I have had at least 10 of these 550's . If you can find tires in the stocks sizes then that will work, , obviously . If not a 120/80-18 rear and a 100/90-19 front seem to work well . Stay away from 120/90 rears and also any 130 rears . These are too tall and your centerstand will no longer lift your rear wheel (and your bike will look silly with a rear tire that is too large). Most of the 550's that I have bought seem to have one of these two oversize rear tires when I get them . I'm not sure if they are just easier to get or if guys think that an oversize rear tire is just too badass to resist ?

Aspect ratio describes the height relative to the width . i.e. a 120/80 is 80% of 120mm high (rim to ground).

Yes, the aspect ratio means the percentage of height vs width. On a 4.00-18 for instance the tire with this number system is a 100% aspect tire, so it would be about 4" wide and 4" high off the wheel. They changed to the metric system and tire were no longer 100% aspect ratio, the ratio was the second number, so a 120/90 tire would be about 120mm wide (devide by 25.4 to calculate inches), and 90% as high as that. A 120/80 would be the same width but only 80% as high. You probably have seen these goofy big wheels people with bad taste put on their cars I assume. They can be as low as a 25% aspect ratio, so barely bigger than the wheel itself. To keep relatively close speedometer and gearing ratios try to keep the tires close to original circumference. Plus the wheels width dictates what tire works right. Rear wheel is a 2.15", front 1.85" I believe. Anything bigger than 120 or 4.00 on the rear is way to wide for the wheel width. Most people want the widest tire they can fit and don't realize or care about "crowning" which is when the wheel is too narrow for the tire fitted and causes the center to crown outwards. You see this situation all day on pickup trucks.

fishybass wrote:

Hi all,

I have a 1980 KZ550-A1. This is my first bike. For the most part I know nothing about bikes and this question proves it.

The Clymer's manual states I need these tires:
front 3.25 H - 19 4 PR
rear 3.75 H - 18 4 PR

the first number is the section width, the letter is speed rating, the next number is rim diameter, the last number is casing strength.

But websites do not use this system. Frustrating!

Some do.

www.jcwhitney.com/Motorcycle-Street-Tires/600014323.jcw

Many of the types listed have dual size ratings for each.

You guys are awesome. I think I have enough info to go on.

The carbs are done. The lights are fixed. The battery is replaced. The oil is new. Everything looks like I will be ready to start for the first time in 3 years in the next day or two.

Then, new tires, and prayers that it will move under it's own power.

Thanks guys,
Ben

fishybass wrote:

You guys are awesome. I think I have enough info to go on.

The carbs are done. The lights are fixed. The battery is replaced. The oil is new. Everything looks like I will be ready to start for the first time in 3 years in the next day or two.

Then, new tires, and prayers that it will move under it's own power.

Thanks guys,
Ben

Have fun the 550's are great bikes , but there aren't too many on here . Most seem to prefer the bigger bikes . I have a GPz750 and don't like it half as much as my 550's .